Trapped State Sensitive Kinetics in LaTiO₂N Solid Photocatalyst with and without Cocatalyst Loading

Abstract

In addition to the process of photogeneration of electrons and holes in photocatalyst materials, the competitive process of trapping of these charge carriers by existing defects, which can both enhance the photocatalytic activity by promoting electron-hole separation or can deteriorate the activity by serving as recombination centers, is also very crucial to the overall performance of the photocatalyst. In this work, using femtosecond diffuse reflectance spectroscopy we have provided evidence for the existence of energetically distributed trapped states in visible-light responsive solid photocatalyst powder material LaTiO2N (LTON). We observe trapped state sensitive kinetics in bare-LTON. CoOx cocatalyst loading (2 wt % CoOx-LTON) shows effect on the kinetics only when presence of excess energy (for above bandgap excitation) results in the generation of surface carriers. Thus, the kinetics show appreciable excitation wavelength dependence, and the experimental results obtained for different λexc have been rationalized on this basis. In an earlier work by Domen and co-workers, the optimized CoOx/LTON has been reported to exhibit a high quantum efficiency of 27.1 ± 2.6% at 440 nm, the highest reported for this class of photocatalysts (J. Am. Chem. Soc. 2012, 134, 8348-8351). In the present work, the mechanism is addressed in terms of picosecond charge carrier dynamics.

Photoanodic and photocathodic behaviour of La5Ti2CuS5O7 electrodes in the water splitting reaction

“…In fact, it was recently suggested that the charge migration distance in LTC was on the order of microns in the case of LTC/Au photocathodes, because PEC deposition of noble metal nanoparticles occurred only onto the tip of rod-like LTC particles a few micrometres in length. 9 In order to further investigate the nature of photogenerated charge carriers in LTC powder, we employed transient absorption spectroscopy (TAS), which has been successfully used in monitoring carrier dynamics in many semiconductor photocatalysts 21,22 (see ESI† for experimental details). Since the powder was opaque, we collected and analyzed the diffuse reflected light from the sample, instead of transmitted light, to obtain information on the kinetics of transient species; femtosecond time resolved diffuse reflectance (fs-TRDR) spectroscopy was employed.…”

Reduced graphene oxide supported titanium dioxide nanomaterials for the photocatalysis with long cycling life

“…In the effort to develop photocatalysts based on TiO 2 , a large number of recent researches have been devoted to investigation of integrated composite TiO 2 catalysts [12][13][14][15][16][17][18][19][20][21]. For example, transition metal doping TiO 2 is effective to improve the Page 6 of 27 A c c e p t e d M a n u s c r i p t photocatalytic activity by decreasing the charge carrier recombination rates [12,13]; and other various non-metal-doped TiO 2 have been widely studied for the visible light photocatalytic activities [11,15,[21][22][23].…”

Dendritic Tip-on Polytriazine-Based Carbon Nitride Photocatalyst with High Hydrogen Evolution Activity

“…In contrast to classical bulk heterojunction, the full surface of CN should not be covered by the cocatalyst because the hole (which remains inside the CN after the dissociation) must react with the hole scavenger at the interface between CN and the electrolyte. The presence of this silica might help scavenge the surface holes 75 and thereby, surface electrons can have time to go to the Pt active site, precluding the loss due to electron-hole recombination, which is prevalent in bare CN. Thus, the competitive process of trapping the charge carrier, particularly the hole, by the existing defects in the silica in a way hinders the recombination loss and enhances the photocatalytic activity by promoting electron-hole separation.…”