Alvaro Mercedes, Atienzar Pedro, Corma Avelino, Ferrer Belén, Garcia Hermenegildo, Navarro Maria T
Instituto de Tecnología Química CSIC-UPV and Departamento de Química, Universidad Politécnica de Valencia, Avenida de los Naranjos s/n, 46022 Valencia, Spain.
J Phys Chem B. 2005 Mar 3;109(8):3696-700. doi: 10.1021/jp0471047.
Laser flash photolysis of germanium-containing ITQ-17 zeolite (Ge/ITQ-17, a single polymorph of beta zeolite) at 266 nm generates a transient spectrum decaying in the sub-millisecond time scale that is compatible with the formation of two transient species. The shorter lived transient (tau approximately 45 micros under nitrogen) has been assigned to trapped electrons due to the characteristic spectroscopic absorption (single band at 480 nm) and its quenching by typical electron scavengers such as N(2)O and CH(2)Cl(2). The second longer lived transient (lambda(max) = 500, 540, and 600 nm; tau approximately 390 micros) is not quenched by O(2) or electron scavengers, but it is quenched by methanol as hole scavenger and has been assigned to positive holes. Also there is a remarkable similarity of the transient spectrum of the Ge/ITQ-17 with the optical spectrum reported previously for electron-hole pairs in ZSM-5 zeolite. Under the same irradiation conditions, photoejection of electrons and photogeneration of positive holes has not been observed for conventional aluminosilicate zeolites, all-silica zeolites, or GeO(2)-impregnated zeolites. Therefore this photochemical behavior has been ascribed to the presence of framework germanium atoms opening the way for photoresponsive zeolites. The ability of Ge/ITQ-17 to generate photochemically electrons and holes has been confirmed by adsorbing naphthalene and propyl viologen sulfonate as electron donor and acceptor, respectively, and observing the generation of the corresponding radical ions.
在266纳米波长下对含锗的ITQ - 17沸石（Ge/ITQ - 17，β沸石的单一多晶型物）进行激光闪光光解，会产生一个在亚毫秒时间尺度上衰减的瞬态光谱，这与两种瞬态物种的形成相符。寿命较短的瞬态（在氮气下τ约为45微秒）由于其特征光谱吸收（480纳米处的单峰）以及被典型的电子清除剂如N₂O和CH₂Cl₂猝灭，已被归因于捕获电子。第二个寿命较长的瞬态（λmax = 500、540和600纳米；τ约为390微秒）不会被O₂或电子清除剂猝灭，但会被作为空穴清除剂的甲醇猝灭，已被归因于正空穴。此外，Ge/ITQ - 17的瞬态光谱与先前报道的ZSM - 5沸石中电子 - 空穴对的光谱有显著相似性。在相同的辐照条件下，对于传统的铝硅酸盐沸石、全硅沸石或GeO₂浸渍的沸石，未观察到电子的光发射和正空穴的光生。因此，这种光化学行为归因于骨架锗原子的存在，为光响应沸石开辟了道路。通过分别吸附萘和丙基紫精磺酸盐作为电子供体和受体，并观察相应自由基离子的生成，证实了Ge/ITQ - 17产生光化学电子和空穴的能力。
