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Journal ArticleDOI

Redox and acidic properties of the borate radical B(OH)˙4. A flash photolysis study

01 Jan 1989-Journal of the Chemical Society, Faraday Transactions (The Royal Society of Chemistry)-Vol. 85, Iss: 8, pp 2249-2254
Abstract: Flash photolysis of an aqueous solution of sodium metaborate and potassium peroxydisulphate at pH 115 gives rise to a new transient species with an absorption maxima at 590 nm (Iµ= 80 m2 mol–1) and 650 nm (Iµ= 90 m2 mol–1) The laser-Raman and 11B nmr spectra of metaborate solutions at pH 115 are consistent with the presence of the tetrahydroxyborate ion, B(OH)–4 The pKa and reduction potential of the radical B(OH)˙4, produced on flashing a mixture of B(OH)–4 and S2O2–8 are found to be 1075 ± 002 and + 14 V, respectively The rate constants for the oxidation of several amines and phenols by this one-electron oxidant have been determined Salt-effect studies are consistent with the reactive species being B(OH)3O˙–
Topics: Sodium metaborate (57%), Flash photolysis (55%)
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Journal ArticleDOI
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.

42 citations


Journal ArticleDOI
Abstract: 30) L mol -1 cm -1 and 580 ) (56 ( 30) L mol -1 cm -1 . The ¥ NHCl radical undergoes self-decay and can react also with O2 to form a peroxyl radical. It is suggested that the peroxyl radical exists in equilibrium NHClO 2 ¥ / ¥ NHCl + O2 with an estimated equilibrium constant of (3 ( 2) 10 -3 mol L -1 . The reaction of chloramine with the carbonate radical is suggested to form a complex [CO3NH2Cl] ¥- with kf ) 2.5 10 5 L mol -1 s -1 and kr ) 4 10 2 s -1 , and this complex decomposes with k ) 7 10 2 s -1 to form ¥ NHCl.

34 citations


Journal ArticleDOI
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...

9 citations


Journal ArticleDOI
Jianjun Zhao1, Bangde Luo1, Xianqiang Xiong1, Xiao Zhang1, Yiming Xu1 
Abstract: Rutile TiO2 (RT) is usually used as photocatalyst for water oxidation, but seldom for organic oxidation, probably due to the slow reduction of O2. Herein we report a mutual effect of Ag nanoparticles and borate anions greatly increasing the photocatalytic activity of RT for phenol oxidation in neutral aqueous solution. RT was home-made, followed by calcination at 200―800 °C. With a given RT, the rates of phenol oxidation on the addition of Ag and borate were increased and decreased, respectively. In the presence of both Ag and borate, interestingly, the rate of phenol oxidation was larger than that in the presence of Ag. A (photo)electrochemical measurement revealed that Ag and borate, in contact with the irradiated RT, could catalyze O2 reduction and phenol oxidation, respectively. Since the electron and hole transfer processes would promote each other, the positive effect of Ag is further enhanced in the presence of borate. This work demonstrates that RT could be developed as a promising photocatalyst for organic oxidation through a surface co-catalyst.

7 citations


Journal ArticleDOI
Abstract: Rate constants for the reactions of the borate radical B(OH) 3 O⨪ with various para -substituted benzoic acids were measured by flash kinetic spectrophotometry. The product analyses and kinetic studies are consistent with an electron transfer mechanism followed by decarboxylation. In the case of the p -aminobenzoate anion the —NH 2 and —COO − groups react simultaneously with the borate radical providing two parallel pathways with different rate constants.

2 citations