Chemical Synthesis Methods of Nanomaterials
The goal of any nanomaterial synthesis approach is to create a material that acquires properties due to its length in the range of 1-100 nanometers. Therefore, synthetic methods should exhibit size control in this range so that novel properties can be obtained. There are two methods for the synthesis of nanomaterials and the preparation of nanostructures. The top-down approach refers to the slicing or sequential cutting of bulk materials to obtain nanoparticles. The bottom-up method refers to the bottom-up accumulation of matter, that is, the gradual accumulation of an atom or molecule. Both approaches play an important role in nanotechnology.
Figure 1: Schematic diagram of designing nanomaterials based on sol-gel and polymer-based chemical strategies
Types of Chemical Synthesis
Sol-Gel Method
The sol-gel method is a well-established industrial process for the preparation of colloidal nanoparticles from the liquid phase. It is an advanced nanomaterial synthesis and coating preparation method developed in recent years. During this process, the sol (or solution) gradually forms a gel-like network consisting of liquid and solid phases. Typical precursors are metal alkoxides and metal chlorides, which undergo hydrolysis and polycondensation reactions to form colloids. The basic structure or morphology of the solid phase varies from discrete colloidal particles to continuous chain-like polymer networks. The preparation of oxide nanoparticles and composite nanopowders by the sol-gel method has good application prospects. Its main advantages are low processing temperature, high versatility, flexible rheology, and easy molding and embedding.
Aerosol Method
Aerosols are suspensions of fine solid particles or liquid droplets in air or other gases. Aerosols can be natural or man-made. Examples of natural gas soles are fog, dust, forest seepage, and geyser vapors. Aerosols produced by chemical methods are a type of artificial aerosols. The aerosol method uses a similar principle to form a solid or liquid in the gas phase into products ranging in size from molecular sizes to 100 microns. This is a common method for producing nanoparticles industrially.
Atomic/Molecular Condensation Method
This method is mainly used for the synthesis of metal-containing nanoparticles. The bulk material is heated in a vacuum to generate a vaporized and atomized stream of material that is directed to a gas chamber containing an inert or reactive gas. The rapid cooling of the metal atoms leads to the aggregation and formation of nanoparticles due to their collisions with gas molecules. If a reactive gas such as oxygen is used, metal oxide nanoparticles are produced.
Hydrothermal Synthesis
Hydrothermal synthesis is a method for producing various compounds and materials by flowing materials in an aqueous solution at 100°C and 1 atmosphere or more in a closed system. The method is based on improving the solubility of water and aqueous solutions under high temperatures and pressure, so that almost insoluble substances under normal conditions, such as certain oxides, silicates, sulfides, etc., can be dissolved in aqueous solutions to synthesize nanomaterials.
Spray Drying
Spray drying is a method in which liquid droplets are injected into a carrier gas (usually air), heated to 100-300°C, and then solid particles are separated, solvents are removed from solutions and suspensions. The main difference between this method and aerosol pyrolysis is that the temperature of the gas carried by it is lower, which usually does not cause complete thermal decomposition of the salt in solution, and the generation of aerosol is completed using a nozzle, so as to create a larger scale, performance Better nanomaterials. Spray drying is one of the main methods for the production of dry products and pharmaceuticals in the food and pharmaceutical industries.
Low-Temperature Chemical Synthesis
Low-temperature chemical synthesis is a method for synthesizing materials and nanomaterials based on low-temperature chemical processes. The most common of these methods is low-temperature chemical synthesis using aqueous solutions. In this case, a solution, suspension, or chemical co-precipitate containing the components of the initial solution of the cations of the synthetic material is snap-frozen in a stoichiometric ratio and freeze-dried in a vacuum, followed by thermal decomposition to synthesize a grain size (40- 300 nm) oxide powder.
References
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2. Tour, J. M. (2000). Molecular electronics. synthesis and testing of components. Accounts of Chemical Research, 33(11), 791-804. https://doi.org/10.1021/ar0000612
3. Mukasyan, A. S. , & Dinka, P. . (2007). Novel approaches to solution-combustion synthesis of nanomaterials. International Journal of Self-Propagating High-Temperature Synthesis, 16(1), 23-35. https://link.springer.com/article/10.3103/S1061386207010049