Study On Preparation Of The Novel Semiconductor Nanocomposites Based On ZnO And Their Photo-/Electro-Catalytic Properties

Energy crisis and environmental pollution have become urgent problems to be solved for human development.Solar energy was regarded as a kind of abundant,pollution-free,renewable and clean energy.The development and utilization of solar energy is of great significance to solve the energy crisis and ecological environment pollution.Photocatalysis is the most potential and promising solar energy utilization technology,which includes photocatalytic degradation of organic dyes and photo-/electrocatalytic water splitting to achieve clean energy with high energy density.Semiconductor play a decisive role in photocatalytic process.For example,zinc oxide(ZnO)is a commonly used semiconductor material but zinc oxide(ZnO)as the representative of metal oxide has the following problems.1)The wide band gap narrows the optical response range of sunlight.2)Due to poor conductivity and the slow oxidation kinetics of water,the transfer rate of photogenerated charge carriers is slow with the serious recombination.As a result,the number of photogenerated charge carriers reaching the surface of the reactant or the interface between the reactant and electrolyte decreases,which leads to the decline of quantum efficiency.3)The photochemical stability of semiconductor materials is poor due to corrosion.Therefore,the development and research of ideal semiconductor photocatalytic materials can be conducive to the development of photocatalytic technology.Therefore,several novel semiconductor nanocomposites based on ZnO have been constructed using g-C3N4,Ag,AgBr and BiOCl as additives,including 3-D flower-like nanorods(ZnO/CN),a series of new foamed zinc oxide-silica spheres coupled with g-C3N4 nanosheets(FZSS/CN),foamed zinc oxide-silica spheres coupled with Ag-AgBr(Ag-AgBr/FZSS)and BiOCl/ZnO/g-C3N4 nanocomposite.The photocatalytic degradation of organic dyes and photo-/electrocatalytic water splitting performance were studied.The ability of light capture is improved and the separation of photogenerated.charge carriers are accelerated through the synergetic effects among the components,hence the effective utilization of solar energy can be realized.The main contents of this thesis are as follows:1.An efficient 3-D photo-/electrocatalyst ZnO/CN was fabricated via in-situ coupling of ZnO with g-C3N4 by hydrothermal and subsequent calcination.The results prove this electrocatalyst as suitable band structure semiconductor(2.4 eV).Results revealed that the sample acts as excellent electrocatalyst with OER current density at 10 mA cm-2@335 mV and the HER at 100 mA cm-2@-225 mV.While upon illuminations its catalytic properties further enhance at OER 10 mA cm-2@326 mV and for HER current density of 100 mA cm-2@-167 mV.2.A novel foamed zinc oxide-silica spheres and Ag-AgBr nanocomposite(Ag-AgBr/FZSS)was engineered by microemulsion and calcination treatments and passes through a complete characterization profiling.Advanced photo-/electrocatalyst is devoted for O2 and H2 evolution reactions(OER and HER).The Ag-AgBr/FZSS possesses the distinctive porous surface with open cavities.The hierarchical morphology provides many active sites and mesoporous conducting channels for visible light absorption and charge carrier transportation.The Ag-AgBr/FZSS act as outperformed photo-/electrocatalyst for OER(overpotential 348 mV at 10 mAcm-2)and HER(potential-217 mV at 100 mA cm-2).While under illumination conditions it reduced to 337 mV and-195 mV.The lustrous durability further justified it as a highly efficient photo-/electrocatalyst for renewable energy conversions.3.A novel foamed zinc oxide-silica spheres and carbon nitride nanocomposite(FZSS/CN)was fabricated by microemulsion and calcination treatments.The preparation process conditions of the material are optimized.The photocatalytic performance was investigated by the degradation of textile dyes such as methylene blue(MB)and Rhodamine B(RhB)under visible light.The optimized nanocomposite exhibited the superior photocatalytic degradation performance up to 95%for MB and 90%for RhB with rate constant(k)=0.0516 min-1 and 0.0464 min-1 respectively.This excellent performance was attributed to the hierarchical morphology,high surface area and mesoporous channels with open cavities.This uniqueness is responsible to enhance the optical and kinetic capabilities of the material for effective photocatalysis.4.Graphitic-carbon-nitride(g-C3N4)and bismuth oxychloride(BiOCl)semiconductors were effectively incorporated into the ZnO crystal structure by hydrothermal and calcination treatments.The obtained BiOCl/ZnO/g-C3N4 nanocomposite has improved visible light capability with efficient separation and low recombination rate of photo generated charges.The synergistic effect of semiconductors coupling endues BiOCl/ZnO/g-C3N4 with superior photocatalytic activity up to 98.6%for Rhodamine B(RhB)and 93.5%for Methyl Orange(MO)with rate constant(k)=0.2134 min-1 and 0.1380 min-1 respectively.Furthermore,BiOCl/ZnO/g-C3N4 sample has outstanding stability and reusability.