*3.3.2 Solvothermal/hydrothermal method*

Solvothermal or hydrothermal synthesis method is termed depending upon the solvent used in the synthesis method. In the hydrothermal method, water is generally taken as solvent whereas organic solvent instead of water is used in solvothermal method. In these methods, aqueous solutions of metal nitrates, chlorides and acetates are generally used as precursor materials for the synthesis of metal oxides [8, 10]. In this method, the precursor materials and solvents are taken in a particular stoichiometric ratio and stirred for a particular time period to obtain a homogeneous solution. Then, the solution is transferred into a Teflon coated stainless steel autoclave and placed it in an oven at elevated temperature for a certain time. Finally, the autoclave is allowed to cool down at room temperature and the precipitates obtained is dried and cured at higher temperature. Different indium oxide based bulk nanomaterials have been synthesized by solvothermal/hydrothermal method. In this regard, Suzuki *et al.* [54] synthesized indium tin oxide nanoparticles *via* solvothermal method for sustainable coating application.
