| Fe(III) is widely present in natural waters, and it can form Fe(Ⅲ)/H2O2system with H2O2 that generated from some sunlight-absorbing components. So far only few studies involved the effect of Fe(III)/H2O2system on organic contaminants. Humic acids (HA), the major components of dissolved organic matter (DOM), and also one of the most important natural sunlight-absorbing matters,too, it can associate withFe(III) to form complicated complexes that have a significant effect on organic pollutants photodegradation in environments. So, study on pollutants degradation in Fe(III) system effect by HA have important environmental implications. However, HA not only a single source in natural water, making a systematic research on the photochemistry properties of HA in different origins and their complexes with Fe (III) will help we understand the transfer and transformation of organic pollutants in natural water. Therefore, the influence of the presence or absence of two different sources HAs ondegradation of Reactive Brilliant BlueKN-R undersimulated irradiation in Fe(III)/H2O2system was studied first in this work, and then the effects of 4 different HAs, and their complexes with Fe(Ⅲ) on the photodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D) were investigated. Moreover, The mechanisms of 2,4-D photodegradation under simulated solar irradiation in 4 different HAs, and their complexes with Fe(Ⅲ) solutions were also studied too.The main results are as following:(1) Under simulated irradiation(λ>400nm), KN-R degradation in the Fe(III)/H2O2 system was mainly due to hydroxyl radical(-OH)generated; pH value have a significant effect on H2O2/Fe(III) system, KN-R removal efficiencies decreased from 60.6%to 43.9%as the pH rising from 3 to 5; However, KN-R removal efficiencies increased from70.4% to 78.9%as the pH riseswhen the two different sources HA was present in H2O2/Fe(Ⅲ) system. On one hand, the results demonstrated that both HA act as a accelerator in the H2O2/Fe(Ⅲ system; On the other hand, HA presence in waterextended pollutants photodegradationto a wide range of pH, thus affecting the conversion of pollutants in the environment.(2) By adding hydroxyl radical quencher KI and KN-R degradation in different systems in kinetic experiments show:The mechanisms of RB degradation in H2O2/Fe(III)/HA system included 4 pathway:the ·OH radicals produced from H2O2/Fe(III) system contributed to RB degradation, the·OH radicals produced from H2O2/Fe(III)/HA system, adsorption by Fe(III)-HA complexes and other reactive species produced from H2O2/Fe(Ⅲ)/HA system. The ·OH radicals leaded to RB degradation was the major pathway, accounted for 72.2%about total RB degradation.(3) Under the simulated sunlight irradiation(λ>400nm),2,4-D photo-degradation followed the pseudo-first-order reaction kinetics in4 different HAs and their complexes with Fe(III) solutions. The pseudo-first-order rate constantsof 2,4-D photo-degradation in4 different HA solutions were kd=0.0189 h-1(humic acidderived fromGermany forest)、 kh=0.0110 h-1 (humic acidderived fromHulun Buir grassland、kc=0.0162h-1(humic acidderived fromChiFengforest) and k1=0.0206-1(humic acidderived fromDaLian river sediment), respectively; The pseudo-first-order rate constants of 2,4-D photo-degradation in4 different HA complexes with Fe(III) solutions were kd=0.0330 h-1, kh’=0.0182 h-1、kc’=0.0307 h-1 and k-1=0.0368 h-1, respectively.(4) Under the simulated sunlight irradiation(λ>400nm), the mechanism of 4 different sources HA and their complexes with Fe(III) were similar.photosensitizing to produce hydroxyl radical is the main pathway leading to the degradation of 2,4-D; However, there were differences in the photochemistry properties of 4 different sources HA and their complexes with Fe(III),the differences in the photochemistry properties mainly as follows:humic acid derived from river sediment> humic acid derived from forest soil> humic acid derived from grassland soil. |
PDF Full Text Request