Preparation Of Physically Crosslinked Gel Composite With Underwater Superoleophobicity And Its Oil/water Separation Performance

Ever increasing oil pollution from oily industrial wastewater and frequent oil spill accidents are threatening the ecological environment,and even human beings.Therefore,constructing a new high performance oil-water separation material to treat oily wastewater in different environment has brought about the widespread attention.As a special wettability material which can effectively separate oil/water mixtures,it has attracted in-depth exploration by researchers from different fields in recent years,such as superhydrophobic/superoleophilic,superhydrophilic/superoleophobic and superhydrophilic/underwater superoleophobic materials.Among them,the affinity of superhydrophilic/superoleophobic or superhydrophilic/underwater superoleophobic surface material to oil droplets is very low,so it can prevent the mesh from being polluted or blocked by oil.As a result,the material has excellent recyclability.This type of oil/water separation material is called dewatering material,which has great potential in industrial oilly wastewater treatment and oil spill cleaning.As a kind of soft material with three-dimensional hydrophilic network and high water content,hydrogels are often coated on porous substrates（such as stainless steel mesh,copper mesh,filter paper,glass fiber,etc.）for oil-water separation.However,most of them are not only cumbersome and costly to prepare,but also vulnerable to mechanical damage or chemical erosion.which restricts the wider application of hydrogel composites in oil-water separation.In view of above problems,we developed three kinds of physically crosslinked gel soft materials by a simple one-pot method.And they were coated on the stainless steel mesh to prepare corresponding superwettable gel-coated mesh for various oil/water separation.The main research contents and conclusions were as follows:（1）A novel pure physical hydrogel（P（AM-co-AA）/CS hydrogel）formed by intermolecular hydrogenation and ion-crosslinking between CS and acrylamide and acrylic acid copolymer（P（AM-co-AA））was fabricated.The hydrogel not only had good ductility properties（tensile strain=1360%）,but also possessed very low swelling rate（swell ratio=2.25 g/g）and good self-healing properties.To construct a rough surface that helps to increase the oleophobicity,we incorporated amino-functionalized silica（APTES-Si O₂）nanoparticles in the hydrogel,resulting superior superhydrophilic in air and underwater superoleophobic properties,better than most reported hydrogels.Notably,the underwater superoleophobic properties could be well maintained in acid,alkali and salt aqueous solutions due to the strong interaction of each component.Then,the hydrogel was in situ reacted on the metal mesh for oil/water separation by dip-coating method.The obtained gel-coated meshes have excellent oil-water separation ability.（2）A fully physically crosslinked double-network hydrogel and the corresponding superwettable hydrogel-coated mesh were developed.In the new gel networks,PVA network was designed as a network.And electrostatic interaction linked P（AM-co-AA）/CS network was selected as the other network.The PVA/P（AM-co-AA）/CS hydrogel（HEPC-Gel）was provided with a reversible energy dissipation mechanism to greatly promote its the mechanical properties（tensile stress=164 k Pa,tensile strain=28 mm/mm）.Meanwhile,three reversible interactions in the dual network gave the hydrogel better self-healing ability.And the strong electrostatic interactions in P（AM-co-AA）/CS network also endowed HEPC-Gel with extremely low swelling ratio of 1.4 g/g.Interestingly,due to the crystallization of PVA in the hybrid hydrogel system,a large number of micro-nano crystalline mastoid on the gel surface was produced.Moreover,the hydrogel-coated mesh formed by combining micron-sized porous substrate（stainless steel mesh）showed stable underwater superoleophobicity in different water conditions.Impressively,they could achieve rapid and efficient separation of oil/water mixtures in various water environment.（3）An underwater superoleophobic APTES-Si O₂/PVA organohydrogel with anti-freezing ability was prepared through a simple freezing process.In this system,the binary solution of H₂O/EG was selected to enhance the antifreezing properties of PVA hydrogels.In addition,to construct a rough surface that helps to increase the oleophobicity,amino-functionalized silica（APTES-Si O₂）nanoparticles were incorporated in the PVA organohydrogel,resulting superior underwater superoleophobic properties（OCAs>157°）.The organohydrogel not only had underwater superoleophobicity and outstanding anti-freezing ability,but also good mechanical property（tensile stress>160 k Pa,tensile strain>250%）,high chemical tolerance and excellent remodeling.Then,the organohydrogel-coated mesh could effectively separate oils from various water environments（deionized water,1 mol/L Na OH solution,1 mol/L HCl solution,saturated Na Cl solution,artificial seawater,saturated Na Cl solution（-20℃））.Notably,the fabrication process of the organohydrogel-coated mesh is quite simple and easy with all the raw materials being low in cost.Moreover,the work could achieve perfect self-healing of gel-coated mesh and recovery of gel coating,greatly verifying high economic and environmental benefits.