Fe^(3+)与碳量子点共修饰TiO_(2)复合催化剂微结构调控及可见光下降解双酚A

Microstructure Regulation of TiO_(2) Doped with Fe^(3+)and Carbon Dots and Photocatalytic Degradation of BPA Under Visible Light Irradiation

针对TiO_(2)光谱响应范围较窄、光生载流子易复合的缺点,本研究采用溶胶–凝胶共混法成功制备了微结构可控的Fe^(3+)与碳量子点(CDs)共修饰TiO_(2)的复合催化剂Fe^(3+)/CDs–TiO_(2)。结果表明,Fe^(3+)与CDs共修饰不仅拓宽了TiO_(2)光谱响应范围,而且形成的界面化学键为光电子转移提供通道,抑制载流子的复合,提高光电子转移效率,当Fe^(3+)与CDs的负载量为0.5%(质量分数)和1.5%时,复合材料对双酚A的降解效果最佳,可见光下光照120 min,BPA降解率可达92.8%,Fe^(3+)/CDs–TiO_(2)循环使用7次后,去除率保持在86%以上。Fe^(3+)/CDs–TiO_(2)降解双酚A光催化反应符合一级反应动力学方程,反应速率常数为0.02216 min^(-1),自由基捕获实验证实空穴是降解BPA的主要物种,光催化降解产物毒性逐渐消减。

Introduction Environmental pollution caused by personal care products and synthetic substances become worse. Bisphenol A (BPA) asa type of endocrine disrupting chemical is detected in water, soil, air, urban waste and food. BPA is difficult to be removed from waterbody due to its strong biological toxicity and environmental persistence, so it is beneficial to designing the related efficient treatments.At present, main methods removing BPA include adsorption, nanofiltration, photochemical oxidation and electrochemical oxidation,in which photocatalytic oxidation technology has received much attention. TiO_(2) is extensively investigated due to its advantages.Although TiO_(2) has an excellent photocatalytic performance, it has significant drawbacks, such as low visible light utilization and easyrecombination of photo generated carriers. Loading is an effective method to improve photocatalytic capability. In this paper,Fe^(3+)/CDs–TiO_(2) composite photocatalyst was prepared by a sol–gel method.Methods For the preparation of Fe^(3+)/CDs–TiO_(2) catalyst, Ti(OBu)4, anhydrous ethanol and acetic acid were mixed under stirring toobtain a transparent solution. CDs and Fe(NO_(3))3·9H2O were added into the solution under stirring until forming a gel. The gel washeated in an oven at 70 ℃ to obtain yellow particles. The particles were ground into the finer particles and calcined in a mufflefurnace at 300 ℃ for 4.5 h, hence obtaining Fe^(3+)/CDs–TiO_(2). The photocatalytic performance of Fe^(3+)/CDs–TiO_(2) was analyzed withBPA as a target pollutant. Fe^(3+)/CDs–TiO_(2) was added into BPA aqueous solution, stirred in a dark environment for 20 min to achieveadsorption equilibrium. The photocatalytic reaction occurred after turning on an Xenon lamp. The concentrations of samples taken atregular intervals were determined by the HPLC method. The samples were analyzed by X-ray diffraction (XRD), scanning electronmicroscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet visible diffusereflection spectroscopy (UV-Vis DRS) and electrochemical method.Results and discussion Compared with TiO_(2), the absorption spectra of Fe^(3+)/CDs–TiO_(2) range to visible light zone and photoinducedelectrons transfer quickly through interface chemical bonds, indicating that the co-doping of Fe^(3+)/CDs boosts a photocatalyticefficiency. The degradation efficiency of BPA can be 92.8% after 120 min with Fe^(3+)/CDs–TiO_(2) at a loading ratio of Fe^(3+)/CDs of 0.5%or 1.5%. Fe^(3+)/CDs–TiO_(2) has a satisfied stable and reusable performance for 86% BPA, which is still degraded after 7 cycles. Thephotocatalytic degradation process of BPA with Fe^(3+)/CDs–TiO_(2) follows the first-order kinetic equation, and the reaction rate constantis 0.022 16 min^(-1). Based on the results of free radical capture experiments, the holes are the dominant species for BPA degradation,and the toxicity of the intermediates decreases, which is simulated by Toxicity Estimation Software Tool (T.E.S.T). The mechanism ofFe^(3+)/CDs–TiO_(2) photocatalytic degradation of BPA was analyzed based on main degradation substances and dominant intermediates.There is an electron coupling phenomenon between the orbital and the conduction band of TiO_(2), forming Ti—O—C bonds. Electronscan quickly transfer from the TiO_(2) conduction band through Ti—O—C bonds at the interface to the surface of the composite catalyst,and react with dissolved oxygen to generate ·O_(2)–. The holes on the valence band can directly react with organic molecules or formhydroxyl radicals, which almost decompose organic molecules. In addition, the photogenerated electrons on the conduction band alsoreduce the loaded Fe^(3+) in-situ to Fe2+, which reacts with dissolved oxygen to generate Fe^(3+)and ·O_(2)–. The Fe^(3+)→Fe2+→Fe^(3+)microcirculation effectively transfers photogenerated electrons.Conclusions The co-modification of Fe^(3+) and CDs widened the spectral response range of TiO_(2), and formed interface chemicalbonds that provided channels for photoelectron transfer, suppressing carrier recombination and improving photocatalytic efficiency.When the loading amounts of Fe^(3+) and CDs were 0.5% and 1.5%, respectively, the composite material had the optimum degradationperformance. In the presence of visible light, the degradation efficiency of BPA could reach 92.8% after 120 min. After 7 cycles,Fe^(3+)/CDs–TiO_(2) still performed well and degradation efficiency was 86%. Fe^(3+)/CDs–TiO_(2) photocatalytic reaction of BPA followed thefirst-order reaction kinetic equation, with a reaction rate constant of 0.022 16 min^(-1). According to the results of free radical captureexperiments, the holes were the main species for the degradation of BPA, and the toxicity of the photocatalytic degradation productsgradually decreased.