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V2O5和BiF3/BiOCl的可控合成及净化染料废水性能研究

Controllable Synthesis of V2O5 and BiF3/BiOCl Used for Removal Dyes in Wastewater

【作者】 杨洋

【导师】 滕飞;

【作者基本信息】 南京信息工程大学 , 环境工程, 2017, 硕士

【摘要】 本论文主要围绕两个方面进行,一是V205对亚甲基蓝染料废水吸附性能研究;二是BiF3/BiOCI异质结光催化降解染料废水性能研究。(1)采用简单的水热法制备出了直角L型结构的V205吸附剂。在合成过程中,研究了反应温度、时间、硝酸浓度的影响,提出了一种可行性的生长及机理。除此之外,我们还研究了 F离子对材料形貌、结构以及吸附性能的影响。利用扫描电子显微镜(SEM)、高分辨率的透射电子显微镜(HRTEM)、选区电子衍射(SAED)、X-射线衍射(XRD)、傅里叶红外变换光谱(FT-IR)、紫外可见漫反射光谱(UV-DRS)、荧光光谱(PL)以及N2比表面积分析仪等分析测试手段对产物形貌和结构进行了表征。结果表明,F离子可以抑制直角结构的形成,暴露高能面以及增加氧缺陷。这与我们DFT的理论计算结果几乎一致。模拟结果表明,线性相关系数达到0.99,因此我们推断V205对亚甲基蓝(MB)的吸附符合准二级动力学模型。(2)时至今日,对电荷的转移行为的研究依然是一大挑战。本论文中通过简单的后处理方式构建了新型BiF3/BiOCl异质结。表面光电压(SPV)结果显示,对于BiOCl,只有负的SPV信号,说明只有光生电子迁移并聚集在表面;对于38% BiF3/BiOCl异质结既有正信号也有负的SPV信号,说明电子和空穴在不同波长范围下电荷的转移行为有所变化;对于BiF3,几乎没有SPV信号,表明很少有电子或者空穴到达表面。在紫外光的照射下,BiF3/BiOCl异质结对2-硝基苯酚的降解速率分别是BiOCl和BiF3的5.3和5.8倍。我们认为在表面电场、内建电场和界面电场的共同作用下,BiF3/BiOCl异质结的电子空穴分离传输效率都大大提高,因此其光催化活性也有很大的提高。我们相信,我们的工作将更加有利于人们去理解电荷在异质结表面的传输分离行为,从而开发出更加高效的光催化剂。

【Abstract】 This thesis mainly contains two important parts. One is controlable synthesis of L-shaped V2O5 and application in methylene blue (MB) adsorbtion; the second part is to fabricate heterojunction and investigate its photocatalytic activities for degrading methyl orange (MO).(1) In the first part, V2O5 with an interesting "L"-shape was successfully prepared by a simple hydrothermal method without using any surfactant or template.The formation mechanism of "L"-shaped V2O5 has been proposed. We have also investigated the effect of fluoride on the morphology, crystal structure and adsorption ability of the samples. The samples were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy(HRTEM) with select area electron diffraction (SAED), X-ray diffraction (XRD),Fourier transform infrared spectrum (FT-IR), UV-vis diffuse reflectance spectra(UV-DRS), Photoluminescence (PL) spectra and N2 sorption isotherms. It is found that the addition of fluoride can refrain the formation of "L"-shaped V2O5, resulting in the high-energy {010} facets exposed and the increased oxygen vacancy. The density functional theory (DFT) calculations and PL spectra further confirm the results above. As a result, F-doped V2O5 shown a significantly improved adsorption capacity for methylene blue (MB) than undoped one. The adsorption kinetics well follows a pseudo-second-order model, with the higher correlation coefficients (R)than 0.99.(2) To date, it is still a big challenge to investigate the charge transfer behavior from bulk to surface for the solar energy conversion and utilization. Herein, the BiF3/BiOCl heterojunction has been prepared through a mild post-synthesis method.Surface photovoltage spectra (SPV) results show that only negative SPV signal can be observed for BiOCl, suggesting that the photogenerated electrons mainly move to the surfaces and accumulate on the surface; both negative and positive signals can be observed for 38% BiF3/BiOCl, indicating that photogenerated electrons and holes can both move to the surfaces and accumulate on the surface; but nearly no SPV signal can be observed for BiF3, demonstrating that nearly no electrons or holes can accumulate on the surface. Furthermore, under ultraviolet light irradiation (X < 420 nm), the degradation rate was 5.3 and 5.8 times higher than that of BiOCl and BiF3 for the degradation of 2-nitrophenol, respectively. We hold that the charges transfer and separation efficiency of BiF3/BiOCl have been significantly improved by the synergetic effect of the surface electric field, bulk internal electric field and interface electric field. This work could help us to intensively understand the charge transfer behavior of a heterojunction photocatalyst.

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