Construction Of Ultra-thin Bi₄O₅Br₂-based Nanosheets 2D/2D Photocatalytic Composite Material And Its NO_x Sub>Photocatalytic Removal

BixOyXz(X=CI,Br,I)is a new type of bismuth halide with unique graphene-like layered structure.The built-in electric field can be formed between bismuth oxide layer((BiO)2+)and bromide ion layer(Br-),which can effectively separate the photogenerated electrons and holes in BixOyXz,thus exhibiting excellent photocatalytic degradation of pollutants.BiOBr,Bi3O4Br and Bi24O31Br10 in BixOyBrz compounds show unique optical properties due to their suitable band structure.Compared with BiOBr(Eg=2.85 eV),Bi4O5Br2 has narrow band gap(Eg=2.4 eV)and more negative conduction band position(-0.4 eV).Pure Bi4O5Br2 nanosheet materials still have the disadvantage of low quantum efficiency,which affects the ability of photocatalyst to degrade pollutants.The construction of 2D/2D heterojunctions based on Bi4O5Br2 nanosheets to enhance ability for photocatalytic degradation of pollutants by accelerating the separation efficiency of electron holes,intensifying the redox ability of the surface.Therefore,the 2D/2D heterojunction was constructed based on 2D ultrathin Bi4O5Br2 nanosheets,the heterojunctions were characterized by using a series of methods to analyze the phase,morphology and optical properties,and NOx were degraded as target gas pollutants to analysis their properties.The work in research of this paper is as follows:(1)2D/2D Bi2O2CO3/Bi4O5Br2(BOC/BOB)direct Z-type flake-like photocatalyst was synthesized by one-step hydrothermal method.Atomic force microscopy(AFM)and high resolution transmission electron microscopy(HRTEM)results both showed that the formation of heterostructures was successfully interconnected with ultra-thin BOC and BOB nanosheets.It was found that the optimizing BOC content of 30%in BOC/BOB composites endowed with higher photocatalytic activity(53.2%)than single-phase BOC(20.4%)and BOB(37.9%)under simulated solar irradiation.The main active substances in the photocatalytic reaction was identified as·O2-and OH according to capture experiments and DMPO-ESR spin capture experiments.On the basis of DFT calculations,the photoinduced electrons of BOC combined with the holes of BOB constructed Z-type heterojunction between BOC and BOB ultrathin nanosheets.This process can effectively inhibit the recombination of photo-induced charge carriers in BOC/BOB nanocomposites,leading to the businesslike charge separation efficiency.(2)In this study,a 2D/2D titanium TiO2/Bi4O5Br2(TNS/BOB)direct Z-type heterostructure photocatalyst was constructed by employment the surface of anatase titanium dioxide(110)and Bi4O5Br2(020).SEM,TEM and EDS Mapping results showed that the as-prepared TNS with the size of 100 nm coated on the BOB nanosheet,successfully forming a heterojunction structure by interaction on surface.The synthesized TNS was more outstanding than P25 in photocatalytic activity aspect,indicating the TNS equipped with a higher exposure surface and 15%TNS/BOB composite endowed with an optimizing photocatalytic activity under visible light(54.4%).In this composite heterojunction,both·O2-and ·OH exhibited superior redox ability,and Z-type heterojunctions are formed between the two nanosheets on the surface.The photoinduced electrons in TNS assembled with the holes in BOB is consistent with the theoretical calculation.The photocatalytic activity was profited from effectively hinders the recombination suppression of electron and hole pairs in TNS/BOB structure due to the formation of 2D/2D heterojunction.(3)2D/2D Ti3C2/Bi4O5Br2(TC/BOB)heterojunction photocatalyst was fabricated by a hydrothermal method.The phase,morphology and optical information of the heterojunction were analyzed by various testing methods.TEM and EDS Mapping results showed that a formed 2D/2D heterojunction was consisted of nanosheets BOB cover on TC.As an electron recipient,TC absorbs more electrons generated on BOB,leaving only holes on BOB.The photocatalytic activity of TC/BOB photocatalyst was evaluated by using NOx as pollution source under visible light irradiation.TC showed little photocatalytic activity,but the mass ratio of TC to BOB was 15%TNS showed good photocatalytic activity(57.6%).In addition,the composite sample was demonstrated well stability and reuse ability.Finally,the photocatalytic enhancement mechanism of TC/BOB composite heterojunction photocatalyst was analyzed.