Borate-Mediated Hole Transfer from Irradiated Anatase TiO2 to Phenol in Aqueous Solution
03 Sep 2015-Journal of Physical Chemistry C (American Chemical Society)-Vol. 119, Iss: 37, pp 21376-21385
TL;DR: In this paper, the authors reported that the addition of sodium borate to an aqueous suspension of anatase TiO2 at neutral pH can result in a significant enhancement in the rate of phenol degradation.
Abstract: The development of a highly active TiO2 photocatalyst for energy and environmental use is a great challenge. In this work, we report that the addition of sodium borate to an aqueous suspension of anatase TiO2 at neutral pH can result in a significant enhancement in the rate of phenol degradation. Similar results were also observed from 2,4-dichlorophenol degradation, spin-trapped OH radical formation, H2O2 decomposition, and chromate reduction in the presence of phenol. This borate-induced rate increase for phenol degradation was determined not only by the amount of borate adsorption but also by the structure of borate species (pH effect). A (photo)electrochemical measurement with the TiO2 film revealed that upon addition of borate, the hole consumption by phenol and the electron consumption by O2 were accelerated and decelerated, respectively. Moreover, the flat band potential of TiO2 was negatively shifted by 81 mV. Since the hole oxidation of water to O2 remained unchanged, it is proposed that a borate...
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23 Mar 2018
TL;DR: This work demonstrates the improved stability of zinc oxide nanorods (ZnO NRs) for the photoanode of solar water splitting under voltage biases by the addition of borate or carbonate ions in the aqueous electrolyte with suitable pH ranges and proposes a possible mechanism for the protective behavior of ZnO in borate and carbonate solutions.
Abstract: This work demonstrates the improved stability of zinc oxide nanorods (ZnO NRs) for the photoanode of solar water splitting under voltage biases by the addition of borate or carbonate ions in the aqueous electrolyte with suitable pH ranges. The ZnO NRs prepared by the hydrothermal method are highly active and stable at pH 10.5 in both borate and carbonate buffer solutions, where a photocurrent higher than 99% of the initial value has been preserved after 1 h polarization at 1.5 V (vs reversible hydrogen electrode) under AM 1.5G. The optimal pH ranges with a minimum morphological change of ZnO NRs for photoelectrochemical (PEC) water splitting in borate and carbonate buffer solutions are 9-13 and 10-12, respectively. The working pH range for PEC water splitting on ZnO NR photoanodes can be extended to 8.5-12.5 by the combination of borate and carbonate anions. The lifetime of ZnO NR photoanodes can be synergistically prolonged for over an order of magnitude when the electrolyte is the binary electrolyte consisting of borate and carbonate in comparison with these two anions used individually. On the basis of the experimental results, a possible mechanism for the protective behavior of ZnO in borate and carbonate solutions is proposed. These findings can be used to improve the lifetime of other high-performance ZnO-based catalysts and to understand the photocorrosive and protective behaviors of ZnO NRs in the borate and carbonate solutions.
56 citations
TL;DR: In this article, the ratio of 1T to 2H and the relative concentration of sulfur vacancies could be adjusted by changing the Mo-precursor (Na2MoO4 and (NH4)2MoS4) and hydrothermal temperature.
42 citations
TL;DR: UV irradiation of Au/TiO2 photocatalysts in the presence of borate and phosphate anions can produce H2O2 at a millimolar level in alkaline water solution thanks to the anion-mediated hole transfer from Au/ TiO2 to an electron donor which accelerates the two-electron reduction of O2 to H2 O2.
Abstract: UV irradiation of Au/TiO2 photocatalysts in the presence of borate and phosphate anions can produce H2O2 at a millimolar level in alkaline water solution. The positive effect of the anions is ascribed to the anion-mediated hole transfer from Au/TiO2 to an electron donor which thus accelerates the two-electron reduction of O2 to H2O2.
23 citations
TL;DR: In this paper, a synergism between Pt and borate greatly improved the photocatalytic activity of anatase TiO2, and a maximum rate of phenol degradation was observed at 0.52 wt % Pt, 3.0 mM Na2B4O7 and initial pH 9.0.
Abstract: It has been reported that Pt and borate can promote the TiO2-photocatalyzed degradation of phenol in an aerated aqueous suspension, respectively. Herein, we report a synergism between Pt and borate greatly improving the photocatalytic activity of anatase TiO2. The rate of phenol degradation was dependent on Pt loading, borate concentration, and solution pH. A maximum rate of phenol degradation was observed at 0.52 wt % Pt, 3.0 mM Na2B4O7, and initial pH 9.0, respectively. Under such conditions, the rates of phenol degradation, upon the addition of Pt, borate, and Pt plus borate, were increased by 1.34, 0.22, and 4.87 times, respectively. This mutual action of Pt and borate were also observed from the photocatalytic degradation of 4-chlorphenol, and 2,4-dichlrophenol. A separate experiment with the TiO2 and Pt/TiO2 film electrodes showed that borate could mediate the hole oxidation of phenol, but not water. Furthermore, the electrochemical reduction of O2 over TiO2 and Pt/TiO2, upon addition of borate, bec...
22 citations
TL;DR: In this paper, a positive effect of Na2CO3 on the degradation of phenol, 2,4-dichlorophenol, and H2O2 in an aerated aqueous suspension at initial pH 80 was reported.
Abstract: Carbonate anions are often present in aqueous solution, but their effect on the semiconductor-photocatalyzed reaction has been rarely studied In this work, we report a positive effect of Na2CO3 on the TiO2-photocatalyzed degradation of phenol, 2,4-dichlorophenol, and H2O2 in an aerated aqueous suspension at initial pH 80 The rate of phenol degradation, upon the addition of 20 mM Na2CO3, 052 wt% Pt, and 20 mM Na2CO3 plus 052 wt % Pt, was increased by 178, 338, and 663 times, respectively Such positive effect of carbonate was also observed from a TiO2 and Pt/TiO2 film electrode for the photoelectrochemical oxidation of phenol, but not water However, the rates of phenol degradation over TiO2 and Pt/TiO2 became decreased as carbonate concentration exceeded 50 and 20 mM, respectively It is proposed that CO3•– radicals are formed mainly from the hole oxidation of dicarbonate adsorbed on TiO2, followed by phenol degradation At a high concentration, the CO3•– radicals would recombine to a peroxoca
17 citations
References
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