This protocol describes the hydrothermal synthesis of silicon nanoparticles using sodium silicate solution as the silicon source under controlled alkaline conditions. The process begins with dilution of sodium silicate in deionized water followed by controlled pH adjustment to initiate hydrolysis and condensation reactions that form nanoscale silicate nuclei. The reaction mixture is transferred into a Teflon-lined stainless-steel autoclave and subjected to hydrothermal treatment at elevated temperature and autogenous pressure. Under these conditions, nucleation and growth of silicon-based nanoparticles proceed uniformly, resulting in well-dispersed nanoscale particles with narrow size distribution. After completion of the reaction, the system is allowed to cool naturally to room temperature to prevent sudden aggregation. The product is separated, washed repeatedly to remove residual ions, and dried at moderate temperature to obtain free-flowing silicon nanoparticles.

The hydrothermal environment enhances particle uniformity, reduces uncontrolled agglomeration, and improves structural stability compared to conventional precipitation methods. The synthesized nanoparticles are suitable for dispersion in aqueous nanofluids for reservoir wettability modification, permeability enhancement, corrosion-resistant coatings, and scale inhibition systems. This method is scalable, cost-effective, and compatible with industrial material preparation requirements in oil and gas sector applications.