Preparation Of Metal Sulfide Based Composites And Investigation On Photocatalytic Hydrogen Evolution Properties

With the rapid development of human society,environmental pollution and energy crises have become increasingly severe,developing and using green and clean secondary energy to replace traditional fossil fuels can help solve these problems.Photocatalytic water splitting for hydrogen production via sunlight directly converting renewable solar energy into storable green hydrogen has significant importance for sustainable energy development globally.Zinc cadmium sulfide（CZS）is a popular metal sulfide photocatalytic material due to its visible light response,tunable band structure,simple preparation,and low cost.However,the easy aggregation and recombination of photogenerated charge carriers of pristine CZS nanoparticles lead to its low photocatalytic activity,which is difficult to meet the practical needs of industrial production.Therefore,constructing heterojunctions could improve the separation efficiency of photogenerated charge carriers and subsequently increase the photocatalytic activity of the materials.This paper focuses on CZS and addresses issues such as high photogenerated charge carrier recombination rates in photocatalytic materials.By multidimensional design,two-dimensional sheet-like nitrogen-doped graphene carbon/nitride carbon（NCN）and three-dimensional rod-shaped titanium dioxide（3DTiO₂）were complexed with CZS nanoparticles to construct heterojunctions,which effectively improved the photocatalytic hydrogen production activity and stability of CZS composite materials.The main research content and achievements of this paper are as follows:1.Study on photocatalytic performance of NCN/CZS for water splitting for hydrogen production.NCN/CZS composite photocatalysts were prepared by a simple two-step method（high-temperature solid-phase synthesis and hydrothermal synthesis）.Under visible light irradiation,using 0.35 M Na₂S/0.25 M Na₂SO₃ as a sacrificial agent,the optimized NCN/CZS had the highest hydrogen production rate of 56.35 mmol·h^-1·g^-1,which was 268 times and 2.01times that of the original NCN(0.21 mmol·h^-1·g^-1)and CZS(27.98 mmol·h^-1·g^-1),respectively,and exhibited excellent stability.The Type II heterojunction built by coupling NCN and CZS effectively promotes the rapid separation of photogenerated charge carriers.Additionally,the ultrathin nano-sheet structure of NCN provides more active sites,and the nitrogen-doped graphite carbon in NCN has excellent conductivity,acting as a"bridge"for the transfer of photogenerated electrons,thereby accelerating the rapid transfer of photogenerated electrons and improving the photocatalytic hydrogen production activity of NCN/CZS composite materials.This simple and ingenious design provides a new approach for preparing high-performance photocatalytic composite materials.2.Study on photocatalytic performance of 3DTiO₂/CZS for water splitting for hydrogen production.3DTiO₂ was prepared using electrospinning and hydrothermal synthesis methods,and CZS nanoparticles were grown on the nanorods of 3DTiO₂ by secondary hydrothermal synthesis,resulting in the preparation of 3DTiO₂/CZS composite photocatalysts.Under visible light irradiation,using 0.35 M Na₂S/0.25 M Na₂SO₃ as a sacrificial agent,the optimized3DTiO₂/CZS had the highest hydrogen production rate of 75.38 mmol·h^-1·g^-1,which was 2.4times that of the original CZS(31.07 mmol·h^-1·g^-1)and exhibited high stability.The unique morphology of 3DTiO₂ provides more active sites and effectively reduces the aggregation of CZS nanoparticles.By characterizing the photoelectrochemical properties,it was demonstrated that the synergetic effect between 3DTiO₂ and CZS accelerated the separation and transfer of photogenerated electron-hole pairs.In addition,the introduction of 3DTiO₂ results in a more negative position of the conduction band in the composite material compared to CZS,which is more conducive to the hydrogen evolution reaction.This unique morphology design provides new research ideas for the development and design of new highly active photocatalytic composite materials in the future.