Facet-Dependent Heterostructure Formed By BiOCl And ZnCr-LDH And Its Visible Light Photocatalytic Properties

Visible-light photocatalysis is widely used in alleviating energy crisis and solving environmental problems because of low energy consumption,complete mineralization and less by-pollution.The key problem of visible-light photocatalyst is to enhance the range of light response and the efficiency of photogenerated carriers.The construction of 2D heterojunction is one of international hotspots.2D heterojunction photocatalyt has the advantages of broadening light response range,suppressing electron-hole recombination,accelerating photoelectron hole pair separation at the binding interface.Based on the energy band engineering and our previous work,we found that LDH had a controllable photocatalytic performance.This thesis aimed to form an efficient 2D BiOCl/ZnCr-LDH surface-oriented heterojunction,which was then applied to the visible photocatalytic degradation of water pollutants.In detail,the feasibility of BiOCl/LDH composite was explored by recombinating BiOCl and LDH in various ways.Then,the formation route of BiOCl/ZnCr-LDH oriented heterojunction was investigated through component control.The relationship was detailedly investigated between the combination method and active species,obtaining the synthetic method beneficial to exciton production and activity enhancement.The main conclusions of this paper are as follows:?1?Efficient BiOCl and LDH photocatalysts were formed by adjusting components and structures.ZnCr-Cl-LDH showed best visible light response range?Eg=2.95 eV?after investigating effects of interlayer anions and laminate cations on the visible light response range and catalytic activity of LDH.The decolorization efficiencies of ZnCr-Cl-LDH for MO and RhB was 95.8%and 8.8%,respectively,which were better than ZnCr-CO₃-LDH?90.1%,4.0%?and MgAl-Cl-LDH?0%,0%?.The adsorption and catalytic activities of LDH were affected by the surface electrical properties of dye solutions.The advantages of ZnCr-Cl-LDH lied in the role of oxygen bridge between metals,the influence of zinc on oxygen vacancy on surface and the broadened visible light response range.The effects of different crystal surface and pH of synthesis on the catalytic effect of RhB were compared.As a result,the decolorization efficiency of BiOCl₀₁₀ was 97.8%and that of BiOCl₀₀₁ was only 47.0%.Thus,the?010?crystal surface in BiOCl had a higher photocatalytic activity than?001?for RhB degradation.?2?Combining BiOCl with LDH obviously improved photocatalytic activity.The effects of addition sequence and combining method on photocatalytic activities of BiOCl/LDH were compared.The results showed that the optimal method was hydrothermal synthesis of an as-prepared BiOCl₀₁₀ in LDH precursor.Under the same reaction conditions,the decolorization efficiency of BiOCl₀₁₀/ZnCr-Cl-LDH obtained by the above synthetic method was 62.2%for 30 ppm RhB.By comparison,the decolorization rate of BiOCl₀₁₀ was 52.4%;the 24.0 wt.%BiOCl/NiFe-LDH was only22.9%for the decolorization of 30 ppm RhB.This photocatalyst was obtained by adding NiFe-LDH to the source solution of BiOCl precursor?3?BiOCl₀₁₀/ZnCr-Cl-LDH oriented heterojunction facilitated exciton production and improved photocatalytic activity.The composite of BiOCl/LDH was adjusted by controlling LDH interlayer anions,LDH laminate metal cations,BiOCl crystal surface and pH of synthesis.As a result,the BiOCl/LDH synthesized through ZnCr-Cl-LDH and BiOCl₀₁₀?pH=5?showed to be the best,which reduced97.5%of 20 ppm RhB in 90 min.SEM and TEM characterizaitions clearly showed that LDH with diameter of 1?m was dispersed on the surface of BiOCl₀₁₀ with diameters of 500 nm-2?m.Besides,the lattice space between BiOCl₀₁₀?002?and LDH?018?was 0.370 nm and 0.195 nm.Moreover,the visible light response was enhanced and the spectral response range was widened?Eg=2.97 eV?,indicating that BiOCl₀₁₀ and ZnCr-Cl-LDH had a matched band structure to construct energy band engineering.HRTEM also showed that LDH grew along?001?side of the?010?crystal surface to form a BiOCl₀₁₀/ZnCr-Cl-LDH oriented heterojunction.The existence of ¹O₂ in BiOCl₀₁₀/ZnCr-Cl-LDH proved that exciton was generated and the heterojunction interface produced ¹O₂.The surface-oriented heterojunction was beneficial to exciton production and photocatalytic performance improvement.?4?Main active species of BiOCl₀₁₀/ZnCr-LDH oriented heterojunction were H₂O₂ and O₂^-·.Free-radical captures showed that the degradation rate decreased to53.0 and 37.8%after adding benzoquinone and catalase,indicating that the main active species of BiOCl₀₁₀/ZnCr-LDH heterojunction were H₂O₂ and O₂^-·.Besides,HO·?h⁺and ¹O₂ also enhanced the photocatalytic activities.The fluorescence spectra and photocurrent tests suggested that the optical emission intensity of BiOCl₀₁₀/ZnCr-LDH was lower than that of BiOCl₀₁₀.BiOCl₀₁₀/ZnCr-LDH and ZnCr-LDH photocurrent densities were 0.157 and 0.142?A,respectively,indicating that the interface heterojunction of BiOCl₀₁₀/ZnCr-LDH effectively reduced electron-hole recombination,prolonged carrier lifetime and enhanced photocurrent density.The deethyl and oxanthracene conjugated structures occurred simultaneously in RhB degradation,which produced a series of by-products from N deethyl.The phenomenon was due to the synergies of photocatalysis and photosensitization.Moreover,the photocatalytic activity of the reused catalyst reached 70.0%after five cycles of recycling.Considering the actual application,a BiOCl₀₁₀/LDH-PVDF film was prepared,and its decolorization efficiencies of RhB were 85.7%after 3 h under visible light and 89.9%after 6 h under natural light,which solved the problem of the difficulty in photocatalyst powder recovery.