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CRITICAL REVIEWG. Chatel et al.Heterogeneous catalytic oxidation for lignin valorization into valuable chemicals: what results? What limitations? What trends?

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Shenashen, H. Yamaguchi, A. S. Alamoudi and S. El-Safty, Green Chem., 2018, DOI:

10.1039/C7GC03673F.

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DOI: 10.1039/x0xx00000x

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Extraction and recovery of Co2+

ions from spent lithium-ion

batteries using hierarchal mesosponge γ-Al2O3 monolith

extractors

H. Gomaaa, M. A. Shenashen

a, ⃰, H. Yamaguchi

a, A. S. Alamoudi

b, S. A. El-Safty

a, c, ⃰

Visual extraction, detection, and recovery of Co2+

ions from spent lithium-ion batteries (SLIBs) via a one-step process

become a new attractive simple route for management of urban electronic wastes (e-wastes), which in turn lead to exploit

of the accumulated e-waste ideally and protect the green environment. The Co2+

ion-capture system was achieved by

selective binding with synthesized chelating agents, namely, (E)-4-((2-mercaptophenyl)diazenyl)-2-nitrosonaphthalen-1-ol

(MPDN) and (E)-5-((1,3,4-thiadiazol-2-yl)diazenyl)benzene-1,3-diol (TDDB), at controlled pH solution. The dense dressing

assembly of MPDN and TDDB into microscopic, mesospongy γ-Al2O3 monoliths enabled the design of solid/sponge Co2+

ion

extractor (IE) from SLIB leach liquor. Our recycling process of Co2+

ions from SLIBs showed evidence of (i) Co2+

ion waste

management, (ii) low-cost collection/recovery of Co2+

ions, (iii) sensitive and selective extraction of ultra-trace Co2+

ion,

and (iv) reduction of e-waste volume through multiple reusability or recyclability. Furthermore, our sponge IE design with

large surface area-to-volume ratios, macro/mesopores, and grooves along the micrometric, hierarchal monolith structures

results in a facile, naked eye monitoring of the ultra-trace Co2+

ion collection/binding to a detection limit of approximately

3.05 × 10−8

M during multifunction extraction steps from SLIBs. Our result also showed evidence of the extraction of Co2+

ions (196 mg/g) from SLIBs by a one-step process. This finding provides a basis for the control of multifunction processes

(i.e., extraction, detection, and recovery) and the high performance for selective extraction and recovery of Co2+

ions from

SLIBs in a one-step process.

Introduction

To date, given the rareness and high cost of metal sources in the

industrial sustainability, global attention is devoted to electronic

waste (e-waste) recycling as an alternative sustainable source. E-

waste is expected to increase by 33% (~72 million ton/year)

worldwide by the end of 2017; this waste includes laptops, digital

cameras, watches, cellular telephones, leisure apparatus,

pacemakers, etc.1-3

The USA alone produces approximately 400

million e-waste items annually. The European Union and Japan

wastes are about 8.9 and 4 million tons, respectively. In addition to

other gross domestic products, a total of 1.5 million tons of illegal e-

waste enter China each year. In India, the e-waste increases by 25%

annually. Developing countries are also producing large quantities

of e-wastes due to expansion in complex uses and electronic

devices. 1-3

In the past, e-waste is destroyed by milling and burial or

incineration; nevertheless, recently, the reuse of these wastes is

considered because of its economic value and the high costs of

disposal.4 Furthermore, e-waste accumulation may lead to adverse

effects on the surrounding environment and bio-systems due to

their toxic ingredients. Therefore, innovative ways to exploit these

wastes properly through recycling and extraction of their main

components should be determined.

The increasing use of electronic devices worldwide results in large

quantities of spent batteries due to number of charging and

discharging processes.5

Lithium-ion batteries (LIBs) are used to

produce power for many electronic devices, such as portable

electronics, electric vehicles, and other modern appliances; the first

LIB was marketed by Sony Corporation in Japan in 1991. 6

Approximately 500 million cells are produced worldwide in 2000,

which causes 200–500 million tons of spent LIB wastes annually. 6

The global annual production of LIBs increases by 800% between

2000 and 2010, and it is expected to increase by 2025. According to

the United Nations Environment Programme report in 2011, only

less than 1% of spent LIB (SLIB) from diverse applications is

recycled. 7

Recycling of SLIBs is a significant process to reduce the

environmental pollution and recover precious metals, such as

cobalt.8

Cobalt (Co2+

) is an important element in various industrial

applications.8 Cobalt ions can be used in LIBs as a positive

electrode,9

in magnet and alloy manufacturing,10, 11

and in

electroplating.12

Cobalt-60 is used in food preservation.13

Co2+

is

present in LIBs in a mass ratio of 5%–15%; thus, LIB is considered an

important secondary source of cobalt.14

Therefore, the present

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work aims to selectively detect and efficiently extract/recover Co2+

from SLIBs.

Many methods have been developed to extract or separate cobalt

from SLIBs;15

these methods include hydrometallurgical,16

biohydrometallurgical,17

and pyrometallurgical processes.18

Given

the high cost, slow operation, toxic gas production, and inefficiency

of biohydrometallurgical and pyrometallurgical methodologies, the

hydrometallurgical process is the most remarkable and most

suitable method. In this process, SLIB recycling requires two main

stages to recover the metal contents of SLIBs; these stages are

mechanical processes (crushing and grinding) and dissolution

processes under thermal treatment at high temperature (i.e., acid

or alkaline leaching).19, 20

Several techniques have been utilized to

detect, determine, and recognize the Co2+

content quantitatively

even at considerably low concentrations; these techniques include

inductively coupled plasma-atomic emission spectroscopy,

inductively coupled plasma-optical emission spectrometry,

inductively coupled plasma mass spectrometry (ICP-MS), graphite-

furnace atomic absorption spectrometry, and electrochemical,

potentiometric, and spectrophotometric techniques.21-27

Among

these techniques, spectrophotometric quantitative detection of

Co2+

is the most preferred due to its fast metal detection, low cost,

and simple methodology. Thus, UV-Vis detection of Co2+

ion is

becoming popular worldwide due to accurate and rapid detection,

selective determination, and highly sensitive determination of ultra-

trace concentrations.28, 29

A wide variety of physical and chemical methods, such as chemical

precipitation, ion exchange, electrochemical treatment, and reverse

osmosis, is used to remove and extract Co2+

ions from its solutions

(i.e., an aqueous solution or leach liquor).30-33

However, optical

adsorption process remains the most remarkable among these

methods due to its fast adsorption response (time-dependent

process), simple process, follow-up interaction, naked eye

observation of colour change with concentration change, suitability

in low target concentrations (i.e., sensitive process), high efficiency

in the presence of other competitive ions, high adsorption capacity,

large-scale applicability, and the possibility of recycling spent

adsorbents for consecutive times.34

Currently, several chemical optical adsorbents or extractors have

been synthesized as a new technology for many actual applications,

such as recognition, determination, and removal of metals in water

purification and e-waste management fields.35

Optical adsorbents

are still used for specific sensing, extraction, and recovery

applications for a wide range of metals.36

The most remarkable

feature of optical adsorbent or extractor approach is the qualitative

and semi-quantitative detection of target metals without using any

complicated spectroscopic instrumentation or methodology.37

Optical extractors consist of two main parts, namely, solid

carrier/substrate/platform material and organic chromophore as a

selective chelating agent, namely as indicator/ligand/probe.38

Recently, a wide range of carriers, such as metal oxides, is

developed in mesoscale architectures (2 nm < pore size < 50 nm)

and high surface area; these carriers exhibit controllable mesopore

size, shape, and surface charge, which made them promising

materials for different applications, such as separations, sensing,

extraction, and electronic systems.39-41

Mesoporous materials

facilitate material diffusion and enhance the amount of accessible

active sites.

Among metal oxides, alumina γ-Al2O3 is intensively applied in

various industries because of its favorable characteristics, such as

thermal stability, moderate Lewis acidity, and economic cost. In

addition, porous γ-Al2O3 monoliths provide a remarkably strong,

open, and tunable periodic scaffold on the nanometer scale.42, 43

Therefore, high-order mesoporous γ-Al2O3 monoliths with uniform

pore size, monodisperse porosity, and microsized particles display

promising potentials as a new class of carrier materials. The

preparation of highly stable and efficient extractors is highly

required in successful application fields.

Additionally, chromophore receptors, such as azo dyes, have been

synthesized and applied to form considerably stable complexes with

transition metal ions. Therefore, different trapped ligands on a

variety of solid matrices are successfully utilized for the removal or

extraction with a low detection limit of Co2+

ions.44

The –N=N–, –

OH, –N=O, and –SH functional groups of chromophore receptors

also play key roles in the adsorption or extraction selectivity.45

In

this report, we discuss the grafting techniques used in fabrication of

chemical optical extractors for colorimetric and visual extraction,

detection, and recovery of cobalt ions at low concentrations. These

techniques are commonly used methods to control the

immobilization of the chromogenic receptors onto solid materials.

In the present study, the (E)-4-((2-mercaptophenyl)diazenyl)-2-

nitrosonaphthalen-1-ol (MPDN) and (E)-5-((1,3,4-thiadiazol-2-

yl)diazenyl)benzene-1,3-diol (TDDB) chelating agents were

synthesized. These agents were subsequently attached to the

micro-structured mesospongy γ-Al2O3 monoliths by direct

immobilization process to produce a pair of selective, sensitive, and

efficient Co2+

ion extractors (IEs). IEs were used to extract or collect

Co2+

ions rapidly from SLIB solution even at low concentrations. Our

strategy depended on the naked eye monitoring of the colour

change of extractors. Several remarkable parameters affecting

extraction behavior, such as pH, limit of detection (LOD), contact

time, initial Co2+

concentration, and interfering ions, were

systematically investigated. The wasted IEs can be recycled using

HCl and reused for several uptake–elution cycles without losing its

functionality or platform surface features. These IEs are promising

materials in terms of cost effectiveness and suitability for large-

scale recycling of SLIBs. Therefore, our IEs are highly applicable to

the environmental clean-up of precious cobalt metal and

administration of urban e-wastes.

Experimental

Materials

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All chemicals were used without further purification. Aluminum

isopropoxide (AIP) ≥ 98%, cetyltrimethylammonium bromide

(CTAB), 2-amino-1,3,4-thiadiazole and NaNO2 were obtained from

Sigma Aldrich, Company Ltd., USA. Ethanol 99.5%, phosphoric acid

85% and HCl 37% were procured from Nacalai Tesque, INC., Japan.

O-aminothiophenol, 2-nitroso-1-naphthol, and NaOH from Wako

Pure Chemicals, Osaka, Japan. Where, resorcinol >99.0% was

purchased Tokyo Chemical Industry, Co. LTD., Japan (TCI).

Instrumentation

The absorbance spectrum of the IE materials was measured before

and after adsorption by UV-Vis spectrophotometer (Shimadzu 3700,

Japan). The Co2+

ions concentration was determined by using ICP-

MS (ICP-MS, Perkin Elmer, Elan-6000). Shape and surface topologies

of γ-Al2O3 monoliths and IE samples were studied using scanning

electron microscope FE-SEM (JEOL Model 6500) at 20kV. Small-

Angle and Wide-Angle X-ray diffraction (SA/WA-XRD) was applied

using a 18kW diffractometer (Bruker D8 Advance) to investigate the

phase and crystal structure of γ-Al2O3 monoliths. The porous

structure and specific surface area of the samples were measured

by N2 adsorption-desorption isotherms at 77° K using a BELSORP36

analyzer (BEL Co., Ltd., Japan). Scanning TEM-energy dispersive X-

ray spectroscopy (STEM-EDS) characterization was carried out using

a JEOL JEM model 2100F microscope. 27

Al magic-angle spinning

nuclear magnetic resonance (27

Al MAS-NMR) analysis of γ-Al2O3 and

IEs were investigated using a Bruker AMX-500 spectrometer. HNMR

and FT-IR analysis of prepared chromophores were conducted using

ECS-400 (JEOL Ltd. Japan) and IR Tracer-100 (Shimadzu Corporation,

Japan), respectively. Thermal stability of used material was

investigated using a simultaneous DTA–TG Apparatus TG-60

(Shimadzu Corporation, Japan).

Fabrication of hierarchical mesospongy γ-Al2O3 in monolith-

shaped rocks

The tunable micrometric, mesospongy γ-Al2O3 monolith was formed

through soft templating-assisted synthesis using CTAB as a cationic

surfactant (Scheme 1A). CTAB (0.75 g) was dissolved in a mixture of

2 g of Milli-Q H2O and 10 g of ethanol under continuous stirring at

room temperature for 0.5 h. AIP precursor (7.5 g) was added to the

previous solution, until a homogeneous sol-gel was obtained. The

pH of the final product was adjusted to 1.3 by adding a few drops of

concentrated H3PO4. The isopropanol produced from the AIP

hydrolysis was removed by using a diaphragm vacuum pump

connected to a rotary evaporator at 45°C for 1 h. To complete the

drying process, the resulting optical gel-like carrier material was

dried at 60°C overnight. The as-made solid was calcined at 550 °C in

open air for 5 h to remove the organic moieties or templates and

produce mesospongy γ-Al2O3 monolith scaffold. The

carrier/platform material was crushed to fine powder and stored

for further use in IE manufacturing. The architectural and surface

characteristics of the as-synthesized platform were analyzed using

FE-SEM, HRTEM, XRD, 27

AlNMR, and N2 adsorption isotherm. The

acidic properties of the mesoporous γ-Al2O3 platform provide

positive attributes in creating IEs, thereby enabling easy, intense,

and strong interaction with MPDN and TDDB ligands inside/outside

the mesopores. Moreover, the atomic structural configuration of γ-

Al2O3 platform shows a face-centered cubic Fm-3m crystalline

geometry (Scheme 1B). The crystalline matrices of alumina surface-

coverage domains exhibit that the [O2−

] and [Al3+

] distributions

provide partially negative active sites to form hydrogen bonds with

the hydroxyl groups of MPDN and TDDB chromophores.

Scheme 1

Synthesis and characterization of MPDN and TDDB

Azo dyes of MPDN and TDDB were fabricated by the standard

coupling of diazonium salt of o-aminothiophenol and 2-amino-

1,3,4-thiadiazole with 2-nitroso-1-naphthol and resorcinol,

respectively under freezing temperature (see Electronic

Supplementary Information ESI). The final dye-products were

investigated by 1H-NMR and FT-IR spectroscopies. The

1H-NMR

spectrum of MPDN (at 400 MHz and using CDCl3 as solvent) shows

the corresponded proton peaks as follow: at δ 3.42ppm (H, thiol

group (HS-ph)), δ 5.3ppm (H, phenolic group (HO-ph)), around δ

7.5~7.8ppm (multiplet H, aromatic ring of thiophenol), δ 8.2ppm

(2H, naphthalene). On the other hand, the 1H-NMR spectrum of

TDDB shows the following peaks, δ 5.3ppm (H, equivalent phenolic

proton, Ar-OH), δ 6.2~6.42ppm (H, equivalent aromatic proton), δ

8.3ppm (H, heterocyclic proton). Meanwhile, the FT-IR spectra

confirm disappear of –NH2 peaks because of the azo-dye formation.

FT-IR spectrum of MPDN shows the following peaks: at 3062cm-1

(aromatic C-H, stretch), 1582cm-1

(stretching N=N), 2627cm-1

(stretching, aromatic S-H), 1127-1318cm-1

(stretching C-N), 651cm-1

(stretching C-S), and 1318-1582cm-1

(stretching N=O) and 1039cm-1

(-C-O stretch). While, the FT-IR spectrum of TDDB shows strong

peaks at 3250cm-1

(phenolic, O-H stretching), 3093cm-1

(aromatic C-

H stretching), 1670cm-1

(stretching C=C), 1070cm-1

(stretching C-O),

682-696cm-1

(stretching C-S) and 1551cm-1

(stretching N=N).

Design of mesostructured IEs by direct grafting technique

To obtain the studied IEs, the solid carrier monoliths were well

crushed to fine powder with a mortar to obtain the desired surfaces

for the homogeneity of material sensing and facilitate the analysis

process. Approximately 10 mg of the prepared chelating agents

(MPDN and TDDB) were dissolved well in 100 mL of absolute

ethanol. In a direct grafting procedure, 1 g of ground γ-Al2O3 solid

was added to the ethanolic solution of MPDN and TDDB probes

under continuous stirring for 12 h at room temperature. The

ethanol was removed by a gentle vacuum connected to a rotary

evaporator at 35±1°C temperature. The resulting solid IE monoliths

were thoroughly washed with Milli-Q H2O until no elution of the

chromophore colour was observed. The IEs were dried at 65 °C for 2

h to produce IE-1 and IE-2. The obtained IEs were ground to a fine

powder prior to the Co2+

extraction operation (see Scheme 2). The

acidic characteristic of γ-Al2O3 framework resulted in the strong

binding of ligands, which increased the stability of IEs during the

uptake-elution processes. The immobilized amounts (Qe, ~0.14

mmol/g) of MPDN and TDDB into mesoporous γ-Al2O3 scaffold can

be determined using the following equation:

Q� = �C� − C� V w� �1

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Where Cb and Ca (mmol/L) are the concentrations of MPDN and

TDDB before and after immobilization process, respectively, V is the

volume of ligand solutions (L), and w is the weight of the γ-Al2O3

scaffold (g). The good dressing assembly of ligands inside the

mesoscale pores of γ-Al2O3 improved the interaction/adsorption of

targeted ions. Despite the repeated embedding of chromophores

along γ-Al2O3 pores, γ-Al2O3 preserved their architectural texture.

SLIB remediation stages

The spent and scraped LIBs were remediated in two main stages in

accordance to the method used by H. Zou et al.,46

as shown in

Scheme S1. In the first stage, the scraped SLIBs were collected from

the urban e-waste, crushed to extract the black internal contents,

and ground to obtain a leachable fine powder. SLIB fine powder (1

g) was leached through refluxing with 50 mL of sulfuric acid (H2SO4,

4M) and hydrogen peroxide (H2O2, 30wt%) at 70°C-80°C under

constant stirring for 3 h. The residual solid waste was filtered and

washed with 50 mL of Milli-Q H2O; this stage is called leaching

process. In the second stage, the Fe3+

ion content was separated by

adding NaOH solution until pH ≥ 5, where Fe3+

ions precipitated as

brown Fe(OH)3 precipitates, which presented a considerably low

solubility constant, and other metals remained in the solution. The

final obtained solution was subjected to the following

extraction/adsorption process.

Batch extraction, detection, and recovery of Co2+

ions

In a typical Co2+

ion batch extraction experiment, 20 mg of the

optical IE-1 and IE-2 were stirred with 20 mL of Co2+

ion solution at

the appropriate pH values of 5 and 4 at room temperature, thereby

enabling the accuracy control and sensing efficiency of the IEs

towards Co2+

ion. The clear change in the IE colour as a result of the

formation of [Co2+

/IE]n+

complexes was observed by the naked eye,

as shown in Scheme 2. A blank sample was also prepared by the

same procedure without cobalt for comparison. After the

equilibrium stage, the optical IEs were filtered at room temperature

using a nitrocellulose filter membrane (0.45 μm, Ireland) under mild

vacuum at a pressure of 0.02 MPa to facilitate the colorimetric

analysis. UV-Vis spectrophotometer measurements obtained the

absorbance intensities and visual colours of the blank and

[Co2+

/IE]n+

samples, which provided evidence for the direct

proportionality of absorbance intensities with the concentration of

Co2+

ions. The LOD of the IEs for Co2+

ion-sensing was determined as

follows: 47

�LOD = 3S�S �2

Where Sd and S are the standard deviation and slope of the

calibration graph, respectively. The optical IE-1 and IE-2 were

filtered, and the filtrate was analyzed using ICP-MS to determine

the remaining Co2+

ion concentration after the complete ion-

sensing process. The adsorption capacity and uptake efficiency of

Co2+

ions were determined by measuring a wide-range

concentrations of standard Co2+

ion solutions and estimated using

the following equations: 48, 49

q� = �C� − C� V m� �3

Uptake% = �C� − C�C� ! × 100�4

Where qe is the adsorption capacity (mg/g) of applied IE extractors,

Co and Ce are the concentrations of Co2+

ions before and after

adsorption (mg/L), respectively, V is the volume of the applied Co2+

ion solution (L), and m is the mass of used IEs (g). The effects of pH,

contact time, initial concentration of Co2+

ions, and coexisting ions

were examined to assess the optimal extraction conditions. The

adsorbed Co2+

ions can be released/desorbed/eluted using suitable

stripping agent, such as HCl, to enable the recycling of the

consumed IEs and consequently decrease the extraction cost and

produce pure cobalt. All the experiments were conducted using the

prepared IEs, a standard solution of Co2+

ions or simulated

solutions, and real solutions of SLIBs as a secondary source of

cobalt. E-wasted LIBs were collected from the urban mine, crushed,

and leached using H2SO4 and H2O2 through hydrometallurgy process

to produce a leach liquor, which contained Co2+

ions and other

competitive ions. The practical implementations or actual

extraction processes of Co2+

ions (i.e., from the leach liquor) were

performed at the optimum adsorption conditions.

Scheme 2

Results and discussion Characterization of hierarchical mesoporous γ-Al2O3 monolithic

rocks and IEs

Herein, the microscopic mesospongy γ-Al2O3 monolith particles

were synthesized through direct soft templating and stirring-

assisted approach using CTAB as a cationic surfactant. The

mesostructured γ-Al2O3 monolith was formed using the quaternary

emulsion composition of AIP, CTAB, ethanol, and H2O acidified with

H3PO4 at pH 1.3 in the mass ratio of 1:0.1:0.26:1.3. The current

approach controlled the creation and expansion of new tunable

pores that resemble worm’s channels to produce mesostructured

architectures using CTAB. Quaternary emulsion phases were utilized

for engineering surveillance of pore arrangements, as proven by SA-

XRD, N2-adsorption isotherm, and HRTEM. The cage-shaped

mesoporous feature of the γ-Al2O3 monolith is a considerably

desired trait in chromophore trapping. Consequently, ions were

targeted into the interfaced cavities. The mesoporous γ-Al2O3

monolith was used as a solid support platform to create optical

chemical adsorbents for the detection, capture, and extraction of

Co2+

ions from SLIBs. Despite the vigorous stirring conditions, the

mesostructured alumina monolith maintained the microsized

morphology with the surface pore matrices, which resulted in the

structural stability during cobalt extraction processes.

Figure 1 shows the real and synthetic sample images (Fig. 1A-a, B-

a, and C-a) and FE-SEM micrographs of calcined, hierarchal

mesoporous sponge γ-Al2O3 monolithic rocks (Fig. 1A),

solid/mesosponge MPDN-γ-Al2O3 ion-extractor (IE-1) and Co2+

-

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ion-IE-1 samples (Fig. 1B&C, respectively). Fig. 1A-a, B-a, and C-c

shows evidence of the colour changes (white-to-yellow-to-reddish)

of the synthetic γ-Al2O3 sample with MPDN modification/dressing

and during the extraction/sensing/trapping of Co2+

ions using IE-1,

respectively.

Figure 1Ab-c shows FE-SEM micrographs of solid γ-Al2O3 in

micrometer-sized non-uniform/irregularly shaped rocks in a range

of 25–150 μm with a smooth surface. The outer side

microarchitectures of γ-Al2O3 surface contain small pores/holes in

nanoscale (100-120 nm). These holes are scattered along the top

surface of the γ-Al2O3 monolith to yield a sponge-like shape (as

shown in Fig. 1A-b&A-c). The distance between every two holes is

estimated at approximately tens of nanometers. These neat holes

help in facilitating the diffusion/mass transfer of chromophores and

cobalt ions along carrier’s pores. The upper view of γ-Al2O3 surface

shows evident lines, such as ridges; these ridges may refer to the

overlapping of hierarchical plate sheets during the formation of the

microsized alumina architectures (as shown in Fig. 1A-b, insert). FE-

SEM images of IE-1 (Figure 1B-b, and B-c) show the same

architecture specification of γ-Al2O3 carriers. The images shows the

existence of nanocaves-like grooves, which suggested that

(i) the suitable accommodation of chromophores during the

chemical immobilization process,

(ii) the interior decoration into cage porous frameworks, and

(iii) a formation of layered-probe dressing along the exterior

surface of mesoporous γ-Al2O3 (see Fig. 1B-b&c).

In the same context, Figure 1C-a displays the change in the IE-1

colour from yellow to reddish colour, thereby indicating the

chemical capture/trapping of Co2+

ions at the active sites of IE-1.

Figure 1C-b shows the retention of microarchitectures of IE-1,

despite the severe chemical capture/trapping/extraction process of

Co2+

ions under pH conditions.

Fig. 1C-c shows the SEM-EDX profile of monolithic Co2+

-ion-IE-1

sample, where the elemental content of Al, O, C and Co are 55.23,

42.31, 2.23 and 0.23 %. Furthermore, SEM-EDX profiles provided a

real evidence of the elemental composition of our IEs before and

after adsorption of Co2+

ions. As shown in Fig. S1, the EDX analysis

of γ-Al2O3 substrates showed the Al and O mass ratios of 58.9% and

41.1%, respectively, which are close to the theoretical values. The

high carbon content in the IE framework confirmed the grafting of

chromophores to solid carriers to produce the optical extractors IE1

and IE 2 (see Figs. S1B&C). Figures S1D&E provide evidence about

the adsorption of Co2+

ions and well-defined distribution along IE

monoliths, as shown in the elemental mapping of Al, O, C, and Co.

For example, monolithic Co2+

-ion-IE-1 sample contains 55.23%,

42.31%, 2.23%, and 0.23% of Al, O, C, and Co atoms, respectively.

Figure 1

The top view of FE-SEM clearly exhibits the formation of the spongy

γ-Al2O3 monolith-shaped rocks, as shown in Figs. 2A and 2B. The

microsized γ-Al2O3 framework shows sharp edges and nanorooms

along the surface, which are evident in the HRTEM analysis. Figs. 2C

and 2D show the HRTEM profiles of the γ-Al2O3 monolith, which

present the top-surface edge of the γ-Al2O3 architecture with a

downhill angle of less than 90°; the distance between the two rims

is approximately 110 nm. The end of the edge surfaces is tortuous,

and these sinuous edges enhance the flow of target ion solution

through the solid adsorbents. HRTEM nanographs show that the

worm-like mesopores (~14 nm) are diffused along the surface

regions of γ-Al2O3 domains, which agreed with the SA-XRD profiles.

Fig. 2E displays the electron diffraction profile of γ-Al2O3 monolith.

The profile clearly shows five luminous evident rings, which

correspond to the (220), (311), (400), (511), and (440) planes (from

the inside out). This result shows that the monolithic γ-Al2O3

framework is composed of polycrystalline cubic Fm-3m alumina,

thereby indicating that the γ-Al2O3 crystal grows around the

mesoscale pockets like worm channels; this growth presents the

mesostructured features of γ-Al2O3 carriers. STEM-energy

dispersive spectroscopy (STEM-EDS) mapping profiles provide

evidence of the uniformly distributed Al and O along the

mesosponge surface of the γ-Al2O3 monolith, that is, 58.3% and

41.7%, respectively, and the [Al]:[O] ratio is 1:0.71 (Figs. 2F–2H).

These values are largely close to the EDX mapping values that were

estimated using FE-SEM. The SEM-EDS mapping of solid IE-1, IE-2,

Co2+

-ion-IE-1, and Co2+

-ion-IE-2 samples is shown in Fig. S1.

Figure 2

N2 adsorption–desorption analysis was performed to determine the

specific surface area and porosity of γ-Al2O3 monolith before and

after immobilization of the organic chromophore and after cobalt

trapping.50

Fig. 3A illustrates N2 adsorption–desorption isotherms

with type IV of adsorption behaviour and sharp inflection in

adsorption–desorption isotherms (H2-type hysteresis loops), which

confirmed the mesoporosity of spongy γ-Al2O3 with a typical and

uniform mesocage structure with cramped inlet/nozzle. The

obtained findings can be attributed to the stepwise capillary

condensation of adsorbed species through a tight area of tubular

pores, depending on the amount of CTAB. Evidently, γ-Al2O3 shows

a high BET surface area of 419.8 m2/g, total pore volume

1.3115cm3/g, and pore size of 13.91 nm according to the NLDFT

pore size distributions (Fig. 3B and Table S1). Moreover, the high

surface area and large pore size of this material are remarkably

advantageous in the fabrication of nanocollectors that recognize

and capture ultra-trace amounts of Co2+

ions. The decreases in the

surface area from 419 m2/g to ~ 395 and 399.6 m

2/g, the pore

volume from 1.31 cm3/g to 0.9586 and 0.9598 cm

3/g, and pore size

from 13.9 mm to 12.1 and 12.2 nm for IE-1 and IE-2, respectively,

provide further evidence that a large quantity of chromophores

settled inside the interior mesocavities without blocking/damaging

the cage window of mesopores. The large decreases in surface area,

pore volume and pore size values emphasize the trapping of Co2+

ions (see Table S1).

Figure 3

SA-XRD analysis confirmed the mesoporosity of the γ-Al2O3

monolith. Fig. 3C shows the SA-XRD patterns of as-synthesized γ-

Al2O3, IE-1, and Co2+

-ion-IE-1. All of the examined samples show a

highly acute diffraction peak (Bragg peaks) at ~1.5° (2Ɵ) that is

indexed to (100) reflection with d-values of 10.5, 10.1, and 8.9 nm

for γ-Al2O3, IE-1, and Co2+

-ion-IE-1, respectively. The (100) peak

refers to the highly ordered mesoporous cubic Fm-3m γ-Al2O3

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domains, with of the mesoporosity frameworks retained after CTAB

removal. The decreased Bragg reflection peak and d-values may be

due to the small deficiency of internal pore structure through filling

the pores with organic ligands and Co2+

ions (not a significant

change). The diffraction (100) peaks of IE-1 and Co2+

-ion-IE-1 shift to

angles higher than those of the γ-Al2O3 reflections, thereby

indicating the successful immobilization of chelating agents and

trapping of cobalt ions. Our findings indicated that the highly

intense Bragg peak proves the mesoporosity of γ-Al2O3 despite the

high stuffing level of ligands and cobalt ions inside pores. A typical

diffraction pattern of WA-XRD of calcined γ-Al2O3 monoliths shows

poor crystallinity properties with three main reflections at 2Ɵ of

30°, 46°, and 67°, which correspond to (220), (400), and (440) with

d-values of 2.85, 2.05, and 1.51 nm, respectively. These diffraction

peaks are assigned to the standard values of the γ-Al2O3 with a

cubic unit cell according to JCPDS 10-0425 card number (Fig. 3D).51,

52 In addition, the broad and weak peak lines suggest the poor

crystallinity of the γ-Al2O3 phase. The existence of boehmite crystal

phase during the synthesis procedures can be confirmed by the FT-

IR spectra and TG analysis. Furthermore, the WA-XRD results of IE-1

and Co2+

-ion-IE-1 samples showed the same reflection peaks with

an intensity that is less than that of γ-Al2O3; this result is attributed

to the successful immobilization of chelating agents and trapping of

Co2+

ions into the interior cavities of γ-Al2O3 without change in the

orientational framework of γ-Al2O3 mesopores. The stability and

durability of the mesopore matrices enhance the flow and the

uptake of targeted ions during the extraction process even after

multiple reuse cycles.

The Al coordination frameworks of mesosponge γ-Al2O3 monolith

were investigated using 27

Al MAS NMR, depending on the chemical

shift values. Fig. 4A illustrates the 27

Al NMR spectrum of γ-Al2O3,

where the obtained spectra show two featured coordination

environments at ~0 and ~56 ppm (δ), which correspond to

octahedral (Oh) and tetrahedral (Th) aluminum, respectively; this

result showed that the Al atom is surrounded with six and four O

atoms as AlO6 (AlVI

) and AlO4 (AlIV

), respectively.53, 54

Fig. 4A exhibits

that the formed γ-Al2O3 monolith consists of the equivalent ratio of

AlO6 and AlO4 (approximately 1:1), which indicated the same

intensity of AlO6 and AlO4 peaks. As demonstrated in Fig. 4B, the

functionalization of γ-Al2O3 by chromophores (ligand decoration)

highly decreases the AlO4 peak intensity compared with that in the

AlO6 peak (slight change ) , which suggested that the tetrahedrally

coordinated aluminum is more active than the octahedral

configuration. In the same context, trapping, capture, and

adsorption of Co2+

ion result in a considerable reducing effect in

AlO4 peak intensity, as shown in Fig. 4C. Therefore, interaction and

diffusion occur at the outer surface of the carrier and at the inner

wall surface.

Figure 4

The FT-IR spectra of calcined γ-Al2O3 are presented in Fig. S2. The

broad and strong peak at 3500 cm−1

and the weak one at 1600 cm−1

are strongly attributed to the stretching and bending of adsorbed

water of γ-Al2O3 powder, respectively. The small broad peak at

approximately 2050 and 1390 cm−1

can be assigned to the

vibrational overtones of the surface, namely, the –OH groups of

AlOOH and Al–OH, respectively. The small peak at ∼1500 cm−1

can

be assigned to the C–O asymmetric stretches due to the presence

of AIP as an initial precursor. The peaks in the range of 1000–400

cm−1

are attributed to the Al–O band stretching vibration of

boehmite or pseudoboehmite.55-57

The absorbance of γ-Al2O3

functional groups is more remarkable than that of the functional

groups of immobilized chromophores due to the majority of γ-Al2O3

compared with the considerably low concentration of

chromophores. Therefore, the peak intensities at 1390, 1510, 1640,

and 2350 cm−1

increase as a result of the immobilization process.

The thermal attributes of γ-Al2O3, IE-1, and IE-2 were investigated

to evaluate the durability of the carrier and extractors with

increased temperature, as shown in Fig. S3. The obtained TG profile

of γ-Al2O3 exhibits that γ-Al2O3 as solid carrier loses approximately

5% of its original weight in the range of 27°C–650°C due to the

evaporation of moisture and bound H2O and the remaining

surfactant. The weight losses of IE-1 and IE-2 are ~6% and ~6.5% in

27°C–650°C, respectively. The increased weight loss of IE-1 and IE-2

may be attributed to the removal of the immobilized organic

chelating agent MPDN and TDDB as carbon and nitrogen oxides.

Moreover, the removal of MPDN and TDDB largely occurs in the

range of 27°C–300°C. These results inspire us to regenerate the

solid carrier (i.e., γ-Al2O3) and remove the consumed chelating

agents after repeated use and loss of its effectiveness in the

extraction or trapping of Co2+

ions. The TG studies of γ-Al2O3 and

current extractors presented that the weight loss is diminutive,

which indicated that the used carrier is highly durable under high-

temperature conditions.

Visual detection/adsorption/extraction of Co2+

ions

a. Influences of pH and contact time on the optical

extraction behavior of Co2+

ions

pH plays a pivotal role in the optical monitoring, sensitivity,

selectivity, and rapid extraction of Co2+

ions among other coexisting

ions. Thus, the effect of medium pH to optimize the most

remarkable absorbance signals and obtain stable (target ion–IE)

complex should be studied. Here, pH controls the functionality of

the attached chromophore, thereby making it either neutral or

protonated functional group. A set of optical extraction assays was

conducted by stirring 20 mg of IE-1 and IE-2 with 20 mL of Co2+

solution (1 ppm) at a wide pH range of 1–10. The pH values were

adjusted by adding 5 mL of buffer solutions to the reaction vessel.

The colorimetric detection of Co2+

ions at low and high

concentrations was conducted using UV-Vis spectroscopy. Fig. 5A

indicates that the colorimetric measurements of Co2+

-ion-IE-1 and

Co2+

-ion-IE-1 solids can be carefully studied at the maximum

absorbance (λmax) peaks of 370 and 410 nm, respectively. The

obtained results in Figure S4A exhibited that the highest

absorbance signals (most remarkable signal response) can be

achieved at pH 5 and 4 for IE-1 and IE-2, respectively. The

remarkable changes in absorbance peak are attributed to the high

sensitivity and visual monitoring efficiency of Co2+

ions as a result of

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formation of [Co2+

/IE-1]n+

and [Co2+

/IE-2]n+

complexes. At low pH

values, the optical sensing of studied adsorbents toward Co2+

ions

decreases due to the high protonation of interaction medium,

thereby leading to intense competition with cobalt ions at the

active sites of IE’s surface. This concept inspires us to regenerate

the consumed IEs under acidic pH conditions. After pH 5 and 4, the

absorbance intensities of [Co2+

/IE-1]n+

and [Co2+

/IE-2]n+

complexes

tend to decrease slightly. This decrease in optical signals of IE-1 and

IE-2 may be due to the obstruction of some effective group

functionalities of the impregnated MPDN and TDDB chelating

agents, especially in the alkaline medium, which consequently

decreases the extraction efficiency. Thus, our findings indicated

that the optimum changes in the colour intensity of the [Co2+

/IE-1]n+

and [Co2+

/IE-2]n+

complexes are at pH 5 and 4, respectively. Scheme

2 shows the colour switching of IEs to another colour as a result of

[Co2+

/IE-1]n+

and [Co2+

/IE-2]n+

formation. Our findings indicated that

the mesosponge IEs offer the following advantages: (i) pH-

dependent controlled Co2+

-sensing process, (ii) naked eye

monitoring of the change in IE colour after trapping Co2+

ions, and

(iii) efficient adsorption of Co2+

ions from aqueous solutions.

The effect of contact time on the colorimetric determination of Co2+

ions (i.e., required time to obtain the most remarkable signals) was

also investigated because contact time is significant in the intensity

of the corresponding signals of complex colour as a result of the

binding of Co2+

ions with IEs during the formation of the [Co2+

/IEs]n+

complexes (Fig. S4B.) A series of batch contact tests was performed

through mixing 20 mg of the IE-1 and IE-2 with 20 mL of Co2+

solution (1 ppm) at pH 5 and 4 and room temperature under

continuous stirring for 1–40 min. These findings exhibited that the

most remarkable signal response of the [Co2+

/IEs]n+

complexes at a

specific pH can be achieved within 7–10 min when mixing began,

regardless of the volume of Co2+

ion solution. The absorbance

signals show a relative stability, which provides evidence of the

quick interaction between targeted cobalt and used IEs due to the

chemical bonding with the functional groups of the chromophore

probes. Consequently, the subsequent colorimetric measurements

of Co2+

concentration were conducted after the actual rejoinder

time (≥ 10 min) to guarantee access to the equilibrium state. These

findings are considered satisfying result at the actual extraction of

Co2+

from SLIBs. The analytical ICP-MS data (see Fig. S4C) show the

ability of our extractors to adsorb more than 98.5% and 99% of Co2+

ions within 15 min of contact using IE-1 and IE-2, respectively. This

result proved that the adsorption or extraction of cobalt ions is a

rapid and time-dependent process. Increasing the contact time

enhances the adsorption efficiency to >99% within 30 min, which is

considered a good result in the cobalt extraction and removal

applications. In general, the obtained findings agree with the results

of the spectrophotometric analysis.

b. [Co2+

/IE] complex formation mechanism

The trapping/adsorption of Co2+

ion was studied at pH 5 and 4 using

IE-1 and IE-2, respectively. The chromophoric MPDN and TDDB

ligands immobilized into the platform γ-Al2O3 mesopores show

three charged groups, namely, –SH, –N=N–, and –N=, which can be

neutral or protonated based on the pH of the interaction. The

electronic structures of MPDN and TDDB contain three types of

electron transition orbitals from bonding and nonbonding electron

orbitals to antibonding orbitals as n→ π*, π → π*, and n→ σ* due

to the presence of nonbonding lone pair electrons on the nitrogen

and sulfur atoms. Given the required high transition energy, n→ π*

and π → π* are considered the most common electron donors

during the complex formation, which explained the emergence of

two peaks in the wavelength (λ) range of 350–600 nm (n→ π*) and

200–400 nm (π → π*) (Fig. 5A). The MPDN and TDDB chelacng

agents contain two electron donor groups, and each group

contributes to a pair of free electrons to form coordination bond

with the targeted ion. The metal complexes are created due to the

electron deficiency in the d-orbitals (empty orbitals). Thus, Co2+

ions

can be highly associated with –SH, –N=N–, and –N= groups due to

the electronegativity and protonation of these groups at the

studied pH. Consequently, symmetrical five-membered rings in

octahedral [Co2+

/IEs]n+

complexes with high stability constants are

formed, and hence the colour changes (Scheme 2).

c. Detection boundaries and performance assessment of

prepared IEs

The use of mesosponge IEs causes the high adsorption ability due to

the high surface area, mesoporosity, and pore volume features. IEs

show remarkable results for simultaneous visual detection,

sensitivity monitoring, and simple extraction even at relatively low

Co2+

ion concentrations under the optimum adsorption/sensing

conditions (Fig. 5). The concentration-dependent batch experiments

were conducted to determine the minimum limits of cobalt ions

that can be detected/extracted, where 20 mg of IEs were stirred

with 20 mL of a wide range of Co2+

concentration at pH 5 and 4 and

room temperature for 30 min. Fig. 5B illustrates that the increase in

Co2+

ion concentration results in the increased absorbance intensity

and the colour visible to the naked eye due to the chemically

expanding interaction of Co2+

ions with the exterior/interior

decoration of mesoporous IEs with actively functional MPDN and

TDDB groups, leading to the formation of [Co2+

/IE-1]n+

and [Co2+

/IE-

2]n+

complexes, respectively. As shown in Figs. 5C and 5D, the UV-

Vis spectra of IE-1 and IE-2 show the emergence of new response

peaks at λmax of 370 and 410 nm, respectively, due to the formation

of [Co2+

/IE-1]n+

and [Co2+

/IE-2]n+

complexes. The increase in

absorbance intensity depends on the strength of the obtained

colour between the IEs and Co2+

ions. Figs. 5C and 5D also show the

gradually increased values of (A–Ao) with the increased Co2+

concentration (ppm), where A and Ao are the absorbance values of

[Co2+

/IEs]n+

samples and IEs blank, respectively. Accordingly, the

obtained results indicated that the IE-1 and IE-2 offer a one-step,

fast, and direct optical sensing/adsorption/extraction technique for

Co2+

ions. This finding proved that the optical IE monoliths are

highly efficient in the detection and extraction of Co2+

ions from

SLIB solutions at low and high concentrations.

The sensitivity of the functionalized mesoporous IEs was estimated

through the calibration curve between the absorbance response of

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the IEs blank and Co2+

-ion-IEs samples at λmax of 370 and 410 nm as

a function of Co2+

ion concentration (Figs. S5A and S5B). The

linearity calibration curves of IE-1 and IE-2 show a linear correlation

at wide-range Co2+

ion concentrations, thereby indicating the

possibility of detection, adsorption, and extraction of ultra-trace

and high Co2+

ion concentrations. This observation is attributed to

the highly sensitive/sensing characteristic of the prepared optical

IEs. The accuracy of the calibration curves is considerably significant

to ensure the precision of Co2+

ion detection/extraction. Thus, many

quantitative measurements were performed using a wide range of

standard Co2+

ion concentrations under the optimum pH conditions.

The obtained data of calibration curves suggested that the standard

deviation of the Co2+

ion analysis using IE-1 and IE-2 is less than

0.5%, as shown in Fig. S5. The LOD values of Co2+

ions were

determined from the linear part of the calibration curve (Fig. S5

inserts), where the LOD values of IE-1 and IE-2 are 4.5 × 10−8

and

3.05 × 10−8

M (i.e., equivalent to 2.7 and 1.8 ppb or μg/L),

respectively. These findings demonstrated that our optical IEs can

be used effectively for the detection and extraction of ultra-trace

amounts of Co2+

ions from their sources.

Figure 5

Selective and visual detection/extraction/adsorption of Co2+

ions

In this section, we carried out a basic study of Co2+

ion-selectivity in

water at optimal pH condition using our IEs as an important

function of optical sensor functionalities, in which the selectivity,

sensitivity and visual detection were considered (see Figure 6). Our

study was carried out to evaluate the sensitive detection and

extraction of Co2+

ions in the presence of an equivalent amount of

other competitive cations. Target selectivity is a fundamental

property in the extraction of a Co2+

ion from SLIB wastes. Therefore,

a series of batch-contact tests was carried out as follows: 20 mg of

IE-1 and IE-2 were stirred for 30 min with 20 mL of Co2+

, Li+, Ca

2+,

Mg2+

, Al3+

, Pb2+

, Hg2+

, Cd2+

, Cu2+

, Ni2+

, Fe3+

, Mn2+

, Cr3+

, and Au3+

(1

ppm) separately at optimized pH conditions of Co2+

extraction. The

obtained spectrophotometric results showed that the difference

between the blank (i.e., IE-1 and IE-2) and the [Mx+

/IEs]n+

complexes

is negligible in terms of the visual absorbance intensities, as shown

in Fig. 6A and B. Interfering ions, such as Cu2+

and Ni2+

, show weak

signal responses in UV-Vis spectra upon interaction with the studied

IEs due to the rapprochement/similarity of the chemical and

physical properties of Cu2+

and Ni2+

with those of Co2+

.

Consequently, the extraction process and the IE efficiency are

adversely affected. This challenge can be overcome by using

suitable masking agent. Furthermore, the same experiments were

conducted in binary and mixture systems under the optimum

extraction conditions in the presence of one or more coexisting

cations with Co2+

ions at equivalent concentrations (G1 to G15), as

listed in Fig. 6. The UV-Vis colorimetric spectra indicated that the

existence of foreign ions exerts no significant effect on the visual

colour or the absorbance intensity of the [Co2+

/IEs]n+

complexes, as

illustrated in Fig. 6C.

Due to the SLIBs may contain numerous anionic ingredients. Thus,

our experiments must be conducted to evaluate the extraction of

Co2+

ions among other anionic interfering components. In batch

contact vessel containing 20 mg of applied IEs, 50 ppm of sodium

salt of Cl−, NO3

−, SO3

2−, SO4

2−, and HCO3

−; 75 ppm of PO4

3−, NO2

−, and

C6H5O73−

; and 100 ppm of C2O42−

, C2H3O2−, C4H4O6

2−, CO3

2−, HAsO4

2−,

and CTAB were added separately to 20 mL of 1 ppm Co2+

ion and

stirred for 30 min under optimum pH conditions. Figure S6 showed

that the optical signalling of IEs in the presence of interfering

anionic species. No remarkable influence on the optical signal of

Co2+

ion-IES, indicating the high performance/efficiency of cobalt

ions adsorption/extraction from their solutions into IEs surfaces.

Therefore, our findings indicated the effective feasibility of the

extraction process of Co2+

ions even with increased concentrations

of coexisting ions under the optimum extraction conditions from

SLIBs (see Scheme S1).

To obtain high accuracy, we evaluated the efficiency of the studied

IEs in the extraction/adsorption of Co2+

ions among other

competitive ions in water via ICP-MS analyses. The batch contact

experiments were performed under room temperature and at pH 5

and 4 for IE-1 and IE-2, respectively, in the presence of equivalent

concentrations of the competitive cations in binary and mixture

systems, as listed in Fig. 6D. The obtained results in Fig. 6D

demonstrated that more than 99% of the Co2+

content can be

adsorbed in the absence of other interfering ions. In the presence

of comparable concentrations of other completive cations, the

adsorption efficiency of our optical IEs decreases to 96%–98% due

to the competitive effect of the interfering ions at the

interior/exterior active sites of IEs. The existence of Cu2+

and Ni2+

results in the largest negative effect. Our findings indicated the

possible fast extraction of Co2+

from its ion solutions efficiently,

selectively, even at low concentrations through extraction/

adsorption process. The high adsorption efficiency may be due to

the IEs surface functionalities in terms of (i) meso-/macro-porous

cavities, (ii) effective surface coverages, (iii) high surface are-to-

pore volume ratio, and (iv) the abundance of active sites of our IE-1

and IE-2. These features enable the microsized IEs particles with

multidirectional monolithic hierarchy to adsorb/uptake a large

amount of Co2+

ions. Our findings exhibited that the selectivity of

IEs may be due to the higher thermodynamic binding stability of

Co2+

ions with the active groups of MPDN and TDDB chromophores

than those with other competitive ions under fixed pH conditions.

Figure 6

Adsorption isotherm study of Co2+

ion

The Co2+

ion removal/adsorption isotherms of applied IEs were

investigated under the optimum experimental conditions to

evaluate the relation of the optical IEs with an adsorbed Co2+

ion in

terms of the quantity of adsorbed target ions qm (mg/g) at 25°C ±

2°C, as shown in Fig. S7. Batch experiments were carried out by

stirring 20 mL of Co2+

ions (0.01–500 ppm) with 20 mg of IE-1 and

IE-2. Fig. S7A shows that with the increased amount of the

adsorbed Co2+

(qe, mg/g) according to the increased initial Co2+

concentration, a stable state is reached. After this steady state, the

used IEs cannot accommodate additional Co2+

ions because the

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maximum saturation capacity is reached, where the experimental

qm values of IE-1 and IE-2 are 141.3 and 193.5 mg/g, respectively.

The high saturation capacities may be due to the high surface area

and the mesoporosity features of used IEs, which consequently

increase the number of active sites and allow the good propagation

of Co2+

ions. Thus, many [Co2+

/IEs]n+

complexes are formed along

the macro/meso-grooves of the micrometric monolith surfaces of

IEs, indicating the visual detection/signalling, and removal of Co2+

ions from solution. Moreover, the high surface area is attributed to

the well-accumulated chromophores/chelating agents inside the IE

mesopores. The interaction between Co2+

ions with IEs and the

capacity of these IEs were evaluated at the equilibrium stage using

the linearized form of the Langmuir and Freundlich equations as

follows: 58, 59

%&'& = (

)*'+ + - ('+. C��5

ln q� = lnK3 + (4 ln C��6

Where qm and KL are the theoretical maximum capacity of IEs

(mg/g) and the sorption equilibrium constant, respectively, and KF

and n are the constants relative to the adsorption capacity of IEs

and sorption intensity, respectively. These constants were

estimated from the slopeand intercept of the linear relations by

plotting Ce/qe versus Ce and ln qe versus ln Ce, as illustrated in Table

1 and Figs. S7B&C. The adsorption isotherm of the current optical

IEs for adsorption/trapping of Co2+

ions indicated that the Langmuir

isotherm model more satisfactorily fits than the Freundlich

isotherm model according to the correlation coefficient (Fig. S7C)

(R2 = 0.995 and 0.996 for IE-1 and IE-2, respectively). Theoretical

data of Langmuir constants demonstrated that the qm values of IE-1

and IE-2 are 142.8 and 196.07 mg/g, respectively, which agree with

the experimental findings. Hence, our findings indicated that 1 g of

studied IEs can accommodate approximately 0.143 and 0.196 g of

Co2+

ions from the real solution of leached SLIBs. The obtained data

also showed that all KL and 1/n values are < 1, thereby indicating

the reversibility of the adsorption process. Furthermore, the

adsorption/trapping of Co2+

ion is a chemisorption process, which

suggested that the adsorbed Co2+

ions bind to the active sites or

functional groups of IEs through real chemical bonds.60

The high

adsorption capacity can qualify our IEs effective in the recyclability

of SLIBs and other urban e-wastes.

Adsorption kinetics of Co2+

ion

Evaluation of the kinetic adsorption mechanism of Co2+

ions is

significant for understanding the adsorption behavior based on the

alteration in the contact time. Therefore, a set of batch experiments

wascarried out at a contact time of 2.5–60 min by stirring 20 mg of

optical IE-1 and IE-2 with 20 mL of [2 ppm] Co2+

ions at pH 5 and 4

and at room temperature. Here, the adsorption kinetic models,

such as pseudo-first- and pseudo-second-order models, were

applied according to the following equations.61, 62

log�q� − q8 = log q� −- )9:.<=<. t (7)

8'> = (

)?'&? + - ('&. t (8)

Where k1 (min-1) and k2 (g/mg.min) are the pseudo-first- and

pseudo-second-order rate constants, respectively, and qt is the

adsorbed Co2+

amount (mg/g) at time t (min). The obtained data

indicated that the studied optical adsorption process is considerably

quick; more than 98% of Co2+

ions can be adsorbed within 15 min

(Fig. S8). Complete adsorption/extraction (>99%) can be achieved

quickly using both IE-1 and IE-2. The massiveness of active sites and

easy Co2+

ion diffusion accelerate the extraction process. Numerical

values of unknown parameters can be estimated from the plot of

log (qe–qt) and t/qt versus t, as summarized in Table 1 and Fig. S8.

These findings showed that according to the R2 (>0.97) values, the

pseudo-second-order model is more suitable than the pseudo-first-

order model for the assessment of the optical extraction process of

Co2+

ions using the present IEs. The qe values of pseudo-second-

order model are fitted to the experimental data using 2 ppm as

initial Co2+

concentration (see Table 1). The qe values of pseudo-

first-order model also agree with the experimental saturation

capacity (qm, mg/g).

Table 1

Releasing of adsorbed Co2+

ions from IEs surfaces (i.e.,

recyclability)

In this study, one of the most significant steps in extraction process

is the success elution/releasing of adsorbed Co2+

ions from IEs

surfaces. We offer a comprehensive study to complete the

extraction cycle of Co2+

ions from the leach liquor of SLIBs and

reproduce the spent optical IEs. In this study, the recyclability of the

IEs has gained considerable attention in terms of reduced extraction

cost and the exploited time and effort in the replacement of used

extractors during each operation (see Figure 7-A and 7-C). Basically,

the mechanistic concept of the Co2+

ion-releasing from IEs surface

occurred through the decomplexation of Co2+

-to- ligand binding

events. We can emphasize the success releasing of Co2+

ion via

colorimetric measurements of solid Co2+

-ion-IE-1 sample using

UV-Vis spectroscopy, in which indicating the colour change of

the solid formed [Co2+

/IEs]n+

complexes at IEs surface to its original

colour of IEs visible to the naked eyes. Furthermore, we

quantitatively measured the released Co2+

ion in effluent

solution via ICP-MS analysis (Figure 7A&B).

The Co2+

ion-releasing process allows the recycling of used IEs for

further extraction process. Therefore, many stripping experiments

were performed through a liquid exchange process to elute/desorb

the adsorbed Co2+

ions from solid Co2+

-ion-IEs samples and

consequently obtain cobalt-free IEs in effluent solution, where the

applied IEs were liquidated and dried prior to further extraction

step. In each Co2+

ion-releasing experiment, 50 mg of dried Co2+

-

ion-IEs solids were stirred with 50 mL of [0.2 M] HCl solution. Figure

S9 shows the influences of HCl concentration (0.05–0.35 M) and

stripping time (5–60 min) on the elution process were examined.

Figure S9A presents that the elution % of adsorbed Co2+

ions

increases with the decreased pH of the elution process (i.e., with

increased HCl concentration), where elution % increases from ~30%

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to >99.5% for both IE-1 and IE-2 from 0.05 M to 0.2 M of HCl. At low

pH, the adsorbed Co2+

ions at Co2+

-ion-IEs surfaces may be

replaced with the strong competitive H+ ions, thereby causing the

easy release of cobalt ions (as a CoCl2) in solution. Moreover, the

effect of stripping/elution time was studied from 5 min to 60 min

using HCl (0.2 M) as eluent agent. As depicted in Fig. S9B, the

adsorbed Co2+

ions are completely released (>99.9%) from the

complexes within 30 min.

Our finding shows that a monoprotic acid, such as HCl, effectively

used as eluent or stripping agent to strongly bind with Co2+

ions and

released as CoCl2 in effluent solution, and then form Co2+

-free IEs

solids. IEs solids were subsequently filtered to further extraction

process (i.e., reused/cycles). The elution % of de-trapped/de-

adsorbed Co2+

ions from solid Co2+

-ion-IEs samples can be

calculated by using the following equation: Elution% = (CR/CA) × 100,

where CR and CA are the released and adsorbed Co2+

concentrations

(ppm), respectively (Figure 7A). After 10 cycles of the adsorption–

elution–regeneration processes (1st

round of IEs cycling), the

uptake/adsorption efficiencies of both current IE-1 and IE-2

decrease to 48% and 45% of their original efficiency, respectively

(Fig. 7A). In turn, the elution efficiency (i.e., collection of Co ion

from surface per each experiment) is still high; >99.5% of adsorbed

cobalt can be released even after 10 reuse/cycles, as exhibited in

Fig. 7A. It seems that the building of IEs onto acidic nature carriers

such as γ-Al2O3 may cause a strong linkage with the accumulated

ligands, which results in the retention of ligands during repeated

Co2+

ion adsorption–elution processes. The repeated use of IEs may

lead to the release or decomposition of impregnated chromophores

because of vigorous mechanical stirring during the repeated

operations, as evidenced from the colour response intensity (i.e.,

absorbance) by using UV-Vis spectroscopy. Consequently, the

functional groups and active sites at the IE surface decrease, which

minimizes the extraction efficiency.

Reusability and reproducibility of IEs recycling

To investigate the possibility of extending reusability and

reproducibility of IEs recycling, named as 1st

round IEs recycling

(Figure 7A) to be used for further rounds of recycling (i.e. dead-end

recycling process), see Figure 7B and 7C. To explore the dead-end

usage of IEs recycling, the 10 cycle regenerated IEs (after 1st

round

cycling) surfaces were re-activated to be ready for 2nd

round of

extraction cycling of Co2+

ions (i.e., for further 10 reuse/cycles

continuously), see Figure 7B. This study will open new avenue to

extract cobalt from urban e-waste (such as SLIBs) efficiently and

cost effectively.

As evidently from our experimental sets using UV-Vis. Spectroscopy

of the optimum corresponding absorbance signals of 10 cycling

reused-IEs, there is a significant decrease in chromophore-dressed-

surface functionality within 1st

round, 10 cycling. The decrease in

the potential of the chelating/capturing probes at IEs surfaces leads

to the reduction of cobalt extraction efficiency and thus increase

the required extraction time. For example, the adsorption

capacities of IE-1 and IE-2 decrease after 1st

round, 10 reuse/cycles

from 141 and 193 to 85 and 122 mg/g, respectively. The decrease of

the adsorption/extraction efficiency after 10 reuse/cycles may be

due to the potential influence of the eluent HCl agent on the 1st

round reused-IEs surfaces. Our finding indicated that the eluent

agent inhibits the active-surface-site binding of reused IEs. Thus,

the reactivation of active-surface-binding sites was considered to

any further extraction steps (i.e., 2nd

round of IEs recycling, Figure

7B). Here, we consider two methodology for reactivation of IEs

surfaces: (i) direct re-impregnation through the immobilization of

current chromophores (MPDN and TDDB) into the consumed IEs

after the 10th

cycle directly or (ii) calcination of the consumed IEs

after the 10th

cycle at 250°C–300°C under air atmosphere to remove

the residual organic chelating agent completely as carbon and

nitrogen oxides; consequently, pure mesoporous γ-Al2O3 is

produced as a white solid material with retained effective

functionality and original surface textures. The latter method shows

drawbacks in (i) high-capital cost, (ii) consumed time and

temperature, (iii) mounting poisonous gases, and (iv) prevention of

potential negative effect of calcination in green environment. On

the base of our eco-efficiency e-waste recycles, we considered the

former method of re-addressing of IEs surfaces is more convenient

(named as 2nd

round reused-IEs). We carried out the decoration of

process of MPDN and TDDB probes into reused IES-1 and IES-2,

respectively, as shown in experimental section of first preparation

of IEs. Then we carried out the cobalt uptake/elution processes

(i.e., the 2nd

round of IEs recycling for further 10 reuse/cycles),

Figure 7B. The obtained results (Figure 7B) showed that the uptake

efficiency of Co2+

ions using the re-produced IE-1 and IE-2 (2nd

round IEs recycling) decreases by 2-3% compared with the freshly-

prepared IEs in the 1st

round cycling (Figure 7A), as an axiomatic

result of the reproduction/reactivating of the surface sites of 1st

round reused IEs. By contrast, the elution efficiencies of adsorbed

Co2+

ions remain at ≥ 99%. The extraction process was repeated for

another 10 times of reuse/cycles process and the decrease of Co2+

ion uptake efficiency was observed. For example, at the 10th

cycle

of 2nd

round of reused IEs, the uptake efficiencies of IE-1 and IE-2

decrease to 45% and 43%, respectively (see Fig. 7B).

Significantly, the consumed IEs surfaces (2nd

round recycling) can be

re-activated through direct reimpregnation of MPDN and TDDB

colorants to produce 3rd

round reused IEs. For instance, Figure 7C

shows the representative design of dead-end re-cycling mechanism

of Co2+

ion-uptake/elution processes using IEs. The retention of the

sponge IE design with large surface area-to-volume ratios,

macro/mesopores, and grooves along the micrometric, hierarchal

monolith structures (Figure 7C) enables the reduction of the Co2+

ion extraction cost by recycling the spent extractors for several

reuse/cycle processes (i.e. dead-end recycling process) without

significant changes in the distinct IEs architecture. The design shows

evidence of the full ion-uptake/trapping/recovery into the interior

pores IEs.

Figure 7

Extraction/recovery of Co2+

ions from simulated and real leach

liquors of SLIBs

ICP-MS analysis of the SLIB solutions indicated that the internal

black powder mainly consists of Co2+

, Li+, Ni

2+, Cu

2+, Al

3+, Mn

2+, and

Fe3+

. Therefore, a set of batch experiments was conducted using

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simulated solution similar to the metal content of SLIB leach liquor;

20 mL of 2 ppm Co2+

, Li+, Ni

2+, Cu

2+, Al

3+, Mn

2+, and Fe

3+ ions were

stirred with 20 mg of solid IE-1 and IE-2 in two different beakers

under the optimum pH conditions with continuous stirring for 30

min (Scheme S1). To suppress the interfering cations, few drops of

citrate (0.1 M), thiosulfate (10 mM), and tartrate mixture solution

were added to the above solutions as concealing agents. The

obtained filtrate solution was analyzed by ICP-MS, as summarized in

Table 2. The obtained data showed that 95% and 96.6% of Co2+

ions

are extracted using the optical IE-1 and IE-2, respectively. In

addition, ≥ 99% of the adsorbed Co2+

can be released by using HCl

(0.2 M) as stripping agent. Our findings indicated that the optical IEs

are highly selective for Co2+

ions even in the presence of equal

concentrations of competing ions. These IES can also be recycled.

In actual extraction process (see Scheme S1), the black powder of

SLIBs was leached using a mixture of H2SO4 and H2O2 solution.

Subsequently, the Fe3+

content was eliminated through

precipitation with NaOH. The metal content of the obtained

solution analyzed by ICP-MS is as follows: 1.75 ppm Co2+

, 418 ppm

Ni2+

, 362 ppm Mn2+

, 375 ppm Li+, 1 ppm Al

3+, and 3 ppm Fe

3+, as

listed in Table 2. To evaluate the optical extraction of a Co2+

ion

from the leach liquor of SLIBs, a series of batch contact experiments

was carried out under the optimum extraction conditions (pH 5 and

4 for IE-1 and IE-2, respectively, with continuous stirring for 3 h at

25°C±2°C). Further clarification about the real leaching and optically

tracked extraction is shown in Scheme S1. Optical-IEs (20 mg) were

mixed with 20 mL of the leach liquor in the presence of a mixture of

0.1 M citrate and 10 mM thiosulfate and tartrate solution as a

masking agent to avoid the negative effect of other ions. The

removal/adsorption efficiencies of Co2+

ions decrease at the first

cycle from 95% and 96.6% of the simulated solution to 87.5% and

89% in actual adsorption from leach liquor of SLIBs using IE-1 and

IE-2, respectively (Fig. 8 and Table 2). The decreased uptake may be

attributed to the high concentration of coexisting ions, such as Ni2+

,

Mn2+

, and Li+, which causes the strong competition at the active

sites of the IE surfaces. Furthermore, the adsorbed Co2+

ions can be

extracted/separated (~98%) using HCl (0.2 M) as stripping agents to

produce Co2+

-free IEs. The regenerated IEs extractors can be utilized

for several reuse/cycles through uptake–elution processes. Our

findings indicated that the current optical IEs can be successfully

applied in the extraction of ultra-trace and high concentrations of

Co2+

ions from SLIBs and other urban e-wastes as secondary sources

of cobalt.

Table 2

Figure 8

Conclusion

Laboratory-scale experiments were conducted for fast, selective,

and sensitive extraction, detection, and recovery of Co2+

ions from

SLIBs even at low concentration levels of approximately 3.05 × 10−8

M using effective and low-cost IEs. IEs were fabricated by

functionalization of mesospongy γ-Al2O3 monoliths using MPDN and

TDDB chelating agents. The use of mesosponge IE architecture

results in quick particle diffusion between pores, high adsorption

capacity, and cost-effective operation. The colour change of IEs with

increased cobalt ion concentration can be tracked visually. The key

experimental values, such as pH solution, contact time, Co2+

concentration, and coexisting matrices, are significant for the

efficient extraction of Co2+

ions. Our findings proved that the

extraction process of Co2+

ions is a pH- and time-dependent

process. Langmuir and pseudo-second-order models are the most

convenient models to describe the optical extraction mechanism of

Co2+

ions. In addition, the consumed IEs can be regenerated or

recycled using HCl (0.2 M) as a stripping agent to release or recover

the adsorbed Co2+

ions completely and produce IE-free-surfaces

with retained functionality for multiple usages (i.e.,>20

reuse/cycles). The obtained findings offer a simple, one-step,

efficient, and widely applicable technique to extract cobalt from e-

wastes. This technique can enable e-waste administration and

recycling to obtain precious metals, thereby reducing a large

amount of accumulated e-wastes.

Conflicts of interest

“There are no conflicts to declare”.

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2017, 2, 11083–11090.

38 (a) E. A. Elshehy, S. A. El-Safty, M. A. Shenashena and M.

Khairy Sens. Actuator B-Chem., 2014, 203, 363–374. (b)

S. A. El-Safty, S. Abdellatef, M. Ismael, and A. Shahat, Adv

Healthc Mater., 2013, 2, 854–862. (c) M. A Shenashen, A.

Shahat and S. El-Safty, J. Hazard. Mater., 2013, 244–245,

726–735. (d) M. A. Shenashen, D. Hassen, S. A. El-Safty,

H. Isago, A. Elmarakbi and H. Yamaguchi, Chem. Eng. J.,

2017, 313, 83-98.

39 (a) M. Y. Emran, M. A. Shenashen, M. Mekawy, A. M.

Azzam, N. Akhtar, H. Gomaa, M. M. Selim, A. Faheem

and S. A. El-Safty, Sens. Actuator B-Chem., 2018, 259,

114–124. (b) M. S. Selim, A. Elmarakbi, A. M. Azzam, M.

A. Shenashen, A. M. EL-Saeed and S. A. El-Safty, Prog.

Org. Coat., 2018, 116, 21-34. (c) M. S. Selim, M. A.

Shenashen, A. Elmarakbi, A. M. ELSaeed, M. M. Selimd

and S. A. El-Safty, RSC Adv., 2017, 7, 21796–21808. (d) M.

A. Shenashen, D. Hassen, S. A. El-Safty, M. M. Selim, N.

Akhtar, A. Chatterjee and A. Elmarakbi, Adv. Mater.

Interfaces. 2016, 3, 1600743-1600755.

40 (a) S. A. El-Safty, M. Ismael, A. Shahat and M. A.

Shenashen, Environ Sci Pollut Res., 2013, 20, 3863–3876.

(b) S. A. El-Safty, M. A. Shenashen, M. Khairy, Talanta,

2012, 98, 69–78. (c) M. A. Shenashen, N. Akhtar, M. M.

Selim, W. M. Morsy, H. Yamaguchi, S. Kawada, A. A.

Alhamid, N. Ohashi, I. Ichinose, A. S. Alamoudi and S. A.

El-Safty, Chem Asian J., 2017, 12, 1952-1964.

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41 (a) M. Y. Emran, H. Khalifa, H. Gomaa, M. A. Shenashen,

N. Akhtar, M. Mekawy, A. Faheem and S. A. El-Safty,

Microchim. Acta, 2017, 184, 4553–4562. (b) N. Akhtar,

M. Y. Emran, M. A. Shenashen, H. Khalifa, T. Osaka, A.

Faheem, T. Homma, H. Kawarada, S. A. El-Safty, J. Mater.

Chem. B, 2017, 5, 7985-7996. (c) M. Y. Emran, M.

Mekawy, N. Akhtar, M. A. Shenashen, I. M. EL-Sewify, A.

Faheem and S. A. El-Safty, Biosens Bioelectron., 2018,

100, 122-131.

42 (a) A. Derbalah, S. A. El-Safty, M. A. Shenashen, and N. A.

Abdel-Ghany, Chempluschem., 2015, 80,1119–1126. (b)

M. S. Selim, M. A. Shenashen, N. A. Fatthallah, A.

Elmarakbi, and S. A. El-Safty, ChemistrySelect., 2017, 15,

9686 – 9695.

43 (a) S. A. El-Safty and T. Hanaoka, Chem. Mater., 2004, 16,

384–400. (b) M. Shenashen, A. Derbalah, A. Hamza, A.

Mohamed and S. El Safty, Pest Manag Sci., 2017, 73,

1121-1126.

44 M. Shamsipur, A. Avanes, M. K. Rofouei, H. Sharghi and

G. Aghapour, Talanta, 2001, 54, 863–869.

45 (a) W. Warkocki, S. A. El-Safty, M. A. Shenashen, E.

Elshehy, H. Yamaguchi and N. Akhtar. J. Mater. Chem. A,

2015, 3, 17578–17589. (b) S. A. El-Safty and M. A.

Shenashen, Sens. Actuator B-Chem., 2013, 183, 58-70.

46 H. Zou, E. Gratz, D. Apelian and Y. Wang, Green Chem.,

2013, 15, 1183–1191.

47 A. Shrivastava and V. B. Gupta, Chron. Young Sci., 2011,

2, 21-25.

48 S. A. Al-Jlil, Appl Water Sci., 2017, 7, 383–391

49 S. Hashemian, H. Saffari and S. Ragabion, Water Air Soil

Pollut., 2015, 226, 2212-2222.

50 (a) A. M. Azzam, M. A. Shenashen, M. M. Selim, A. S.

Alamoudi and S. A. El-Safty, ChemistrySelect, 2017, 2,

11431–11437. (b) X. Li, M. A. Shenashen, X. Wang, A. Ito,

A. Taniguchi and S. A. EI-Safty, Adv. Biosys., 2018, 2,

1700114-1700121. (c) X. Li, M. A. Shenashen, X. Wang, A.

Ito, A. Taniguchi and S. A. EI-Safty, Scientific Reports,

2017 7, 16749-16759.

51 (a) S. A. El-Safty , M. A. Shenashen , M. Ismael and M.

Khairy, Adv. Funct. Mater. 2012, 22, 3013–3021. (b) Y.

Jian-hong, S. You-yi, G. Jian-feng and X. Chun-yan, Trans.

Nonferrous Met. Soc. China, 2009, 19, 1237−1242.

52 (a) S. Liu, C. Chen, Q. Liu, Y. Zhuo, D. Yuan, Z. Dai and J.

Bao, RSC Adv., 2015, 5, 71728–71734. (b) S. A. El-Safty, A.

Shahat, M. Ismael, J. Hazard. Mater., 2012, 201–202, 23–

32.

53 (a) S. K. Lee and C. W. Ahn, Sci. Rep., 2014, 4, 4200-4205.

(b) S. A. El-Safty, M. Sakai, M. M. Selim and A. A.

Alhamide, RSC Adv., 2015, 5, 60307–60321.

54 (a) J. R. Houston, R. S. Maxwell and S. A. Carroll,

Geochem. Trans., 2009, 10, 1-14. (b) S. A. El-Safty, J

Porous Mater., 2011, 18, 259–287.

55 J. Yu, H. Bai, J. Wang, Z. Li, C. Jiao, Q. Liu, M. Zhanga and

L. Liu, New J. Chem., 2013, 37, 366-372.

56 L. Wei, F. Li, C. Liu, C. Liu, M. Chen and Q. Lan, Clean:Soil,

Air, Water, 2013, 41, 856–864.

57 Y. Wang, W. Li, X. Jiao and D. Chen, J. Mater. Chem. A,

2013, 1, 10720–10726.

58 (a) D. Zhang, Q. Chen, L. Hu, X. Chen and J. Wang, J.

Mater. Chem. B, 2015, 3, 4363-4369. (b) H. Gomaa, M.

Farid, M. A. Abd-Elraheem, T. A. S. El-Naser and I. H.

Zidan, Biol. Chem. Res., 2016, 3, 313-340.

59 (a) S. Siva, S. Sudharsan and R. Sayee Kannan, RSC Adv.,

2015, 5, 23340–23349. (b) A. M. Azzam, M. A.

Shenashen, M. M. Selim, H. Yamaguchi, I. M. ElSewify, S.

Kawada, A. A. Alhamid and S. A. El-Safty, J. Phys. Chem.

Solids, 2017, 109, 78-88.

60 L. Dolatyari, M. R. Yaftian and S. Rostamnia, J. Environ.

Manage., 2016, 169, 8-17.

61 (a) M. K. Sureshkumar, D. Das, M. B. Mallia and P. C.

Gupta, J. Hazard. Mater., 2010, 184, 65–72. (b) H. G.

Abdien, M. F. M. Cheira, M. A. Abd-Elraheem, T. A. S. El-

Naser and I. H. Zidan, Elixir Appl. Chem., 2016, 100,

43462-43469.

62 S. Mishra, J. Dwivedi, A. Kumar and N.

Sankararamakrishnan, RSC Adv., 2015, 5, 33023–33036.

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Scheme 1 (A) Systematic synthesis and (B) crystal structure/composition framework of micrometric sponge, mesoporous cage γ-Al2O3 carriers using CTAB as a directing agent and AIP as a precursor in an acidic condition. B) The crystal structures provide evidence of the formation of dense electron along the active Al and O species in the exterior/interior surfaces, leading to facile and

strong binding with target species during the extraction/detection/recovery process.

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Scheme 2 The systematic perspective of Co2+

ion-optical/adsorption/recovery process using IE- and IE-2 designs that were built by direct impregnation/dressing of organic chelating agents (such as MPDN and TDDB colourants) onto meso-γ-Al2O3 carriers,

respectively. Under the visualization protocol of our process, the IE-1 and IE-2 changed their original colour within the Co2+

trapping at pH 5 and 4, respectively.

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Fig. 1 Real and synthetic sample images (A-a, B-a, and C-c) and representative top-view FE-SEM micrographs of calcined, hierarchal mesoporous sponge γ-Al2O3 monolithic rocks (Fig. 1A), solid/mesosponge MPDN-γ-Al2O3 ion-extractor (IE-1) and

Co2+

-ion-IE-1 (Fig. 1B &C, respectively). Figure C-c shows the SEM-EDX of monolithic Co2+

-ion-IE-1 sample, proving that the elemental composition of IE-1 and the trapping of Co

2+ ions.

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Fig. 2 (A, B) Representative FE-SEM, (C, E) HRTEM and (E) electron diffraction mico-graphs of

mesoporous, micro-sponge γ-Al2O3 monoliths. Figs. F-H show the STEM-EDS mapping of γ-

Al2O3 monoliths with display the distribution map of aluminum (G) and oxygen (H).

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Fig. 3 (A) N2 adsorption-desorption isotherm profiles of calcined γ-Al2O3 (blue line), IE-1 (red line) and IE-1/Co2+

(green line) including the values of surface area (SBET, m2/g ), pore size (D, nm) and pore volume (Vp, cm

3/g). (B)

NLDFT profile to explain the pore size distribution of γ-Al2O3, IE-1 and IE-1/Co2+

. (C and D) SA/WA-XRD pattern of

γ-Al2O3, IE-1 and IE-1/Co2+

.

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Fig. 4 27

Al MAS NMR spectra of γ-Al2O3 (A), IE-1 (B) and IE-

1/Co2+

(C).

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Fig. 5 (A) Real UV/Vis spectra of IEs-1 and 2 in blank form (before adsorption/trapping Co

2+ ions) and [Co

2+/IE]

n+ form. Indicating the generate new

peak at wavelength λmax= 370 and 410 nm for IE-1 and 2 at pH 5 and 4, respectively.

(B) Colour-profile shows the increasing of [Co2+

-IE]n+

colour with increasing of Co2+

ion concentration under the optimum sensing conditions. (C and D) UV-Vis spectra show the gradual proportional change of absorbance intensity of IE-1 (C) and IE-2

(D) depending on Co2+

concentration at pH 5 and 4, respectively.

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Fig. 6 Representative selective-profile of [2ppm] Co2+

adsorption/extraction among other competitive cations

in water using IE-1 and IE-2 at the optimal detection/extraction/capture conditions: We added the

competitive ions to the IEs assays as we called single/individual ion-system (A), binary and mixture systems

G1-G15 (colorimetric study, at wavelength λmax= 370 and 410 nm) (B) and (ICP-data) (C) at pH 5 and 4,

respectively. Our UV-Vis spectroscopic study and ICP-MS analyses show the high selective-extraction of Co2+

ions. G1{Co2+

+Li+}, G2{Co

2++Ca

2+}, G3{Co

2++Mn

2+}, G4{Co

2++Cu

2+}, G5{Co

2++Ni

2+}, G6{Co

2++Al

3+}, G7{Co

2++Hg

2+},

G8{Co2+

+Pb2+

}, G9{Co2+

+Cr3+

+Au3+

}, G10{Co2+

+Hg2+

+Pb2+

}, G11{Co2+

+Cd2+

+Li+}, G12{Co

2++Al

3++Pb

2++Hg

2+},

G13{Co2+

+Cu2+

+Mn2+

+Li++Ca

2+}, G14{Co

2++Ni

2++Cu

2++Ca

2++Mn

2++} and

G15{Co2+

+Li++Mg

2++Ca

2++Pb

2++Hg

2++Cr

3+}.

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Table 1 shows the isotherm and kinetic models of Co2+

adsorption using optical-IEs 1 and 2 at pH 5 and 4, respectively.

Langmuir

isotherm

Freundlich

isotherm

pseudo

first-order

pseudo

second-order

IE-1

Experimental

qm (mg/g) 141.3

R2 0.9952 R

2 0.9313 R

2 0.501 R

2 0.994

qm 142.8 KF, mg/g 22.2 qe, mg/g 140.05 qe, mg/g 2.29

KL, L/mg 0.161 1/n 0.3611 K1, min-1

1.8X10-4

K2, g/mg.min 0.139

IE-2

Experimental

qm (mg/g) 193.5

R2 0.9969 R

2 0.8843 R

2 0.51 R

2 0.996

qm 196.07 KF, mg/g 29.2 qe, mg/g 192.2 qe, mg/g 2.27

KL, L/mg 0.183 1/n 0.3969 K1, min-1

2.6X10-5

K2, g/mg.min 0.15

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Fig. 7 (A & B) Uptake and elution efficiencies of Co2+

ions using IE-1 and IE-2 as a function of adsorption-releasing cycle

numbers. To evaluate reusability and reproducibility of IEs in the extraction process, we carried out a set of experimental assays based on monitoring the Co

2+ extraction efficiency under continuous IE regeneration protocol. In this regard, we

treated 1st

used-IEs after 10th

reuse/cycles (A) by re-addressing and activating their surfaces by decorated-probes (MPDN and TDDB) to develop and generate 2

nd used-IEs. Note: The 1

st and 2

nd used-IES re-cycling protocol showed the dead-end

regeneration/extraction of Co2+

ions. The elution efficiencies of adsorbed Co2+

ions are more than ≥99% of the adsorbed Co

2+ ions. (C) Representative scheme of dead-end re-cycling protocol of Co

2+ ion-uptake/elution processes using

mesoporous IEs. The scheme shows evidence of the full ion-uptake/trapping/recovery into the interior pores IEs.

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Table 2. ICP-MS analysis data of Co2+

ions before and after adsorption and after elution in the presence of other competitive ions using

optical-IEs 1 and 2

[Co2+

], ppm % [Competitive ions], ppm

Simulated-Extraction

Before adsorption 2.1± 0.004 -- Li

+ 2.05, Ni

2+ 1.98, Cu

2+ 2.0, Al

3+ 1.89, Mn

2+ 2.1, Fe

3+ 2.05, Ca

2+ 3, K

+ 10

After adsorption

IE-1

IE-2

0.105±0.006

0.07±0.005

95.0

96.6

Li+

2.01, Ni2+

1.95, Cu2+

1.98, Al3+

2.1, Mn2+

2.03, Fe3+

2.03, Ca2+

2.99, K+

9.99

Li+

1.98, Ni2+

1.93, Cu2+

1.95, Al3+

2.14, Mn2+

2.07, Fe3+

2.04, Ca2+

3, K+

9.98

After elution

IE-1

IE-2

1.98±0.001

2.01±0.002

99.2

99.0

Li+

0.04, Ni2+

0.032, Cu2+

0.02, Al3+

0.08, Mn2+

0.06, Fe3+

0.02, Ca2+

0, K+

0.003

Li+

0.06, Ni2+

0.046, Cu2+

0.048, Al3+

0.12, Mn2+

0.031, Fe3+

0.012, Ca2+

0, K+

0.01

Real-Extraction

Leach liquor

3.5±0.006

--

Li+

375, Ni2+

3.6, Cu2+

1.5, Al3+

1.0, Mn2+

362, Fe3+

0.3, Ca2+

4.9, K+

47.5

After adsorption

IE-1

IE-2

0.435±0.003

0.39±0.0015

87.5

89.0

Li+

360, Ni2+

3.4, Cu2+

1.4, Al3+

1.45, Mn2+

345, Fe3+

0.2, Ca2+

4.8, K+46.5

Li+

363, Ni2+

3.2, Cu2+

1.37, Al3+

1.5, Mn2+

350, Fe3+

0.25, Ca2+

4.8, K+47.3

After elution

IE-1

IE-2

3.0±0.0062

3.05±0.0025

97.8

98.0

Li+

3.2, Ni2+

0.08, Cu2+

0.08, Al3+

0.3, Mn2+

3.2, Fe3+

0.055, Ca2+

0.05, K+

0.1

Li+

4.5, Ni2+

0.15, Cu2+

0.09, Al3+

0.2, Mn2+

2.54, Fe3+

0.063, Ca2+

0.02, K+

0.05

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Fig. 8 Real applicability shows the high efficient extraction process of Co2+

ions from a real solution of SLIBs using IEs-1 (A) and

IE-2 (B) at pH 5 and 4, respectively. These figures show the concentration (in ppm) of Co2+

ions and other co-existing ions (Li+,

Ni2+

, Cu2+

, Al3+

, Mn2+

, Fe3+

, Ca2+

, and K+) in leach liquor, after adsorption and after elution.

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ARTICLE Journal Name

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Page 26 of 26Green Chemistry

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