黑磷纳米片光催化甲基橙降解机理

偶氮废水大量排放到环境中会对生态系统和人类健康造成严重威胁,发展偶氮染料废水的高效处理技术具有实际意义。光催化法由于工艺简单、处理彻底等优点具有应用前景。本研究利用液相剥离法制备黑磷纳米片(LBP),以甲基橙(MO)为例,考察LBP对偶氮染料的光催化能力;利用淬灭及荧光探针试验判断体系中参与反应的主要瞬态物种;结合液相色谱-质谱的产物鉴定结果,阐明光催化降解机理。结果表明: MO在酸性(pH=3.0)和碱性(pH=11.0)条件下的降解速率(k_obs)高于中性条件下(pH=7.0)。LBP光照下产生羟基自由基(·OH)进攻偶氮键使双键断裂生成中间产物,后者被·OH继续氧化,生成主要降解产物N,N-二甲基-4-(2-对苯甲基肼)苯胺、2-二甲胺基-5-((4-(二甲胺基)苯基)二氮基)苯酚和N,N-二甲基-4-硝基苯胺。

Mechanism underlying photocatalyzed degradation of methyl orange by layered black phosphorus

A large amount of azo dye wastewater is discharged into the environment, with serious risks to ecosystems and human health. Therefore, the development of treatment technology of azo dye wastewater was of practical significance. Photocatalytic methods showed promising application prospects due to easy to implement and effective. In this study, layered black phosphorus nanosheet (LBP) was used as a catalyst through liquid phase exfoliation method. Methyl orange (MO) was employed as a model azo dye to investigate the catalytic mechanism of LBP. The dominant transient species involved in the photocatalytic reaction was probed by quenching and fluorescence probe experiments. Degradation pathways of MO were proposed according to degradation products identified by the liquid chromatography-mass spectrometry. The results showed that degradation rate (k_obs) of MO at acidic condition (pH=3.0) or alkaline condition (pH=11.0) was higher than that at neutral condition (pH=7.0). Degradation pathways of MO included that the azo bond was attacked by hydroxyl radicals (·OH) photogenerated by the LBP, and the intermediate products were further oxidized by ·OH to produce N, N-dimethyl-4-(2-p-phenylmethylhydrazine) aniline, 2-(dimethylamino)-5-((4(dimethylamino) phenyl) diazenyl) phenol and N, N-dimethyl-4-nitroaniline.