化学学报 ›› 2019, Vol. 77 ›› Issue (4): 351-357.DOI: 10.6023/A19010009 上一篇    下一篇

研究论文

锐钛矿光催化降解苯酚:氟离子吸附的影响大于磷酸根

刘胜伟, 赵建军, 许宜铭   

  1. 浙江大学化学系 硅材料国家重点实验室 杭州 310027
  • 收稿日期:2019-01-04 出版日期:2019-04-15 发布日期:2019-03-05
  • 通讯作者: 许宜铭 E-mail:xuym@zju.edu.cn
  • 基金资助:

    项目受NSFC创新群体基金(No.21621005)资助.

Larger Adsorption Effect of Fluoride than Phosphate on Phenol Degradation over the Irradiated Anatase TiO2 and Pt/TiO2

Liu Shengwei, Zhao Jianjun, Xu Yiming   

  1. Department of Chemistry and State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027
  • Received:2019-01-04 Online:2019-04-15 Published:2019-03-05
  • Contact: 10.6023/A19010009 E-mail:xuym@zju.edu.cn
  • Supported by:

    Project supported by the Funds for Creative Research Group of NSFC (No. 21621005).

已知氟离子和磷酸根能加快锐钛矿和P25 TiO2光催化降解苯酚等有机物,但作用机理仍存在争议.合成了不含无机阴离子的锐钛矿,并在其表面沉积0.52 wt% Pt(Pt/TiO2).在初始pH 5.2的水溶液中,99%的氟离子和磷酸根分别为F-和H2PO4-.加入0.1~30 mmol/L阴离子,苯酚的光催化降解速率常数(kobs)都增大,证实了氟离子和磷酸根均具有正效应.有趣的是,kobs增加倍数均与阴离子吸附量呈线性关系,其中氟离子的斜率大于磷酸根,而Pt/TiO2的斜率大于TiO2.这表明阴离子的正效应源于吸附于固体表面的阴离子,并且氟离子的活性大于磷酸根.(光)电化学测试表明,氟离子和磷酸根分别抑制和促进O2还原,但它们都促进苯酚氧化.此外,氟离子和磷酸根分别使TiO2平带电位移动-159 mV和89 mV.前者有利于TiO2价带与苯酚发生轨道重叠,后者有利于TiO2导带分别与O2发生轨道重叠,进而加快界面电荷转移.由于阴离子广泛存在,该结果将有助于半导体光催化的机理研究及其环境应用.

关键词: 锐钛矿TiO2, 氟离子, 磷酸根, 吸附, 光电催化, 电荷转移

It is known that fluoride and phosphate in aqueous solution can accelerate the photocatalytic degradation of phenol over anatase or P25 TiO2. But the mechanism still remains under debate. In this work, an anion-free anatase TiO2 is prepared, followed by deposition with 0.52 wt% Pt (Pt/TiO2). Reaction was performed in aqueous solution at initial pH 5.2, where 99% of anions were in the form of F- or H2PO4-. On the addition of 0.1~30 mmol/L anions, the rate constants of phenol degradation (kobs) were all increased, confirming the positive effect of fluoride and phosphate, respectively. Interestingly, there was a linear relationship between the increase of kobs and the amounts of anion adsorption, the slope of which became larger in the order of fluoride>phosphate, and Pt/TiO2>TiO2. These observations indicate that the positive effect of anions originates from the adsorbed anions on solid, and that fluoride was more active than phosphate. A (photo)electrochemical measurement showed that fluoride and phosphate were negative and positive, respectively, to O2 reduction, but they were all beneficial to phenol oxidation. Furthermore, in the presence of fluoride and phosphate, the flat band potentials of TiO2 were shifted by -159 and 89 mV, respectively. The former favors orbital overlapping of phenol with TiO2 valence band, and the latter favors orbital overlapping of O2 with TiO2 conduction band, all of which promotes the interfacial charge transfers. Since inorganic anions are widely present, this result would benefit the mechanism study of a semiconductor photocatalyis and its application. As a reference, pure anatase was prepared from the hydrolysis of tetrabutyl titanate, followed by calcination in air at 400℃ for 2 h. The solid was then deposited with Pt, produced in situ from the photocatalytic reduction of H2PtCl6 in the presence of methanol. Solid was characterized with X-ray diffraction, N2 adsorption, Raman, and X-ray photoelectron spectroscopy. After Pt deposition, anatase phase remained unchanged, but the solid pores were blocked by a mixture of Pt and PtO2. Photoreactions were performed at room temperature under UV light at wavelengths equal to and longer than 320 nm. Organic compounds and inorganic anions were quantitatively analyzed with a high performance liquid and ionic chromatography, respectively. (Photo)electrochemical measurement was performed in a three-electrode compartment, where a Pt gauze was used as counter electrode, and a AgCl/Ag as reference electrode.

Key words: anatase TiO2, fluoride, phosphate, adsorption, photoelectrocatalysis, charge transfer