Preparation Of Zn_xIn₂S_x+3-based Photocatalyst And The Reaction Mechanism Of Antibiotic Removal And Bacterial Inactivation

Since the beginning of the 21st century,the overuse of antibiotics has led to an increasing problem of water pollution,which also resulted in the generation of more and more drug-resistant bacteria.Due to its pollution-free,simple operation,strong processing capacity and mild reaction conditions,semiconductor photocatalysis technology driven by solar energy is expected to become a new generation of water pollution control technology.Indium zinc sulfide(Zn _xIn₂S_x+3),as a metal sulfide semiconductor material,has great light-harvesting,regulable band structure and unique physical and chemical properties,which is considered as a promising photocatalytic material that has aroused the interest of scientific researchers.However,due to the shortages of low photo-excited carrier separation efficiency,limited optical absorption capacity and high photo-generated charge recombination rate,the photocatalytic performance of Zn_xIn₂S_x+3 is weak,which is difficult to meet the actual needs of environmental treatment.To solve the above problems,a series of highly efficient photocatalysts were prepared by modifying Zn_xIn₂S_x+3（morphology optimization,defect engineering,co-catalyst and heterostructure constructi on）,which were applied for degrading antibiotics and killing bacteria.Combining with a series of characterization methods,the phase composition,morphological char acteristics,elemental composition and valence changes,band structure and photo-generated charge migration rate of Zn_xIn₂S_x+3-based catalytic materials were systematically investigated,and the internal reaction mechanism between these characteristics and Zn_xIn₂S_x+3 materials with the reinforced photocatalytic ability was explored.The detailed research contents and test results are as follows:（1）Via two-step hydrothermal method,the Sn S₂ was integrated with Zn In₂S₄ to establish the conventional type-II heterojunction,and the photocatalytic performance of Sn S₂/Zn In₂S₄（SZ）composite was investigated by the degradation of doxycycline hydrochloride（DC）.The results show that the modification of Sn S ₂ can improve the light-harvesting ability and photo-generated carrier separation efficiency of Zn In ₂S₄.The type-II heterojunction formed by Sn S₂ and Zn In₂S₄ with matching band structure provides the driving force for photo-excited electrons and holes to transform in reverse directions,thus speeding up the spatial separation of carriers.The separated photo-generated electrons can effectively activate molecular oxygen to generate main reactive oxygen species（ROS）,such as·OH and·O₂^-,which participate in DC degradation reaction together with holes.Therefore,compared with pristine Zn In₂S₄,the photocatalytic degradation activity of SZ-2 with the optimal ratio is significantly improved,and 81.16%of DC can be effectively removed after exposure to visible light for 100 min.The pseudo-first-order kinetic model was employed for fitting the degradation data,and the highest DC degradation rate constant is 0.015 min^-1,which is 1.58 times that of Zn In₂S₄ under the same conditions.（2）In order to promote the separation of photo-generated charges in space,the oxygen-doped g-C₃N₄ nanosheet（OCN）with layer porous structure was attached on the surface of Zn In₂S₄ nano-flower with abundant Zn defect（ZIS-Z）and ultrathin structure by hydrothermal method in this study.A series of novel ZIS-Z/OCN composites with direct Z-scheme heterojunction were constructed and applied to the degradation of doxycycline hyclate（CTC）.Based on the DFT calculation,when ZIS-Z and OCN are in close contact,the difference in the work function between them leads to the generation of a built-in electric field,and the energy band of ZIS-Z and OCN bend up and down.After the composite is excited by visible light,the built electric field induces the photo-generated electrons at OCN CB to combine with the photo-generated holes at ZIS-Z VB,resulting in the formation of direct Z-scheme heterojunction,thus realizing the effective space separation of photo-generated charges.Moreover,Zn defects can also serve as electron capture sites to accelerate the separation of photo-generated carriers,synergistically improv ing the molecular activation capacity of ZIS-Z/OCN and producing ROS（·OH,¹O₂,H₂O₂ and·O₂^-）that jointly act on the removal of CTC.Finally,after 100 min of visible light irradiation,88.43%of CTC can be degraded by 40ZIS-Z/OCN with the optimal ratio,which are1.69 and 1.29 times of OCN and ZIS-Z under the same conditions.Based on the analysis of LC-MS,the possible degradation pathways of CTC are proposed.In addition,40ZIS-Z/OCN photocatalyst also has excellent recycling performance,anti-interference performance and structural stability,revealing its distinguished possibility in photocatalytic degradation of antibiotics.（3）For further investigating the role of defects and energy band bending in carriers diversion,Co B with powerful electron-withdrawing capacity was acted as a co-catalyst to load on the surface of Zn In₂S₄ nanosheet（ZIS-S）with S defects by electrostatic self-assembly method.A series of Co B/ZIS-S Schottky junction photocatalysts were constructed and applied to the photocatalytic inactivation of Escherichia coli（E.coli）.The theoretical calculation results show that the work function difference between ZIS-S and Co B will produce an upward energy band bending in the Co B/ZIS-S Schottky junction.In Co B/ZIS-S,because of the powerful electron-withdrawing capacity of Co B,the photo-generated carrier separation in ZIS-Z can be accelerated.Simultaneously,the upward band bending can be capable of restrainting the electrons reflux to ZIS-S,uncovering the phot-ogenerated carrier separation in space.Moreover,the S defects can use as an electron trapping site to effectively promote the separation of photogenic charge,so that more highly active electrons reduce O₂ rapidly in two steps,thus increasing the production of ROS（·OH,H₂O₂ and·O₂^-）in the 2Co B/ZIS-S photocatalytic system.Finally,Co B/CNs-2 can completely inactivate 1.5×10⁶ CFU/m L E.coli after exposure to visible light for 100min,Co B/ZIS-S efficiently decompose the leaked products in the inactivation process.（4）Through introducing W₁₈O₄₉ to modify with Zn₂In₂S₅,a series of novel Zn₂In₂S₅/W₁₈O₄₉（ZW）photocatalysts with direct Z-scheme heterojunction and LSPR effect were prepared to achieve full spectrum response from visible light to near-infrared region,and were applied to tetracycline hydrochloride（TC）degradation and E.coli inactivation.It is found that Zn₂In₂S₅ can be excited by visible light,and W₁₈O₄₉ with LSPR effect has strong light absorption in the near infrared region,which greatly broadens the optical response range of ZW composites.Under the synergistic action of Z-scheme heterojunction and hot electrons injection process induced by LSPR effect,the photo-generated charges in ZW composite can realize effective spatial separation,generate more highly active charge and enhance its molecular oxygen activation ability,thus increasing the production of ROS.Finally,after 60 min of visible light irradiation,ZW-3 can effectively degrade 87.80%of TC and inactivate 8.3 log₁₀ CFU/m L E.coli;After 180 min of near-infrared light irradiation,50.8%of TC can be degraded and 2.3 log₁₀ CFU/m L E.coli can be inactivated.