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.

Environmental transformation of natural and engineered carbon nanoparticles and implications for the fate of organic contaminants

“…134 Changes in the intrinsic pore size distributions of pCNPs as a result of transformation and leaching of soluble phases can also affect the pCNP-contaminant binding potential. 137 Changes in water chemistry, surface functionality, and NOM loading all affect the aggregation of CNPs. 15,47,107 Changes in CNP aggregation as a result of transformation in natural environments can alter the pore structure and pore volume, thus affecting the sorption and desorption of contaminants as well as their co-transport with the CNPs.…”

“…130,[140][141][142][143] In addition, interactions between CNPs and NOM can result in the blockage of micropores and mesopores, thereby trapping contaminants within these pore spaces. 132,137 Organic contaminants sorbed by CNTs, fullerenes, fossil coal, and biochar are generally not very bioaccessible because of their high contaminant-binding capacities. 116,144,145 However, when comparing these materials, which are generally produced under controlled conditions, with their counterparts from unintentional emissions (e.g., soot, 24,25 biochar produced under poorly controlled conditions, 146 or wildfire charcoal 29 ), the sorption and release of organic contaminants can differ considerably.…”

Sorption to soil, biochar and compost: is prediction to multicomponent mixtures possible based on single sorbent measurements?

“…For instance, it has been suggested that ageing in soil has a limited impact on the pore size distribution of some biochars ( Sorrenti et al, 2016 ; Sigmund et al, 2017a ), but it is not known whether this applies to all biochar-soil systems. Our results show that soil and compost can significantly reduce the sorption of contaminants to biochar, and it has also been shown that pore blockage can entrap sorbed contaminants and reduce their desorption potential ( Yang & Xing, 2007 ; Wang et al, 2017 ). How ageing and weathering processes affect the remobilisation of contaminants (desorption) has been relatively poorly considered up to now, although it an essential aspect impacting the long term performances of soil amendments.…”

“…In realistic settings where biochar is amended to contaminated soil, biochar is subject to a range of biological, physical and chemical processes involving its interactions with various soil components, and leaching of its most soluble fractions ( Hale et al, 2011 ; Wang et al, 2017 ). These processes can have a direct impact on the surface chemistry and porosity of biochar and the way it interacts with contaminants.…”

Organo-Mineral Interactions Involved in Herbicide Sorption on Soil Amended with Peats of Different Maturity Degree

“…In particular, the aromaticity of humic substances or, conversely the hydrophobicity/aromaticity ratio, seems to be a determining factor and explains much of the variability of atrazine absorption [20][21][22]. Several studies have found that the application to soil of highly aromatic organic amendments (such as humus with a high degree of maturity or different forms of fossil or pyrogenic organic matter, i.e., black carbon) has an outstanding influence on atrazine sorption [23][24][25]. In the case of alachlor, it was found that, although tillage practices did not significantly affect its sorption into the soil, biochar (highly aromatic soil amendment) increased its sorption between 4× and 33× compared to unamended soil [26].…”