Phosphoric Acid Activation for Preparation of Walnut Shell Biochar and Adsorption of Rhodamine B

Using walnut shell as raw material, walnut shell biochar (WSBC) was synthesized via H₃PO₄ activation for Rhodamine B(RhB) removal. The obtained WSBC was characterized by FTIR, XRD, SEM, BET and the adsorption process was investigated by UV–vis. The effects of concentration of H₃PO₄, roasting temperature, adsorption temperature, adsorbent dosage, initial concentration, pH value were investigated on RhB adsorption over WSBC. Results suggested that WSBC had available porosity and rich functional groups on the surface of WSBC. There was no obvious change in crystal phase before and after adsorption. When the concentration of H₃PO₄ was 0.5 mol/L, roasting temperature was 600 ℃, roasting time was 2 h, reaction temperature was 20 ℃, the initial concentration of RhB was 10 mg/L, the amount of WSBC was 2 g/L and adsorption time was 60 min, the removal rate of RhB could reach 90%. The adsorption of RhB on WSBC could well-fitted by pseudo-second-order kinetic model and Langmuir isotherms model, the maximum theoretical adsorption capacity of WSBC for RhB is 12.61 mg/g.