Fe（Ⅲ）对不同来源溶解性有机质的光化学活性的影响

Effect of Fe（Ⅲ）on the photochemical activity of dissolved organic matter from different sources

为研究水环境中普遍存在的Fe(Ⅲ)对溶解性有机质(DOM)的光化学活性的影响,分别以糠醇(FFA)、对氯苯甲酸(pCBA)和2,4,6-三甲基苯酚(TMP)作为1O2、·OH和3DOM*的分子探针,研究了不同光源和pH条件下,Fe(Ⅲ)对不同DOM产生1O2、·OH的稳态浓度和TMP降解的反应速率的影响。结果表明:汞灯照射下DOM产生活性物种的能力显著高于氙灯照射条件下,说明光强越大,DOM产生的活性物种越多;不同光源和pH条件下,不同DOM产生活性物种的能力是不同的,总体上表现为Suwannee河腐植酸(SRHA)和Suwannee河天然有机物(SRNOM)具有更高的1O2和·OH生成效能,而污水处理厂二级出水有机物(EfOM)具有更高的3DOM*生成效能。低浓度的Fe(Ⅲ)(10μmol·L^-1)对DOM产生活性物种的能力无显著影响,高浓度的Fe(Ⅲ)(25~50μmol·L^-1)则会抑制DOM产生活性物种的能力,且随Fe(Ⅲ)浓度的增加,抑制效应增强。DOM/Fe溶液的E2/E3值随Fe(Ⅲ)浓度的增加而逐渐减小,其与单一DOM/Fe体系产生的1O2、·OH的稳态浓度以及TMP的光降解反应速率常数具有正相关关系。在实际水体中,Fe(Ⅲ)的存在可能会抑制DOM的光化学活性,进而抑制水体中有机污染物的光化学转化,导致有机污染物的生态风险提高。

To study the effects of Fe(Ⅲ),which commonly occurs in aquatic environments, on the photochemical activity of dissolved organic matter(DOM), furfuryl alcohol(FFA), 4-chlorobenzoic acid(pCBA), and 2,4,6-trimethylphenol(TMP)were employed as molecular probes for 1O2, ·OH, and 3DOM*.This was done to study the effects of Fe(Ⅲ)on the steady state concentration of 1O2 and ·OH generated and the degradation reaction rate of TMP caused by the photosensitizer of DOM under different light sources and pH conditions. The results showed that the ability of DOM to produce reactive species under the irradiation of a mercury lamp was significantly higher than that under a xenon lamp, indicating that more reactive species were produced at a higher light intensity. Under different light sources and pH conditions, the ability of DOM to produce reactive species differed. Overall, Suwannee River humic acid(SRHA)and Suwannee River natural organic matter(SRNOM)had better 1O2 and ·OH generation capabilities, while effluent organic matter(EfOM)had higher3 DOM* generation capabilities. A low concentration of Fe(Ⅲ)(10 μmol·L^-1)had no significant impact on the photochemical reactivity of DOM, while a high concentration of Fe(Ⅲ)(25~50 μmol·L^-1)inhibited DOM from producing reactive species, and the inhibitory effect was enhanced with the increase of the Fe(Ⅲ)concentration. The E2/E3 value of the DOM solution decreased with the increase of the Fe(Ⅲ)concentration,which showed a positive correlation with the steady state concentration of 1O2 and ·OH and the photodegradation rate constant of TMP caused by a single DOM and Fe system. In real aquatic environments, the presence of Fe(Ⅲ)may inhibit the photochemical reactivity of DOM, inhibiting the photochemical transformation of organic pollutants, eventually causing a higher ecotoxicology risk.