Sulfide-induced reduction of nitrobenzene mediated by different size fractions of rice straw-derived black carbon: A key role played by reactive polysulfide species

Chenhui Wei; Shujun Yin; Heyun Fu; Xiaolei Qu; William A Mitch; Dongqiang Zhu

doi:10.1016/j.scitotenv.2020.141365

Sulfide-induced reduction of nitrobenzene mediated by different size fractions of rice straw-derived black carbon: A key role played by reactive polysulfide species

Sci Total Environ. 2020 Dec 15:748:141365. doi: 10.1016/j.scitotenv.2020.141365. Epub 2020 Jul 29.

Authors

Chenhui Wei¹, Shujun Yin¹, Heyun Fu², Xiaolei Qu², William A Mitch³, Dongqiang Zhu⁴

Affiliations

¹ School of Urban and Environmental Sciences, Key Laboratory of the Ministry of Education for Earth Surface Processes, Peking University, Beijing 100871, China.
² School of the Environment, State Key Laboratory of Pollution Control and Resource Reuse, Nanjing University, Jiangsu 210046, China.
³ Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305, United States.
⁴ School of Urban and Environmental Sciences, Key Laboratory of the Ministry of Education for Earth Surface Processes, Peking University, Beijing 100871, China. Electronic address: zhud@pku.edu.cn.

PMID: 32810807
DOI: 10.1016/j.scitotenv.2020.141365

Abstract

Here we investigated the mediation efficiency of different size fractions of rice straw-derived black carbon (BC) using sulfide-induced nitrobenzene reduction as a model system. The bulk BC was divided into three size fractions: dissolved BC (size <0.45 μm), colloidal BC (0.45 μm < size < 1 μm), and particulate BC (size > 1 μm). With the presence of BC fractions (250 mg/L) nitrobenzene reduction by Na₂S was significantly facilitated, wherein the mediation efficiency was positively correlated with the BC fraction's oxygen group content in an order of particulate BC < colloidal BC ≪ dissolved BC. Consistently, the oxidation treatment of particulate BC with O₃ or HNO₃ improved the mediation efficiency, whereas the reduction treatment with NaBH₄ reduced the mediation efficiency. The supernatant collected with dialysis or filtration of suspension of BC materials pre-reacted with Na₂S could effectively reduce nitrobenzene, suggesting that reactive reducing sulfur species were produced in aqueous solutions by reacting sulfide only with BC materials. This was evidenced by the fact that polysulfides and polysulfide radicals were both detected in the supernatant. As demonstrated by electron paramagnetic resonance analysis, the quinone moieties at the surface of BC materials accepted electrons from sulfide and turned into semiquinone free radicals, consequently leading to formation of reactive reducing sulfur species and thus enhanced nitrobenzene reduction. The strong mediation efficiency on redox reactions observed for colloidal BC and dissolved BC combined with their significant mobility in subsurface environments indicate that these carbonaceous materials may play an important role in the fate process of organic contaminants as both carriers and catalysts. CAPSULE: The surface quinone moieties of BC induce the formation of reactive reducing sulfur species by acting as one-electron acceptors and facilitate nitrobenzene reduction by sulfide.

Keywords: Black carbon; Nitrobenzene; Quinone moieties; Reactive reducing sulfur species.