In situ photoluminescence of titania as a probe of photocatalytic reactions

Abstract

2, gives an activation energy of 7.4 ± 0.2 kcal/mol and a preexponential factor equal to 11•1*0•1 s"1. This low A factor is consistent with the highly organized transition state proposed by Bird et al.8The rate constant of reaction 2 with 1-hexene, kq, was obtained by analyzing, as a mixture of firstand second-order processes, the decay of the 250-nm transient in the presence of 1-hexene (HEX). A plot of the observed pseudo-first-order rate constant ki vs [HEX] is linear, and with ki = k, + &q[HEX], its slope yields fcq = 3 X 105 M"1 s"1. Also, this rate constant can be obtained

Photocatalytic degradation of cationic blue X-GRL adsorbed on TiO2/SiO2 photocatalyst

“…It is apparent that the photodegradation fits a pseudo-first-order kinetic model, and the rate increases as pH is increased. On the basis of our experimental observations and from these briefly reviewed mechanisms, the increase of CBX degradation with increasing pH can be interpreted by assuming that two different reaction pathways take place under conditions of different acidity [14,15]. We suggest that indirect hydroxyl radical attack and direct charge transfer are the predominant reaction mechanisms at low and high pH, respectively.…”

Photoluminescence properties of a hollandite compound K2Ga2Sn6O16

“…6, the PL intensity of the rutile TiO 2 powder in air increased by adding the ethanol vapor. This result is explained by the band bending model [8,9,17,18] as follows: adsorbed O 2 on the rutile TiO 2 powder is photo-desorbed by the illumination for the PL measurement. Instead, ethanol adsorbs dissociatively and inhibits O 2 from re-adsorbing on the powder.…”

Photoluminescence Spectroscopic Studies on TiO2 Photocatalyst

“…Here, the quenching of the photoluminescence is mainly due to the electron transfer from the excited states of the catalyst to the added O 2 or N 2 O molecules. Anpo et al (1989) also systematically studied the influence of the different adsorption molecules on the photoluminescence properties of TiO 2 powder. The TiO 2 powder exhibits a photoluminescence band at 450-550 nm when excited with the light of photon energy larger than the band gap of TiO 2 .…”

“…On the contrary, addition of various unsaturated hydrocarbons, such as 1-C 4 H 8 , C 3 H 6 , C 2 H 5 CCH, CH 3 CCH, C 2 H 4 , and CHCH, and small molecules such as H 2 O and H 2 , can considerably enhance the photoluminescence of TiO 2 powder. Furthermore, the extent of the photoluminescence enhancement strongly depends on the ionization potentials of the added (Anpo et al 1989) compounds: the lower the ionization potential of the added compound, the higher the photoluminescence intensity. Addition of inert gas, such as N 2 , has negligible influence on the photoluminescence.…”

“…It is well known that the photocatalytic activity of TiO 2 largely depends on its crystal structure (Tsai and Cheng 1997;Tanaka et al 1991;Nishimoto et al 1985;Ding et al 2000;Ohno et al 2001;Fujihara et al 1998) and surface properties (Anpo et al 1989;Yu et al 2000;Wu et al 2004), etc. The crystal structures (Tang et al 1994a;Poznyak et al 1992;Montoncello et al 2003;Nakajima et al 2005) and the surface properties (Anpo et al 1989;Nakajima et al 2002 of TiO 2 also have essential correlation with the luminescence features of TiO 2 . Therefore, photoluminescence spectroscopy study can depict the surface photoactive sites of TiO 2 (Anpo et al 1985a;Nakajima et al 2001Nakajima et al , 2002Jung et al 2005).…”