Heterogeneous Photocatalytic Decomposition of Phenol over TiO2 Powder

Abstract

The photocatalytic decomposition of phenol in oxygenated aqueous suspensions of lightly-reduced anatase TiO2, being the most satisfactory among the semiconductors investigated from the standpoint of the photocatalytic activity and stability, has been investigated at the optimum pH 3.5. The products at the initial stage of the reaction were hydroquinone, pyrocatechol, 1,2,4-benzenetriol, pyrogallol, and 2-hydroxy-1,4-benzoquinone. These intermediates underwent further photocatalytic oxidation via acids and/or aldehydes finally into CO2 and H2O. A reaction scheme involving hydroxyl radicals as real reactive species has been proposed. Although H2O2 was formed via O2\ewdot produced by electron trapping of adsorbed oxygen, its concentration remained constant at a low value during the reaction. About 0.7 mole of O2 was consumed for the consumption of one mole of phenol at the initial stage of the reaction. These results indicated that hydroxyl radicals were formed not only via holes but also via H2O2 from O2\ewdot. It was interesting from the viewpoint of wastewater treatment that phenol was completely mineralized to CO2 in the presence of TiO2 powder under solar irradiation without both aeration and mixing of the solution.

The enhancement of TiO2 photocatalytic activity by hydrogen thermal treatment

“…Since the optimum temperatures to produce OV and Ti 3þ were not exactly same, we herein state that the optimal temperature for the H 2 reduction treatment would fall between 500 and 600°C. This conclusion may support the work done by Okamoto et al (1985), in which they pretreated TiO 2 catalyst by H 2 at 550°C.…”

“…Based on the results reported in the above literature, it seems that oxygen vacancies (OV) and trivalent titanium (Ti 3þ ) may be present in the modified TiO 2 . In the field of photocatalysis, Okamoto et al (1985) adopted H 2 reduction as a simple pretreatment of TiO 2 in photocatalytic degradation of phenol. However, the wide use of the H 2 -treated TiO 2 has not been available.…”

A New Method To Determine the Generation of Hydroxyl Radicals in Illuminated TiO2Suspensions

“…From degradation experiments with organic pollutants it is known that the mineralization efficiency with TiO 2 is dependent on the concentration of dissolved oxygen in the suspension. 32 Oxygen acts as an electron acceptor, scavenging electrons from the conducting band (eq 4) and thus reducing the recombination rate (eq 7). The result in Figure 6 shows that an increasing amount of dissolved oxygen increases the rate constant of the • OH radical formation.…”

“…The result is in good agreement with results derived by the DMPO method 19 and by the mineralization of phenol in aqueous TiO 2 suspensions. 32 Effect of Added Sodium Salts. We have also examined the effect of dissolved sodium salts on the decrease of the spin trap signal and thus on the generation of proxyl-NH.…”

Magnetic recyclable microcomposite silica-steel core with TiO2 nanocomposite shell photocatalysts for sustainable water purification

“…89,95 Scheme 2: Important reaction pathways during TiO 2 photocatalyst degradation of organic molecules (R). 96,97,98,99 In the case of the present organic dye degradation study using silica-steel microcomposite core with TiO 2 shell photocatalyst, any direct interaction between steel particle surface iron oxides and the TiO 2 shell could potentially diminish photocatalytic activity in at least two ways. Firstly, by electron-hole recombination processes through transfer of photogenerated electrons and holes from the 49 Such dissolved Fe 2+ species are then able to react with hydroxyl radicals leading to a quenching of photocatalytic activity.…”