Congo red removal using microwave assisted pyrolysis derived magnetic hemp hurd biochar

Abstract

Industrial hemp hurd (HH) are the residue obtained after the decortication of the hemp plant for fibre production, which is seldom explored for biochar potential and as adsorbent for dye removal. The present study focused on the microwave-assisted pyrolysis (MAP) of HH for biochar production, magnetization and application for Congo red (CR) removal from aqueous solutions. Magnetic hemp hurd biochar (MHB) depicted a heterogeneous surface with 4.84 µm pore size, 17.64 m²/g surface area, and 10.05 wt% Fe. CR removal of 92 % was achieved under optimum conditions i.e., treatment time: 120 min, pH: 8, and initial CR concentration: 10 mg/L with MHB dosage of 0.6 g/L. The CR adsorption on MHB was well-fitted with the Freundlich isotherm (R² - 0.971), owing to the heterogeneous surface of MHB. A strong match with pseudo-second order model (R² - 0.973), indicated chemisorption as the likely adsorption mechanism. MHB exhibited 87 % CR removal efficiency after three successive reutilization cycles. The outcomes of CR removal efficiency and MHB reusability indicated its potential application for adsorptive removal of CR from aqueous systems.