Recycled waste masks as oil absorbent based on stable SiO2 coating for efficient separation of oil-water mixtures and oil-in-water emulsions

Due to the COVID-19 pandemic, mask contamination has become a global concern, and proper disposal of used masks is crucial. In this study, Waste Masks (WM) were modified into a highly efficient oil adsorption material by in-situ growth of SiO2 and subsequent grafting with Octadecyl trichlorosilane (OTS). The modified masks had a water contact angle of 153.2°, showed attractive adsorption capacity (27.33, 31.84, and 32.81 g·g−1) for soybean oil, lubricating oil and engine oil. The modified WM can adsorb not only the light oil on the water surface but also the heavy oil under water. Furthermore, the modified WM was able to separate oil-in-water emulsions of n-hexane and toluene by adsorbing the oil emulsion droplets. Molecular dynamic (MD) simulation was used to investigate the oil-water separation mechanism and calculate the adsorption energy of oil molecules on the OTS-grafted surface. This study provides an interesting solution to the environmental problems caused by discarded masks and the production of low-cost, reusable, and eco-friendly oil-absorbing materials.