The Structural Control Of Bismuth Oxychloride Photocatalysts And Its Dye Sensitization Properties Investigations

Exploring the way to alleviate the increasingly prominent contradictions between the environment and energy is the only way for human sustainable development.Dye-sensitized photocatalytic fuel cell?DSPFC?is a system based on fuel cell combining with semiconductor photocatalysis technology to convert solar energy into chemical energy by using dye molecules as fuel.It has great application prospects because it can continuously produce electricity and decompose polltants at the same time.Bismuth oxychloride?BiOCl?with unique layered structure and facet-dependent properites has been proven as a promising DSPFC electrode material.Firstly,the internal electrostatic field formed between the BiOCl layered structures facilitates the transfer of photogenerated charge carriers.Secondly,owing to its large surface areas and open channel feature,the{010}active facets will endow BiOCl with excellent dye photosensitization performance.Therefore,the design and synthesis of high-performance BiOCl materials is crucial to promote the decelopment of DSPFC.Based on the in-depth study on the structure and chemical propertied of BiOCl materials,the research strategies of enhancing dye adsorption and accelerating charge transfer are proposed in this paper.And a series of functionalized BiOCl materials with unique surface structures and shapes are synthesized by solvothermal,metal ion doping and photoreduction methods.Next,a mechanism for the enhancement of dye photosensitization performances is described combined with systematic analysis of the physical structure and chemical properties of BiOCl matericals.Finally,their photoelectric conversion performance and pollutant removal efficiency in DSPFC are investigated,which can provide a feasible theoretical support and experimental scheme for construcing and developing high-performance DSPFC.The specifical research is carried out from the following five aspects:The first aspect investigated the effect of{010}facets on the dye photosensitization performance of BiOCl.The BiOCl nanosheets exposed different percentage areas of{010}facets were prepared by adjusting the pH of reaction solution.The results showed that the increase of pH value was beneficial for the growth of{010}active facets.At pH=12.0,the samples had the miximum areas of{010}facets.The reason was that high concentration of OH^-would consume the H⁺produced by Bi³⁺ions hydrolysis,resulting in the inhibition effect on the growth of{010}facets.The dye photosensitization performance of BiOCl gradually increased with the increase of{010}facets growth.The mechanism experiments showed that the{010}facets with large surface areas and open channel feature could facilitate the adsorption of dye Rhodamine B?RhB?molecules,which indicated that more active species would be generated for pollutant removal under visible light irradiation.When 40 mL of 5mg/L RhB solution was using as fuel,the J_SCC and V_OCC of cell were measured to be 0.0052mA/cm² and 0.56 V,respectively.Meanwhile,the color removal efficiency of RhB solution was about 52.1%within 240 min.The second aspect investigated the effect of specific surface areas on the dye photosensitization performance of BiOCl.The BiOCl nanflowers with large specific surface area and high{010}exposed facets were synthesized by using ethanol/ammonia as reaction solvent.The results showed that the nanoflower structure was composed of nanosheets with an average thickness of 15 nm and its surface area was 63.82 m² g^-1.The large specific surface area and{010}exposed facets could provide enough space and more active sites for RhB molecules adsorption,which was beneficial to enhance the dye sensitization properties of BiOCl.The color removal efficiency of RhB could reach up to 100%within 25 min,which was higher than other samples.The results of photoelectric measurements showed that the more photoelectrons generation and effective charge transfer were responsible to the enhancement of dye photosensitization activity of BiOCl nanoflowers.In the DSPFC system,the J_SCC and V_OCC of cell were measured to be 0.0058 mA/cm² and 0.689 V,respectively.In addition,67%of RhB color removal efficiency was obtained.The third aspect investigated the effect of surface oxygen vacancies on the dye photosensitization performance of BiOCl.Sb-doped BiOCl ultra-small nanosheets were prepared by using CTAC and Sb doping process.The results showed that the doping of Sb ions would destroy the stable[Bi₂O₂]structure and lead to the formation of oxygen vacancies in BiOCl.When Sb doping amount was 5%?mol%?,BiOCl-Sb samples exhibited optimal RhB removal efficiency.Mechanism experiments demonstrated that the oxygen vacancies can not only provide more active sites for dye adsorption and molecule oxygen activation,but also function as electron capture center to accelerate charge transfer.In the DSPFC system,the presence of oxygen vacancies significantly improved the photoelectric conversion performance and contaminant removal efficiency of the BiOCl photoanode,whose J_SCC and V_OCC were measured to be 0.00624 mA/cm² and 0.682 V,respectively.Meanwhile,about69.1%of RhB color removal efficiency was achieved in 240 min.The fourth aspect investigated the effect of thickness on the dye photosensitization performance of 2D BiOCl nanosheets,the ultrathin BiOCl nanosheets with full{010}exposed facets were prepared by PVP-assisted solvothermal method.The results showed that the average thickness of BiOCl nanosheets was 3.48 nm,which was composed of about 5[Cl-Bi-O-Bi-Cl]units.Moreover,when the thickness of BiOCl nanosheets reduced to the atomic scale,a large number of surface defects(V^?_BiV_O^··V^?_Bi)and oxygen vacancies would be produced,which acted as active sites to promote the adsorption of dye molecules and enhance the photochemical reaction.In addition,the results of charge kinetic demonstrated that the ultrathin structure can shorten the diffusion distance of photocharges and prolongs the average lifetime of electrons.The large areas of{010}facets,abundant surface active sites,and long electron lifetimes were responsible to the excellent dye sensitization performance of ultrathin BiOCl{010}materials.In the DSPFC system,the photoanode exhibits excellent photoelectric conversion performance and contaminant removal capability,whose J_SCC and V_OCC were measured to be 0.00865 mA/cm²and 0.731 V,respectively.And,it achieved 72%RhB color removal efficiency and 10.77%Coulombic efficiency in 240 min.The fifth aspect investigated the photocatalytic activity of BiOCl under visible light irradiation.A visible-light-driven Cr-BiOCl/Ag composite was prepared by solvothermal and photoreduction methods.The results showed that the Cr doping and LSPR effect of Ag NPs could not only broaden the optical absorption ability of BiOCl but also significantly increase the photogenerated carrier generation rate and transfer efficiency.Under visible light irradiation,Cr-BiOCl/Ag exhibited significantly enhanced photocatalytic degradation performance for organic pollutant when Cr doping and Ag loading are 14.4%and 4%,respectively.Free radical trapping experiments and various characterization results proven that the synergistic effect of Cr doping and Ag LSPR effect promoted the formation of oxidizing speices and the efficient transfer of photogenerated charges.When RhB solution was used as fuel,75.1%color removal efficiency and 8.38%Coulomb efficiency could be achived on Cr-BiOCl/Ag photoanode,which were higher than that of methyl orange?MO?and tetracycline?TC?fuel.This result was primarily attributed to the significant enhancement of RhB degradation efficiency via the synergistic effect of indirect dye photosensitization pathway and direct semiconductor photoeccited pathway.In addition,its J_SCC and V_OCC were measured to be 0.0073 mA/cm² and 0.543V,respectively.