Fabrication Of Biomass-derived Superhydrophobic Aerogels With Multi-scale Pore Structure And Their Applications In Oil/Water Separation

At present,the environmental pollution caused by oil discharge has become the focus of global attention,especially the oil spill accidents during the shipping process,which lead to large-scale irreversible damage to the water environment.High porous materials with superwetting properties are widely used for oil cleanup due to their high porosity,adjustable pore structure and high sorption capacity.Biomass aerogels,for example,with abundant raw materials,biodegradability,and environmental friendliness,have become research hotspots for the disposal of oil contaminants.However,biomass aerogels lack sufficient mechanical properties ascribe to their brittle characteristics as well as the internal disordered porous structure and unevenly distributed cross-linking points,which greatly limits the application of biomass-based aerogel materials.In this project,multi-scale pore superhydrophobic aerogels with neurovascular network-like and neurons-like structures were fabricated by assembling kapok and poplar seed fibers with sodium alginate and chitosan,which improved the mechanical compressibility of aerogels.Oil adsorption property and oil/water separation performance of the prepared aerogels were further studied.Biomass superhydrophobic aerogels have been widely studied and applied in separating incompatible oil/water mixtures,but significantly failed to separate surfactant-stabilized emulsified oil contaminants because of the limitation on pore size.Herein,a novel oil-water emulsion breaking mechanism based on in-suit oscillation was proposed which through the conversion of kinetic energy between deformation energy of emulsified oil droplets to achieve high-efficiency oil-water emulsion separation.The main research contents and corresponding results are as follows:Kapok（KF）and sodium alginate（SA）were used as natural building materials to fabricate an oriented neurovascular network-like aerogel（S-KF/SA）by directional freeze-drying and chemical vapor deposition.The obtained aerogel exhibited outstanding unidirectional compressibility perpendicular to the SA cell wall.The aerogel could recover96.0%and 97.3%of its original after dry and wet compression（a strain of 60%）,facilitating stable oil absorption capacity by squeezing（81.1-89.8%of the original）.A gravity-driven filtration combined S-KF/SA separated a wide range of oil/water mixtures with high oil fluxes(32918-37963 L·m^-2·h^-1)and satisfactory separation efficiencies（99.04-99.64%）.However,when the oriented structural aerogels undergo stress paralleling the pore wall direction,the materials are compulsively extruded,which is prone to structural cracking and greater plastic deformation.The compression of such oriented aerogels in axial direction paralleling aligned pores is their fatal weakness.Furthermore,the aerogel with a tubular-lamellar interweaved neurons-like structure was fabricated by assembling poplar catkin fiber（PCF）and chitosan（CS）,which featured excellent longitudinal and transverse compressibility and compression tolerance performance.The hollow flexible PCF acted as second-scale micron capillaries,facilitating the oil absorption rate with a capacity of 28.8-78.1 g/g in 5-25 s for different oils and organic solvents.An oil-water separation experiment with the vacuum liquid pump showed that the aerogel facilely achieved continuous oil recycling from seawater with a permeate flux of 23052-43956L·m^-2·h^-1.This subject proposed an oscillatory-demulsification strategy for the capture of underwater emulsified oil droplets,which breaks the idea of emulsion separation by“size sieving”using 2D microporous membranes.Simply utilizing the repeated high-frequency oscillation to apply kinetic energy to the oil-in-water emulsion,creates conditions for demulsification in the process of deformation.exerting kinetic energy on emulsified oils through repeated oscillation.S-KF/SA achieved capture 99.39-99.68%of emulsified oils from four kinds of emulsions（water-in-hexane,water-in-toluene,water-in-diesel and water-in-soybean oil）;M-PCF/CS achieved 98.07%and 99.11%for water-in-hexane and water-in-toluene,respectively.With S-KF/SA for example,the impacts of oil type,oscillation rate and surfactant on the demulsification effect were investigated.The total demulsification time by S-KF/SA decreased with increasing oscillation rate;the emulsions formed by low-viscosity oils showed a more satisfactory effect compared with that of high-viscosity oils;the demulsification effect on emulsions stabilized by CTAB（cationic surfactant）was more impressive than that of emulsions stabilized by SDS（anionic surfactant）.