Inorganic Synthesis

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• Single Crystals

• Zeolites and Related Materials

• Organic-Inorganic Hybrid Materials

• Ionic and Electronic Conductors

• Nanomaterial

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Single Crystals

• One of the most important applications of the hydrothermal technique

is the synthesis and growth of bulk single crystals.

• bigger, purer, dislocation-free single crystals

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crystal growth

Hydrothermal conventional liquid-solution

slow diffusion high solubility

problem of diffusion

• slow diffusion has little effect on crystal growth in a process of

hydrothermal crystal growth because the viscosity of hydrothermal

mediums is much lower than that of near-ambient solutions.

• Because diffusion is significantly faster at hydrothermal conditions, the

growth rate of crystals is faster and regents of low solubility can be used to

grow crystals.4Fe

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• General, the stages of crystal formation that include small

aggregations of chemical precursors give unstable germ nuclei, some

of these embryos become large enough to be stable nuclei, and

spontaneous deposition of more material on such nuclei results in

larger crystallites.

• native elements, oxides, silicates, phosphates, chalcogenides, halides,

germanates, carbonates, and so on, have been prepared and grown by

this technique.5Fe

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• the hydrothermal technique is being employed on a large scale to

prepare electronic, magnetic, optic, ceramic, and a host of other

materials, both as single crystals and polycrystalline materials.

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ZnO crystals grown by the hydrothermal method

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ZnO crystals grown by the hydrothermal methodFerdo

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Zeolites and Related Materials

• Zeolites are basically prepared from hydrothermal systems.

• In the 1940s, zeolites were firstly hydrothermally synthesized by R.

M. Barrer and his coworkers through the simulation of the

geothermal formation of natural zeolites.

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• scientists at Mobil corp. (1960s) use organic amines and quaternary alkyl-

ammonium cations as templates in the hydrothermal synthesis of high-

silica zeolites.

• In 1982, Wilson S. T. and Flanigen E. M. et al. (Union Carbide

Corporation, UCC) hydrothermally synthesized a novel family of

microporous aluminophosphates AlPO4-n

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• Aluminosilicate zeolites

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Organic-Inorganic Hybrid Materials

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• Organic-inorganic hybrid materials are generally produced using

various methodologies of “soft” inorganic chemistry in liquid or sol-

gel medium.

• Hydrothermal and solvothermal → organic-inorganic hybrid materials

coordination polymers and clusters

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Mo6Cl142−

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• Why Hydrothermal and solvothermal reactions

increase the solubility of reactants

enhance the reactivity of reactants

grow perfect crystal materials

prepare important metastable phases

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• MOF (also known as porous coordination polymer) materials are currently

the hottest in the field of hybrid materials and have attracted wide

scientific attention.

• Promising applications such as the storage of gases, molecular separation

from the gaseous and liquid mixtures, catalysis, sometimes showing the

enantioselectivity, and sensors for special classes of molecules.

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crystal structures of IRMOF-74

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Ionic and Electronic Conductors

• Ionic conductors are useful materials in many fields such as energy

conversion, chemical sensors, combustion control, high temperature

membrane reactors, and chemical processing.

• Traditionally, ionic conductors are produced from high temperature

solid-state reactions with the resulting aggregates requiring a

subsequent milling process.18Fe

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• Since fabrication of advanced and complex ionic conductors always

require homogeneous and pure powders with fine and uniform

particle sizes, an effective synthesis procedure is needed.

• Mild hydrothermal synthesis below 240 °C and under autogenous

pressure has been a promising route for preparing novel ionic

conductors.

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• Advantages

mild synthesis temperature, reaction homogeneity, high purity and

controlled size, and morphology, which tend to improve or

dramatically change the physical properties of the final products.

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• Codoped nanocrystalline ceria-based compositions

Ce1-xMxBi0.4O2.6-x (M = Ca, Sr, and Ba, x = 0.01-0.15)

• HZr2P3O12, Bi17V3O33, K8Sb8P2O29.8H2O

• M3HGe7O16.xH2O (M= NH4+, Liþ, Na+, K+þ, Rb+, and Cs+)

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Nanomaterial

• The hydrothermal or solvothermal technique is not only used to

process the simplest nanomaterials but also acts as one of the most

attractive techniques for processing nanohybrid and nanocomposite

materials. 22

• The hydrothermal or solvothermal technique has become one of the

most important methods for the fabrication of nanostructural

materials.

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HYDROTHERMAL BIOCHEMISTRY

• It was hypothesized that rich chemical reactions occurred in the warm

sea and all microorganisms have high temperature ancestors.

• It is found that most microorganisms living at very high temperatures

are archaea on the molecular biological tree.

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• Hydrothermal process used to decomposed waste.

• hydrothermal synthesis (chemistry) provides new materials, helps to clean

up our environment, and helps to understand the origin of life.

• Current research of hydrothermal biochemistry provides evidence of chemical

synthesis, microbiology, molecular phylogenetic tree, and exploration of the

sea, such as simulated hydrothermal conditions, the abiotic synthesis of H2,

NH3, CH4, CH3COOH, cytosine, uracil, peptide, and computer simulation of

thermodynamic of amino acids synthesis, as well as molecular simulation of

amino acids into peptides on zeolite. 24Ferdo

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SUPERCRITICAL WATER: A NOVELREACTION SYSTEM

• The term “supercritical” is usually restricted to water close to its critical point

(374.1 °C and 22 Mpa (220 bar)), hence close to its critical density.

• At 25 ° C and 0.1013 MPa, liquid water has a density of 0.997 g cm3 and water

vapor has a density of 2×105 g cm3.

Temperature ↑ density of the liquid ↓ vapor density↑

• At the critical point both phases become identical and the dividing meniscus

disappears. The critical temperature, pressure, and density are: 374.1 °C, 22.1 MPa,

and 0.322 g cm3. 25Ferdo

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• SCW technology used to

separation extraction destruction of hazardous wastes

biomass conversion, gasification, synthesis of organic chemicals,

organometallic catalysts, material processing.

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PROPERTIES OF SUPERCRITICAL WATER

• The physicochemical properties of water are highly dependent on the

intensive variables of temperature and pressure.

• At the critical point (374.2 °C and 22 MPa), the vapor and liquid

phases of water become indistinguishable. At or near this state, water

has low density, high diffusivity, low viscosity, high compressibility,

and a breakdown of hydrogen bonding.27Fe

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• Above the critical point, a single homogenous fluid phase exists with

properties intermediate between the gas phase and liquid phase. The

density, compressibility, viscosity, and diffusivity of water in this

region are extremely sensitive to changes in temperature and

pressure.

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• Two of the most important properties of water are its ion product and

dielectric constant.

• The dissociation constant Kw of liquid water

25 °C and 0.1013 MPa 10-14

450 °C and 25 Mpa 10-22

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• At constant pressure,

Temperature ↑ the dielectric constant of water ↓

• 400-500 ºC, pressures (>60 MPa) → dielectric constant above 4

NaCl insoluble in water

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• At the supercritical state → the water hydrogen bonding breaks

IR and X-ray, and Raman spectroscopy

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• the thermal conductivity of SCW is slightly lower than that of liquid water.

Liquid water has a thermal conductivity of 0.598 W m-1 K-1, and the

thermal conductivity of SCW is 0.418 W m-1 K-1.

• The viscosity of SCW at 400C and 50 MPa is about 15 times lower than

that of liquid water (The low viscosity causes high mobility of both water

and solute molecules)

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• As the consequences of high mobility, solute diffusion coefficients, self-diffusion

coefficients, and ionic mobility are much larger in SCW than in liquid water,

which help to form homogeneity in mixtures of SCW and solutes.

• The diffusion coefficient of SCW is much larger than that of liquid water.

• diffusion coefficient (liquid water)) at 25 ºC and 0.1013 MPa → 7.8 × 10-6 cm2 s-1

SCW at 450 ºC and 27.0 MPa → 7.7 × 10-4 cm2 s-1

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CHEMICAL APPLICATIONS OF SUPERCRITICAL WATER

• Water has an advantage over most supercritical fluids as it is safe,

nontoxic, readily available, inexpensive, and environmentally benign.

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TECHNOLOGICAL APPLICATIONS OFSUPERCRITICAL WATER

• Supercritical water oxidation (SCWO) is a novel and innovative

treatment process for the destruction of hazardous waste, which is

made possible due to the special properties of SCW.

• waste treatment technology SCWO can be simply described as

pressurized streams of aqueous waste and oxidant, such as oxygen or

hydrogen peroxide, mixed and heated to supercritical conditions.

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• A typical SCWO process is conducted at temperatures and pressures

of 500-650 °C and 25-35 MPa, respectively. When water achieves

critical temperature and critical pressure (374.1 °C and 22 MPa), it

can act as a nonpolar solvent because of greatly reduced hydrogen

bonding and polarity. Additionally, the dissociation constant of water

decreases from 10-14 at normal conditions to about 10-23 at typical

SCWO conditions.36Fe

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• In SCW condition:

• Organic substances solubility ↑

• inorganic salts substances ↓

• gases are completely miscible

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• 1- one phase reaction

• 2- at typical SCWO conditions, viscosity is approximately one-ortieth

of its value at normal conditions, resulting in high diffusivities.

• Thus, the reactants, including water, organic wastes, and the oxidant,

are brought together in a homogeneous single-phase where oxidation

proceeds rapidly and should be limited primarily by chemical kinetics

and not by transport processes.

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• Short time

• The oxidation of organic wastes will only result in products such as

CO2, molecular nitrogen (N2 or N2O), and water.

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• Heteroatoms such as chlorine, sulfur, and phosphorus can be

transformed to their mineral acids and consequently be neutralized

using a suitable base. Typical undesired and noxious byproducts SO2

or NOx of combustion processes will not be formed because their

oxidation pathways are not favored by the lower temperatures of

SCWO comparing to incineration, which is the most commonly used

waste treatment technology.40Fe

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• These are the three reasons why SCWO has not yet become a current

waste treatment process:

• 1. Severe reactor corrosion caused by acids, which are formed during

the waste treatment process.

• 2. Serious plugging of the reactors caused by precipitating salts at

supercritical temperatures and low densities.

• 3. Due to lack of experimental data, cost evaluations, especially for

the scale-up of SCWO plants to an industrial scale, are unreliable.

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TECHNIQUES AND METHODS

• Reaction Containers

• Reaction Control Systems

• General Experimental Procedure

• In Situ Characterization Techniques

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REACTION CONTAINERS

• High-pressure vessel, popularly known as an autoclave

• 1. Should have high mechanical strength to bear high pressure and

temperature experiments for long duration;

• 2. Should have excellent acid, alkali, and oxidant resistance;

• 3. Should have a simple mechanical structure and easy to operate and

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REACTION CONTAINERS

• 4. Should have good sealing performance to obtain the required

temperature and pressure;

• 5. Should have a suitable size and shape to obtain a desired

temperature gradient.

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• Externally Heated and Internally Pressurized Autoclave

• Externally Heated and Externally Pressurized Autoclave

• Internally Heated and Externally Pressurized Autoclave

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REACTION CONTROL SYSTEMS

• Safety is the utmost important issue when working in chemical

laboratory.

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GENERAL EXPERIMENTAL PROCEDURE

• 1. To choose suitable reagents;

• 2. To determine the mole ratio of reagents;

• 3. To explore addition order of regents and mix the regents;

• 4. To put the mixture of regents into an autoclave and seal the

autoclave;

• 5. To choose suitable reaction temperature, reaction time, and

reaction state (dynamic or static crystallization);

• 6. To take out the autoclave from the oven and cool the autoclave to

room temperature;

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GENERAL EXPERIMENTAL PROCEDURE

• 7. To open the autoclave and take out the products from the

autoclave;

• 8. To process the products (such as wash, filtrate, and dry);

• 9. To observe the appearance of products by using an optical

microscope;

• 10. To characterize the products by using suitable research

instruments48Fe

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IN SITU CHARACTERIZATION TECHNIQUES

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IONOTHERMAL SYNTHESIS

• Recently, a novel synthesis method for preparing inorganic functional

materials, known as ionothermal synthesis, has prompted a

significant amount of research. The term “ionothermal” was used to

describe reactions that are conducted in ionic liquids (IL) at high

temperature.

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• IL, as the reaction medium of ionothermal, are now being defined as

salts composed solely of ions with melting points below 100 °C,

• The first ILs, or organic molten salts, were discovered in 1914

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• The cationic part of most common ILs are organic-based moieties

such as imidazolium, pyridinium, quaternary ammonium, quaternary

phosphonium cations, or nitrogen-rich alkylsubstituted heterocyclic

cations.

• The anionic part can be organic or inorganic and include such

entities as some halides, nitrate, acetate, hexafluorophosphate (PF6),

tetrafluoroborate (BF4), trifluoromethylsulfonate (OTf), and

bis(trifluoromethanesulfonyl)imide (NTf2).

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• It should be noted there is a special class of ILs named as deep

eutectic solvent (DES). Unlike ILs, DES is a type of mixed solvent

composed of two or more compounds which form a eutectic. A DES

consists of ionic compounds and molecular compounds. The melting

point of DES is much lower than either of the individual components.

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• 1. ILs have many unique physicochemical properties, and the

coexistence of ionic and organic groups and the large temperature

windows of ILs make them ideal media for the reactions between

metal ions and organic ligands. With these attributes, ionothermal

synthesis is considered to be more environmentally friendly and safer.

• 2. In the synthesis of inorganic materials, the IL, the reaction medium

of ionothermal synthesis, can participate as solvent, structure-

directing agent or template agent, structure-inducting agent, charge-

compensating group, or ionic liquid (crystal) precursor.54Fe

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• 3. The IL solvent systems offer a novel chemical environment that

can uniquely influence the course of chemical reactions. Therefore,

ionothermal synthesis can result in inorganic materials with special

structure or properties, which are difficult or impossible to obtain by

using other traditional synthesis routs.

• 4. The ionothermal synthesis can be performed at ambient pressure,

which is due to the negligible vapor pressures of almost all ILs. As a

result, ionothermal synthetic reactions avoid the high pressures of

traditional hydro(solvo)thermal reactions and therefore eliminate

safety concerns associated with high pressures. 55Fe

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• 5. ILs have been proven to be a good medium for absorbing

microwaves. Therefore, microwave technique can be safely used in

the ionothermal synthesis reactions.

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