Frontiers of Environmental Science & Engineering ( IF 6.1 ) Pub Date : 2020-06-17 , DOI: 10.1007/s11783-020-1252-y Hanzhong Jia , Yafang Shi , Xiaofeng Nie , Song Zhao , Tiecheng Wang , Virender K. Sharma
The role of humic substance-associated persistent free radicals (PFRs) in the fate of organic contaminants under various redox conditions remains unknown. This study examined the characterization of original metal-free peat humin (HM), and HM treated with varying concentrations of H2O2 and L-ascorbic acid (VC) (assigned as H2O2-HM and VC-HM). The concentration of PFRs in HM increased with the addition of VC/H2O2 at concentrations less than 0.08 mol/L. The evolution of PFRs in HM under different environmental conditions (e.g., oxic/anoxic and humidity) was investigated. Two types of PFRs were detected in HM: a relatively stable radical existed in the original sample, and the other type, which was generated by redox treatments, was relatively unstable. The spin densities of VC/H2O2-HM readily returned to the original value under relatively high humidity and oxic conditions. During this process, the HM-associated “unstable” free radicals released an electron to O2, inducing the formation of reactive oxygen species (ROS, i.e., ⦁OH and ⦁O2−). The generated ROS promoted the degradation of polycyclic aromatic hydrocarbons based on the radical quenching measurements. The transformation rates followed the order naphthalene>phenanthrene>anthracene>benzo[a]pyrene. Our results provide valuable insight into the HM-induced transformation of organic contaminants under natural conditions.
中文翻译:
腐殖酸在氧化还原条件下的持久性自由基及其对多环芳烃转化的影响
在各种氧化还原条件下,腐殖质相关的持久性自由基(PFR)在有机污染物的归宿中的作用仍然未知。这项研究检查了原始的无金属泥炭腐殖质(HM)的特性,以及用不同浓度的H 2 O 2和L-抗坏血酸(VC)(分别称为H 2 O 2 -HM和VC-HM)处理的HM。随着VC / H 2 O 2的加入,HM中PFR的浓度增加。浓度小于0.08 mol / L。研究了在不同环境条件(例如,有氧/缺氧和湿度)下HM中PFR的演变。在HM中检测到两种类型的PFR:一种是在原始样品中存在相对稳定的自由基,另一种是通过氧化还原处理生成的,相对不稳定。VC / H 2 O 2 -HM的自旋密度在相对较高的湿度和高氧条件下很容易恢复到原始值。在此过程中,HM-相关的“不稳定”自由基释放电子至O 2,诱导反应性氧物质(ROS,形成即⦁ OH和⦁ ö 2 -)。基于自由基猝灭测量,所产生的ROS促进了多环芳烃的降解。转化率依次为萘>菲>蒽>苯并[a] py。我们的结果为在自然条件下HM诱导的有机污染物转化提供了宝贵的见识。