Horikoshi Satoshi, Saitou Aiko, Hidaka Hisao, Serpone Nick
Frontier Research Center for the Global Environment Protection, Meisei University, 2-1-1 Hodokubo, Hino, Tokyo 191-8506, Japan.
Environ Sci Technol. 2003 Dec 15;37(24):5813-22. doi: 10.1021/es030326i.
The photocatalyzed degradation (PD) of the cationic rhodamine-B (RhB) dye was examined in aqueous TiO2 dispersions using UV/Vis illumination assisted by microwave radiation (PD/MW). The initial degradation by the PD/MW method is compared to the PD method and to the thermally assisted PD method using conventional heating (PD/TH). Total organic carbon (TOC) assays show that the efficiency of complete mineralization of the dye follows PD/MW > PD/TH > PD > MW. In all cases, microwave radiation alone had no effect on the loss of TOC. The degradation involving microwave radiation was especially efficient when coupled to UV irradiation. By contrast, the extent of degradation of RhB involving suitable excited states through visible irradiation of the dye was rather inefficient when coupled to microwave radiation. Contact angle measurements on the TiO2 photocatalyst particles indicate that microwave radiation also causes an increase in the hydrophobic character of the TiO2 surface, with consequences on the adsorption mode of the dye substrate and thus on the overall mechanism of degradation. Deethylated RhB intermediates were identified by an electrospray ESI ionization mass spectral technique in the positive ion mode and subsequently confirmed by HPLC/absorption spectroscopy. Computer simulations led to estimates of frontier electron densities of all atoms of the RhB structure, affording inferences as to the position of radical attack on RhB. The nitrogen atoms of the dye were all converted to NH4+ ions. The major difference between the thermally assisted PD/TH method and the microwave-assisted PD/MW method showed that nonthermal effects from the microwave radiation impact significantly on the nature of the photocatalyst surface. These effects led to a more efficient photodegradation and mineralization of the dye substrate.
在微波辐射辅助的紫外/可见光照条件下（光催化降解/微波法，PD/MW），研究了阳离子罗丹明B（RhB）染料在TiO₂ 水性分散液中的光催化降解（PD）情况。将光催化降解/微波法的初始降解效果与光催化降解法以及使用传统加热的热辅助光催化降解法（光催化降解/热法，PD/TH）进行了比较。总有机碳（TOC）分析表明，染料完全矿化的效率遵循光催化降解/微波法＞光催化降解/热法＞光催化降解法＞微波法的顺序。在所有情况下，单独的微波辐射对TOC的损失没有影响。当与紫外辐射结合时，涉及微波辐射的降解特别有效。相比之下，通过染料的可见光照射涉及合适激发态的RhB降解程度在与微波辐射结合时效率相当低。对TiO₂ 光催化剂颗粒的接触角测量表明，微波辐射还会导致TiO₂ 表面疏水性增加，这会影响染料底物的吸附模式，进而影响整体降解机制。通过电喷雾电喷雾电离质谱技术在正离子模式下鉴定了脱乙基RhB中间体，随后通过高效液相色谱/吸收光谱法进行了确认。计算机模拟得出了RhB结构中所有原子的前沿电子密度估计值，从而推断出自由基对RhB攻击的位置。染料中的氮原子全部转化为NH₄⁺ 离子。热辅助光催化降解/热法与微波辅助光催化降解/微波法之间的主要差异表明，微波辐射的非热效应会对光催化剂表面的性质产生显著影响。这些效应导致染料底物的光降解和矿化效率更高。
