Research On Controllable Synthesis Of Transition Metal Semiconductor Composites And Their Photocatalytic Performance

In recent years,the increasingly serious energy shortage and environmental pollution have severely restricted the sustainable development of human beings.Therefore,the development of green renewable energy is urgent.Hydrogen has the advantages of high energy density and pollution-free combustion products,which can meet people's demand for new sustainable energy.Hydrogen production based on solar photocatalytic water splitting is one of the important ways to develop and utilize hydrogen energy.Among them,the preparation of high efficient photocatalysts has been the focus of research.Cadmium sulfide(CdS)is considered as a visible photocatalyst material with wide application prospect due to its suitable bandgap width and band edge position.In addition,considering the unique structural advantages of one-dimensional nanostructures can promote the fast transfer and separation of photogenerated charge.Therefore,the design and synthesis of one-dimensional CdS-based hybrids with novel structures and the study of the relationship between structure and performance are of great significance to the development of photocatalytic technology.In this work,one-dimensional CdS-based materials were chosen as the study objects,improving the performance of photocatalyst by optimizing the interface structure and charge transfer mechanism of heterojunction,which provided a new research idea for the development of novel and high efficient photocatalytic materials.The specific works of this paper are summarized as follows:1.Novel all-solid state Z-scheme photocatalysts Cd1-xZnxS@WO3-x and Cd1-xZnxS@WO3-x/CoOx/NiOx composites were designed and synthesized,and their photocatalytic hydrogen production activity were carried out under visible light.Among them,Cd1-xZnxS@WO3-x photocatalyst was prepared by solvothermal method and subsequent room temperature hydrolysis and oxidation process,which consists of Cdi-xZnxS nanorods coated with oxygen-deficient WO3-x amorphous layers.The Cd1-xZnxS@WO3-x exhibits an outstanding H2 evolution reaction(HER)activity due to the generation of stronger reducing electrons through the appropriate Zn-doping in Cdi-xZnxS and the enhanced charge transfer by introducing oxygen vacancies(W5+/OVs)into the ultrathin WO3-x amorphous coatings.The optimal HER rate of Cd1-xZnxS@WO3-x is determined to be 21.68 mmol·h-1·g-1.The HER rate of Cd1-xZnxS@WO3-x/CoOx/NiOx composite is further raised up to 28.25 mmol·h-1·g-1 when Cd1-xZnxS@WO3-x is hybridized by CoOx and NiOx dual cocatalysts through in-situ photo-deposition.2.Novel 1D Cd0.85Zn0.15S@WO3/WS2(CZ0.15S@WO3/WS2)core-shell nanorods comprising amorphous WO3 and few-layered WS2 nanosheets were design and synthesized through two-step solvothermal method,which demonstrate excellent activity and stability for visible-light-driven H2 evolution reaction(HER).It is found that the composition of WO3/WS2 shell varies with the W loading amount,which has a significant impact on the photocatalytic activity of CZ0.15S@WO3/WS2.Under optimized conditions(n(WO3):n(WS2)=3:1),the CZ0.15S@WO3/WS2 composite delivers the maximum HER rate of 76.33 mmol·h-1·g-1.The HER capability of CZ0.15S@WO3/WS2 is much better than that of noble Pt-decorated CZ0.15S and most CdS-based photocatalysts ever reported,probably due to the dramatically enhanced charge transfer and separation by the synergistic cooperation of Z-scheme and type-I charge transfer pathways in the former.3.CdS@Cd0.5Zn0.5S@ZnS hybrid nanomaterials were prepared by epitaxial growth CZ0.5S and ZnS on CdS nanowires through solution chemistry method,and CdS@Cd0.5Zn0.5S@ZnS-Ni(OH)2 p-n junction composites were obtained through further in-situ photo-deposition of Ni(OH)2 nanosheets.The H2 evolution reaction(HER)rate of CdS@Cd0.5Zn0.5S@ZnS in Na2S/Na2SO3 solution is 15.38 mmol·h-1.g-1 under the visible light(?? 420 nm)irradiation,which is further raised up to 86.79 mmol·h-1·g-1 when hybridized by Ni(OH)2 cocatalyst via in-situ photodeposition.The reason for the material's obvious improvement in HER rate was mainly attributed to promoted the transfer and separation of electron-hole pairs caused by epitaxial heterogeneous interface and p-n heterojunction.4.One-dimensional CZ0.15S@ZnS core-shell nanorods were synthesized through simple solvothermal method and hydrothermal method,and then then the final product CZ0.15S@ZnS-Ni2P hybrids were obtained by loading Ni2P nanocrystals onto CZ0.15S@ZnS surface by one-step solvothermal method.The existence of zinc vacancy(Vzn)in ZnS promotes the transfer of photogenerated holes from CZ0.15S core to ZnS shell.On the other hand,the metallic Ni2P can be used as an electron collector to capture photogenerated electrons,thus achieving better spatial separation of photogenerated charge.The CZ0.15S@ZnS-Ni2P nanorods have excellent photocatalytic HER activity,with HER rate up to 339.8 mmol·h-l·g-1 and quantum yield up to 72.65%at 420 nm.