Modification And Catalytic Performance Of Heterogeneous Bismuth Silicate System Materials

Bismuth silicate has stable properties and low cost,and its high photogenerated carrier mobility and narrow band gap broaden the visible light range.In recent years,bismuth silicate semiconductor has received wide attention in water pollution treatment,but its hydrophobicity and low specific surface area limit its application.Therefore,it is particularly important to reasonably modify bismuth silicate photocatalyst from its surface properties and microscopic morphology.Based on this,bismuth nitrate and sodium metasilicate were selected as bismuth and silicon sources,respectively,and Bi₂O₂SiO₃-Si₂Bi₂₄O₄₀（BSO）powders were prepared by solvothermal method as the research basis.Z-scheme/Type-II double heterojunction photocatalyst was prepared by introducing graphite phase carbon nitride（g-C₃N₄）with good photoelectric and thermal stability.The effect of surfactant on photocatalyst was explored by improving the interface binding between heterogeneous BSOs prepared by different methods.Finally,different forms of BSO were modified with the assistance of carbon nitride and surfactant,and composite photocatalysts for degradation of high concentration pollutants were prepared by the construction of solid solution.The phase and structure,microscopic morphology and photoelectric properties of the samples were tested and characterized.Through the experiments of pollutant degradation and capture under visible light,the relationship between the preparation of modified composite photocatalyst,morphology characteristics and photocatalytic properties was explored,so as to prepare bismuth silicate composite with excellent photocatalytic properties.The research results obtain in this paper were summarized as follows:（1）The photocatalyst with different morphologies were successfully prepared by combining the pyrolytic g-C₃N₄ powders with BSO obtained by solvothermal method.The influence of reaction conditions on photocatalyst was explored by controlling the reaction conditions.The results showed that the addition of g-C₃N₄ can affect the crystal nucleation,destroy the preferential growth of BSO,and control crystal morphology,thus improving the photocatalytic efficiency.When the addition amount of g-C₃N₄ was 0.25 g and the solvothermal reaction conditions were 180℃ and 10 h,further calcination at 400℃ resulted in a degradation rate of 99.7%for Rh B within 90 min of light.Compared with BSO,which can only degrade 59.6%Rh B within 90 min of light,the photocatalytic efficiency was increased by 40.1%.（2）By controlling the type and amounts of surfactants,BSO obtained by different preparation methods was surface modified,and the mechanism of the influence of surfactants on the photocatalytic performance of BSO photocatalyst was explored.The addition of surfactants effectively improved the surface hydrophobicity and interface binding of BSO,and enhanced the photocatalytic efficiency to a certain extent.Among them,for the BSO obtained by solvothermal method,when the addition amount of CTAB was 0.5 g,the obtained sample was calcined at 350℃,and the resulting powders can degrade 96.1%Rh B within 60 min of light.For the BSO obtained by the sol-gel method,when CTAC（Hexadecyl trimethyl ammonium chloride）and CTAB were used for composite modification,the modified powders showed better photocatalytic efficiency compared to the single modification.Within 20 min of light,99.0%Rh B（15 mg/L）can be degraded.（3）The porous carbon nitride（UCN）prepared with CTAB as a pore-forming agent was compounded with BSO in different ways to prepare BSO photocatalysts modified with surfactant assisted porous carbon nitride.By controlling factors,such as the type of UCN,the combination mode and the halogenation mode,carbon nitride is combined with surfactant to prepare photocatalyst with high quantum yield and strong interface binding.In addition,through the construction of solid solution,a composite product capable of degrading Rh B at a high concentration of 30 mg/L was further obtained.The results showed that when the solution was acidic,the micro morphology of the composite material changed from coral like to two-dimensional flake like,which indicated that CTAX can displace with BSO under acidic conditions.CTAX and BSO induced the formation of BiOX phase by sharing[Bi₂O₂]²⁺,and CTAX can also served as a structural directing agent to control the microstructure.From the aspects of morphology control,heterostructure construction and energy band regulation,it can promote the separation of photogenerated carriers and greatly enhance the photocatalytic performance.