Study On The Photocatalytic Degradation Properties And Mechanisms Of Tetracyclines Over Bismuth Vanadate-based Plasmonic Photocatalysts

Since antibiotics were invented,they have been widely used in the medical and aquaculture industries.However,antibiotics have brought about some potential ecological safety risks while they play important roles in the treatment and prevention of bacterial infections.Since the sewage treatment plants in China don’t have the specific technologies to remove antibiotics,several scholars have devoted themselves to researches in terms of effectively degradation of antibiotics in aqueous environment.Among various treatment methods such as membrane separation,ozone oxidation and so on,photocatalytic oxidation has been studied widely due to its advantages of high efficiency,mild reaction conditions,stability,and environment-friend.The traditional titanium dioxide photocatalyst has strong photo-oxidation ability,stable chemical properties and low price,but it can only absorb ultraviolet radiation which accounts for 4%of the solar radiation.In that condition,the industrial application of titanium dioxide is limited.In order to deal with the disadvantages of titanium dioxide,researchers have developed a series of novel visible light driven photocatalysts.Bismuth vanadate is a non-toxic,visible light driven photocatalyst,but due to its low visible light response capability and high recombination of photogenerated electrons and holes,its photocatalytic activity is relatively low.To solve the above problems,bismuth vanadate-based ternary surface plasmonic photocatalysts were constructed in this thesis.The surface plasmon resonance effect of noble metal silver improves the visible light absorption capability of the composite photocatalysts and effectively suppresses the recombination of photogenerated electrons and holes.In this thesis,bismuth nitrate and sodium orthovanadate were used as raw materials to synthesize flower-like sphere bismuth vanadate with controllable and uniform morphology by one-step hydrothermal method.Subsequently,Ag2CO3/BiVO4 was synthesized by depositing Ag2CO3 nanoparticles on the surface of BiVO4.Finally,the ternary plasmonic photocatalyst Ag/Ag2CO3/BiVO4 was obtained through ultraviolet reduction of Ag+on Ag2CO3 surfaces by photogenerated electrons.The photocatalysts were characterized via XRD,XPS,SEM,TEM,PL,UV-Vis DRS and so on.The results showed that the ternary plasmonic photocatalyst Ag/Ag2CO3/BiVO4 was successfully prepared with a uniform morphology and exhibited higher and wider absorption in the visible and ultraviolet regions.The separation capability of photogenerated carriers is improved compared to pure BiVO4 and the heterojunction photocatalyst Ag2CO3/BiVO4.In the photocatalytic degradation experiment,tetracycline was chosen as the target contaminant After 150 minutes of visible light irradiation,the degradation rate of tetracycline by the ternary plasmonic photocatalyst 3h-Ag/Ag2CO3/BiVO4 reached 94.9%,which is higher than the other photocatalysts.This phenomenon may be due to the fact that the introduction of silver nanoparticles enhances the light-absorbing ability and electric field of the ternary photocatalyst,and contributes to the separation of photogenerated electrons and holes.The photocatalytic reaction mechanism and the degradation pathway of tetracycline were presumed through the quenching experiment of active species and the identification of intermediate products.Furthermore,the ternary plasmonic photocatalyst Ag/AgCl/BiVO4 with different UV light reduction time was synthesized.With the increase of the illumination time,the content of silver on the surface of ternary photocatalysts increased.In the photocatalytic degradation of oxytetracycline hydrochloride,the ternary plasmonic photocatalyst 1h-Ag/AgCl/BiVO4 showed the best degradation activity and the main active species participating in the reaction were holes and superoxide radicals.According to the experimental results,the 1h-Ag/AgCl/BiVO4 photocatalyst exhibited excellent stability and can effectively degrade oxytetracycline hydrochloride under a wide pH range condition or co-existing ions.The experimental results provided some scientific data for the practical application of the ternary plasmonic photocatalyst 1h-Ag/AgCl/BiVO4 for the treatment of antibiotics in water.