Application Of ZnS Matrix Composites Derived From Framework Materials In Photocatalytic Hydrogen Production

The solar photocatalytic hydrogen production technology boasts numerous advantages,including low energy consumption,zero greenhouse gas emissions,sustainable recovery and straightforward operation.It is expected to solve the problems of energy shortage and environmental pollution in the future.At present,the efficiency of photocatalysts is low,and the modification of precious metals is required to improve the catalytic activity,which greatly limits the practical application.Transition metal sulfide is a promising photocatalyst for hydrogen evolution due to its excellent photocatalytic activity due to its suitable conduction band location and abundant morphology.However,problems such as rapid electron-hole recombination rate,photocorrosion and energy mismatch are unavoidable for single component sulfide,so it is necessary to improve its photocatalytic activity and stability by composite modification.In photocatalytic reactions,high porosity not only enhances the mass transfer efficiency of catalyst surface reactions but also effectively reduces the unit particle size of semiconductors and significantly shortens carrier migration distances.Metal-organic framework materials（MOFs）are a type of porous material in which metal nodes are separated by organic ligands with high precision.By using MOFs as precursors,nanomaterials with exceptional porosity,crystallinity and uniformity can be synthesized.Hydrogen-bonded organic framework materials（HOFs）are a class of ordered materials composed of organic or metal-containing units assembled by hydrogen bonding.Due to the weak hydrogen bond bridging of HOFs,HOFs can be quickly vulcanized without pyrolysis process and obtain high porosity sulfide.In this paper,MOFs and HOFs framework materials were employed for vulcanization derivation.Two types of composite photocatalytic materials with high porosity were designed and synthesized to facilitate efficient photocatalytic hydrogen production.Part I:Porous Zn S materials were prepared by MOFs derivatization,and the ZIF-8@Zn S core-shell structure was constructed by controlling the vulcanization temperature.The Zn S nanomaterials derived from ZIF-8 all have small grain size and high specific surface area,even the Zn S sample after complete vulcanization has a specific surface area of 192 m²·g^-1,while the size of Zn S particles in the ZIF-8@Zn S core-shell structure is only about 10 nm.The core-shell structure of ZIF-8@Zn S ensures the good dispersion of Zn S particles,thus avoiding further agglomeration of Zn S particles.The high specific surface area and small particle size mean that the photocatalyst has a shorter charge migration distance and more active sites,which effectively improves the separation and transport efficiency of photogenerated charge.The hydrogen production performance of ZIF-8@Zn S core-shell material obtained at60℃oil bath temperature is the best,reaching 5.32 mmol·g^-1·h^-1.Part II:Zn（en）₃S₂O₃/Zn Cd S composites（ZCES）with hydrogen bond framework were prepared by MOFs precursor,and Zn S/Zn Cd S heterostructures were obtained by vulcanization derivatives.The specific surface area of Zn S/Zn Cd S porous heterojunction is up to 320 m²·g^-1,and its unit particle size is about 5 nm.Due to the ordered metal ligand units in Zn（en）₃S₂O₃ and abundant hydrogen bond bridging,complex ZCES can be rapidly etched by S^2-in sodium sulfide solution and derived into high porosity and small size sulfide.MOFs precursor strategy can effectively ensure the uniform dispersion of Zn Cd S in ZECS complex and avoid the formation of impurity Zn S（en）_0.5 in the preparation process.The photocatalytic hydrogen evolution rate of Zn S/Zn Cd S-0.3 heterojunction can reach 1.68 mmol·h^-1 under the condition of helpless catalyst.Therefore,the high porosity and small size of the heterojunction design leads to more heterojunction interfaces and shorter heterojunction depths,effectively promoting the effective separation of carrier in the phase.Photoelectric characterization also further proves that the high activity of Zn S/Zn Cd S heterojunction is due to the improvement of charge separation efficiency.