Adsorption of Rhodamine B from Aqueous Solution by Goat Manure Biochar: Kinetics, Isotherms, and Thermodynamic Studies

Biochar was prepared by pyrolyzing goat manure at 600 degrees C (GMB600) and used as an adsorbent for the removal of Rhodamine B (RhB) from aqueous solution. The structure and properties of GMB600 were characterized by elemental analysis, BET, SEM and FTIR. The effects of solution pH, biochar dosage, contact time, initial RhB concentration and temperature on the adsorption behaviors were investigated by batch experiments, which were further used to preliminarily discuss the adsorption mechanism. Results showed that the adsorption equilibrium could attain in 150 min and the RhB removal rate could reach 96.5% under the conditions of solution pH 5.0, GMB600 dosage of 0.4 g/L, initial RhB concentration of 20 mg/L and temperature of 25 degrees C. The adsorption behavior of RhB onto GMB600 followed the pseudo second-order kinetic model, and the adsorption isotherm was better fitted with the Freundlich model. Thermodynamic parameters such as Gibbs free energy change (Delta G degrees), enthalpy change (Delta H degrees) and entropy change (Delta S degrees) indicated that the adsorption of RhB onto GMB600 was a spontaneous and endothermic process with increased entropy. FTIR analysis showed that the oxygen-containing functional groups on GMB600 provided RhB with abundant adsorption sites, and the adsorption mechanism was possibly attributable to the hydrogen bond and pi-pi interactions between RhB and GMB600.