Mechanochemistry: Synthesis that Uses Force

Grinding is a basic physical process, and the grinding tools “mortar and pestle” have been in use since times immemorial. It has been practiced in almost all spheres of human life from kitchen to laboratories as well as in large industrial processes. Chemical synthesis by applying force or the “mechanochemistry” has been employed as a synthetic procedure for a long time but now the need to adopt “greener”, cost-effective and less harmful methods of synthesis has brought back the mechanochemistry to forefront in last decade. It has emerged as the one of the most efficient, advantageous and environmentally benign alternatives to traditional synthesis routes for the preparation of nanomaterials for advanced applications. The features such as ease of operation, simplicity of equipment, high reproducibility, relatively mild reaction conditions and the solvent-free condition (in case of dry milling) have made it the synthesis technique of choice for the synthetic chemist. It is used for synthesizing a wide variety of both single-phasic and composite materials varying from inorganic solids (oxides and non oxides), organic compounds, polymers, metal complexes, metal–organic frameworks. Materials with applications in varied areas such as hydrogen storage materials, energy applications, pharmaceuticals, as well as advanced nanocatalysts have been synthesized using this method. In recent times, the dry grinding or milling has been further modified by addition of a small amount of solvent or polymer, also called liquid-assisted grinding or polymer-assisted grinding that yields different products, speeds up the reaction and also ensures better usage of reactants. The fact that mechanical force or shear is the driving force for the reaction, and it also presents a novel way to obtain hitherto unknown (and interesting) products. The chapter discusses the basics of mechanochemical synthesis along with the above-mentioned points in the details.