Construction Of Fluoride-based Upconversion Material/Sulfide(Oxide) Heterojunctions And Study On Their Photocatalytic Properties

In recent years,semiconductor photocatalysis technology has become a research hotspot because it can be applied to the treatment of environmental pollution and the preparation of new energy.However,due to the limitation of the specific band gap over the semiconductors?such as metal sulfur,metal oxide?,nearly 50%of the near-infrared light in the sunlight can not be directly absorbed and utilized by the semiconductors.On the contrary,upconversion luminescence materials can directly use near-infrared light and convert it into ultraviolet or visible light for semiconductor absorption.In order to improve the utilization of solar energy and photocatalytic efficiency,it is a promising modification way to combine upconversion luminescent materials with semiconductors.As an effective upconversion material,NaYF₄:Yb,Er has been widely concerned owing to its high luminous efficiency and good chemical stability.In this thesis,typical semiconductors ZnS,ZnIn₂S₄ and WO₃ in metal sulfur/oxide were selected as the research objects,and NaYF₄:Yb,Er material was used as energy conversion carrier to improve the separation and migration efficiency of photogenerated carriers and the utilization of sunlight,so as to enhance the photocatalytic activities of the materials.The main contents of this paper are as follows:1.Firstly,NaYF₄:Yb,Er material was compounded with ZnS via a simple hydrothermal method.And the modified YF₃:Yb,Er/ZnS heterojunction photocatalysts with different mass ratio?10%,20%,30%and 40%?were obtained,which were applied to degradation of Rhodamine B,reduction of Cr?VI?and production of hydrogen.Through a series of characterization methods,it was proved that the heterojunction catalysts can effectively utilize near-infrared light,realize the energy transfer between YF₃:Yb,Er and ZnS,and greatly promote the separation and transfer of photogenerated electron-hole pairs.Compared with pure ZnS,the 20%YF₃:Yb,Er/ZnS heterojunction exhibited the more excellent performance in photocatalytic H₂ production and pollutants?Rhodamine B,Cr?VI??treatment under simulated full-spectrum sunlight and different light sources?ultraviolet,visible or near-infrared light?:when 400 W metal halide lamp was used as simulated full spectrum sunlight for 150 min,its photocatalytic removal efficiency of 10 mg/L Cr?VI?,20 mg/L Cr?VI?and 10 mg/L RhB was 80%,35%and 70%,which was 2,2.5 and 3.9 times than that of pure ZnS.What's more,the hydrogen production rate was 372.3?mol?h^-1?g^-1 without co-catalyst under the 300 W xenon lamp as the full spectrum light source,which was 2.1 times than that of the ZnS.2.NaYF₄:Yb,Er material and ZnIn₂S₄ were compounded through two-step simple hydrothermal method.Finally,ZnIn₂S₄ heterojunction photocatalysts modified by YF₃:Yb,Er with different mass ratio?5%,10%,20%and 30%?were obtained,which were applied to Cr?VI?reduction,photocatalytic hydrogen production and nitrogen fixation.A series of characterization methods were applied to prove that when the optimal mass ratio was 10%,YF₃:Yb,Er/ZnIn₂S₄ heterojunction can effectively utilize near-infrared light and also greatly boost the separation and migration of photogenerated carriers.The heterojunction showed the excellent photocatalytic performance:when 400 W metal halide lamp was used as full spectrum light source for 45 minutes,the reduction rate of 10 mg/L Cr?VI?over 10%YF₃:Yb,Er/ZnIn₂S₄ was 100%and the pure ZnIn₂S₄ was only 62%;The photocatalytic hydrogen production rate under 300 W xenon lamp as full spectrum irradiation was 2.6 times than that of pure ZIS.More importantly,compared with pure ZnIn₂S₄,10%YF₃:Yb,Er/ZnIn₂S₄ sample exhibited better photocatalytic activities in Cr?VI?reduction and hydrogen production under ultraviolet,visible and near-infrared light.In addition,due to the more negative conduction band potential of the heterojunction,the photocatalytic nitrogen fixation performance has been greatly improved.3.NaYF₄:Yb,Er material and Au nanoparticles were applied to modify WO₃?0.33H₂O by two step simple hydrothermal method and photo-reductive deposition of noble metal.Finally,a Z-type heterojunction of Au/NaYF₄:Yb,Er/WO₃?0.33H₂O-W₁₈O₄₉ with the synergistic effect of upconversion and local surface plasmon resonance?LSPR?was synthesized.A series of characterization methods were used to prove that there was energy transfer between NaYF₄:Yb,Er and WO₃?0.33H₂O-W₁₈O₄₉.And the LSPR effect of Au NPs and W₁₈O₄₉ can also broaden the absorption range of semiconductor.Under visible-near infrared light irradiation for 100 min,Au/NaYF₄:Yb,Er/WO₃?0.33H₂O-W₁₈O₄₉ showed the best photocatalytic performance and stability.The degradation rate of 20 mg/L nitrobenzene solution was 96%,which was 2.7 times than that of pure WO₃?0.33H₂O.The heterojunction also realized superior photocatalytic performance under visible light and near-infrared light.The above research indicated that NaYF₄:Yb,Er can effectively broaden the absorption spectrum of metal sulfur/oxide semiconductors,improve the utilization rate of sunlight and the efficiency of photogenerated carriers separation,and then enhance the photocatalytic performance.