X射线光电子能谱法研究UV_(254nm)光催化、O_3强化UV_(254nm)光催化和真空紫外光催化降解甲醛中Pt-TiO_2薄膜的表面性质(英文)

Characterization of Pt-TiO_2 film used in three formaldehyde photocatalytic degradation systems: UV_(254nm),O_3+UV_(254nm) and UV_(254+185nm) via X-ray photoelectron spectroscopy

以Pt-TiO2为光催化剂,研究了气相甲醛分别在35 h连续UV254 nm光催化、O3强化UV254 nm(O3+UV254 nm)光催化和真空紫外(UV254+185 nm)光催化中的降解效率,考察了副产物O3的去除率,采用X射线光电子能谱(XPS)法分析Pt-TiO2在不同光催化前后Pt的电子态和累积有机产物,研究纳米Pt对甲醛降解和O3去除的强化机理.连续光催化降解实验表明,以纳米Pt改性TiO2可以同时增强甲醛和O3的去除率,特别是O3的去除率可提高3.1–3.4倍.对催化剂C 1s和O 1s峰分别经分峰拟合处理后,发现Pt-TiO2上累积的含羰基和羟基的有机物含量按以下顺序减少:UV254 nm光催化>O3强化UV254 nm光催化>真空紫外光催化,而在连续35 h光催化降解过程中,催化剂的失活现象却按相反的方向变得越来越不明显.负载的金属Pt在O3+UV254 nm和UV254+185nm光催化过程中被氧化成PtOads和Pt4+物种,而在UV254 nm光催化过程中金属Pt未被氧化,所以推测是气相中的O3和羟基自由基参与金属Pt的氧化过程.Pt-TiO2表面高价态的Pt氧化物种可作为光生电子捕获中心,强化光生载流子的分离过程,增强Pt-TiO2的光催化活性.Pt氧化物种可作为O3分解的活化中心,使Pt-TiO2对O3的分解效率远高于纯TiO2.以XPS对比研究在三种不同光催化环境中Pt-TiO2表面性质,可以解释在UV254+185 nm光催化过程中纳米Pt对甲醛和O3同时去除的强化机理,并说明了催化剂不失活的内在原因.

Photocatalytic degradation of gaseous formaldehyde for 35 h was performed using Pt-TiO2 film in the following irradiation systems： UV254nm, O3＋UV254nm, and UV254＋185mm. Concurrent improvements in formaldehyde degradation and O3 removal were achieved by modifying TiO2 with Pt nanoparticles, resulting in a 3.1-3.4-fold O3 elimination increase. X-ray photoelectron spectroscopy （XPS） of the Pt-TiO2 film was carried out to assess the electronic states of the Pt nanoparticles and accumulated organic species. The deconvoluted C ls and 0 ls XPS spectra revealed that the content of carbonyl and carboxyl groups on Pt-TiO2 and degree of catalyst deactivation in the systems studied decreased in the following order： UVas4nm 〉 O34＂UV254nm UV254＋185 rim. Metallic Pt was oxidized to a mixture of PtOads and Pt4. species under 03＋UV254 nm and UV254.185 nm irradiation owing to the presence of 03 and hydroxyl radicals, but remained stable under UV254 nm irradiation. Pt species at higher oxidation states can act as electron trapping centers, and improve the photocatalytic activity of Pt-TiO2 and provide reactive sites for 03 decomposition under UV irradiation, resulting in a faster 03 removal rate than that displayed by TiO2. The XPS studies provided valuable information to eluci- date the beneficial role of Pt species and the reduction of catalyst deactivation under UV254.185irradiation.