In-situ Construction Of BN Heterojunction Photocatalyst Based On TiB₂ And Its Catalytic Activity

With the rapid development of semiconductor technology,photocatalytic technology as new technology has gradually gained more and more attention,effectively alleviating the issues of environmental pollution and resource shortage caused by industrial development and scientific and technological progress.As the most commonly used photocatalyst,titanium dioxide(TiO2)has a series of problems such as low photon utilization efficiency and fast recombination of carriers during the photocatalytic reaction process due to its large bandgap width and its limitations,which greatly hinder the practical application.Constructing TiO2 heterojunction will improve the generation and separation of photogenerated carriers effectively,and the photogenerated carriers with the reducing and oxidizing properties can be widely used in the environmental and energy fields.Among many synthesis methods of heterojunction catalysts,in-situ growth technology can make efficient use of the active sites of the semiconductor.The as-prepared heterojunction catalysts with chemically bonded interfaces could improve the transmission and separation of photogenerated carriers,effectively enhancing the photocatalytic activity of composites.Therefore,it is of great significance to prepare heterojunction composites with high photocatalytic activity by the in-situ growth method.In this study,urea and boric acid were used as precursor materials to grow hexagonal boron nitride in situ on the surface of titanium boride(TiB2)by the calcination method.Meanwhile,TiB2 was converted into TiO2 and TiBO3 during the calcination process,thus obtaining Ti3+-B co-doped TiO2/BN heterojunction catalyst with stable Ti3+in TiBO3.The effects of the addition of TiB2 on the photocatalytic activities of hydrogen production,nitrogen-fixing synthesis of ammonia and degradation of methyl orange(MO)were investigated.Furthermore,single-walled carbon nanotubes(SWCNT)were introduced to further improve the transmission of photocarriers in order to obtain higher catalytic activity.Finally,the photocatalytic mechanism of Ti3+-B co-dopcd TiO2/BN system was explored based on characterization results.Specific research results are present as follows:(1)A series of Ti3+-B co-doped TiO2/BN heterojunction photocatalysts with core-shell structure was prepared by mixing TiB2 with urea and boric acid,and calcination effects of TiB2 addition on morphology,elemental composition and optical properties were analyzed.The experimental results show that all Ti3+-B co-doped TiO2/BN samples have better photocatalytic activities for hydrogen production,ammonia synthesis and MO degradation than pure h-BN and TiB2.The yield of the best heterojunction sample was 31.78 mmol H2/(g catalyst)within 3 hours,and 91%of the yield was maintained after four cycles.The heterojunction samples showed excellent photocatalytic performance for nitrogen fixation and ammonia synthesis,reaching 0.794 mmol NH3/(h·g catalyst)within 2 hours.The removal rate of MO in the presence of the heterojunction photocatalyst reached 78%within 2 hours.The core-shell photocatalytic mechanism of Ti3+-B co-doped TiO2/BN was summarized based on material characterization,photoelectric properties and DFT calculation.(2)Secondly,SWCNT was introduced into Ti3+-B co-doped TiO2/BN composites to improve the interface transport capacity of photocarriers,and the photocatalytic activities of heterojunction catalysts in hydrogen production,nitrogen fixation for ammonia synthesis and MO degradation were studied in depth.In this section,1TBN samples were selected as the research object for modification,and the effects of SWCNT introduction on morphology,structure and photocatalytic activity were investigated thoroughly.The results show that SWCNT@Ti3+-B co-doped TiO2/BN exhibits a one-dimensional rod-like structure.TiO2,TiBO3 and h-BN in-situ grew on the surface of SWCNT,thus forming a heterojunction with very high electron transport capacity.The introduction of SWCNT further improved the photocatalytic activity of Ti3+-B co-doped TiO2/BN composites.For hydrogen production,the efficiency of 0.15STBN photocatalyst increased to 1.74 times within 3 hours and still reached 95%yield after four cycles.0.05STBN photocatalyst also showed remarkable improvement in nitrogen fixation,and the NH3 yield increased to 2.71 times within 2 hours;the MO degradation rate of 0.05STBN also reached 80.9%in 2 hours.Therefore,the appropriate introduction of SWCNT can significantly reduce the carrier transport resistance in the system,thus promoting the transmission of photogenerated carriers and the photocatalytic activity of the system.Finally,the photocatalytic mechanism of SWCNT@Ti3+-B co-doped TiO2/BN rod-like composite structure was proposed.In conclusion,the efficient Ti3+-B co-doped TiO2/BN heterojunction catalyst was successfully constructed by in-situ growth technology.It can provide a specific reference for the study of TiO2 and BN-based photocatalysts and provide a new idea for improving efficient carrier transport and separation in heterojunction catalysts.