ORIGINAL PAPER

Effect of a spacer on phthalocyanine functionalized cellulosenanofiber mats for decolorizing reactive dye wastewater

Shi-Liang Chen • Xiao-Jun Huang • Zhi-Kang Xu

Received: 31 January 2012 / Accepted: 22 March 2012 / Published online: 5 April 2012

� Springer Science+Business Media B.V. 2012

Abstract We report a novel cobalt tetraaminopht-

halocyanine (CoPc) functionalized nanomaterial by

spacer-arm immobilization of CoPc onto cellulose

nanofiber mats. The spacer-arm was attached through

the reaction of tetraethylenepentamine with oxidized

cellulose nanofiber mats. CoPc was then covalently

immobilized onto the spacer-arm using glutaralde-

hyde. The functionalization processes on the nanofiber

mats were monitored by attenuated total reflection

Fourier transform infrared spectroscopy and X-ray

photoelectron spectroscopy. This CoPc functionalized

nanomaterial (CoPc-spacer-NM) was used for decol-

oration of reactive dye wastewater. Incorporation of

the spacer-arm resulted in enhanced decoloration with

respect to directly immobilized CoPc onto the cellulose

nanofiber mats (CoPc-NM). Compared with CoPc-

NM, CoPc-spacer-NM shows much higher adsorption

capacity when conducted under acidic conditions,

which enhances the catalytic oxidation rate of reactive

dye when H2O2 was used as an oxidant. Reactive dye

wastewater can also be efficiently decolorized by the

CoPc-spacer-NM/H2O2 system under basic condi-

tions, despite a relatively weak adsorption capacity.

Electron paramagnetic resonance results suggested

that the catalytic oxidation process involves the

formation and reaction of hydroxyl radicals. Gas

chromatography–mass spectrometry showed the main

products of the catalytic oxidation of reactive red X-3B

were biodegradable aliphatic acids, such as oxalic acid,

malonic acid and maleic acid.

Keywords Cellulose nanofiber mats �Phthalocyanine � Immobilization � Spacer-arm �Nanomaterial � Decoloration

Abbreviations

CoPc-NM CoPc functionalized nanofiber mats

CoPc-spacer-NM CoPc functionalized, spacer-arm

attached cellulose nanofiber mats

OC-NM Oxidized cellulose nanofiber mats

TEPA-NM Tetraethylenepentamine attached

nanofiber mats

GA-NM Glutaraldehyde activated

nanofiber mats

Introduction

Metal phthalocyanines (MPcs) have attracted consid-

erable interest because of their structural similarity to

metalloporphyrin complexes found at the active sites

Electronic supplementary material The online version ofthis article (doi:10.1007/s10570-012-9701-9) containssupplementary material, which is available to authorized users.

S.-L. Chen � X.-J. Huang � Z.-K. Xu (&)

MOE Key Laboratory of Macromolecular Synthesis and

Functionalization, Department of Polymer Science and

Engineering, Zhejiang University, Hangzhou 310027,

China

e-mail: xuzk@zju.edu.cn

123

Cellulose (2012) 19:1351–1359

DOI 10.1007/s10570-012-9701-9

of metalloenzymes, suggesting their potential as

catalysts for oxidation (Sorokin et al. 1995; Tao

et al. 2001, 2002; Lin et al. 2008; Sorokin and Kudrik

2011). The catalyst effectiveness of MPcs is substan-

tially affected by aggregation of the phthalocyanine

complexes, which is specific to this type of molecule

(Iliev et al. 1999; Kluson et al. 2008b). Consequently,

direct dispersion of MPcs in solvent will reduce their

catalytic activity. In practical applications, MPcs are

often attached to inert and insoluble supports (Sorokin

and Tuel 1999; Chen et al. 2007, 2009; Chang et al.

2009; Ratnasamy and Srinivas 2009; Zanjanchi et al.

2010). Heterogeneous catalysts provide significant

advantages in easy separation of catalysts from

reaction products, re-use of catalysts in subsequent

oxidations, simplified product purification processes,

and reduction of inactive phthalocyanine molecule

aggregates.

The main problems associated with the use of

immobilized catalysts are the diffusion limitations of

target molecules within the reaction medium (Bayra-

moglu et al. 2004; Arica et al. 2009) and steric

hindrance between the support surface and the immo-

bilized catalyst (Fernandez-Lorente et al. 2007;

Ozyilmaz 2009). It is thus important that the choice

of support material and immobilization method are

well understood. Electrospun nanofiber mats are a

promising support for catalyst immobilization due to

several attractive characteristics: they have a high

surface to volume ratio, relatively large pores, and all

pores are fully interconnected to form a three dimen-

sional network. As a result, the entire surface of

nanofiber mats is fully accessible to substrates (Li and

Xia 2004). Incorporation of spacer-arms between

catalyst and support is another effective method to

overcome the effects of diffusion limitations and steric

hindrance (Mita et al. 2003a, b; Arica et al. 2004,

2009; Ozyilmaz 2009). The introduction of a spacer-

arm can, to some extent, locate the catalyst at a

distance from the support surface. As a result,

diffusion limitation effects, steric hindrance and other

undesired interactions can be minimized.

In our previous work, cobalt tetraaminophthalocy-

anine (CoPc) was covalently immobilized onto elec-

trospun cellulose nanofiber mats (Chen et al. 2011).

Cellulose was chosen because of its attractive charac-

teristics, such as low cost, good mechanical properties,

and high stability in most organic solvents. Moreover,

it has a high density of hydroxyl groups, on which

different reactions can be carried out according to

needs (OSullivan 1997; Heinze and Liebert 2001;

Jonoobi et al. 2010). The resultant nanomaterial,

CoPc-NM, is able to efficiently decolorize reactive

dye wastewater. To further minimize the effects of

diffusion limitation and steric hindrance and improve

the decoloration efficiency of this nanomaterial, the

present study aimed to combine the advantages of

cellulose nanofiber mats and spacer-arms for the

preparation of a novel CoPc functionalized, spacer-

arm cellulose nanofiber mat (CoPc-spacer-NM). The

surface of the oxidized cellulose nanofiber mat (OC-

NM) was chemically modified with tetraethylenepent-

amine (TEPA, i.e., spacer-arm) and CoPc was then

covalently immobilized onto the aminated nanofiber

mats using glutaraldehyde (GA) as a coupling agent.

The decoloration capacity of CoPc-spacer-NM for the

treatment of reactive dye wastewater was studied and

compared with that of CoPc-NM. Electron paramag-

netic resonance (EPR) was used to check the forma-

tion of active species during the reaction. The catalytic

oxidation products were analyzed by gas chromatog-

raphy–mass spectrometry (GC–MS).

Materials and methods

Materials and reagents

Cellulose acetate (29.6 %, acetyl content), cobalt

chloride hexahydrate, 4-nitrophthalic acid, ammo-

nium molybdate, urea, hydrogen peroxide and isopro-

panol were analytical reagents and purchased from

Sinopharm Chemical Reagent Co. Ltd. (Shanghai,

China). Tetraethylenepentamine (TEPA) was pur-

chased from Tianjin Fuchen Chemicals Reagent

Factory and used without further purification. Glutar-

aldehyde (GA) was purchased from Wulian Chemical

Factory, Shanghai, China. Cobalt tetraaminophthalo-

cyanine was synthesized from 4-nitrophthalic acid,

cobalt chloride hexahydrate and urea according to the

method described by Achar et al. (Achar et al. 1987).

Reactive red X-3B (C19H10Cl2N6Na2O7S2, C.I. Reac-

tive Red 2, M.W.: 615.33) was purchased from

Shanghai Chemical Reagent Company (China) and

used as received. Hydrogen peroxide (30 wt%) was

obtained from Beijing Chemicals Co. The reagent 5,5-

dimethyl-1-pyrroline-N-oxide (DMPO) used as the

spin-trapping agent was purchased from Sigma

1352 Cellulose (2012) 19:1351–1359

123

Chemical Co. Water used in all experiments was

de-ionized and ultrafiltrated to 18 MX with an

ELGA LabWater system. An initial concentration of

100 lmol/L of reactive red X-3B solution was

prepared using this ultrafiltrated water. All other

chemicals were of analytical grade and used without

further purification.

Preparation of CoPc-spacer-NM

Cellulose acetate nanofiber mats (CA-NM), regener-

ated cellulose nanofiber mats (RC-NM), oxidized

cellulose nanofiber mats (OC-NM) and CoPc func-

tionalized nanofiber mats (CoPc-NM) were prepared

as described in our previous work (Chen et al. 2011).

For preparation of CoPc-spacer-NM, following

steps were performed: 20 mg of OC-NM was added

to 48 mL TEPA solution (8 %, v/v) and shaken for

12 h at 25 �C. The TEPA attached nanofiber mats

(TEPA-NM) were then submerged into 12 mL GA

solution (2 %, v/v) and shaken for 2 h at 25 �C. The

GA activated nanofiber mats (GA-NM) were taken

out, washed 3 times with ultrapure water and dried

at 60 �C under vacuum. The resulting matrix was

suspended in a 2 9 10-2 mol/L CoPc solution. After

reaction for 3 h at 25 �C, the product was washed with

dimethylformamide (DMF) to remove residual CoPc

and then rinsed three times with ultrapure water.

CoPc-spacer-NM was obtained by drying the nanofi-

ber mats at 60 �C under vacuum. CoPc content on the

CoPc-spacer-NM was calculated to be 403 lmol/g,

according to the cobalt content on the CoPc-spacer-

NM measured by atomic absorption spectrometry

(Thermo solar M6). The functionalization steps are

schematically represented in Fig. 1.

Characterization of nanofiber mats

The surface composition of all the nanofiber mats,

including OC-NM, TEPA-NM, GA-NM and CoPc-

spacer-NM, were verified by attenuated total reflection

Fourier transform infrared spectra (ATR/FT-IR) and

X-ray photoelectron spectroscopy (XPS). ATR/FT-IR

spectra were acquired with a Vector 22 FTIR

spectrometer (Brucker Optics, Switzerland) equipped

with an ATR accessory (KRS-5 crystal, 45�). Each

spectrum was taken by 32 scans at a nominal

resolution of 4 cm-1. XPS spectra were drawn on a

PHI-5000C ESCA system (PerkinElmer, USA) with

Al Ka radiation (1,486.6 eV).

Decoloration procedures and analysis

Adsorption of reactive red X-3B was carried out in a

glass flask sealed in a water bath at 50 �C. For a typical

adsorption process, 2 mg of CoPc-spacer-NM or

CoPc-NM was added to 5 mL reactive red X-3B

solution (100 lmol/L). The pH of the synthetic

wastewater was adjusted by H2SO4 or NaOH. At

given time intervals, the samples were analyzed

immediately on a UV–vis absorption spectrometer

UV-2450 at the wavelength of maximum absorbance,

539 nm. The concentration of reactive red X-3B was

calculated from a standard curve of the dye. The

concentration change of reactive red X-3B was

expressed as the change of C/C0 value, where C0 is

the initial concentration of the dye, and C is the

residual concentration of the dye.

The catalytic oxidation was initiated by adding

8 mM H2O2 to a reactive red X-3B solution containing

CoPc-spacer-NM or CoPc-NM, as described above.

Fig. 1 Synthesis route for CoPc immobilized onto spacer-arm attached cellulose nanofiber mats

Cellulose (2012) 19:1351–1359 1353

123

The analysis method for concentration change of

reactive red X-3B during the reaction was the same as

for the adsorption process. The catalytic oxidation rate

for both CoPc-spacer-NM and CoPc-NM was calcu-

lated as follows:

Catalytic oxidation rate ðlmol min�1 g�1Þ

¼ 100� 5� 10�3 � 90%

t � 2� 10�3 � CCoPc � 10�6 � 630ð1Þ

where t is the time needed for catalytic oxidation of

90 % of the reactive red X-3B, CCoPc is CoPc content

on CoPc-spacer-NM or CoPc-NM, which is 403 and

365 lmol/g, respectively. EPR signals of radicals

spin-trapped by 5,5-dimethyl-1-pyrroline-N-oxide

(DMPO) were examined with a Bruker-A300 X-band

EPR spectrometer (Bruker, Karlsruhe, Germany). The

settings for the EPR spectrometer were as follows:

center field, 3480 G; sweep width, 100 G; microwave

frequency, 9.77 GHz; modulation frequency, 100 kHz;

power, 12.72 mW.

GC–MS analysis was performed using an Agilent

Technologies 6,890 N gas chromatography coupled

with 5973i mass spectrometry detection (Helium as

carrier gas, HP-5MS crosslinked 5 % PH ME Siloxane

as separation column, electron impact ionization at

70 eV). For analysis of the products of reactive red

X-3B decolorized by the CoPc-spacer-NM/H2O2

system, CoPc-spacer-NM (20 mg) and H2O2 (8 mM)

were added to 50 mL of reactive red X-3B solution

(100 lmol/L, pH = 10). After 20 min of reaction at

50 �C, the resulting solution was withdrawn, 0.1 mL

H2SO4 was added to reduce the solution pH below 2,

and then the water was removed under vacuum. The

resultant dry residue was dissolved in 5 mL methanol

and 0.1 mL H2SO4 (1 M) was added to the solution for

methanol esterification. The combined methanol frac-

tion was dried with anhydrous sodium sulfate and then

analyzed by GC–MS.

Results and discussion

Preparation and characterization of CoPc-spacer-

NM

CoPc-spacer-NM was prepared through covalent

immobilization of CoPc onto chemically modified

OC-NM. All the functionalization steps were moni-

tored by attenuated total reflection Fourier transform

infrared (ATR/FT-IR) spectroscopy (Fig. S1). After

oxidation (Fig. S1(a)), the characteristic absorption

peak at 1,739 cm-1 was attributed to the vibration of

C=O, suggesting the existence of aldehyde groups on

the surface of OC-NM (Ma and Ramakrishna 2008;

Chen et al. 2011). The obvious decrease of the

characteristic peak for the aldehyde group and

appearance of the new characteristic peak at

1,565 cm-1 (dN–H) confirm the successful introduc-

tion of TEPA spacer-arm on OC-NM (Fig. S1(b)).

After the activation step, the intensity of the charac-

teristic peak at 1,735 cm-1 increased again, corre-

sponding to the unreacted aldehyde group of GA

(Fig. S1(c)). The successful immobilization of CoPc

on cellulose nanofiber was verified by new character-

istic peaks at 1,261, 1,344 and 1,491 cm-1, which

were ascribed to the skeleton stretching and C–N

stretching of CoPc (Stillman and Mack 2001). The

new characteristic peak at 1,608 cm-1 was attributed

to C=N of CoPc (Fig. S1(d)).

The modification of OC-NM involves the attach-

ment of TEPA onto OC-NM and activation of the

resulting product with GA. Covalent immobilization

of CoPc was achieved by reaction between the amino

groups on the peripheral CoPc and the aldehyde

groups on the surface of the chemically modified

nanofiber mats. X-ray photoelectron spectroscopy

(XPS) was used to analyze these reactions and the

results are shown in Fig. 2. After attachment of the

spacer-arm, the spectrum of TEPA-NM shows an

increase in signal at a binding energy (BE) of about

402 eV (Fig. 2b), which is the characteristic peak of

N1 s. The residual amino group of TEPA was then

used for CoPc immobilization with GA as a coupling

agent. After reaction of CoPc, one can see that the

characteristic peak of N1s increased remarkably

(Fig. 2c). Furthermore, two new peaks were detected

at binding energies of 795.6 and 780.8 eV (Fig. 2,

inset). They were assigned to the characteristic peaks

of Co 2p1/2 and Co 2p3/2, respectively. These results

confirmed the immobilization of CoPc on the nano-

fiber mats and the preparation of CoPc-spacer-NM.

Adsorption and catalytic oxidation behavior

The direct immobilization of CoPc onto cellulose

nanofiber mats may result in diffusion limitations for

substrate movement to the CoPc pendants. Further-

more, steric hindrance will occur between the support

1354 Cellulose (2012) 19:1351–1359

123

surface and the immobilized CoPc. We expected to

reduce this steric hindrance by introduction of a

spacer-arm to locate CoPc at a distance from the

support surface. Moreover, after incorporation of the

spacer-arm, CoPc was scattered over a wider area,

which enables easier diffusive transport of dye mol-

ecules to the CoPc (Fig. S2).

In our previous work, we showed that catalytic

oxidation occurs when dye molecules were adsorbed

onto the surface of CoPc-NM. An increased adsorp-

tion capacity can thus improve the catalytic oxidation

efficiency (Chen et al. 2011). Here, we examined the

adsorption of CoPc-NM and CoPc-spacer-NM at

different pH values and the results are shown in

Fig. 3. Clearly, both CoPc-NM and CoPc-spacer-NM

adsorbed dye molecules more efficiently at low pH

values. This phenomenon is attributed to the strong

electrostatic interaction between CoPc and dye mol-

ecules at low pH values (Chen et al. 2011). It is

interesting that the introduction of the spacer-arm

greatly enhanced the adsorption capacity in CoPc-

spacer-NM. At pH 6, the concentration of reactive red

X-3B decreased by 75 % using CoPc-spacer-NM as an

adsorbent, 3-fold higher than that of CoPc-NM. This

result confirms that the introduction of a spacer-arm

can make the contact between dye molecules and

CoPc pendants much easier.

pH is one of the most important parameters for

reactive dye adsorption and thus influences the

catalytic properties of CoPc-spacer-NM. Here, the

catalytic oxidation behavior of CoPc-spacer-NM/

H2O2 at different pH values was examined, compared

with that of CoPc-NM/H2O2. The results are shown in

Fig. 4. In accordance with the adsorption behavior, the

catalytic oxidation rate was high after introduction of

the spacer-arm. At pH 2, 4 and 6, the catalytic

oxidation rates of CoPc-spacer-NM were found to be

19.69, 11.07 and 7.40 lmol min-1 g-1, much higher

than that of CoPc-NM (10.87, 4.65 and 2.96 lmol

min-1 g-1, respectively).

The above results indicate that CoPc-spacer-NM

has a strong adsorption capacity for reactive red X-3B

under acidic conditions. In the presence of H2O2, the

reactive dye can be efficiently oxidized. Here, an

attempt was made to study the decoloration behavior

of this nanomaterial under basic conditions (Fig. 5). In

800 700 600 500 400 300

810 805 800 795 790 785 780 775 770

b

Co 2p1/2

Co 2p3/2

Binding energy (eV)

c

O 1s

N 1s

C 1s

Binding Energy (eV)

a

b

c

Fig. 2 XPS spectra recorded from the surfaces of a OC-NM; b TEPA-NM; c CoPc-spacer-NM. The window included shows in detail

the Co region

Cellulose (2012) 19:1351–1359 1355

123

accordance with the results of acidic conditions,

reactive red X-3B was quite stable and difficult to

decolorize in the presence of H2O2 (Fig. 5a). Although

the adsorption behavior is quite interesting, only about

15 % of dye molecules were adsorbed onto the CoPc-

spacer-NM when dynamic equilibrium was reached in

60 min (Fig. 5b). This phenomenon can also be

explained by the electrostatic interaction behavior

(Chen et al. 2011). Under basic conditions, the

concentration of H? in the dye solution is negligible

and it is difficult for the amino groups of CoPc to

accept a proton to form NH3?, resulting in weak

electrostatic interactions between CoPc and the

anionic dye. Although the adsorption of dye molecules

under basic conditions was much weaker than that

under acidic conditions, the catalytic oxidation rate

was very fast when both CoPc-spacer-NM and H2O2

were present, and the concentration of reactive

dye decreased by 90 % within only 12 min, i.e.,

73.85 lmol min-1 g-1 (Fig. 5c), compared with

28 min (i.e., 34.95 lmol min-1 g-1) for CoPc-NM

under the same reaction condition (Fig. S3). The

catalytic oxidation mainly depends on electron dona-

tion and acceptance after coordination between the

central metal ions of phthalocyanine and reactants

(Tao et al. 2002; Chen et al. 2009). This coordination

process is strongly affected by pH. Under basic

conditions, HOO- is dissociated from H2O2, which

is favorable for coordination with Co2? in the CoPc-

spacer-NM for catalytic oxidation. Although the

adsorption of reactive dye is not strong, this relatively

weak adsorption can still provide efficient decolor-

ation of reactive dye due to the fast catalytic oxidation

rate (see supplementary data in Figure S4).

The reuse and stability of a catalyst are two major

factors to be considered for practical application of a

process. The catalytic activity of CoPc-spacer-NM in

cyclic utilizations was carried out and slightly

decrease in decoloration efficiency was found. The

catalytic activity was still excellent after recycling five

times (Fig. 6). No CoPc absorbance peak in the range

of 600–800 nm was observed by UV during the

reaction. This indicates that the CoPc-spacer-NM is

recyclable for consecutive catalytic oxidation of

reactive red X-3B in water, which is of vital impor-

tance in industrial applications.

1 2 3 4 5 6 70.0

0.2

0.4

0.6

0.8

1.0 CoPc-NM CoPc-spacer-NM

(C0-C

)/C

0

pH

Fig. 3 Effect of initial pH value on adsorption of reactive red

X-3B in the presence of CoPc-spacer-NM or CoPc-NM

1 2 3 4 5 6 70

75

150

225

300

375

CoPc-NM CoPc-spacer-NM

Tim

e (m

in)

pH

Fig. 4 Effect of initial pH value on time needed for catalytic

oxidation of 90 % of reactive red X-3B with CoPc-spacer-NM/

H2O2 or CoPc-NM/H2O2

0 10 20 30 40 50 600.0

0.2

0.4

0.6

0.8

1.0

C/C

0

Time (min)

a

b

c

Fig. 5 Concentration changes of reactive red X-3B (initial

concentration 100 lM, T = 50 �C, pH = 10) under various

conditions: a H2O2 (8 mM); b CoPc-spacer-NM (2 mg);

c CoPc-spacer-NM (2 mg) and H2O2 (8 mM)

1356 Cellulose (2012) 19:1351–1359

123

Analysis of catalytic oxidation mechanism

The reactive species produced by MPcs during catalytic

oxidation have been studied and free hydroxyl radicals

(Tao et al. 2001, 2002; Kuznetsova et al. 2009), singlet

oxygen (Kluson et al. 2008a) or the metal-peroxo

complex (Sorokin et al. 1995, 1996) were suggested. As

a first step in elucidating the reactive species responsible

for reactive red X-3B degradation, we carried out a

catalytic oxidation experiment in the presence of

isopropanol, an effective •OH radical scavenger (Smith

et al. 2004; Mrowetz and Selli 2005; Salem et al. 2009;

Yang et al. 2009), to inhibit catalytic oxidation mediated

by •OH radicals. We found that the addition of

isopropanol markedly retarded the degradation of dye

in the CoPc-spacer-NM/H2O2 system (Fig. 7). This

result indirectly implies that the •OH radical is indeed

involved in the catalytic oxidation of reactive dye.

To gain insight into the nature of short-lived

radicals formed during catalytic oxidation of reactive

dye by the CoPc-spacer-NM/H2O2 system, the EPR

spin-trap technique was employed to provide useful

information on the reaction mechanism and the result

is shown in Fig. 8. Without the addition of H2O2, no

obvious signal was detected (Fig. 8a). When H2O2

was added in this reaction system, a strong radical

signal was observed (Fig. 8b). The characteristic four

peaks of DMPO-•OH adducts with an intensity of

1:2:2:1 are consistent with similar spectra reported by

others for •OH adducts (Yamazaki and Piette 1991;

0

20

40

60

80

100

(C0-

C)/

C0

Number of cycles

(i)

1 2 3 4 5

1 2 3 4 50

20

40

60

80

100 (ii)

(C0-C

)/C

0

Number of cycles

Fig. 6 Repetitive catalytic oxidation of reactive red X-3B

(100 lM, T = 50 �C) in the presence of CoPc-spacer-NM

(2 mg) and H2O2 (8 mM): (1) pH = 2, reaction time = 50 min;

(2) pH = 10, reaction time = 16 min

0 4 8 12 16 20 24 28

0.0

0.2

0.4

0.6

0.8

1.0

C/C

0

Time (min)

a

b

Fig. 7 Effect of isopropanol on catalytic oxidation of reactive

red X-3B (initial concentration 100 lM, CoPc-spacer-NM

2 mg, [H2O2] = 8 mM, T = 50 �C, pH = 10). a without

isopropanol; b with addition of 1 M isopropanol

3480 3500 3520 3540

Magnetic field (G)

a

b

Fig. 8 DMPO spin trap EPR spectra of reactive red X-3B

solutions (initial concentration 100 lM, CoPc-spacer-NM

2 mg, T = 50 �C, pH = 10). a without H2O2; b with addition

of 8 mM H2O2

Cellulose (2012) 19:1351–1359 1357

123

Sui et al. 2011), and this indicates that •OH radicals

are generated and participate in the degradation of dye.

To further investigate the mechanism of the cata-

lytic oxidation of reactive dye by the CoPc-spacer-

NM/H2O2 system, the products of reactive red X-3B

after catalytic oxidation were directly identified by

GC–MS. The total ion current diagram of GC–MS is

shown in Fig. 9. Additional data are given in supple-

mentary data (Fig. S5–Fig. S12), 8 residual organic

acids can be identified: oxalic acid (4.469 min),

2-hydroxybenzoic acid (5.121 min), malonic acid

(5.964 min), maleic acid (7.528 min), fumaric acid

(7.579 min), benzoic acid (8.802 min), glutaric acid

(9.354 min) and adipic acid (10.949 min).

Conclusion

In this study, CoPc was covalently immobilized onto

spacer-arm modified cellulose nanofiber mats via

glutaraldehyde coupling for the preparation of a novel

nanomaterial CoPc-spacer-NM. This CoPc-spacer-

NM offers a promising catalytic material for the

decoloration of reactive dye wastewater with H2O2 as

an oxidant. Under acidic conditions, the incorporation

of the spacer-arm results in a significant increase in

catalytic oxidation capacity due to an enhanced

adsorption capacity. Reactive dye can also be effi-

ciently decolorized under basic conditions, with more

than 90 % of dye pollutants eliminated in 12 min.

Indirect methods and direct EPR results strongly

indicate the formation of •OH reactive radicals during

the catalytic oxidation process. The main catalytic

oxidation products were biodegradable aliphatic acids,

such as oxalic acid, malonic acid and maleic acid.

Acknowledgments The authors are grateful to the financial

support from the National Natural Science Foundation of China

for Distinguished Young Scholars (Grant no. 50625309).

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