The Influences Of The Loading Of Natural Organic Matters On The Degradation Of Catechol On The Silica-hematite Surface

Natural Organic Matter (NOM) is one of the most important chemical components in the surface environment media, and is widely distributed. The influences of NOMs on the environment behavior of pollutants have attracted much attention from the researchers, but the influence-mechanism is not fully understood. Catechol (CT) is the production material widely used in various industrial fields. The soil pollution by CT is an ongoing problem. This research used tannic acid (TA) and fumaric acid (FA) as the two kinds of model chemical of NOMs, used the silica-hematite (SI-HMT) particle as the model soil particle. The influences of the loading of NOMs on the degradation of CT on the surfaces of the model soil particles were studied, which is significant to understand the environment behavior of organic pollutants in real soil, and will help to reveal the mechanism of the influences of NOMs on the environment behavior of pollutants. By comparing the degradation kinetics and the signal characteristics of the free radicals of CT in the system of TA and that in the systems of FA, the following patterns were discovered:I. The influences of TA and FA on the photo-degradation of CT on SI-HMT surface are different, which is related to their different chemical structure. TA can inhibit the degradation of CT on SI-HMT surface. Because under ultraviolet (UV) light the phenol hydroxy groups of TA can form semiquinone-type radicals that generate phenolic coupling with the semiquinone radicals formed from CT. The structure of phenolic coupling can protect CT from further oxidation. FA can promote the degradation of CT on SI-HMT surface. Because under UV light the carboxyl groups of FA can generate reactive oxygen species (ROS) like superoxide radicals by own or the help of Fe(Ⅲ). These ROS greatly accelerate the degradation rate of CT.Ⅱ. The influences of TA and FA on the signal characteristics of the free radicals in the degradation process of CT on SI-HMT surfaces are different, as well as the reasons:1) The aspect of signal intensity: ①TA can form semiquinone-type radicals under UV light. So the signal intensity of the free radicals on TA-SI is higher than that on SI. The complex formed by TA and Fe(Ⅲ) may reduce Fe(Ⅲ) partly under UV light. The phenolic coupling formed between TA and CT under UV light decreases the quantity of CT which can form Environmentally Persistent Free Radicals (EPFRs). Because of the above two reasons, the quantity of EPFRs is decreased, which leads to that the signal intensity of the free radicals on TA-HMT is lower than that on HMT. ②FA can generate ROS by own or the help of Fe(Ⅲ). These strong oxidizing free radicals can accelerate the degradation of semiquinone radicals and EPFRs. So the signal intensity of the free radicals on FA-SI/FA-HMT is lower than that on SI/HMT. 2) The aspect of g value: ①The g value of the free radicals on TA-SI is 2.0056—2.0059 and that on TA-HMT is 2.0044—2.0052. The g value of the free radicals on TA-SI/TA-HMT is higher than that on SI/HMT, which may be contributed by the higher g value of the semiquinone-type radicals formed by TA. ②The g value of the free radicals on FA-SI is 2.0046—2.0052 and that on FA-HMT is 2.0046—2.0049. The g value of the free radicals on FA-SI is lower than that on SI, which may be explained by FA generating the carbon-center free radicals of low g value under UV light.3) The aspect of peak-to-peak line width (PLW): ①The PLW of the free radicals on TA-SI is 5.5—7.9 G and that on TA-HMT has a big fluctuation range which is 8.5—19.0 G. The PLW of the free radicals on TA-HMT is bigger than that on HMT for the reason that the different semiquinone radicals formed by TA decrease the overall homogeneity of free radicals. ②The PLW of the free radicals on FA-SI is 8—11 G and that on FA-HMT is 9-11G. The PLW of the free radicals on FA-SI/FA-HMT is bigger than that on SI/HMT, which may be explained by the following reason:FA can generate the carbon-center free radicals and various kinds of strong oxidizing free radicals, which increase the complexity of the environment and chemical structure on the surfaces of particles.As the two kinds of model chemicals of NOMs, TA and FA have different influences on the degradation of CT and the signal characteristics of the free radicals on SI-HMT surface. This reflects that NOMs as a group of organic matters have complicated structure and various functional groups having different property, and the influences of NOMs on the photo-degradation of the organic contaminates and the formation of free radicals in soil may be complicated and need to be analyzed comprehensively and studied further.