Abstract
The influence of electron and hole scavengers in the photocatalytic digestion of organic matter in the presence of suspended particles of TiO2 was investigated. The process, aiming at the electrochemical determination of traces of heavy metals in water samples, was followed through the recovery of the voltammetric wave of Cd(II) in the presence of EDTA, chosen as model ligand that mimics the complexing effect of natural dissolved organic matter. The accelerating power of O2, acting as electron scavenger, was confirmed. In the absence of O2, a similar function is played by nitrate ions but not, as it seems, by the analyte, Cd(II). On the other hand, CH3OH exhibits an antagonist effect as hole scavenger. This observation may explain why the acetate (from the pH buffer), used to control the medium acidity, leads to a certain reduction in the photocatalytic yield.
Highlights
The outcome is in agreement with some earlier literature data showing that the photocatalytic degradation of methyl orange in deareated conditions is faster in the presence of Ag and Cu nitrates, than with the sulphate salts of the same metals
Other researchers have detected some photocatalytic formation of ammonium ions upon irradiating a Hg(NO3)[2] solution at pH 8, likely to be ascribed to the nitrate photochemical reduction.[8]
A similar function is exercised by nitrate ions but, interestingly enough, this is completely overshadowed by the presence of O, which makes believe that the electron scavenging role is entirely satisfied by oxygen, at least under the investigated experimental conditions
Summary
Intense investigation has been undertaken on the TiO2-assisted photochemical mineralisation of organic substances by UV radiation, either with the semiconductor catalyst in suspension or immobilized on a solid support.[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26] The method was originally contemplated as a possibility to employ solar radiation as an energy source in water decontamination processes in connection with the treatment of industrial effluents and with water potabilisation.[5,11,18,21] At a certain stage, studies and trials have markedly shifted towards the use of artificial UV source, mainly mercury vapour lamps, because of the scarce efficacy obtained with the solar radiation, theThis decomposition method has set foot in the area of analytical chemistry. Intense investigation has been undertaken on the TiO2-assisted photochemical mineralisation of organic substances by UV radiation, either with the semiconductor catalyst in suspension or immobilized on a solid support.[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26] The method was originally contemplated as a possibility to employ solar radiation as an energy source in water decontamination processes in connection with the treatment of industrial effluents and with water potabilisation.[5,11,18,21] At a certain stage, studies and trials have markedly shifted towards the use of artificial UV source, mainly mercury vapour lamps, because of the scarce efficacy obtained with the solar radiation, the. In an attempt to upgrade the conventional UV photolysis in TOC determination devices.[24]
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