Direct Z-scheme BiOBr/g-C3N4 Photocatalyst Synthesized By Bio-template Assistant Hydrothermal Method And Its Properties Exploration

In recent years,semiconductor bismuth oxybromide（BiOBr）and graphite-like carbon nitride（g-C₃N₄）have received extensive attention on account of its relatively wide photoresponse range and high photocatalytic activity in the field of photocatalysis.Nevertheless,such monomer photocatalysts still have some intrinsic performance defects,limiting their practical applications to some extent.In this work,microspheric BiOBr and sheet g-C₃N₄monomer photocatalytic materials have been therefore synthesized and modified.The direct Z-scheme BiOBr/g-C₃N₄heterostructure has been constructed by compounding two kinds of components.The effects of different preparation parameters on the micromorphology,as well as light absorption,photoelectrochemical and photocatalytic properties of photocatalysts were analyzed and evaluated.The morphology and properties of samples were characterized and analyzed by XRD,FESEM,TEM,BET,UV-vis DRS and electrochemical workstation,etc.Moreover,a series of reasonable photocatalytic degradation mechanisms were proposed.The particular research content is as follows:（1）The microspheric BiOBr photocatalytic material with hierarchical structure was prepared via a bionic-template assistant hydrothermal method.The results shows that the size of BiOBr microspheres was minished to 300 nm and the light absorption edge was promoted to 445 nm as the p H=5,hydrothermal temperature reached 120℃and n（BiOBr）/n（L-lysine）=1:1.Simultaneously,the BiOBr sample exhibits optimal photocatalytic activity whose degradation efficiency can respectively reach 99.5%/90min and 79.9%/150 min for Rh B and TC-HCl.Moreover,its total organic carbon removal rate of Rh B solution can reach 62.2%.These enhanced performance are mainly due to the effective regulation of moderate biological templates on the growth and self-assembly process of BiOBr crystal.（2）The bulk g-C₃N₄photocatalytic material was synthesized by a thermal polycondensation method,and modified by the gas phase-hyperthermal exfoliation.The g-C₃N₄with optimal photocatalytic performance whose photocatalytic degradation rate is 5.08 times than that of unmodified g-C₃N₄was obtained by sintering at 550℃in air and NH₄Cl addition of 42.9 wt%during the modification.The enhanced photocatalytic performance mainly thanks to the gas release and hyperthermal environment effectively destroying the interlayer and intralayer bonding force of g-C₃N₄,gradually exfoliating the bulk g-C₃N₄into a sheet structure and promoting the visible absorption edge to 467nm.（3）The Z-scheme BiOBr/g-C₃N₄heterojunction system was successfully constructed by a simple template-assisted hydrothermal method which enabled BiOBr microspheres in situ grown on the surface of g-C₃N₄flakes.The results show that the composite displays optimal photocatalytic performances on degradation Rh B and TC-HCl as the content of BiOBr is 20%in BiOBr/g-C₃N₄composites.Its photocatalytic degradation rate for Rh B is 1.87 and 1.57 times than that of g-C₃N₄and BiOBr monomers,respectively.The construction of Z-scheme heterojunction system can effectively promote light absorption property（483 nm）,accelerate the transfer of interfacial charge and facilitate the separation of photo-generated electron-hole pairs.（4）Through active group capture experiments,the active groups of materials were confirmed during photocatalytic degradation.h⁺and·OH were the primary active groups,while·O₂^-was the secondary active group for BiOBr.h⁺and·O₂^-were the main active groups and·OH was the secondary active group for g-C₃N₄.·OH,h⁺and·O₂^-were the main active groups for BiOBr/g-C₃N₄.Additionally,the three kinds of photocatalytic materials showed excellent photostability and reusability in the experiment of cyclic degradation of Rh B.