Photoassisted Oxidation of the Recalcitrant Cyanuric Acid Substrate in Aqueous ZnO Suspensions

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• 作者：Elisa Garcí ; a-Ló ; pez ; Giuseppe Marcí ; Nick Serpone ; Hisao Hidaka
• 刊名：Journal of Physical Chemistry C
• 出版年：2007
• 出版时间：December 13, 2007
• 年：2007
• 卷：111
• 期：49
• 页码：18025 - 18032
• 全文大小：116K
• 年卷期：v.111,no.49(December 13, 2007)
• ISSN：1932-7455

文摘

The photoassisted oxidative transformation of the highly recalcitrant cyanuric acid was examined in the liquid-solid regime at pH 3 and natural pH 7.5 under UV irradiation in oxygen- and ozone-saturated ZnO suspensionsusing ZnO as a photomediator. Loss of cyanuric acid was assayed by HPLC UV absorption spectroscopy,whereas intermediates and final products were determined by HPLC ion chromatography (IC), by MStechniques using an electrospray ionization mass spectrometer operated in the negative-ion mode, and byFT-IR spectroscopy. Final reaction products were CO₂ gas and NO₃^- ions. The measure of nitrate in solutionquantified the degree of mineralization of the substrate; its concentration in solution was lower than indicatedby the loss of cyanuric acid owing to adsorption of the latter to the ZnO surface. Some degree of corrosionof ZnO occurred as evidenced by the quantity of Zn²⁺ present in acidic and near-neutral aqueous mediabefore and during the photoassisted process. The possible site(s) and mode(s) of adsorption of cyanuric acidon ZnO have been inferred from theoretical calculations of point charges; the position(s) of attack of thesubstrate by OH radicals was inferred from frontier electron density calculations. Mechanistic considerationsare based on the possible involvement of Zn²⁺-cyanurate species (chemisorbed cyanuric acid) in the degradationof such a recalcitrant substrate, inasmuch as the use of TiO₂-photoassisted processes under similar conditionshave so far failed to oxidize cyanuric acid.