Preparation And Properties Of ZnIn₂S₄-based Photocatalytic Materials

The burning of fossil fuels promotes the rapid development of society and industrialization,resulting in environmental pollution and climate issues,which influences the survival and sustainable development of human beings and other creatures in nature.Photocatalysis is a highly efficient oxidation-reduction technology,and has been used in various areas,such as energy conversion,environmental remediation,and bacteria inactivation.However,the narrow light response range and the fast reformation rate of photogenerated electron-hole pair restrict photocatalytic activity,further limiting their practical application.Therefore,the selection,modification and design of photocatalyst are important research of this area.As a ternary sulfide semiconductor material,Zn In₂S₄ exhibits the commendable absorption capacity for visible light due to its suitable band gap.In addition,Zn In₂S₄ with a microsphere morphology is composed of nanosheet,which can provide large specific surface area and abundant photocatalytic active sites and decrease diffusion distance for carriers.However,the photocatalytic efficiency of single Zn In₂S₄ photocatalyst is constrained by rapid combination rate of photogenerated carries and photocorrosion.Combined Zn In₂S₄with other photocatalyst to construct heterojunction is a promising modification way,which can inhibit photogenerated carriers recombination and reduce photocorrosion of photocatalyst,further enhancing photocatalytic H₂ evolution rate via water splitting.The main contents of this thesis are as follows:（1）Zn In₂S₄/Ag₆Si₂O₇ nanocomposites with Z-type heterojunction structure were prepared by self-assembly method.Firstly,Zn In₂S₄ microspheres were prepared by hydrothermal method,and Ag₆Si₂O₇ nanoparticles were prepared by co-precipitation method.Then,the above two photocatalysts were dispersed in water,and Ag₆Si₂O₇ particles were evenly distributed on the surface of Zn In₂S₄ nanospheres with the assistance of electrostatic attraction.The photocatalytic H₂ evolution efficiency of the obtained Zn In₂S₄/Ag₆Si₂O₇-7composite is three times higher than that of the pure Zn In₂S₄.Based on the photocatalytic H₂ evolution experiments and a series of photoelectric-chemical tests,the Z-scheme carriers migration process of Zn In₂S₄/Ag₆Si₂O₇ composite was confirmed.（2）Zn In₂S₄/Ag Fe O₂ nanocomposites with p-n junction structure were synthesized by self-assembly method.Compared with the above work,Zn In₂S₄ nanospheres with a larger space between the nanosheets were prepared via a solvothermal method,and Ag Fe O₂ with a smaller and uniform size were prepared by coprecipitation method.Then the above two photocatalysts were dispersed in ethanol.Ag Fe O₂ nanoparticles were uniformly distributed on the surface of Zn In₂S₄ microspheres with the assistance of electrostatic attraction.Based on photocatalytic H₂ evolution experiment and photoelectric tests,the migration route of photogenerated carriers was studied.The results show that the p-n junction was formed in the interface of composite.The internal electric field at the interface accelerated the separation of electrons and holes,and further improved the photocatalytic H₂ evolution activity.（3）Fe WO₄/Zn In₂S₄ nanocomposites were prepared by in-situ growth process.Firstly,Fe WO₄ flower was prepared via a solvothermal method.Then,the Fe WO₄,Zn Cl₂,In Cl₃ and thioacetamide were placed in an 80°C water bath.And the Fe WO₄/Zn In₂S₄ composite was obtained through in-situ growing of Zn In₂S₄ nanosheets on the surface of Fe WO₄.This2D/2D face to face contact has larger interface contact area,which can effectively shorten the electron migration path and inhibit the recombination of electron-holes pairs.In addition,Fe WO₄/Zn In₂S₄ composite has better visible light response and hydrophilicity,which also contribute to the improvement of photocatalytic performance.Theoretical calculation and experimental results provide the evidence for the p-n junction structure at the interface after the two photocatalysts contact,boosting the separation of charge carriers and enhancing the photocatalytic activity.