Design,Construction And Photocatalytic Activity Of ZnIn₂S₄ Based Catalyst

Energy shortage and environmental pollution have become an increasingly severe global concern.Photocatalytic technology could utilize clean and sustainable solar energy to alleviate the current environmental pollution and future energy shortage efficiently.However,rapid recombination of photogenerated electron-hole pairs results in a low photocatalytic efficiency.Constructing an efficient and stable heterojunction photocatalyst system could realize the effective transport and separation of photogenerated carriers under the action of the built-in electric field,thus improving the photocatalytic activity.Herein,a series of ZnIn2S4 heterojunctions were constructed via structural modulation,component optimization,and functional enhancement,and their photocatalytic hydrogen production,sulfamethazine(SMZ)and chlorophenols removal were conducted to investigate their photocatalytic activities.The charge transport mechanism of the heterojunction has been deeply explored through analytical characterization and first-principles calculations.The built-in electric field that effectively facilitates the transfer of photogenerated carriers.This work provides an effective solution for the rational design and structural modulation of heterojunctions and provides a reference for developing other efficient photocatalytic reactions.The research contents are as follows:1.The construction of ZnWO4-ZnIn2S4 S-scheme efficient photocatalysts with two-dimensional coupled interfaces have been successfully constructed by a simple calcination and water-bath technique to reduce the cost,where photogenerated carriers can be efficiently transported and separated between the interfaces.Band structure analysis(e.g.,UPS,Mott-Schottky,and VB-XPS)determined the charge migration direction at the heterojunction interface,revealing the photo-excited carriers’ separation mechanism.The built-in electric field established at the interface of ZnWO4-ZnIn2S4 heterojunction contributes to the effective separation of charges,leading to enhanced photocatalytic activities.The optimal photocatalyst exhibited a high hydrogen production performance(up to 4925.3μmol·g-l·h-1)and efficient SMZ and chlorophenol degradations.Also,the heterojunction catalysts exhibited excellent cyclic stability during the photocatalytic reaction.2.The structure and components of the ZnIn2S4 photocatalyst could be optimized and tuned by introducing BN with strong adsorption capacity and the electron acceptor MXene into the photocatalytic system to enhance the visible-light-driven catalytic activity.The introduction of BN in the ternary heterojunction provided more adsorption and reaction sites.Meanwhile,the composite of MXene enhanced the system’s visible light absorption and charge transfer efficiency.Etching part of the A1 layer from the MAX-BN complex enhanced the bonding strength between the MXene and BN interfaces and reduced the transport resistance.The BN/MXene/ZnIn2S4 photocatalyst heterojunction was obtained by constructing ZnIn2S4 nanosheets on the etched BN/MXene.The photogenerated carrier transport mechanism in the heterojunction was determined by UPS,EPR,VB-XPS and Mott-Schottky tests.The ternary heterojunction photocatalyst exhibited excellent hydrogen production performance(～1455 μmol·g-1·h-1)and 4-chlorophenol(4-CP)degradation(90%)compared with pure BN/MXene and ZnIn2S4 samples.The modulation of catalyst composition further improved the photocatalytic redox ability,which provided a feasible strategy for constructing heterojunction catalysts for energy and environmental remediation.3.In constructing heterostructures,efficient heterojunction photocatalysts can be obtained by selecting semiconductor heterojunctions with reasonable band structure and matching work functions,which can further enhance the carrier transport between interfaces and realize the effective separation of photogenerated carriers.Combined with DFT theoretical calculations,CdLa2S4/ZnIn2S4 heterojunction with suitable Fermi energy levels and work functions was designed and constructed.The heterojunction also provided a large contact area and active sites for the photocatalytic process.The CdLa2S4/ZnIn2S4 heterojunction photocatalyst exhibited excellent performance in hydrogen production and degradation of organic pollutants.The hydrogen production rate of the composite sample under visible light was as high as 1582.3 μmol·g-1·h-1,which was 2.65 and 89.4 times higher than that of the pristine ZnIn2S4 and CdLa2S4,respectively.The photocatalytic degradation efficiencies of 2,4-dichlorophenol(2,4-DCP)and SMZ reached 74.1%and 98.9%,respectively.Characterizations and DFT theoretical calculations revealed the S-scheme electron transfer mechanism.Theoretical calculations revealed that In in ZnIn2S4 can contact with CdLa2S4 to form a substantial interfacial coupling effect.The carriers are driven by the Fermi energy level difference and the built-in electric field at the interface to move in the reverse direction,and the coupling interface further promotes the effective separation of the photogenerated carriers.In this work,the optimization of the energy band structure and the functional design of the interface provide a reference for the preparation of ZnIn2S4-based heterojunction photocatalysts.4.To address the low degradation efficiency of 2,4-DCP by photocatalysis in the studies of the previous three chapters and achieve the efficient removal of 2,4-DCP by ZnIn2S4-based heterojunctions,piezoelectric materials were introduced during constructing the heterojunctions to realize piezo-photocatalytic coupling degradation of 2,4-DCP.BiFeO3/ZnIn2S4 heterojunction piezo-photocatalysts were prepared to efficiently degrade 2,4-DCP under the synergistic effects of light and mechanical vibration.The charge transfer was verified and analyzed using various techniques,such as DFT calculations,XPS,UPS,and EPR analyses.The piezoelectric properties were further investigated by PFM characterization and COMSOL simulation.The COMSOL simulation results confirmed that the constructed heterojunctions exhibited strong interfacial bonding.The degradation efficiency of BiFeO3/ZnIn2S4 piezo-photocatalyst for 2,4-DCP reached 95.2%when light and ultrasonic vibration were applied simultaneously.The band tilt caused by piezoelectric potential effectively weakens the shielding effect of the charge at the heterojunction interface,further promotes the efficient separation of carriers,and provides more hydroxyl and superoxide radicals for the reaction system.This study combines sustainable solar energy with mechanical energy to degrade organic pollutants in wastewater efficiently.Overall,different ZnIn2S4-based photocatalysts were constructed to increase the investigation of interfacial engineering,which realized the improvement of the photocatalytic hydrogen production capacity and the effective removal of organic pollutants.This research provides effective solutions in terms of the rational design of ZnIn2S4 heterostructures and regulation of interfacial energy band engineering while providing a basis for the application of photocatalysts in the energy and environment fields.