Fabrication Of Micro/nano Composite Functional Surface By Femtosecond Laser And Its Experimental Study On Oil-water Separation

Oil–water separation has attracted more and more attention because of increasing amounts of industrial oily wastewater and the occurrence of oil spill accidents.Finding a high-efficiency oil-water separation method is the focus of current research.In recent years,researchers have found that the fish scale would not be contaminated by oil in water,and the reason is that the micro/nano composite structures provides superhydrophilic and superoleophobic properties for the scale surface.Inspired by fish scale,scientists fabricated micro/nano composite structures on the thin film that was full of microholes inside,and manipulated the surface free energy by chemical method.After procession,the surface of thin film exhibited superhydrophilic and underwater superoleophobic properties.Such prepared film could separate water solution from oil-water mixture with high efficiency and high flux.However,the commonly used approaches for preparing this kind of oil-water separation films are chemical methods,which need two or more steps and the chemical reagents are not environmentally friendly.Therefore,these methods are not suitable for a wide range of promotion.With the rapid development of laser technology,fabrication of superhydrophobic/superhydrophilic surface by laser ablation has attracted great attention.Femtosecond laser possesses ultrashort pulse duration and ultrahigh peak power,which can significantly improve the processing accuracy and precisely control the surface morphology.Therefore,the femtosecond laser has a unique advantage on fabricating micro/nano composite functional surface.In this article,we fabricated micro/nano structures and TiO₂ layers on the titanium meshes and titanium foils by femtosecond laser irradiation.The as-prepared surfaces exhibited superhydrophilic and underwater superoleophobic properties,and it could be used for oil-water separation with high efficiency and high stability.The main work and innovation points are as follows:1.The oil-water separation film was prepared by femtosecond laser processing method for the first time.Femtosecond laser could control the morphology of micro/nano composite structure and the surface chemical composition synchronously,further resulting the prepared surface exhibited superhydrophilicity and underwater superoleophobicity.This method simplifies the preparation steps and improves the controllability of the surface morphology.2.The titanium meshes with small aperture were innovatively selected as the substrates to improve the stability and recyclability of the prepared oil-water separation films.In this article,we selected titanium meshes as substrates and used femtosecond to directly scan the meshes.By controlling the laser parameters,the papillary micro/nano structures were fabricated on the surfaces.Such prepared films exhibited superhydrophilic and underwater superoleophobic properties,and it could be used for oil-water separation.For different oil-water mixtures,the separation efficiency of the prepared films was all more than 97%and the water flux all exceeded 15 L?m^-2?s^-1.Compared with the stainless steel meshes and copper meshes used in the previous study,the as-prepared titanium meshes could anti-erosion of acid,alkali and salt solution.Moreover,under UV illumination,the TiO₂ layers on the prepared surfaces could catalytic degradation of organic pollutions.Thus,such prepared oil-water separation films exhibited better stability and recyclability.3.A new method for preparing oil-water separation filter was presented and it has been successfully verified on the titanium foil.We used femtosecond laser to fabricate the through-hole array on the titanium foils.After laser ablation,the functional surfaces with superhydrophilic and underwater superoleophobic properties were obtained,and the through-holes on the prepared surfaces provided micro-channels for aqueous solution permeating through.By systematic studying the influence of laser energy and microhole spacing on the surface morphology and the hole-aperture,the efficiency and the speed of oil-water separation were effectively improved.The separation efficiency of the optimum filter was as high as 99.5%and the water flux exceeded 20 L?m^-2?s^-1,and it could be recycled use for more than 40 times.This method simplifies the processing steps and realizes the controllable preparation of micro-channels.More importantly,other hydrophilic membrane materials can also be applied to this one-step approach.After femtosecond laser drilling of microhole array on the hydrophilic membranes,the oil-water separation filters with high efficiency can be obtained.Thus,this provides a new scheme for the practical preparation and application of oil-water separation films.