Preparation Of Bismuth Oxyhalide Based Floating Photocatalysts And Its Performance For Degrading Organic Pollutants

Water pollution problem caused by excessive use and mismanagement of organic dyes would pose significant risks to the ecosystem and the living beings.Photocatalytic technology is an emerging technology with low energy consumption,sustainability and minimized byproduct generation,has exhibited excellent application prospects in the degradation of organic dyes.Recently,bismuth oxyhalides（Bi OX,X=Cl,I,Br）semiconductors have attracted ever-increasing interest from researchers for the sake of its unique layered structure.However,the deficiencies existed in Bi OX greatly affect its photocatalytic efficiency.For example,poor visible-light absorption capacity caused by the wide band gap and low photocatalytic efficiency caused by the rapid recombination rate of photogenerated carriers.In addition,the traditional powdery Bi OX photocatalyst is hard to be applied in practical wastewater treatment due to the low light utilization efficiency and difficulties in recycling.In order to overcome the above-mentioned disadvantages,the floating bismuth oxyhalides-based composites was constructed by combining Bi OX with suitable carriers to improve its photocatalytic performance and practical application ability in this paper and the modified photocatalysts were characterized systematically.Besides,the organic dyes degradation experiments under simulated sunlight or visible-light irradiation were conducted to evaluate the photocatalytic performance.The specific research contents are as follows:1.In-situ synthesis of floating Bi OCl/EP photocatalyst and study on photocatalytic degradation towards Rhodamine B.The floating Bi OCl/EP photocatalyst was successfully synthesized through an in-situ deposition method to deposit the Bi OCl on the pores of expanded perlite（EP）,in which bismuth nitrate pentahydrate（Bi（NO₃）₃·5H₂O）and potassium chloride（KCl）were used as the sources.The properties of prepared samples were characterized by XRD,SEM,UV-vis DRS,FT-IR,XPS,BET and PL.The results showed that the Bi OCl was well dispersed on the surface of EP and exhibited well photocatalytic performance.95.8%of Rhodamine B(100 m L,15 mg L^-1)could be degraded by Bi OCl/EP composite within 125 min under simulated solarlight irradiation,which was higher than that of pure Bi OCl.This highly enhanced photocatalytic activity could be mainly attributed to the Bi-O-Si bonds in Bi OCl/EP composites,which could act as an electron transportation channel to promote the separation and migration of photogenerated electron-hole pairs;higher solar energy utilization efficiency and reactive oxygen species production brought by the floating characteristic.The photocatalytic efficiency still could reach up 91.0%even after five consecutive cycles and the Bi OCl/EP composite presented satisfactory reusability.Moreover,a possible photocatalytic mechanism of Rh B degradation of Bi OCl/EP composite was proposed by radical species trapping and semi-quantitative analyses experiments.2.Preparation of 3D porous floating Bi OCl/Bi₂S₃/graphene aerogel（Bi OCl/Bi₂S₃/GA）and study on photocatalytic degradation towards Rhodamine B（Rh B）and Methyl Orange（MO）.In this work,the Bi OCl/Bi₂S₃/GA was successfully synthesized through the water bath method,in which bismuth chloride（Bi Cl₃）,thioacetamide（TAA）and graphene oxide（GO）were used as the sources.And the prepared samples were characterized by XRD,SEM,TEM,UV-vis DRS,FT-IR,XPS,EDS,PL,Raman and EIS instruments.The degradation experiments indicated that the synthesized Bi OCl/Bi₂S₃/GA sample presented excellent photocatalytic degradation activity towards Rh B and MO under visible light irradiation,which could degrade 97.0%of Rh B within50 min and 74.2%of MO within 105 min.The excellent photocatalytic activity of the composite was mainly attributed to the construction of the heterojunction between Bi₂S₃ and Bi OCl,which enhanced the visible light absorption capacity and promoted the transfer efficiency of photogenerated electrons and holes.The three-dimensional structure of GA could greatly inhibit the accumulation of Bi OCl/Bi₂S₃ and enhance the exposure of active sites.After five consecutive cycle experiments,the photocatalytic efficiency of Bi OCl/Bi₂S₃/GA still could reach up to 89.9%,showing satisfactory stability and recycling ability.Finally,a possible photocatalytic degradation mechanism was proposed according to the energy band structure analysis.3.Preparation of 3D porous floating Bi₇O₉I₃/nitrogen doped graphene aerogel（Bi₇O₉I₃/NGA）composites and study on photocatalytic degradation towards Rhodamine B.In this work,a novel floating 3D porous Bi₇O₉I₃/NGA composite was successfully synthesized through a facile hydrothermal route,in which graphene oxide（GO）,potassium iodide（KI）and bismuth nitrate pentahydrate（Bi（NO₃）₃·5H₂O）were used as the sources.The prepared samples were characterized by XRD,SEM,TEM,UV-vis DRS,FT-IR,XPS,EDS,PL,Raman and EIS instruments.The Bi₇O₉I₃/NGA composite exhibited highly enhanced photocatalytic performance toward degrading Rhodamine B under visible-light irradiation,which reached up96.3%in 100 min and increased about 6.0 and 2.3 times compared with the Bi₇O₉I₃ and Bi₇O₉I₃/GA,respectively.The enhancement of photocatalytic degradation activity could be ascribed to the extensively promoted charge generation and migration efficiency,visible-light utilization ability and reactive oxygen species production.Besides,the special 3D macroscopic block structure of Bi₇O₉I₃/NGA allowed it to float,making it easy to recycle.The photocatalytic degradation efficiency of Bi₇O₉I₃/NGA composite still could reach up to 92.7%after four consecutive cycles and presented satisfactory stability and reusability.Moreover,a possible photocatalytic degradation mechanism was revealed by radical species trapping and semi-quantitative analyses experiments.