Sodium silicate based aerogel for absorbing oil from water: the impact of surface energy on the oil/water separation

Industrial organic pollutants and oily wastewater are becoming a serious worldwide problem that are threatening the environments. Silica aerogels with hydrophobicity and oleophilicity have a significant potential to develop their use as an oil absorption and can be used to absorb different oils emulsion. Herein, inspired by lotus leaves and gecko toes, we fabricate superhydrophobic and superoleophilic silica aerogel from inexpensive sodium silicate precursors by a facile sol-gel method followed by the low-cost ambient drying process. The microstructural properties of the silica aerogel are investigated by TEM and BET analysis. The resulted aerogels are ultra-lightweight (0.23 g cm^-3) and highly porous (90%) with a pore distribution of 24 nm. Furthermore, oleophilic-hydrophobic characteristics of silica aerogel are investigated by the chemical structure and the surface energy of the silica aerogel using solid-state NMR, FTIR and also measuring the water/alcohol contact angle, sliding angle and oil spill absorption. Silica aerogel shows superior water repellency with the contact angle of 150°, super oleophilicity to different oils, outstanding absorption capacity for oils (up to 4 g of oil/g of aerogel), and eminent absorption recyclability (100%, even after 10 cycles). Due to its low density, lightweight, superhydrophobicity, low-cost materials, and considerable oil absorption properties, we expected that silica aerogel can be used for oil-spill cleanup. Besides, we establish the relationship between surface energy and water/oil contact angle to understand the mechanisms that occur during the oil/water separation process.