Preparation Of Bismuth-based Semiconductor Coating With Special Wettability And Their Photocatalytic Bactericidal And Oil/Water Separation Properties

Water contamination caused by organic,oily and microbial pollution has become more and more serious problems.Therefore,it is of great significance to develop a novel oil/water separation materials with stable performance,high efficient anti-biological adhesion and bactericidal properties.However,most of the reported powder materials are easy to precipitate and aggregate,difficult to separate and recover,which would cause secondary pollution and restrict their further practical application.The fabrication of film or coating is one of the most effective way to solve these problems.In this work,bismuth-based semiconductor nanomaterials with good photocatalytic performance and environment-friendly properties was selected as research target,a series of single-component,metal-loaded and composited bismuth-based material coatings with the special wettability were prepared via simple methods on different substrats,which endows the coating with corrosion resistance,friction resistance,oil resistance,anti-biofouling and bactericidal properties.The oil/water separation efficiency and photocatalytic bactericidal properties of the bismuth-based material coatings with different special wettability were evaluated.It is anticipated that the bismuth-based coatings could realize oil/water separation and remove organic pollutants and bacteria from sewage simultaneously,which would solve the problem of oily wastewater purification and disinfection and microbial biofouling.This work provides theoretical guidance and technical support for further practical application of photocatalytic technology.The main works are summarized as follows:1.Au/Bi OCl composite nanomaterials with different morphologies were prepared by simple solvothermal method and sodium borohydride reduction method.Due to the surface plasma effect of Au and special three-dimensional hierarchrical micro/nano structures,the flower-like Au/Bi OCl nanostructures showed the best photocataiytic bactericidal performance against S.aureus under visible light irradiation,a common pathogenic bacteria in water.The trapping experiment of free radical confirmed that the hole played a key role in Au/Bi OCl photocatalytic bactericidal process.Owing to the problems existing in the practical use of powder catalyst,such as separation and recovery difficulties and easy to be contaminated by oily sewage,the superhydrophilic/underwater superoleophobic Au/Bi OCl coating were further prepared on stainless steel wire mesh via in-situ synthesis method.The bactericidal activity and recycling performance of the Au/Bi OCl coating were tested.It was found that the bactericidal rate of the Au/Bi OCl coating for S.aureus could reach99.95%.After six cycles,the bactericidal rate remained above 99%.Compared with Au/Bi OCl powder catalyst,the coating not only possessed high photocatalytic bactericidal activity,but also has stable and good recycling performance,can achieve anti-oil in water,and has obvious advantages in the treatment of bacteria-containing wastewater.2.Sn-modified Bi/Bi OBr coating with superhydrophilic/underwater superoleophobic were prepared via one-step solvothermal method 304 stainless steel wire mesh substrate,by using bismuth nitrate pentahydrate and sodium bromide as raw materials,stannous chloride dihydrate as the morphology guide and reducing agent and ethylene glycol as solvent,respectively.The results showed that the addition of stannous chloride dihydrate plays an important role in the formation of the flower-like hierarchical structure on the the coating.The Sn-modified Bi/Bi OBr coated mesh presented underwater superoleophobic property owing to the flower-like hierarchical micro/nano structure improved the surface roughness of the coating.The superhydrophilic/underwater superoleophobic coating after pre-wetting by water could be achieved separation of various oil/water mixtures,and the separation efficiency was higher than 95%,which was expected to be applied in the purification of oily wastewater.Under visible light irradiation,the photocatalytic bactericidal performance of Sn-modified Bi/Bi OBr coating was significantly improved compared with single-component Bi OBr coating and Bi/Bi OBr coating.This may be owing to the Sn element and the bismuth monomer synergistically promoted the separation of photogenerated electrons and holes,improving the photocatalytic performance of the coating.Sn-modified Bi/Bi OBr coated mesh can kill all bacteria after 3 hours of illumination,with a bactericidal rate of 99.99%.This kind of superhydrophilic/underwater superoleophobic coating with high photocatalytic bactericidal activity has a great application prospect in solving the biofouling on the surface of oil/water separation materials.3.The superhydrophilic/underwater superoleophobic Bi OCl/Bi₂O₃ composite coating was prepared directly on the stainless steel wire mesh by a simple one-step hydrothermal method.When the Bi³⁺/Cl O₃^-mole ratio was 1:2,hierarchical micro/nano structures composed of nanosheets and nanoneedles could be obtained.The hierarchical micro/nano structure could effectively improve the surface roughness of the coating and facilitate the superhydrophilic/underwater superoleophobic properties of Bi OCl/Bi₂O₃ composite coating.The Bi OCl/Bi₂O₃coating with superhydrophilic/underwater superoleophobic exhibited excellent oil/water separation efficiency and recycling performance.The continuous oil/water separation efficiency of hexane/water was as high as 99.5%,and remained at 98.2%after 10 cycles.The Bi OCl/Bi₂O₃coating also exhibited excellent photocatalytic activity.After two hours of visible light irradiation,the photocatalytic bactericidal rates of Bi OCl/Bi₂O₃coating aganist S.aureus was 99.93%.And the photocatalytic degradation rate Bi OCl/Bi₂O₃coating for Rh B and tetracycline hydrochloride(TCHCl)was 87%and 58%,respectively.The highly efficient photocatalytic performance can prevent the adhesion of microorganisms in water to the coating surface.In order to effectively utilize the photocalytic ability and the oil/water separation performance of Bi OCl/Bi₂O₃ coating,the superhydrophilic Bi OCl/Bi₂O₃ coating was modified by octadecanethiol to obtain the superhydrophobic Bi OCl/Bi₂O₃ coating.After that,the dual-layer mesh(DLM)was fabricated by simply overlaying the superhydrophilic Bi OCl/Bi₂O₃ composite coating onto the superhydrophobic Bi OCl/Bi₂O₃composite coating.The DLM can realize the separation of oil/water mixture and degradation of pollutants simultaneously.For the oil/water mixture system simulated by hexane/Rh B/S.aureus,the oil and water separation efficiency of DLM was up to 99.5%.At the same time,80%Rh B can be degraded and all bacteria can be killed after 90 minutes of visible light irradation.Moreover,the DLM also has stable mechanical properties,such as wear resistance,water erosion resistance,acid and alkali resistance,etc.,and has a good application prospect in the practical application of sewage purification treatment.4.Bismuth-based oxysalt coatings(Bi₂WO₆,Bi₂Mo O₆ and Bi VO₄)with superhydrophilic/underwater superoleophobic were fabricated via hydrothermal method by using Bi OCl/Bi₂O₃ coating prepared in chapter 3 as the template.Bi₂WO₆,Bi₂Mo O₆and Bi VO₄ coating showed high oil/water separation efficiency for various oil/water mixtures after pre-wetting by water.The separation efficiency of these coatings for hexane/water,cyclohexane/water,dichloromethane/water and chloroform/water mixtures could reach above 97.5%,and also remain more than 95%for kerosene/water,diesel/water,and olive oil/water mixtures.After 20 cycles,the separation efficiency of the coatings for hexane/water and kerosene/water could maintain more than 96%,indicating that the coating has good recycling performance.The Bi₂WO₆,Bi₂Mo O₆ and Bi VO₄ coatings displayed stable superoleophobic properties in water and high oil/water separation efficiency in corrosive liquids such as acid(kerosene/HNO₃),alkali(kerosene/Na OH)and salt(kerosene/Na Cl)solution,which could achieve up to 99%.The photocatalytic bactericidal rates of Bi₂WO₆,Bi₂Mo O₆ and Bi VO₄ coating upon two hours of visible light irradiation aganist S.aureus was 97.6%,66.2%and 63.5%,respectively.It indicated that the three kinds of coating presented good bactericidal activities under visible light.5.Superhydrophobic bismuth coating with dendritic hierarchical micro/nano structure was prepared by electroless deposition and stearic acid modification on the surface of zinc flake using bismuth trichloride as bismuth source and ethylene glycol as solvent.The bismuth coating have a high water contact angle of 164.8^o and a low sliding angle of 3^o.The synergistic effect of hyperbranched hierarchical micro/nano structure and low surface energy molecule was beneficial to the formation of bismuth coating superhydrophobicity.The superhydrophobic bismuth coating could be transformed into superhydrophilic after 50minutes of UV-visible light irradiation.The photoinduced hydrophilic bismuth coating can be restored to superhydrophobic by stearic acid re-modification.This switchable wettability between superhydrophobic and superhydrophilic can be repeated by alternating light and stearic acid modification.After 5 cycles,the bismuth coating still maintained the switchable wettability of the transition from superhydrophobic to superhydrophilic.This switchable wettability of bismuth coating can be attributed to photocatalytic degradation of surface hydrophobic layer and regeneration of stearic acid layer.Photoinduced switchable wettability bismuth coating could realize anti-oil-fouling by photoinducing superhydrophilic reduce the adhesion of oil and by photocatalytic degradation of surface oily pollutants,which provides a new idea to solve the oil pollution problem of photocatalytic materials in sewage treatment.