Highly Efficient Removal of Cr(VI) by Biochar Derived from Vietnamese Young Durian Fruit: Comparison of Traditional and Microwave-Assisted Pyrolysis

This study compares the material characteristics and evaluates the Cr(VI) adsorption capacity of biochar derived from a novel byproduct (young durian fruit, YDF), synthesized using two pyrolysis methods (traditional and microwave-assisted). The optimal pyrolysis conditions for porosity were 800 °C and 800 W for 30 min, respectively. The traditional pyrolysis method yielded a very high surface area and pore volume (668 m²/g; 0.332 cm³/g). XRD patterns and FTIR spectra demonstrated structural and functional group differences, significantly impacting the Cr(VI) removal efficiency in water. pH was a critical factor with optimal adsorption at pH 2.0. The adsorption process reached equilibrium at 180 and 100 min at initial concentrations of 100 and 125 mg/L for biochar synthesized by traditional and microwave-assisted pyrolysis, respectively. The adsorption mechanisms proposed based on modern analytical methods include adsorption-reduction, ion exchange, electrostatic interaction, and surface complexation. Industrial wastewater containing chromium was effectively treated under natural conditions (pH = 5.88; <i>C</i>_o = 129.9 mg/L) using biochar synthesized via microwave, achieving a <i>Q</i>_e of 21.41 mg/g. The research results pave the way for new directions in the synthesis and application of biochar in environmental treatment, specifically using young fruit materials and microwave methods.