Physicochemical characterization of biochar derived from the pyrolysis of cotton gin waste and walnut shells

Abstract

Abstract. The sustainable management of agricultural waste has gained increasing attraction worldwide, especially regarding production of value-added products that are renewable and carbon-rich. Further, as beneficial reuse of treated wastewater increases, there is a need to remove contaminants that persist in the effluent to mitigate potential impacts on the agroecosystems to which they are land-applied. Here, we characterized biochar produced from the pyrolysis of two agricultural waste products: cotton gin waste (pyrolyzed for 2 h at 700°C, CG700) and walnut shells (pyrolyzed for 2 h at 800°C, WS800) to better understand their potential applications for water quality improvement. Each biochar was characterized by Brunauer-Emmett-Teller (BET) analysis to determine the specific surface area, scanning electron microscopy (SEM) to elucidate change in morphology, Fourier Transform Infrared Spectroscopy (FT-IR) to determine surface functional groups, and zeta potential to establish the pH point of zero charge. The higher temperature used to produce WS800 led to an increase in the specific surface area and increased dehydration of the biochar (i.e., loss of the O-H group). Pyrolysis led to destruction of the acidic functional groups and an increase in ash content, resulting in the production of hydrophobic alkaline biochars with pH values of 9.85 and 10.93 for WS800 and CG700, respectively. Zeta potential measurements demonstrated that WS800 and CG700 biochars are negatively charged, suggesting suitable applications for the removal of cationic contaminants from the environment. Overall, results demonstrated that biochars obtained from agricultural waste have the potential to be effective sorbents for decontamination of wastewater and soil.