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化石燃料的迅速消耗导致环境污染与能源危机日益加剧.太阳能高效利用与转换是解决该难题的有效途径之一.在众多光催化剂中,TiO_2因其高催化活性、高稳定性、低毒性以及低成本等优势而普遍受到关注,但TiO_2存在着带隙过宽而无法利用可见光的缺陷,严重制约了其在光催化方向的实际应用.核壳型复合纳米材料具有较大的比表面积、较高的光吸收能力以及所吸附的污染物分子易于从吸附面扩散到光致降解面等特点,而表现出较强的有机污染物吸附性能以及良好的光催化活性.以磁体材料为核将TiO_2包覆于磁体表面,可以制备具有磁分离特性的磁载光催化剂.而铁酸铋作为一种在室温下同时具有铁电性和铁磁性的钙钛矿型材料,由于其较窄的带宽(2.1 e V)在可见光催化氧化方面也受到了极大的关注.本文首先通过柠檬酸自燃烧法制备了可磁性分离的BiFeO_3粉体,再以水解沉淀法将TiO_2包裹在BiFeO_3前驱体上形成了不同质量比(1:1,1:2,2:1)的核壳结构的BiFeO_3@TiO_2复合粉体,并以甲基紫为例,对其在紫外光和可见光照射下的光催化性能分别展开了研究.结果表明,BiFeO_3@TiO_2复合粉体的光催化性能较单独的BiFeO_3或TiO_2均有所提升.其中质量比为1:1的BiFeO_3@TiO_2复合粉体(TiO_2壳层厚度为50–100 nm)展现出最强的光催化氧化活性,且在可见光下有更高的光催化效率.经表征分析,该复合粉体光催化性能高的原因可能归结于BiFeO_3与TiO_2两者之间形成了p-n异质结界面,有效地提高了电荷载流子的传输分离效率,同时BiFeO_3较窄的禁带宽度拓展了纳米TiO_2的光谱吸收范围,增强其光吸收能力.光电化学Mott-Schottky测试结果进一步证实:BiFeO_3粉体在与TiO_2复合之后,其电荷载流子传输与供体密度均有显著提升.自由基猝灭实验表明,在甲基紫光催化降解中起主要作用的为羟基自由基与光生电子,并结合能带理论与自建电场理论对降解机理进行了阐述.进一步研究表明,甲基紫降解效果最优条件为:复合粉体的投加量为1 g/L,甲基紫初始浓度为10 mg/L,初始pH为5.另外,质量比1:1的BiFeO_3@TiO_2对甲基橙和刚果红染料废水也具有较好的降解效果,表现出良好的工业应用前景.
The rapid consumption of fossil fuels has led to the increasing environmental pollution and energy crisis.Efficient utilization of solar energy and conversion is one of the effective ways to solve this problem.For many photocatalysts, TiO 2 has many potential applications due to its high catalytic activity, high stability, low toxicity and low Cost and other advantages, but widespread attention has been paid to TiO 2, however, there is a defect that the band gap is too wide and the visible light can not be utilized, which seriously restricts the practical application of TiO 2 in the photocatalysis direction.Nuclear-shell composite nanomaterials have large specific surface area Of the light absorption capacity and adsorption of pollutants from the adsorption surface easy to diffuse to photodegradable surface and other characteristics, and showed strong adsorption of organic pollutants and good photocatalytic activity of the magnet material as the core of the TiO 2 package On the surface of the magnet, a magnetic photocatalyst with magnetic separation properties can be prepared, while bismuth ferrite, as a perovskite material with both ferroelectric and ferromagnetic properties at room temperature, due to its narrow bandwidth (2.1 eV) has also received great attention in the visible light catalytic oxidation.In this paper, a magnetically separable BiFeO_3 powder was prepared by citric acid self-combustion method Hydrolytic precipitation method was used to form BiFeO_3 @ TiO_2 composite powders with different mass ratios (1: 1, 1: 2, 2: 1) of core-shell structure by wrapping TiO_2 on BiFeO_3 precursors. The results show that the photocatalytic activity of BiFeO_3 @ TiO_2 composite powders is higher than that of BiFeO_3 or TiO_2 alone, and the BiFeO_3 @ 1: 1 mass ratio BiFeO_3 @ TiO_2 composite powders (the thickness of TiO_2 shell was 50-100 nm) exhibited the strongest photocatalytic oxidation activity and higher photocatalytic efficiency under visible light.The photocatalytic activity of the composite powder was high May be attributed to the formation of a pn heterojunction interface between BiFeO_3 and TiO_2, which effectively improves the charge carrier transport separation efficiency. Meanwhile, the narrower band gap of BiFeO_3 expands the spectral absorption range of nano-TiO_2, Enhances its light absorption ability.The result of Mott-Schottky test further confirms that the charge carrier transport and donor density of BiFeO_3 powders are significantly improved after composites with TiO_2.The results of free radical quenching show that in the presence of methyl Violet photocatalytic degradation plays a major role The role of hydroxyl radical and photogenerated electron, combined with the energy band theory and self-built electric field theory of degradation mechanism were further studied showed that the optimum conditions for the degradation of methyl violet: compound powder dosage of 1 g / L, the initial concentration of methyl violet was 10 mg / L and the initial pH was 5. In addition, BiFeO 3 @ TiO 2 with mass ratio of 1: 1 also had good degradation effect on methyl orange and Congo red dye wastewater, Good industrial application prospects.