title: Micropore clogging by leachable pyrogenic organic carbon: A new perspective on sorption irreversibility and kinetics of hydrophobic organic contaminants to black carbon.
abstract: Black carbon (BC) plays a crucial role in sequestering hydrophobic organic contaminants in the environment. This study investigated key factors and mechanisms controlling nonideal sorption (e.g., sorption irreversibility and slow kinetics) of model hydrophobic organic contaminants (nitrobenzene, naphthalene, and atrazine) by rice-straw-derived BC. After removing the fraction of leachable pyrogenic organic carbon (LPyOC) (referring to composites of dissoluble non-condensed organic carbon and associated mineral components) with deionized water or 0.5 M NaOH, sorption of these sorbates to BC was enhanced. The sorption enhancement was positively correlated with sorbate molecular size in the order of atrazine > naphthalene > nitrobenzene. The removal of LPyOC also accelerated sorption kinetics and reduced sorption irreversibility. These observations were attributed to increased accessibility of BC micropores initially clogged by the LPyOC. Comparison of BC pore size distributions before and after atrazine sorption further suggested that the sorbate molecules preferred to access the micropores that were more open, and the micropore accessibility was enhanced by the removal of LPyOC. Consistently, the sorption of nitrobenzene and atrazine to template-synthesized mesoporous carbon (CMK3), a model sorbent with homogeneous pore structures, showed decreased kinetics, but increased irreversibility by impregnating sorbent pores with surface-grafted alkylamino groups and by subsequent loading of humic acid. These findings indicated an important and previously unrecognized role of LPyOC (i.e., micropore clogging) in the nonideal sorption of organic contaminants to BC.
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse/School of the Environment, Nanjing University, Jiangsu 210023, China.
authors.forename: Bingyu
authors.initials: B
authors.lastname: Wang
authors.affiliation: Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, MI 48824, United States; Environmental Science and Policy Program, Michigan State University, East Lansing, MI 48824, United States.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, MI 48824, United States.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse/School of the Environment, Nanjing University, Jiangsu 210023, China.
authors.forename: Heyun
authors.initials: H
authors.lastname: Fu
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse/School of the Environment, Nanjing University, Jiangsu 210023, China.
authors.forename: Xiaolei
authors.initials: X
authors.lastname: Qu
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse/School of the Environment, Nanjing University, Jiangsu 210023, China; School of Urban and Environmental Sciences, Peking University, Beijing 100871, China. Electronic address: zhud@pku.edu.cn.
authors.forename: Dongqiang
authors.initials: D
authors.lastname: Zhu
mesh_terms: D000327:Adsorption; D001280:Atrazine / Q000737:chemistry; D002244:Carbon / Q000737:chemistry*; D006812:Humic Substances / Q000032:analysis; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D009578:Nitrobenzenes / Q000737:chemistry; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis / Q000737:chemistry*
chemical_list: D006812:Humic Substances; D009578:Nitrobenzenes; D012987:Soil; D012989:Soil Pollutants; D002244:Carbon; C036077:nitrobenzene; D001280:Atrazine
keywords: Black carbon (BC); Leachable pyrogenic organic carbon (LPyOC); Pore clogging; Sorption irreversibility; Sorption kinetics