硝酸纤维素膜光降解水中对硝基苯酚的机制

为研究硝酸纤维素膜(NCM)作为新型污染物降解材料在水处理领域的应用潜力,本文以对硝基苯酚为目标污染物,NCM为活性氧物种来源,考察了溶液p H、光照条件、水体成分等因素对光解的影响及其作用机制.结果表明,NCM光致·OH量子产率为1. 30×10~(-4),是传统光催化材料TiO_2的1. 86倍.纯水中对硝基苯酚的直接光解速率仅为9. 52×10-4min-1,而在NCM存在情况下光解速率达到0. 005 5 min-1.这种促进作用主要是由NCM表面光致·OH引起的,其中UVA对光解起重要作用.水体酸性条件有利于NCM光解对硝基苯酚,在p H=2. 0时,降解率达到90%以上,相应的光解速率为0. 016 5min-1.对硝基苯酚的光解速率随光照强度、膜面积的增大而提高.水体成分对光解影响呈显著差异,NO-3可通过光致·OH的生成促进光解;而可溶性有机质主要通过滤光作用抑制对硝基苯酚的光解.气相色谱-质谱分析中间产物主要有苯酚、对苯二酚、丙二酸和草酸等,由此给出了可能的光解途径.

Photolysis Mechanism of p-Nitrophenol by Nitrocellulose Membrane in Aqueous Solution

To investigate the potential application of nitrocellulose membrane (NCM) in water treatment, this study examined the photolysis of p-nitrophenol, with NCM as the source of reactive oxygen species. Effects of solution pH, light conditions, and water dissolved substances on p-nitrophenol photolysis were investigated, and possible mechanisms were discussed. The results demonstrated that the quantum yield for hydroxyl radicals from the NCM was 1.30×10^-4, which is approximately 1.86 times higher than that from TiO₂. The photolysis rate of p-nitrophenol in the presence of NCM was 0.0055 min^-1, which is much higher than that in pure water (9.52×10^-4 min^-1). This promotion was mainly caused by photo-induced generation of ·OH on NCM surface under light, in which UVA plays an important role in photolysis. The photolysis rate of p-nitrophenol increased with the increase of light intensity and membrane area. Acidic solution (pH=2.0) was preferred for the degradation of p-nitrophenol, with a photolysis rate of 0.0165 min^-1; the corresponding degradation of p-nitrophenol exceeded 90% in 120 min. The effects of dissolved substances on photolysis were significantly different. NO₃^- promoted photolysis by generation of ·OH, and dissolved organic matter decreased photolysis through light attenuation. The intermediate products of gas chromatography-mass spectrometry analysis mainly included phenol, hydroquinone, malonic acid, and oxalic acid, and the possible photolysis pathway was given accordingly.