About the sector - EUON
Manufacturing - Bottom-up - About the sector Text
Bottom-up methods often involve self-assembly processes. Many of these methods are often called nucleation growth methods because the growth often forms periodically and, as a result, certain crystal networks are formed. The output of these methods is often much lower than top-down approach. Therefore, it is often used for specific applications or for providing a tailored solution to a problem. However, there are bottom-up methods, which are used to produce nanoparticles commercially. The controllability of the process is generally much higher compared to top-down methods, which leads to the production of high-quality nanomaterials.1
Bottom-up manufacturing approaches include chemical vapor deposition (CVD), sol-gel, solvothermal and hydrothermal, soft and hard templating, co-precipitation, reverse micelle methods, among others. The description of several common methods is provided below.
- Chemical vapour deposition (CVD) is significant in the production of carbon-based nanomaterials. In this approach, a chemical reaction of vapour-phase precursors is used to form a thin film on the substrate surface. The choice of a catalyst is important for the morphology and the type of nanomaterial obtained. This method is great for producing high-quality nanomaterials and is well-known for the synthesis of two-dimensional nanomaterials.
- Sol-gel method is a wet-chemical technique that is extensively used for the manufacturing of various kinds of high-quality metal-oxide-based nanomaterials. Several steps are taken to complete the synthesis of nanoparticles via this method. The steps include hydrolysis, condensation, aging, drying, and calcination. Sol-gel manufacturing method is economically friendly and has other advantages, such as low processing temperature, homogeneous nanomaterials, and simplicity of the process to produce composites and complex nanomaterials.
- Solvothermal and hydrothermal method is one of the most extensively used processes to produce nanomaterials. In hydrothermal method, the nanostructured materials are obtained through a heterogeneous reaction that is performed in an aqueous hydrothermal medium at high temperature and pressure around a critical point in a sealed vessel. In solvothermal method, the only difference is a non-aqueous medium. These two processes are useful methods for the production of nanowires, nanorods, nanosheets, and nanospheres.
- Soft and hard templating methods are widely used to manufacture nanoporous materials. The soft template method is a simple conventional method for the generation of nanostructured materials. The soft template method is advantageous due to its relatively mild experimental conditions, straightforward implementation, and the development of materials with a range of morphologies. Nanoporous materials are produced using soft templates, such as flexible organic molecules, block copolymers and various surfactants. In the hard template method, also called nano-casting, well-designed solid materials are used as templates, and solid template pores are filled with precursor molecules to achieve nanostructures for required applications. A broad range of unique structured nanomaterials can be produced using these two methods (Baig et al., 2021).
- Co-precipitation method is one of the earliest processes used to synthesised nanomaterials. It is the most basic, extensively used approach to produce a wide range of nano-structured materials. This approach uses a precipitation reaction to achieve a consistent composition of two or more cations in a homogeneous solution. Precipitates are aged to produce bigger particles, which are collected via filtration or centrifugation. Additional wash with ethanol, distilled water or other solvent is required to remove contaminants and obtain high purity nanoparticles. This approach has the advantage of producing homogenous nanomaterials with small sizes and size distribution (Abid et al., 2021).
1 Critchley, L. (2019). Nanoparticle Manufacture - What Methods Are There? AzoNano. Available at: https://www.azonano.com/article.aspx?ArticleID=5122