Photocatalytic Degradation Of Tetracycline In Water By Modified Bismuth Vanadate And Zinc Oxide Hybrid

Tetracycline is a kind of commonly used antibiotics which is widely spread in aquaculture water and difficult to be completely removed by conventional water treatment technology.Tetracycline has been detected in many water environments,and it may pose a potential threat to the health of human beings.Photocatalysis is a clean and efficient technology to remove the organic pollutants from water.Therefore,it is necessary to develop an efficient and environmental-friendly photocatalyst for the degradation of tetracycline in water.Bismuth vanadate?BiVO₄?is a promising photocatalyst with narrow band gap,high visible light response and stable chemical properties.However,there is the deficiency that photogenerated electrons and holes of BiVO₄ are easily get combined.In order to improve the application space of BiVO₄,the crystal facet of BiVO₄ was modified due to its active{010}facet.The oxidation ability towards tetracycline was further improved by compounding with zinc oxide?Zn O?,and the degradation mechanism of tetracycline in water was further discussed.The specific conclusions are as follows:?1?A series of BiVO₄ with different{010}crystal facet area were synthesized by hydrothermal method with titanium trichloride?Ti Cl₃?as structure directing agent.Zn O nanoparticles were grown on the surface of BiVO₄ in situ by hydrothermal method and BiVO₄/Zn O hybrid photocatalysts with different composition ratio were synthesized.?2?By SEM,TEM,XRD methods,it was proved that the exposure degree of{010}crystal facet of monoclinic BiVO₄ increased after modification,and 2-BiVO₄ had the largest{010}facet exposure degree and shaped in 10?20?m flakes.Through the analysis of XRD,TEM and XPS,it is confirmed that nano-flake Zn O with the size of20?100 nm is wurtzite-type hexagonal structure,and was successfully compounded with BiVO₄.Via UV-vis DRS characterization,it is revealed that BiVO₄/Zn O with different proportions are responsive to visible light,and the absorption band edge of BiVO₄/Zn O appears blue shift when increasing Zn O content in the component.Through the photocurrent test,it is observed that the strengthening of{010}crystal surface in BiVO₄ can effectively promote the separation of photogenerated carriers,and the combination of Zn O and BiVO₄ can further prolong the lifetime of electrons in the system.?3?TC was used as the target pollutant to carry out degradation experiments under visible light.When the initial concentration of TC was 10 mg/L and the dosage of photocatalyst was 0.3 g/L,2-BiVO₄ had the best TC removal rate?98.84%?among the series of BiVO₄ with different{010}exposure.The reaction conform to the pseudo-first-order kinetic model,and reaction rate constant is 10.39 times than that of primeval BiVO₄.When the initial concentration of TC was 10 mg/L and the dosage of photocatalyst was 0.1 g/L,the TC removal rates of BiVO₄/Zn O is generally higher than that of single component under the same condition,and 6BZ achieved the highest removal rate?95.54%?.The reaction conform to the pseudo-first-order kinetic model in as well,and 6BZ has the largest reaction rate constant which is 3.7 times than that of modified BiVO₄.The effect of different initial p H?3?11?on TC degradation was analyzed,and the results showed that the removal rate in BiVO₄ increased with the increasing of p H.The removal rate of BiVO₄/Zn O increased first and then decreased with the increasing of p H,and reach the maximum value?98.95%?at p H=9.By setting different initial concentrations of TC?5?30 mg/L?,the removal efficiency of BiVO₄/Zn O decreased with the increasing of initial concentration of TC.?4?Through the radical quenching experiments and EPR characterization,it is proved that the dominant radical in the TC degradation by BiVO₄/Zn O is superoxide radical?·O₂^-?.Through UV-Vis DRS and VB-XPS characterization,the band structure of BiVO₄/Zn O was calculated,and combining with the results of radical experiments,it was proved that BiVO₄/Zn O is a direct type Z heterojunction.The reason for the formation of the direct type Z heterojunction may be that the interface band bending caused by contact of semiconductors prevents the migration of electrons in the Zn O conduction band.The{010}facet as electron accepter is attribute to the heterojunction formation as well.Through the identification of the degradation products of TC by LC-MS,it is inferred that the possible degradation paths of TC include the removal of methyl from dimethylamino group,the removal of amide group and the removal of amino group.?5?After four rounds of recycle experiments,it is proved that BiVO₄/Zn O still maintains a high TC removal rate?70.55%?after four times of recycling.Through the detection of TOC in solutions before and after the degradation,it is showed that BiVO₄/Zn O has a high TC mineralization rate?68.87%?comparing with similar reports.BiVO₄/Zn O is a promising photocatalyst due to its high activity,low consumption and good regeneration ability.