Synergistic Investigation Of Composite And Cocatalysis On Hydrogen Production From Photocatalytic Water Splitting Of ZnIn₂S₄-based Materials

With the development of human society and continuous progress of science and technology,environmental pollution and energy consumption have being become two urgent problems to be solved.The key issue to solve the above problems is to find a kind of safe and eco-friendly clean energy.Photocatalytic water splitting for hydrogen production is an efficient way to solve the above problems.In order to obtain higher efficiency of hydrogen production from photocatalytic water splitting,the most important thing is to develop stable and efficient semiconductor photocatalysts.ZnIn₂S₄（ZIS）,as a new type of ternary sulfide semiconductor,has achieved extensive attention because of its unique layered structure,suitable band gap and hydrogen evolution potential.However,the practical application of ZnIn₂S₄is limited by its low carrier separation efficiency and slow carrier migration rate.In this thesis,ZnIn₂S₄-based ternary composite materials were constructed,the separation efficiency of photogenerated electrons and holes was adjusted by the built-in electric field formed at the heterogeneous interface,the transfer and utilization of charges were synergistically improved by cocatalysts,and ultimately stable and efficient ZnIn₂S₄-based photocatalytic hydrogen production systems were obtained.The specific research contents are as follows:（1）The preparation and photocatalytic properties for MoS_x/hollow carbon spheres/ZnIn₂S₄（MS/HCSs/ZIS）composites.MS/HCSs/ZIS composites were successfully synthesized by multi-step method.The effect of two cocatalysts on the morphology,lattice fringe,chemical states,element distribution,composition,spectral absorption,interfacial impedance,carrier transport and photogenerated electron-hole recombination rate of ZnIn₂S₄was investigated in detail.The results showed that the phase composition and morphology of ZIS didn’t change significantly after loading HCSs and MS.Compared with pure ZIS,the band gap of MHZ-4.0 samples with optimal photocatalytic performance was significantly narrowed,indicating effective utilization of visible light.Under visible light irradiation,the performance of photocatalytic hydrogen evolution was improved obviously.The hydrogen evolution rate of optimal photocatalytic system,MHZ-4.0,was 620.9μmol·h^-1·g^-1,which was5.4 times higher than that of pure ZIS.Electrochemical and photoluminescence tests showed that loading HCSs and MS could reduce the transfer resistance of photogenerated carriers and inhabit the recombination rate of photogenerated carriers,so as to improve the separation efficiency of photogenerated electron/hole pairs.（2）The preparation and photocatalytic properties of Ni_xP/Cu WO₄/ZnIn₂S₄（NP/CWO/ZIS）composites.NP/CWO/ZIS composites were successfully synthesized through chemical precipitation/photodeposition method.The synergistic effect of Z-scheme heterojunction and ohmic junction on the morphology,chemical state,element distribution,composition,spectral absorption,interfacial impedance,carrier transport and photogenerated electron/hole recombination rate of pure ZIS was studied in detail.The results showed that the visible-light utilization of NP/CWO/ZIS composites was significantly improved,and the hydrogen production performance was much higher than that of pure ZIS.Among them,2NP/CWO/ZIS-5 was the best for photocatalytic hydrogen production.Under visible-light irradiation,its hydrogen evolution rate is 13319μmol·h^-1·g^-1,approximately 14 times as much as pure ZIS.Electrochemical and photoluminescence tests showed that the synergistic effect of Z-scheme heterojunction and ohmic junction could accelerate the carrier transport rate,inhibit the recombination of photogenerated electron-hole pairs,and prolong the carrier life.（3）The preparation and photocatalytic properties of Ni（OH）₂/Ni In₂S₄/ZnIn₂S₄（NOH/NIS/ZIS）ternary composites.NOH/NIS/ZIS ternary composites were successfully prepared by a three-step method,and the effect of heterojunction on the phase structure,morphology,band gap,photocatalytic stability and photocatalytic hydrogen production performance of ZIS was studied in detail.The results showed that the morphology of ZIS didn’t change after loading Ni In₂S₄,but the characteristic peaks of XRD disappear after the formation of Ni（OH）₂under the illumination.The performance of photocatalytic hydrogen production was much higher than that of pure ZIS,and NIS/ZIS-0.6 samples owned the best performance for hydrogen production.Under visible-light irradiation,the hydrogen production rate for NIS/ZIS-0.6 samples was 3409μmol·h^-1·g^-1,about 6.6 times higher than that of pure ZIS.Further studies showed that Ni In₂S₄was partially transformed into Ni（OH）₂by hole corrosion during the photocatalytic process,and thus formed NOH/NIS/ZIS composites.The formation of p-n-n heterojunction significantly accelerated the carrier transport rate,inhibited the carrier recombination,prolonged the carrier life,and ultimately leaded to the improvement of hydrogen production efficiency.There are 49 pictures,13 tables and 134 references in this thesis.