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The kinetics of the removal of stearic acid (SA) islands by photocatalytic coatings is controversial, with some reporting that the islands fade as their thickness, h, decreases with the irradiation time, t, but maintain a constant area, a, −da/dt = 0, and others reporting that −dh/dt = 0 and −da/dt = −constant, i.e., the islands shrink, rather than fade. This study attempts to understand the possible cause for these two very different observations through a study of the destruction of a cylindrical SA island and an array of such islands, on two different photocatalytic films, namely, Activ self-cleaning glass, and a P25 TiO2 coating on glass, which have established uniform and heterogeneous surface activities, respectively. In both cases, using optical microscopy and profilometry, it is shown that, irrespective of whether there is as a single cylindrical island or an array of islands, h decreases uniformly with t, −dh/dt = constant, and −da/dt = 0, so that the SA islands just fade. However, in a study of the photocatalyzed removal of SA islands with a volcano-shaped profile, rather than that of a cylinder, it is found that the islands shrink and fade. A simple 2D kinetic model is used to rationalize the results reported in this work. Possible reasons for the two very different kinetic behaviors are discussed. The relevance of this work to self-cleaning photocatalytic films is discussed briefly.

Dataset for "Probing P25 TiO2 Photocatalysis using Photoinduced Absorption Spectroscopy (PIAS)" Abstract: Photoinduced absorption spectroscopy, PIAS, is used for the first time to probe the kinetics exhibited by the most commonly employed powder photocatalyst, P25 TiO2, in mesoporous film form, in the photocatalysed oxidation of a commonly used test organic pollutant, 4-chlorophenol, 4CP. The results show that PIAS can provide previously unobtainable, invaluable, direct kinetic, and mechanistic, information concerning photogenerated holes in powdered photocatalysts. Dataset contains 4 figures from research paper. These files are xlsx format. Details of the figures are included below: : Fig. 1 LSV’s (5 mV s-1) recorded for a P25 TiO2 photoanode in the absence (black line) and presence (red line) of 0.1 M 4CP (in O2-free, 1 M HClO4), with (solid line) and without (broken line) UV irradiation (365 nm, 40 mW cm-2). Fig. 2 Plots of the measured (a) photocurrent, J, and (b) change in absorbance at 500 nm, ΔAbs, as a function of time, exhibited by a P25 TiO2 photoanode poised at -0.19 V vs. Ag/AgCl and in 0.1 M 4CP (in O2-free, 1 M HClO4), before, during and after steady state irradiation, produced using different 365 nm UV irradiances. In both plots the UV irradiances used were (from bottom to top): 113, 56, 36, 33, 21 and 6 mW cm-2, respectively. In (b), lines of best fit to the light-off decays all give excellent fits to first order kinetics with a 1st order rate constant, k1 = 0.3 s-1. Fig. 3 (a) Plots of the steady state photocurrents, Jss and the changes in absorbance, ΔAbsss, due to the photocatalysed oxidation of 4CP by a P25 TiO2 photoanode polarised at -0.19 V vs. Ag/AgCl (in O2-free, 1 M HClO4), as a function of UV irradiance, ρ. In both profiles the solid lines of best fit have been calculated assuming Jss and ΔAbsss are proportional to ρθ, where θ = 0.60; and (b) plot of Jss vs. ΔAbsss, revealing a good straight line with zero intercept. Fig. 4 Plots of the measured change in absorbance at 500 nm, ΔAbs, as a function of time, exhibited by a P25 TiO2 photoanode in 0.1 M 4CP, O2-saturated, 1 M HClO4, solution, before during and after steady state irradiation, using different 365 nm UV irradiances. The UV irradiances used were (from bottom to top): 76, 36, 17, 9 and 2 mW cm-2, respectively. The lines of best fit to the light-off decays all give excellent fits to first order kinetics with a 1st order rate constant, k1 = 0.29 s-1.

Dataset for "Water oxidation by P25 TiO2 photoanodes in acidic solution"

BACKGROUND With an increase in global bioenergy production, the ‘biorefinery concept’ has now become a significant focus of research. The desire to achieve efficient conversion of biomass material into both energy and value‐added products requires a combination of technologies and processes. As such, the photocatalytic reforming of feedstocks such as glycerol to hydrogen (H2) has a lot of potential. RESULTS Reported here is the first example of a thin film‐based photocatalytic system capable of achieving H2 evolution using a glycerol feedstock. Using a titania (TiO2) sol–gel, glass columns were coated with a thin TiO2 layer before using photodeposition to add platinum (Pt) as a co‐catalyst. The coated columns were assembled into a simple yet effective recirculating system which used low power UV irradiation. Under optimum conditions (two coated columns and a 40 mL min−1 flow rate), a steady state of 0.9 μmol min−1 H2 with a photonic efficiency [ηphoton (%)] of 10.22 % was achieved. Furthermore, only one column showed flaking and loss of coating whereas the remaining columns were stable for the duration of the study, which equated to > 100 h of experimental testing including replicates and determining optimal parameters. CONCLUSION H2 evolution via photocatalytic glycerol reforming in a Pt‐TiO2 thin film catalyst recirculating system has been demonstrated under UV irradiation and ambient conditions. The system developed highlights that it is both catalyst development and reactor engineering that are required to continue to advance the field of photocatalysis.

The widespread utilisation of solar driven water is hindered by the use of expensive and unstable materials. Herein, we show that highly active earth abundant metal oxide oxygen and hydrogen evolution electrocatalysts can be synthesised using the Adams method, in which the metal salts are oxidised in a melt of sodium nitrate and that such oxides are usually highly crystalline powders with high specific surface areas. Disc electrodes of the Adams method metal oxides: RuO2, Mn2O3, Co3O4 and NiO are prepared using a recently reported mechanical, solvent-free method, involving pressing a mixture of the metal oxide and a small amount (5 wt%) of PTFE powder. Each electrode is tested as an electrode for the hydrogen evolution reaction, HER, and oxygen evolution reaction, OER, in 1 M NaOH. In the former role, Mn2O3 appears better than a platinum wire electrode (overpotential at 10 mA cm-2, 10, = 61 mV, cf. 70 mV, for Pt). In the OER study, although RuO2 is the best electrocatalyst, 10, = 267 mV, Co3O4 is also very effective, 10, = 330 mV. Using Mn2O3 as the cathode and Co3O4 as the anode, a silicon solar cell is used to photocleave water into H2 and O2. The wide spread utilisation of solar driven water is hindered by the use of expensive and unstable materials. Herein, we show that highly active earth abundant metal oxide oxygen and hydrogen evolution electrocatalysts can be synthesised using the Adams method, in which the metal salts are oxidised in a melt of sodium nitrate and that such oxides are usually highly crystalline powders with high specific surface areas. Disc electrodes of the Adams method metal oxides: RuO2, Mn2O3, Co3O4 and NiO are prepared using a recently reported mechanical, solvent-free method, involving pressing a mixture of the metal oxide and a small amount (5 wt%) of PTFE powder. Each electrode is tested as an electrode for the hydrogen evolution reaction, HER, and oxygen evolution reaction, OER, in 1 M NaOH. In the former role, Mn2O3 appears better than a platinum wire electrode (overpotential at 10 mA cm-2, 10, = 61 mV, cf. 70 mV, for Pt). In the OER study, although RuO2 is the best electrocatalyst, 10, = 267 mV, Co3O4 is also very effective, 10, = 330 mV. Using Mn2O3 as the cathode and Co3O4 as the anode, a silicon solar cell is used to photocleave water into H2 and O2.