Fabrication Of Super-Wetting Sponge And Study On Its Mechanical Properties And Oil-Water Separation Performance

The rapid development of textile,steel,metallurgy,petrochemical and other industries has produced a large amount of oily wastewater,causing serious water pollution and endangering ecological balance and human health and safety.Therefore,how to efficiently and quickly treat oily wastewater is an important environmental problem which needs to be solved urgently.Traditional straw,activated carbon,fabric and other adsorbent materials and ordinary membrane filter materials have low adsorption capacity,poor oilwater selectivity,ease of contamination which are difficult to reuse after recycling causing second pollution.Therefore,there is an urgent demanding to develop a new oil-water separation material.In 1997,German botanist Baethlott discovered the "lotus effect",which achieved super-wetting properties by adjusting the surface chemical composition and structure.Subsequently,bio-inspired superhydrophobic self-cleaning materials have been developed rapidly.Because of its high porosity,long pore path,and good mechanical properties,super-wetting 3D porous sponges can selectively separate oil and water quickly by adsorbing or filtration.In particular,the oil can be recycled after being compressed and discharged,so it has become one of the research hotspots in the field of oil-water separation.According to different types of oil-water mixtures,it can be divided into superhydrophilic/underwater super-oleophobic sponge to separate floating oil and emulsified oil on water surface,and super-hydrophobic/super-oleophilic sponge to separate oil of water's surface in situ.In this paper,firstly,the inorganic nano particles were successfully embedded on the surface of the epoxy resin skeleton by using the porous sugar template as the template transfer mode,and the super-hydrophilic/underwater super-oleophobic epoxy composite sponge was prepared.The influence of the embedding of different inorganic oxides on the mechanical properties of epoxy resin sponge and the efficiency of oil-water separation was investigated.Then,a hydrophobic and oleophilic Graphene-polydimethylsiloxane(PDMS)sponge was prepared by embedding Graphene into PDMS sponge skeleton.The effects of Graphene on the mechanical properties,wettability and oil adsorption properties of PDMS sponge were investigated.Finally,due to the problem of oil adhesion,Ag-PDMS sponge was prepared.We investigated the effects of different nano-silver types for PDMS sponge's conductivity.The main findings are as follows:(1)By using “mold transfer and surface embedding” and porous sugar as template,three-dimensional porous epoxy composite sponge embedded by Si O2,Ti O2,La2O3 was successfully prepared,which possesses the characteristics of superhydrophilicity and underwater superoleophobicity.The research on curing agent types and ratios verified that the polyether structure can effectively improve the flexibility of epoxy resins,and the optimum ratio between epoxy resin and polyetheramine D400 and polyetheramine D2000 is 1:0.3:0.7 to prepare the most flexible epoxy.The mechanical test of the inorganic nano-particles embedded epoxy resin/polyetheramine sponge showed that embedding a small amount of La2O3(0.16wt%)can significantly improve the toughness and softness of the epoxy resin sponge skeleton.Further testing and analysis proved that La2O3 chemically bonded to the epoxy resin while embedding it on the surface of the epoxy resin,forming a stable C-O-La chemical bond.The oil-water separation efficiency of La2O3-Epoxy resin/polyetheramine sponge is higher than 95%.The separation efficiency is stable after 10 cycles of use,and the flux reaches 2800 L·m-2·h-1,which indicates that the sponge has good stability and reusability.(2)Graphene surface embedded PDMS sponge with three-dimensional porous structure was fabricated by the same method.The hydrophobicity test shows that the sponge has high hydrophobic and excellent underwater superoleophilic performance.It only takes 4 seconds to completely adsorb the oil in the water,which can not only adsorb the floating oil but also the heavy oil.The modification of graphene can significantly improve the softness of the PDMS sponge skeleton,and the compressive load at 80% strain is nearly doubled(Only 0.4 MPa).In the oil-water separation tests,the adsorption capacity of PDMS sponge and Graphene-PDMS sponge is between 400% and 1500%.In the recycling oil/water separation test,these two type sponges maintain relatively stable adsorption capacity of lower adhesion oils,while the adsorption capacity decreases significantly of adsorbing larger adhesion oils leading to the oil contamination and fails in long-term oil/water separation(3)In order to solve the problem of oil adhesion,it is proposed to use the electro-joule heating effect to reduce the viscosity of the oil,thereby reducing the adhesion.Research on the conductive properties of different types of nanosilver embedded into the PDMS sponge framework proves that Ag NPs cannot form conductive pathways.Ag flakes can form conductive paths,and further adding Ag NWs can improve the conductivity of PDMS sponges.In the mechanical property tests,the compressive loading of Ag flakes-PDMS sponge reaches 80% deformation under the stress of 2.8 MPa(comparing that PDMS sponge requires 0.8 MPa stress to reach 80% strain).The addition of nanosilver reduces the softness of the sponge skeleton,but the 100 cycles compression curve matched well indicating that the sponge has good elasticity.The investigation of sponge heat generation indicates that the contact between Ag flakes and Ag NWs is unstable.By applying a large voltage,a weak electric spark is generated reducing the stability of the circuit.Therefore,it is necessary to improve the contact between Ag flakes and Ag NWs to ensure the stability of the conductive path.