Synthesis And Photocatalytic Hydrogen Evolution Performance Of Narrow Band Gap (ZnSe?CdSe) And Wide Band Gap (Eu₂O₃) Photocatalysts

Semiconductor photocatalytic water splitting reaction can realize the conversion of solar energy to clean hydrogen energy,and it is one of the most promising technologies to solve energy crisis and environmental pollution.However,the low visible-light utilization and fast carrier recombination limit the development of photocatalytic hydrogen evolution technology.Therefore,the development of novel and high-efficience photocatalysts for visible-light-driven has always been a research hotspot in the field of photocatalytic hydrogen evolution.In this paper,two types of semiconductor materials,narrow band gap(ZnSe,CdSe)and wide band gap(Eu₂O₃)were selected,and we prepared a series of photocatalytic materials based on the morphological control,the construction of heterojunction/Schottky junction,loading nanoclusters,dye sensitization and other methods.We analyzed and researched the morphology,phase composition,surface carrier recombination rate,photogenerated electron lifetime,overpotential,apparent quantum yield and electrochemical properties of the prepared samples.Meanwhile,we deeply investigated the photocatalytic hydrogen evolution performance of composite materials,and explored the photocatalytic mechanism.Our works provide an effective guide to design and construct stability,high-effeciency and wide visible-light-driven photocatalysts in the future.The research results are as follows:1.Three types of ZnSe materials with different morphologies(nanoparticles,microsphere and rod)were synthesized by one-step solvothermal method.Their structure,composition and photocatalytic hydrogen evolution activity were initially explored.Using ZnSe nanoparticles as a main photocatalyst,a novel and noble-metal-free heterojunction photocatalyst,which was ZnSe nanoparticles(NPs)deposited on the surface of bulk WC,was successfully fabricated via one-pot solvothermal method.The photocatalytic results indicated as a replacement of noble-metal cocatalyst,bulk WC could remarkably improve the photocatalytic H₂ evolution activity of ZnSe NPs under visible light irradiation in the heterojunction system.The H₂ evolution of the optimal sample achieved 2978.31 ?mol g^-1 in 5 h,which was 5.4 times higher than that of ZnSe NPs.The observably boosted H₂ generation activity could be ascribed to the ample reactive sites and the broadened visible-light absorption.Moreover,intimate interfacial contact between ZnSe NPs and bulk WC engenders synergetic effect and Schottky junction.Electrochemical,steady-state and time-resolved PL measurements further confirmed that the novel heterojunction photocatalyst could effectively accelerate the separation of charge carriers,decrease the overpotential and prolong the lifetime of photoinduced electrons.This study provides a novel and cost-effective approach for designing efficient noble-metal-free photocatalysts and improving H₂ evolution activity of selenides under visible-light-driven photocatalytic water splitting.2.On the basis of exploring ZnSe materials,we developed facile synthesis to construct a novel chrysanthemum-like cadmium selenide(CdSe)/bulk tungsten carbide(WC)Schottky-junction photocatalyst.The characteristic results for the components,microstructure and chemical state of photocatalysts revealed that chrysanthemum-like CdSe was intimately decorated onto the bulk WC surface using an ultrasonic-hydrothermal method.The photocatalytic results indicated that the optimal sample obtained the maximum H₂ evolution amount(2711.9 ?mol g^-1 in 5 h)under visible light irradiation,which was 7.4 times higher than that of chrysanthemum-like CdSe.The observably improved H₂ evolution activity is attributed to the ample active sites,the lower onset overpotential(-0.25 V)and the slower surface charge recommendation rate(0.011 s^-1).Meanwhile,intimate contact at the CdSe/WC interface can engender synergistic effect and actuate the formation of Schottky barrier,which effectively facilitates the reduction of water to H₂.This study uncovers an easily available synthesis for shape-controlled CdSe and in-depth explore the design of CdSe-based Schottky-junction photocatalyst for promoting photocatalytic H₂ evolution performance.3.We explored and prepared the wide band gap semiconductor europium oxide(Eu₂O₃).Eu₂O₃ was successfully developed as a newly active photocatalyst and used for H₂ evolution with Eosin Y(EY)-sensitized photocatalytic water splitting under visible light irradiation.A series of Pt nanoclusters(NCs)-deposited europium oxide photocatalysts were fabricated by an in-situ chemical deposition method.Electrochemical analysis showed that the conduction band potential of Eu₂O₃ was-0.82 V(vs NHE),which was more negative than the reduction potential of H₂O/H₂.High-resolution transmission electron microscopy revealed that the Pt NCs had excellent dispersion and ultrasmall size(?1.81 nm).The optimal photocatalytic H₂ evolution activity could be obtained by EY-sensitized 5 wt%Pt/Eu under visible light and reached 807.4 ?mol in 2 h.In addition,a reasonable mechanism for the enhancing photocatalytic H₂ evolution activity has been investigated and presented.This research indicates that lanthanide oxides with dye sensitization could be very promising photocatalysts for the reduction of water to H₂.Therefore,the above work has designed and constructed three types of composite materials through reasonable topic selections and effective modification methods,which provided a certain theoretical guidance for solving the rapid carrier recombination of photocatalysts and the low utilization rate of visible light.This paper furnishes a theoretical basis for the development of novel and high-efficiency photocatalytic materials and expands the development prospects of photocatalytic hydrogen evolution technology.