Study Of Preparation And Photocatalytic Property Of Bismuth Acetate Based Photocatalysts

Semiconductor photocatalysis technology has been widely concerned because of its promising application in solving environmental pollution and energy shortage.Compared to traditional techniques,as an advanced oxidation technology,semiconductor photocatalysts have the merits of high efficiency,economy and no secondary pollution.As a novel photocatalytic material,similar to HCOOBi O,bismuth acetate Bi O(CH₃COO)(denoted as Bi OAc)has a unique layered structure,electronic structure and good optical properties,and becomes the research hotspot of semiconductor photocatalytic materials.However,broad band gap energy(3.28 e V)of Bi OAc enables it to be excited only by UV light and thus limits its utilization to sunlight.Therefore,expanding optical response and boosting photocarrier separation efficiency of Bi OAc are the primary tasks to enhance its photocatalytic performance.The purpose of this paper is to modify Bi OAc by forming solid solution and constructing heterojunction,so as to broaden the visible light response and accelerate the separation efficiency of charge carriers,thus enhancing its photocatalytic performance.The main research contents are as follows:(1)BiOCl_1-xBr_x solid solution with highly exposed(001)crystal surface was synthesized by a facile solid state reaction using wide-band gap Bi OAc as the precursor.More importantly,all of the as-prepared Bi OCl_1-xBr_x possessed superior visible light photocatalytic activity to the corresponding ones obtained by previously reported solution route.Especially at an optimal x value of 0.5,the solid solution showed the highest photodegradation efficiency(?100%)for rhodamine B(Rh B)with a concentration of 30 mg L^-1,whereas the degradation efficiency was only 63%over that obtained by solution route.Furthermore,the as-prepared Bi OCl_0.5Br_0.5 also exhibited excellent photodegradation activity for malachite green(MG).The superior photocatalytic performance of the as-prepared Bi OCl_0.5Br_0.5 could be attributed to its thinner sheetlike structures and highly exposed(001)facets,which enable effective separation of the photogenerated electrons and holes along the[001]direction.In addition,Bi OCl_0.5Br_0.5 has strong adsorption capacity to Rh B,methyl violet(MV)and(Cr₂O₇)^2-.(2)BiOAc_xI_1-x solid solutions were easily synthesized by co-precipitation method.The Bi OAc_xI_1-x solid solutions with x=0.67 possessed the ultrathin sheetlike structures and optimal energy levels,which could greatly expedite separation efficiency of photoinduced electron-hole(e^--h⁺)pairs,bringing about the enhanced visible-light photocatalytic performance for the degradation of multiple organic pollutants like Rh B,MG and colorless salicylic acid(SA).In addition,based on the band structure and the type of active species,the feasible photocatalytic mechanism was deduced.(3)Spherical Bi OAc was prepared by a green,non-polluting and easily treated solid grinding method.On this basis,solid solution Bi OAc_xI_1-x was synthesized.XRD also confirmed that Bi OAc and Bi OAc_xI_1-x solid solution was successfully prepared by the solid grinding method.The as-prepared Bi OAc_xI_1-x solid solution exhibited outstanding visible-light photocatalytic activity for dye Rh B,methylene blue(MB),MG,MV and antibiotic tetracycline(TC)degradation.In addition,the as-prepared Bi OAc_xI_1-x solid solution also possessed desirable photodegradation efficiency for Rh B in real wastewater or in the presence of some electrolytes.(4)Given that the construction of step-scheme(S-scheme)system could prolong the lifetime of the more reactive charge carriers,a novel S-scheme photocatalyst Ag I/I-Bi OAc was constructed via a facile and green one-pot milling method.The as-prepared Ag I/I-Bi OAc S-scheme photocatalyst exhibited prominent visible-light photocatalytic activity for the removal of colored dye MV,methyl orange(MO),MG,and colorless bisphenol A(BPA).Mott-Schottky analysis indicated that the formation of I-Bi OAc solid solutions with suitable I content could optimize energy band structure,which transformed type-I Ag I/Bi OAc heterojunction to typical S-scheme Ag I/I-Bi OAc photocatalyst.This work provides a facile way to design S-scheme system by modulating the composition of the solid solutions.(5)Uniformly dispersed flowerlike Bi OAc was were prepared by simple chemical precipitation using urea as morphological regulator.Moreover,the amount of urea,Na Ac content and reaction time are important factors affecting morphology regulation.Based on the above analysis,we deduced that the optimal reaction condition was to treat with 7 mmol Na Ac as raw material and 6 g urea as morphological regulator for 12 h at room temperature.This work expands a new field of view in the exploration of morphology regulation,realizes controllable synthesis,and proves that morphology regulation is also the main factor to improve photocatalytic activity.(6)A novel flower-like S-scheme heterojunction Bi OBr/Bi OAc_1-xBr_x was synthesized via a facile co-precipitation method at room temperature.The as-prepared Bi OBr/Bi OAc_1-xBr_xexhibited outstanding visible-light photocatalytic activity for TC and Rh B degradation.The enhanced photocatalytic activity could be attributed to two main aspects.Firstly,the formation of the solid solution Bi OAc_1-xBr_x could not only enlarge visible light response of Bi OAc,but also successfully transform type-I heterojunction of Bi OBr/Bi OAc to typical S-scheme heterojunction of Bi OBr/Bi OAc_1-xBr_x,which thus prolong the lifetime of charge carriers with stronger redox ability.Secondly,by adding urea to the reaction system as a morphology modifier,uniform ultrathin nanosheet-based flowerlike Bi OAc was obtained,and more importantly,the heterojunction Bi OBr/Bi OAc_1-xBr_x inherited the flowerlike contour of Bi OAc and thus improved the dispersion,which benefit to the transfer of carriers at the interfaces and to the surface of nanoparticles.In addition,the as-prepared S-scheme heterojunction also possessed desirable photodegradation efficiency for TC and Rh B in real wastewater or in the presence of some electrolytes.This study provides a simply and energy-saving strategy for simultaneously optimizing energy band structures and microstructure to highly efficient heterojunction photocatalysts.Through the above studies,it was found that the formation of Bi OAc_1-xX_x solid solution not only expanded the visible light response,but also obtained a continuously adjustable energy band structure,thus improving the photocatalytic performance.The construction of heterojunctions is an effective strategy to accelerate the separation efficiency of carriers.According to the solid solution to expand the light absorption,combined with the heterojunction to accelerate the light carrier separation advantages,we constructed the Bi OAc_1-xX_x based heterojunction photocatalyst.The construction of Bi OAc_1-xX_x based heterojunction photocatalyst not only widened the visible light response,but also accelerated the separation efficiency of photoinduced e^--h⁺pairs.This study provides an effective strategy for developing novel visible light catalysts to enrich the types of photocatalysts and for further understanding the photocatalytic mechanism.