Synthesis of Magnetic Biochar and Their Application in the Treatment of Methylene Blue in Aqueous Solutions

Abstract

Magnetic biochar materials were synthesized by heating rice husk at 500°C under nitrogen environment, then fixing iron oxides on biochar surface using hydrothermal method applied to Fe(OH)2 and Fe(OH)3 which were generated from respective precursors Fe2+ and Fe3+ in alkaline environment. The presence of iron oxides on the surface of biochar and the surface characteristics of iron-composite materials were studied with the aid of modern physicochemical analysis techniques (SEM/EDX, BET, FT-IR, XRD). Magnetic biochar materials were relatively porous, with an average spectific surface area of 62.1 m2, an average capillary size of about 17.2 nm. The mixture of iron oxide particles were revealed within the nano scale (about 15 nm). The methylene blue adsorption efficiency depended upon the amount of adsorbent, adsorption time, pH of solution and pollutant concentrations. Specifically, the optimal conditions for maximum adsorption efficiency were as follows: 0.02 g/L of magnetic biochar, the adsorption equilibrium time was 3 hours at room temperature, in a solution of pH7; The efficiency of methylene blue adsorption in optimal conditions reached over 98.82%. The Langmuir and Freundlich isotherm adsorption models all described well the methylene blue adsorption process at room temperature, with the regression coefficients R2 of 95.0 and 90.0, respectively. The maximum adsorption capacity of methylene blue calculated by Langmuir model was 22.4 mg/g.