Rice husk derived biogenic silica coated cotton as an effective, sustainable oil-water separation platform

Abstract

Oil-spills present a significant threat to the environmental marine bio-diversity. Conventional cleaning approaches such as skimming are costly. In this regard, alternative approaches utilizing functional nanoparticles (NP) are on the rise due to their effectiveness in separating the non-aqueous phase. This work presents a facile yet sustainable methodology using environmentally-friendly biogenic silica for removing oil from an oil-water mixture. To begin with, an agricultural-waste, rice husk (RH), is subjected to slow pyrolysis under CO2 environment to obtain bio-char. Bio-char is then treated at different pH and calcined, to generate silica NP. Process parameters such as reactor temperature, and pH of biochar-treating solution, are varied to understand their effect on silica NP characteristics. Experiments reveal that pH 5 and temperature 500 °C, facilitate generation of silica NP (∼18 nm). XRD analysis uncovers cristobalite phase presence in NP, which is reported to possess low unit cell volume, thereby contributing to an overall less particle size. Silica NP are modified by treating them with different silanes. PFDS treated silica NP is observed to possess superhydrophobicity, (water contact angle ∼ 160°) and oleophilicity (oil contact angle below 10°). This characteristic is attributed to low surface energy of PFDS. Silica NP coated cotton substrate is then utilized as a sorbent. Repeatability tests reveal that the natural sorbent can effectively separate oil-water mixture even after 40 cycles, with an efficiency of 97%. The findings of this study can aid in development of economical, sustainable platforms for separating oil/water mixtures or harmful components from aqueous/non-aqueous mixture.