Surface And Interface Design Of Porous Materials For Crude Oil/Water Separation

The surging oily sewage discharge,especially generated from oil extraction processes and crude oil spill accidents,has continuously caused significant risks for environmental sustainability and human health to a large extent.Crude oil/water separation is still regarded as a worldwide challenge.Various materials and technologies have been reported to separate or collect oil from oily wastewater.And membrane separation and adsorption technologies stand out since they have advantages of high efficiency,low energy consumption and simple manipulation while most of other methods always need either lots of chemicals or expensive equipments.In the past decades,lots of membrane and adsorption materials have been reported to separate or collect oil from oily wastewater.However,most of them only work well in separating model oil/water mixture while fail in crude oil/water separation because of the high viscosity and adhesion property of crude oil.More specifically,adhesion property makes crude oil extremely sticky to most of the superhydrophilic membrane,leading to dramatic decline of membrane performance.As for the high viscosity,crude oils have poor mobility and then low diffusion rate into the inner pores of porous materials,resulting in a low separation and treatment efficiency.To address the issue of oil adhesion,we report cellulose including amorphous and crystalline cellulose as the oil-repellent materials for the first time.The results indicate that both of them are indeed available to eliminate oil contamination from their surfaces not only in the water-wetted state,but also in the dry state because of their excellent water-binding capability.Moreover,grazing-angle-reflectance Fourier transform infrared(GAR-FTIR)spectra and sum frequency generation(SFG)vibrational spectra were firstly used to characterize the orientation of the hydrophilic groups in different mediums.It has been found that hydrophilic groups of cellulose can keep their outward orientation even when they were exposed to non-polar media,while the flexible hydrophilic groups of other materials prefer to orient inward spontaneously to minimize the overall surface energy in oil surroundings.Thus,the cellulose can remain their surface hydrophilicity even in the dry state.Based on their superior hydration capability and anti-oil adhesion property,we have developed a series of cellulose materials for crude oil/water separation.For example,we facilely fabricated cellulose nanocrystal nanopapers by simple vacuum-filtration methods.They can be applied for the separation of crude oil-in-water nano-emulsions due to the small pore size;In addition,by integration of the anti-oil mechanism for nanocelluloses and the chemical composition of natural wood,we prepared delignified wood by selectively removing the lignin and hemicellulose.Indeed,the delignified wood has excellent anti-fouling property.Moreover,they exhibited ultrahigh separation efficiency resulting from the microstructures of the delignified wood.Plenty of vertically aligned channels are throughout the wood along the growth direction,are particularly helpful for water pass though because of low resistance and high porosity;Carboxylated wood-based sponges with underoil superhydrophilic property were developed for the dehydration of water-in-crude oil emulsions.In a word,these cellulose-based materials can be applied for the separation of almost all kinds of crude oil/water systems.To address the issue of high viscosity,we designed porous absorbent materials with thermal effects including photo-thermal and Joule heating effects since the viscosity of crude oils is usually decreased with increasing temperature.There materials can heat the temperature of the interface between crude oil and absorbents.Thus,the heated crude oil has better mobility and faster diffusion rate into the porous sorbents under the sunlight or direct electric supply.Moreover,these sorbents can be linked with pumps for high-efficiently continuous treatment of crude oil spill.