title: The roles of polycarboxylates in Cr(VI)/sulfite reaction system: Involvement of reactive oxygen species and intramolecular electron transfer.
abstract: In this study, the effects of polycarboxylates on both Cr(VI) reduction and S(IV) consumption in Cr(VI)/S(IV) system was investigated in acidic solution. Under aerobic condition, the productions of reactive oxygen species (ROS), i.e., SO4(-) and OH, have been confirmed in S(IV) reducing Cr(VI) process by using electron spin resonance and fluorescence spectrum techniques, leading to the excess consumption of S(IV). However, when polycarboxylates (oxalic, citric, malic and tartaric acid) were present in Cr(VI)/S(IV) system, the affinity of polycarboxylates to CrSO6(2-) can greatly promote the reduction of Cr(VI) via expanding the coordination of Cr(VI) species from tetrahedron to hexahedron. Besides, as alternatives to S(IV), these polycarboxylates can also act as electron donors for Cr(VI) reduction via intramolecular electron transfer reaction, which is dependent on the energies of the highest occupied molecular orbital of these polycarboxylates. Notably, the variant electron donating capacity of these polycarboxylates resulted in different yield of ROS and therefore the oxidation efficiencies of other pollutants, e.g., rhodamine B and As(III). Generally, this study does not only shed light on the mechanism of S(IV) reducing Cr(VI) process mediated by polycarboxylates, but also provides an escalated, cost-effective and green strategy for the remediation of Cr(VI) using sulfite as a reductant.
authors.affiliation: State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, Shandong, PR China; School of Environmental and Municipal Engineering, Qingdao University of Technology, Qingdao 266033, PR China. Electronic address: bjiang86upc@163.com.
authors.forename: Bo
authors.initials: B
authors.lastname: Jiang
authors.affiliation: State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, Shandong, PR China.
authors.forename: Xianli
authors.initials: X
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, Shandong, PR China.
authors.forename: Yukun
authors.initials: Y
authors.lastname: Liu
authors.affiliation: College of Environmental Science and Engineering, Donghua University, Shanghai 201620, PR China; Southern Cross GeoScience, Southern Cross University, Lismore, NSW 2480, Australia.
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, Shandong, PR China. Electronic address: jtzheng03@163.com.
authors.forename: Jingtang
authors.initials: J
authors.lastname: Zheng
authors.affiliation: State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, Shandong, PR China. Electronic address: wumb@upc.edu.cn.
authors.forename: Mingbo
authors.initials: M
authors.lastname: Wu
keywords: Cr(VI); Polycarboxylates; Reactive oxygen species; Reduction; Sulfite