Design And Fabrication Of Underwater Superoleohobic Materials And Their Application And Mechanism In Water Treatment

According to statistics,the annual production of oily sewage from industry,daily life,oil exploitation and transportation is as high as 3.2 billion tons,which can cause serious damage to the ecological environment and threaten human health along with biological enrichment.Owing to the opposite wettability to nonpolar oil and polar water,superwetting materials possess the advantages of high selectivity and high separation efficiency for oil/water separation,and thus receive wide attention in industry and science.Compared with superhydrophobic and superoleophilic materials,superhydrophilic and underwater superoleophobic materials have excellent oil-resistance performance,which can avoid the problems that the channels of superhydrophobic and superoleophilic materials are easily blocked by oil,resulting in a significant drop in water flux and a serious reduction in separation efficiency.However,most underwater super-oleophobic materials still suffer from low water flux,poor mechanical stability,invalidation in complex environments such as strong acid,strong alkali and high salt environments,as well as an inability to separate multiple pollutants.Therefore,it will be great significance to develop a new micro-nano structure design and surface modification strategy for the preparation of underwater superoleophobic materials with high performance or multifunction.In this thesis,we have successfully fabricated a series of high-performance underwater super-oleophobic materials based on the design and construction of surface component and micro-nano structure with the help of interface theory.Meanwhile,the related mechanisms have been clarified.The main research contents and conclusions are as follows:（1）A robust underwater superoleophobic carbon foam with"lotus leaf-like"structure was prepared via dip-coating and carbonization process.The lotus leaf-like circular protrusion consisted of a metallic nickel core and a graphite carbon shell.Due to the hydrophilicity of nickel and the increased roughness from"lotus leaf-like"structure,the modified foam exhibited superhydrophilicity and underwater superoleophobicity.The water flux of the modified foam for oil/water separation was as high as 93496 L h^-1m^-2,which preceded most reported super-wetting materials.Owing to the chemical inertness of graphite carbon and the chemical robustness of nickel,the modified foam could still effectively separate oil/water mixture in complex environments such as strong acid,strong alkali and high salt environments.This study has crucial referential value on the design and construction of superhydrophilic and underwater superoleophobic materials with ultra-high water flux and high environmental suitability.Moreover,it provided a new instance to overcome the problems that the pores of carbonized foam are easily block by the adsorbed oil,leading to a decline in performance and service life as well as an increase of the difficulty in recycling.（2）With regard to the complex preparation and poor mechanical stability of underwater superoleophobic materials,in this paper,waste polyurethane foam was chosen as a matrix,and the iron hydroxide@polydopamine@polyurethane foam（Fe（OH）₃@PDA@PU）was prepared by simultaneous polymerization of dopamine and in situ growth of iron hydroxide through a facile and mild"one-pot"reaction.Owing to the abundant hydrophilic groups from PDA and Fe（OH）₃ as well as the enhanced roughness from Fe（OH）₃ nanoparticles,the wettability of waste foam changes from hydrophobicity to superhydrophilicity and underwater superoleophobicity.Due to the ultra-low oil adhesion,after 100 separation cycles,the modified foam still preserved a high separation efficiency above 97.3%,along with a slight decrease in water flux,revealing its excellent recyclability.More importantly,owing to the existence of strong interfacial interaction,the separation efficiency of the modified foam for hexane/water mixture could still be over 97.1%under the erosion of saturated sodium chloride even after 10 min sonication treatment.The scalable preparation method combined with excellent oil/water separation performance and outstanding mechanical stability endowed the modified foam with a great application prospect in the treatment of oily sewage in marine environment.Meanwhile,it also paved a new path to eliminate the negative effects of waste foam and realize its high-value utilization.（3）To expand the application of underwater superoleophobic materials,a multifunctional La（OH）₃@cellulose nanofibrous membrane（L-CNM）was prepared through one-pot electrospinning during which the sheet-like La（OH）₃ was in situ grown on cellulose nanofibers.The electron-deficient La（OH）₃ nanosheets endowed the membrane with a high adsorptive capacity toward electron-rich Congo red（CR）.Interestingly,the obtained membrane was able to not only remove CR from dye mixtures with opposite charges,but also effectively separate CR from dye mixtures having the same charge,which has rarely been reported.Meanwhile,the as-prepared membrane could also separate a series of oil/water mixtures with high fluxes and separation efficiencies due to its underwater superoleophobicity and low oil adhesion.More importantly,its intrusion pressure is as high as 6.95 k Pa,which is superior to most reported superhydrophilic and underwater superoleophobic materials.This work may open the new application of lanthanum hydroxide in oil/water separation and selective adsorption separation,and provides a novel strategy for the development of new-generation multifunctional materials for wastewater treatment.（4）In order to overcome the poor recycling performance of lanthanum hydroxide@cellulose nanofibrous membrane（cellulose@La（OH）₃）origin from the ineffective desorption of Congo red,cellulose@Ti O₂@La（OH）₃membrane nanofiber membrane was prepared by simultaneous in situ loading titanium dioxide and in situ growing La（OH）₃ nanosheets during one-step electrospinning.The introduction of titanium dioxide not only enhanced the wetting behavior of nanofibrous membrane,but also endowed its photocatalytic activity.The experiment results demonstrated that the photo-generated carrier separation efficiency was obviously improved when titanium dioxide anchored with lanthanum hydroxide.Mechanism analysis indicated that superoxide radical was the main active species for the photocatalytic degradation of Congo red.Owing to the stable load of Ti O₂ by the nanofiber membrane and the strong interface interaction between them,the photodegradation efficiency of cellulose@Ti O₂@La（OH）₃nanofiber membrane is almost unchanged after three recycles,suggesting excellent recycling performance.This research provided an effective solution to prolong the service life of high-performance selective adsorption material and improve its reusability.