Role of Platinum Deposited on TiO₂ in Phenol Photocatalytic Oxidation

Abstract

Photooxidation of phenol has been studied in aqueous suspensions of titanium dioxide Hombikat UV100 and Degussa P25 loaded with various amounts of Pt. The rates of phenol decomposition and total carbon removal rose by a maximum factor of 1.5 when Hombikat was loaded with 1 wt % Pt; further increase of Pt deposition did not increase the photoactivity any more. The electron movement across the Pt−anatase junction is discussed, and the positive influence of Pt on phenol oxidation over Hombikat is explained by the increase of charge separation in agglomerates of primary particles. The photocatalytic activity of P25 was higher than that of platinized and pure Hombikat. But loading P25 with Pt resulted in a decrease of phenol decomposition and total carbon removal rates. The decrease of Degussa P25 activity after platinization means that Pt cannot further increase the efficiency of charge separation in this TiO2, whose two-phase composition already provides a very efficient suppression of recombination in liquid photocatalytic reaction. The charge separation in P25 is illustrated with the scheme of P25's band structure. The possible side effects brought by Pt deposition are also discussed.

A review on plasmonic metal⿿TiO2 composite for generation, trapping, storing and dynamic vectorial transfer of photogenerated electrons across the Schottky junction in a photocatalytic system

“…In some instances, metal deposition can also decrease the activity of TiO 2 in photocatalytic reaction, because of the possible water reduction on Pt particles which otherwise cannot take place on the surface of pure TiO 2 . Water reduction to hydrogen will consume a part of photogenerated electrons which otherwise could take part in the oxygen reduction forming reactive oxygenated species [84]. With high metal loading concentration, electron transfer from TiO 2 particles to metal can also deform the potential field in TiO 2 particles and draw a portion of holes near the metal/TiO 2 junction, which increases the recombination rate.…”

“…When the two gradients are too small to increase the electron flux through the metal/TiO 2 contact, a new equilibrium is reached and hence it can be concluded that high level of metal deposition cannot enhance the charge separation and therefore the decomposition rate stops growing. The deformation of potential field in TiO 2 particles and drawing the hole near the Pt/TiO 2 junction also increases the recombination rate [84]. The deposited metal can act as shield for absorption of photons, enhance recombination at higher metal concentration and it can also activate trapped electrons.…”

Photocatalytic activity for H2 evolution of TiO2 with tuned surface crystalline phase

“…Many researchers [42][43][44][45][46][47] indicated that mixed phases of anatase and rutile exhibited higher photocatalytic activity than pure anatase and rutile phase, and attributed the enhancement of photoactivity to synergistic effect between anatase and rutile. Based on the results of EPR, Hurum et al [45] published explanation of high photocalytic activity of anatase-rutile mixtures represented by the Degussa P25 TiO 2 .…”

Hydrogen Generation through Solar Photocatalytic Processes: A Review of the Configuration and the Properties of Effective Metal-Based Semiconductor Nanomaterials

“…Compared to pristine anatase or rutile TiO 2 , P25-TiO 2 exhibits higher photoefficiency attributed to asynergistic effect of the mixed phases enhancing photogenerated electron/hole pairs' separation [49]. As regards the electron flux direction within the P25-TiO 2 structure (rutile-to-anatase or vice versa), conflicting hypotheses have been found in the literature review [50][51][52][53].…”