Fabrication Of Special Wettable Sponges And Their Application In Oil/Water Separation

With the development of society,environmental pollution has become a major issue to be addressed.The requirements of oily wastewater treatment are increasingly strict.Special wettable materials for oil/water separation attract much attention due to their excellent selectivity and high separation efficiency.However,there is a scientific problem to be solved,how to break the emulsion by using a special wettable sponge.It is believed that special wettable sponge is not suitable for demulsification because its pore size is much larger than that of microfiltration and ultrafiltration membrane.Herein,a series of special wettable sponges were fabricated and the morphology,wettability and oil/water separation of these sponges were studied.These materials achieved the demulsification of oil-in-water emulsion via absorption instead of filtration.Besides,the effects of sponges with different types of wettability on oil-in-water emulsion were also investigated.Furthermore,a novel response system of metal ion was explored,which can change its wettability with the response to metal ions.Firstly,three types of polyurethane sponges with superhydrophilicity,hydrophobicity and amphiphobicity were developed to separate immiscible oil/water mixtures and oil-in-water emulsion.The superhydrophilic coating of polyurethane sponges can absorb water and constitute a hydrogel layer.In the oil/water separation,the hydrogel layer prevented oil to permeate the superhydrophilic sponge;in the absorption process of demulsification,the hydrogel acted as polymeric flocculants.The surface of hydrophobic sponge had low surface free energy,so water with high surface free energy cannot wet and permeate the sponge during the oil/water separation.In the demulsification of oil-in-water emulsion,hydrophobic sponge adsorbed the emulsified oil droplet to lower the energy of the system.For the amphiphobic sponge,it broken the oil-in-water emulsion not only by the absorption method,but also by the filtration method.Secondly,a novel superhydrophilic free-standing sponge was synthesized for the demulsification of oil-in-water emulsion.This free-standing sponge was obtained by physical blending of polyacrylamide and chitosan.The sponge formed a hydrogel with positive charge upon the adsorption of water.The separation efficiency of positively charged sponge toward anionic surfactant-stabilized emulsion is higher than cationic surfactant-stabilized one.The demulsification efficiency of free-standing sponge was above 92% and the demulsification capacity was about 4 time its own weight.Besides,a new “breathing demulsification” mechanism has been presented to explain the adsorption demulsification.Lastly,a new method to achieve wettability response to Hg2+ with liner polyacrylic acid hydrogel was prepared.This kind of new mesh showed superhydrophilicity and underwater oleophobicity due to ployacrylic acid coating.After soaking the mesh in saturated Hg2+ solution,the oil can penetrate through the mesh but water cannot since the polyacrylic acid was chelated with Hg2+ to generate neutral mercury polyacrylate.The as-prepared mesh could separate immiscible oil/water mixtures effectively driven by gravity.The Hg2+ responsive wettability transition made this mesh fit the separation of different oil/water mixtures by adjusting the concentration of Hg2+.