Abstract

Diclofenac (DCF) photocatalytic degradation with TiO₂-P25 illuminated with UV-A light in aqueous media was investigated. The photodegradation rate was assessed by HPLC and UV–vis spectroscopy, while the mineralization rate was obtained by total organic carbon measurements. The formation and degradation of intermediate compounds were investigated by UV–vis, IR and ¹H NMR spectroscopy and GC/MS analysis. UV–vis absorbance and HPLC results indicated that DCF is completely transformed into some aromatic compounds after several hours of irradiation. TOC analysis indicated that some intermediate compounds are degraded slowly since 90% mineralization was achieved after several hours of irradiation. FT-IR studies demonstrated a rapid conversion of diclofenac into a lactam, which was converted into several aromatic compounds. GC/MS and HPLC analysis indicated that the initial photoproducts are two lactams and several aromatic anilines and phenols. ¹H NMR studies indicated DCF degrades by a rather simple mechanism generating a recalcitrant intermediate acid, namely 2-hydrophenyl acetic acid which is oxidized in several steps by hydroxyl radicals. ¹H NMR studies also indicated that an oxidation route via a quinone is actually a very minor pathway. Based on this and previous investigations, a total photocatalytic degradation mechanism for DCF is presented, first involving hydroxyl radical reactions to generate anilines and phenols, which were all converted into polyhydroxylated compounds and eventually into low molecular saturated and unsaturated amines and carboxylic acids. Basic studies about diclofenac photocatalytic degradation are required for future applications of this process in the removal of DCF and other structurally related pharmaceutical compounds from any water body.

Graphic Abstract

中文翻译：

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TiO 2光催化降解双氯芬酸：中间体和总反应机理

摘要

研究了在水性介质中用UV-A光照射的TiO ₂ -P25对双氯芬酸（DCF）的光催化降解。通过HPLC和UV-vis光谱法评估光降解速率，而通过总有机碳测量获得矿化速率。通过UV-vis，IR和¹研究了中间化合物的形成和降解1 H NMR光谱和GC / MS分析。紫外可见吸收和HPLC结果表明，辐照数小时后DCF完全转化为某些芳香族化合物。TOC分析表明，某些中间化合物降解缓慢，因为在几个小时的照射后达到了90％的矿化度。FT-IR研究表明，双氯芬酸快速转化为内酰胺，内酰胺又被转化为几种芳香族化合物。GC / MS和HPLC分析表明，最初的光产物是两种内酰胺以及几种芳族苯胺和苯酚。¹ H NMR研究表明，DCF通过相当简单的机理降解，产生顽固的中间体酸，即2-氢苯基乙酸，该羟在多个步骤中被羟基自由基氧化。^1个1 H NMR研究还表明，经由醌的氧化途径实际上是非常小的途径。基于此和先前的研究，提出了DCF的总光催化降解机理，首先涉及羟基自由基反应以生成苯胺和苯酚，它们全部转化为多羟基化化合物，最后转化为低分子饱和和不饱和胺和羧酸。对于双氯芬酸光催化降解的基础研究，对于该方法在从任何水体中去除DCF和其他与结构相关的药物化合物的未来应用中都是必需的。

图形摘要