Effect of Hexamethyldisilazane (HMDS) coupling agent on SiO2 nano-powder for oil/water separation application

An optimization framework was developed to investigate the combined influence of surface chemistry, surfactant concentration, and thermal treatment on the wettability characteristics of nano-silica synthesized via the sol–gel method. Under the optimized conditions, a maximum water contact angle of approximately 142° was achieved for hexamethyldisilazane (HMDS)-modified silica at a treatment temperature of 350 °C. The stability and durability of the contact angle were further evaluated at regular intervals over a period of 40 days, confirming the sustained hydrophobic performance of the HMDS-treated silica surface. The oil–water separation performance was systematically investigated using readily available substrates such as commercial polyurethane (PU) sponge, stainless steel (SS) mesh, and filter paper, modified via a facile spray-coating technique. The separation efficiency was evaluated across a range of water-to-oil ratios (1:200, 1:100, 1:50, and 1:10) to assess the versatility and robustness of the developed materials. For the 1:200 oil–water mixture, the average filtration efficiencies were determined to be approximately 75 ± 2% for filter paper and 85 ± 2% for SS mesh, while the PU sponge exhibited a superior oil absorption efficiency of ~ 99%. These findings demonstrate an effective, scalable, and environmentally benign strategy for oil–water separation, offering significant potential for sustainable wastewater treatment and environmental remediation applications.