Factors Affecting Sorption of Nitro Explosives to Biochar: Pyrolysis Temperature, Surface Treatment, Competition, and Dissolved Metals

Abstract

The application of rice straw-derived biochar for removing nitro explosives, including 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), from contaminated water was investigated through batch experiments. An increase in the pyrolysis temperature from 250 to 900°C in general led to higher pH, surface area, cation exchange capacity (CEC), point of zero charge, and C:O ratio of biochar. The maximum sorption capacity estimated by a mixed sorption-partition model increased when pyrolysis temperatures were elevated from 250 to 900°C, indicating that C content and aromaticity of biochar were strongly related to the sorption of nitro explosives to biochar. Surface treatment with acid or oxidant increased the sorption capacity of biochar for the two strong π-acceptor compounds (DNT and TNT) but not for RDX. However, the enhancement of sorption capacity was not directly related to increased surface area and CEC. Compared with single-sorption systems, coexistence of explosives or cationic metals resulted in decreased sorption of each explosive to biochar, suggesting that sorption of nitro explosives and cationic metals to electron-rich portions in biochar was competitive. Our results suggest that π-π electron donor acceptor interactions are main sorption mechanisms and that changing various conditions can enhance or reduce the sorption of nitro explosives to biochar.

Reductive removal of 2,4-dinitrotoluene and 2,4-dichlorophenol with zero-valent iron-included biochar

“…Similar to biomass-derived biochar, the increasing pyrolysis temperature resulted in increasing pH, BET surface area, and PZC values. The CEC was maximized at 400°C and decreased at lower or higher temperatures, consistent with previous results (Oh and Seo, 2015). Decreasing surface functional groups at high temperatures and less carbonization at lower temperatures were responsible for this trend.…”

“…In general, a low pyrolysis temperature resulted in increasing hydrophobicity of biochar due to the remaining organic residues from the biomass, favorable for hydrophobic sorption of organic compounds to biochar (Chen et al, 2008). According to our previous study (Oh and Seo, 2015), the maximum sorption capacity of DNT at 250°C biochar was 1.1 mg/g. Considering the carbon amount (0.624 g), the sorption capacity was less than the total amount of DNT ($2 mg) in solution.…”

“…However, Fig. 6a demonstrates that more than 95% of DNT was removed, suggesting that other removal mechanisms may be involved, such as hydrophobic partitioning to organic residues at low temperatures (Oh and Seo, 2015). The low pyrolysis temperature also produced less carbonized char where surface functional groups are more dominant than the aromaticity of graphene moieties (Keiluweit et al, 2010).…”

Polymer/biomass-derived biochar for use as a sorbent and electron transfer mediator in environmental applications

“…Increasing the temperature did not significantly change the pH and pH zpc (Table 1). Similar to conventional biochar (Oh and Seo, 2015), increasing the temperature increased the BET surface area of PP/ RS-derived biochar (from 27.5 to 33.6 and 34.8 m 2 /g). In contrast, hydrogen, oxygen, and nitrogen contents decreased significantly (Table 1).…”

Biochar Modification, Thermal Stability and Toxicity of Products Modification

“…4H 2 O + Modifi cation of biochar with MnO x Improvement of sorption capacity to As and Pb KMnO 4 + HCl + Preparation of composite Birnessite -Biochar HNO 3 + H 2 SO 4 (1:1) + Na 2 S 2 O 4 + Amidation of biochar (reduction of NO 2 groups to -NH 2 ), increase of sorption capacity to Cu 2+ (Yang and Jiang, 2014) Chitosan + Sorption of heavy metals and biological activity Fe 3 O 4 + Preparation of sorbents in a ball mill -sorption capacity to antibiotics (Shan et al, 2016) Legend: LO -Reference worldwide-used pharmaceutical products, such as isobrufen (Essandoh et al, 2015), tetracycline (Liao et al, 2013), acetaminophenon (Im et al, 2014), aspirin (Essandoh et al, 2015) toxic industrial substances (Chen and Chen, 2009;Wang et al, 2013), explosives (Oh and Seo, 2014;Oh and Seo, 2015) etc.…”