Pyrogenic carbonaceous matter (PCM) includes environmental black carbon (fossil fuel soot, biomass char), engineered carbons (biochar, activated carbon), and related materials like graphene and nanotubes. These materials contact organic pollutants due to their widespread presence in the environment or through their use in various engineering applications. This review covers recent advances in our understanding of adsorption and chemical reactions mediated by PCM and the links between these processes. It also covers adsorptive processes previously receiving little attention and ignored in models such as steric constraints, physicochemical effects of confinement in nanopores, π interactions of aromatic compounds with polyaromatic surfaces, and very strong hydrogen bonding of ionizable compounds with surface functional groups. Although previous research has regarded carbons merely as passive sorbents, recent studies show that PCM can promote chemical reactions of sorbed contaminants at ordinary temperature, including long-range electron conduction between molecules and between microbes and molecules, local redox reactions between molecules, and hydrolysis. PCM may itself contain redox-active functional groups that are capable of oxidizing or reducing organic compounds and of generating reactive oxygen species (ROS) from oxygen, peroxides, or ozone. Amorphous carbons contain persistent free radicals that may play a role in observed redox reactions and ROS generation. Reactions mediated by PCM can impact the biogeochemical fate of pollutants and lead to useful strategies for remediation.

Recent research has demonstrated that black carbons catalyze the transformation of a range of nitrated explosives sorbed to the carbon surfaces in the presence of sulfides. Although surface oxygenated functional groups, particularly quinones, and electrical conductivity have both been hypothesized to promote these reactions, the importance of these properties has not been tested. In this work, the importance of electrical conductivity was addressed by producing chars of increasing electrical conductivity via pyrolysis of wood shavings at increasing temperature. The reactivity of chars with respect to transformation of the explosive RDX in the presence of sulfides correlated with electrical conductivity. Oxygenated functional groups were apparently not involved, as demonstrated by the elimination of reactivity of an activated carbon after ozone treatment or sorption of model quinones to the activated carbon surface. Although RDX transformation correlated with char electrical conductivity, no RDX transformation was observed when RDX was physically separated from sulfides but electrically connected through an electrochemical cell. RDX transformation occurred in the presence of a surface-associated sulfur species. The correlation with char electrical conductivity suggests that sulfides are oxidized on carbon surfaces to products that serve as potent nucleophiles promoting RDX transformation.

The in situ remediation of sediments contaminated with explosives, including nitroglycerin and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), is desirable, particularly at bombing ranges where unexploded ordnance (UXO) renders excavation dangerous. Sulfides generated by biological sulfate reduction in sediments are potent nucleophiles and reductants that may contribute to the destruction of explosives. However, moderately hydrophobic explosives are likely to sorb to black carbons, which can constitute 10-30% of sediment organic carbon. In this study, we evaluated whether the black carbons accelerate these reactions or simply sequester explosives from aqueous phase reactions. Using environmentally-relevant sulfide and black carbon concentrations, our results indicated that black carbons accelerated the destruction of both compounds, yielding relatively harmless products on the time scale of hours. For both compounds, destruction increased with sulfide and graphite concentrations. Using sheet graphite as a model for graphene regions in black carbons, we evaluated whether graphene regions mediated the reduction of explosives by promoting electron transfer from sulfides. Our results demonstrated that the process was more complex. Using an electrochemical cell that enabled electron transfer from sulfides to explosives through graphite, but prevented nucleophilic substitution reactions, we found that nitroglycerin destruction, but not RDX destruction, could be explained by an electron transfer mechanism. Furthermore, surface area-normalized destruction rates for the same explosive varied for different black carbons. While black carbon-mediated destruction of explosives by sulfides is likely to be a significant contributor to their natural attenuation in sediments, a fundamental characterization of the reaction mechanisms is needed to better understand the process.

Hierarchical nanocomposites of polyaniline (PANI) nanorods array on graphene oxide (GO) nanosheets are successfully obtained by dilute polymerization under -20 °C. They exhibit excellent water treatment performance with a superb removal capacity of 1149.4 mg g(-1) for Cr(VI).

Novel hierarchical core-shell iron oxide@magnesium silicate magnetic nanorods (HIO@MgSi) were fabricated via a versatile sol-gel process through hydrothermal reaction. They contain magnetic iron oxide (Fe 3 O 4 ) cores and hierarchical shells (MgSi) made of ultrathin nanosheets (ca. 5 nm). Using methylene blue as a model compound, the HIO@MgSi nanorods showed fast adsorption kinetics and a superb adsorption capacity. 99.3% of methylene blue was adsorbed onto the surface of the HIO@MgSi nanorods in 40 min contact time. A maximum adsorption capacity of 2020.20 mg g À1 was achieved after 4 h. This study indicated that HIO@MgSi nanorods can be used as a potential super adsorbent to remove cationic organic pollutants effectively and rapidly from large volumes of industrial wastewater or drinking water.