Enhancing The Photogenerated Charge Separation Capacity And Photocatalytic Performance Of Bismuth-based Photocatalysts

The overuse of antibiotics and the wanton discharge of pharmaceutical wastewater pose a serious threat to the ecosystem and public health.Fortunately,photocatalysis stands out from various water antibiotic removal strategies owing to its advantages of low cost and strong oxidation ability.Especially,bismuth-based photocatalytic materials have attracted wide attention in the field of photocatalysis because of the suitable band structure and excellent photocatalytic performance.Nevertheless,the photocatalytic activity of pristine semiconductor materials is always limited by the rapid recombination of photogenerated electron-hole pairs,leading to unsatisfactory practical application.In order to enhance the photogenerated charge separation capacity of bismuth-based photocatalysts and improve their photocatalytic performance,this paper optimized bismuth-based semiconductors by means of loading cocatalysts and constructing heterostructure.Specifically,the synergism of oxidation and reduction cocatalysts accelerated the transfer of photogenerated charge carriers on two-dimensional（2D）bismuth molybdate（Bi₂Mo O₆）nanosheets and bismuth oxybromide（Bi OBr）nanosheets and provided rich active sites for the reaction.The construction of S-scheme and surface heterojunctions effectively promoted the spatial separation of photoinduced electrons and holes to improve the activation efficiency of peroxymonosulfate（PMS）,thus removing the antibiotic pollutants in water effectively.The specific research work is enumerated below:Firstly,different types of cocatalysts Au and CoO_x were successfully loaded on the surface of Bi₂Mo O₆（BMO）nanosheets.Thanks to the electronic attraction of Au and the hole capture properties of CoO_x,the dual-cocatalysts could build a dual-channel of charge transfer on BMO material to accelerate the transfer of electrons and holes,thus inhibiting the recombination of photocarriers.Besides,with the help of dual cocatalysts,the visible-light absorption ability of BMO was enhanced.Noticeably,the ternary BMO/CoO_x/1.5Au composites displayed an enhanced degradation rate toward tetracycline（TC）,which was 2.75times higher than the pure BMO.The photocatalyst also possessed good stability and could maintain high photocatalytic activity after five cycles.Meanwhile,the photoluminescence spectroscopy（PL）and time-resolved photoluminescence spectroscopy（TRPL）demonstrated that BMO/CoO_x/1.5Au sample promoted charge separation and prolonged carrier lifetime.This research provides an effective solution for designing practical and efficient photocatalysts to remove antibiotic pollutants and sheds new lights on the construction of dual charge transfer channels and the promotion of charge separation.On the basis of the previous work,in order to find the more economical cocatalysts to replace noble metals and metal oxides for building the dual-channel of charge transfer,the semimetal Bi and non-metallic material BNQDs were selected as reduction and oxidation cocatalysts to modify photocatalysts.Moreover,regulating Bi OBr（BOB）to two-dimensional nanosheet structure with a larger specific surface area could shorten the charge transfer distance and assist the rapid diffusion of carriers,further inhibiting the recombination of photogenerated charges.Notably,the 4BBOB/3BNQDs samples exhibited an efficient degradation rate(0.0295 min^-1)and sterling reusability for photocatalytic removal of TC.The results of PL and TRPL indicated that the BBOB/BNQDs composites showed enhanced charge separation ability under the synergetic promotion of dual cocatalysts Bi and BNQDs.This research provides a new idea for the design of a low-cost and efficient photocatalytic system,and offers a new avenue to boost the separation of photogenerated electron-hole pairs.Besides introducing cocatalysts to modify bismuth-based photocatalytic materials to elevate the efficiency of charge separation,building heterojunction is also an effective strategy to enhance the spatial separation ability of photoinduced electrons and holes in photocatalysts.Furthermore,the formation of heterojunction is also conducive to retaining the strong redox potential of photocatalyst,thus improving its photocatalytic performance.Hence,a novel S-scheme photocatalyst system was elaborately designed by hydrothermal and in-situ calcination methods.This system was constructed by combining Cu O with Bi VO₄（BVO）containing surface heterojunction,which could realized the efficient degradation of norfloxacin（NOR）through the rapid activation of PMS.Benefiting from the construction of the S-scheme structure and surface heterojunction,the photoexcited electrons migration to Cu O not only promoted the spatial separation of electrons and holes but also expedited the Cu²⁺/Cu⁺cycle.On this basis,the NOR removal capacity of 5Cu O/BVO composites was obviously enhanced,which was 3.65 and 2.45 times that of Cu O and BVO.Moreover,through the analysis of NOR degradation pathways and degradation products,it was found that the toxicity threat of NOR to the environment was reduced during the degradation process.According to the XPS results,the formation of S-scheme heterojunction accelerated the Cu²⁺/Cu⁺redox cycle,thereby boosting the activation of PMS.By exploring the reactive species and energy band structure of the catalysts,it was further verified that the Cu O/BVO system conformed to the S-scheme charge transfer mechanism and possessed enhanced redox ability and charge separation efficiency.