biochar 기반 복합소재를 이용한 오염물질 제거

Abstract

In this study, We synthesized various types of biochar through pyrolysis and examined their application methods to increase the value of biochar. The feasibility of using biochar as a sorbent to remove nitro explosives and metals from contaminated water was investigated through batch experiments. Biochar, synthesized using biomasses, showed a porous structure and a high surface area and included embedded carbonate minerals. Compared with granular activated carbon (GAC), biochar was competitive as a sorbent for removing Cd, Cu, Pb, and Zn from water according to the maximum sorption capacities of the metals. Some biochars also effectively sorbed nitro explosives from water. Correlation analysis between maximum sorption capacities and properties of biochar showed that the sorption capacity of biochar for cationic toxic metals is related to the cation exchange capacity (CEC) and that the sorption capacity of explosives is proportional to the surface area and carbon content. In addition, results from X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR) analyses, and laboratory experiments suggest that surface functional groups may be responsible for the sorption of cationic metals to the biochar surface. In contrast, carbon contents may account for the sorption of explosives, possibly through π–π electron donor-acceptor interactions. The feasibility of using biochar as a sorbent to remove nine halogenated phenols (2,4-dichlorophenol, 2,4-dibromophenol, 2,4-difluorophenol, 2-chlorophenol, 4-chlorophenol, 2-bromophenol, 4-bromophenol, 2-fluorophenol, and 4-fluorophenol) and two pharmaceuticals (triclosan and ibuprofen) from the water was examined through a series of batch experiments. Biochar was synthesized using various biomasses, including fallen leaves, rice straw, corn stalks, spent coffee grounds, and biosolid. Compared to GAC, most biochar samples did not effectively remove halogenated phenols or pharmaceuticals from water. The increase in pH and deprotonation of phenols in biochar systems may be responsible for its inefficiencies at this task. However, when pH is maintained at 4 or 7, the sorption capacity of biochar is markedly increased. Considering the maximum sorption capacity and properties of sorbents and sorbates, the sorption capacity of biochar for halogenated phenols is related to the surface area and carbon content of biochar and hydrophobicity of contaminants. In the cases of triclosan and ibuprofen, the sorptive capacities of GAC, graphite, and biochars were also significantly affected by pH, according to the point of zero charge (PZC) of sorbents and deprotonation of the pharmaceuticals. Pyrolysis temperature did not affect the sorption capacity of halogenated phenols or pharmaceuticals. The synthesis of zero-valent iron [Fe(0)]-included biochar (Fe(0)-biochar] was applied to remove nitro explosives (2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)) and halogenated-phenols (DBP and DFP) from contaminated waters. Due to the presence of biochar on the outside, the removal of nitro explosives and halogenated phenols was significantly enhanced via sorption. The sorbed contaminants were further transformed into reducing agents, indicating that the inner Fe(0) played the role of a reductant in the Fe(0)-biochar. Compared to direct reduction with Fe(0), the reductive transformation with Fe(0)-biochar was markedly enhanced, suggesting that the biochar in Fe(0)-biochar may act as an electron transfer mediator. Further experiments showed that the surface functional groups of biochar were involved in the catalytic enhancement of electron transfer. Co-pyrolysis of polymer and biomass wastes was investigated as a novel method for waste treatment and synthesis of enhanced biochar. Co-pyrolysis of RS with polypropylene (PP), polyethylene (PE), or polystyrene (PS) increased the carbon content, CEC, BET surface area, and pH of the biochar. As a result, the sorption of 2,4-dinitrotoluene (DNT) and Pb to polymer/RS-derived biochar was markedly enhanced. The increased aromaticity and hydrophobicity contents may enhance the DNT sorption to the polymer/RS-derived biochar. In contrast, increasing CEC, higher pH, and the newly developed surface area may account for the enhancement in Pb sorption. The addition of polymer to RS did not significantly change the catalytic role of biochar during DNT reduction by dithiothreitol. Biochar was synthesized using wood chips (WC), BS, and biomass obtained in large quantities in Korea, and its adsorption capacity was analyzed through a batch experiment. We evaluated the carbon sequestration capacity using biochar–mortar composites according to characteristics for construction and environmental applications. Characterization of biochar–mortar composites showed that 3-5 vt% biochar inclusion did not significantly change the composites' engineering properties, including flowability, compressive strength, and thermal conductivity. Furthermore, as the biochar content increased in the biochar–mortar, the benzene and toluene concentrations in the air were accordingly reduced, suggesting that biochar inclusion may be favorable to remove volatile toxic contaminants. The toxicity characteristics leaching procedure (TCLP) and Micotox®bioassay tests showed that biochar–mortar composites were not toxic. These results confirmed that biochar and biochar-based composite materials are competitive can be effectively used as sorbents, catalysts, or reducing agents for contaminants. The improving value of biochar suggests that biochar production via pyrolysis may be a promising option for carbon sequestration to release CO2 mitigation.