Polymer/biomass-derived biochar for environmental application: Sorbent and electron transfer mediator

Co-pyrolysis of polymer and biomass wastes was investigated as a novel method for waste treatment and synthesis of enhanced biochar. Co-pyrolysis of rice straw (RS) with polypropylene (PP), polyethelyene (PE) or polystyrene (PS) increased carbon content, cation exchange capacity (CEC), surface area and pH of biochar. In contrast, contents of hydrogen, oxygen, and nitrogen were decreased. Fourier transform infrared (FT-IR) spectra and thermogravimetric analysis (TGA) showed that aromaticity of biochar was enhanced by addition of polymers to RS in pyrolysis. As a result, the sorption of 2,4-dinitrotoluene (DNT) and Pb to polymer/RS-derived biochar was markedly enhanced. Compared to RS-derived biochar (4.63 and 32.1 mg/g for DNT and Pb), the maximum sorption capacity for DNT and Pb were increased up to 15.1 and 136 mg/g, respectively. Increasing aromaticity and hydrophobicity may be responsible for the enhancement of DNT sorption to polymer/RS-derived biochar. In contrast, increasing CEC and pH, and developed surface area may account for the enhancement of Pb sorption. The addition of polymer to RS did not much change the catalytic role of biochar during the reduction of DNT by dithiothreitol. Our results suggest that in addition to waste treatment, co-pyrolysis of RS and polymer can upgrade biochar properties to enhance the sorption of DNT and Pb.