Preparation of high specific surface area activated carbon from walnut shells by microwave-induced KOH activation

We prepared activated carbon with high specific surface area from walnut shells by chemical activation with KOH and microwave heating. To optimize the preparation process, we applied the response surface methodology technique. We then investigated the influences of microwave power, activation time, and KOH/C weight ratio on the yield and iodine adsorption capacity of the activated carbon. The results revealed that the optimum conditions were: microwave power 700 W, activation time 20 min, and KOH/C weight ratio 4, corresponding to a yield of 40 % and an iodine number of 2558 mg/g. The pore structure parameters of the activated carbon, i.e., Brunauer–Emmett–Teller surface area, total pore volume, and average pore diameter, were estimated to be 3923 m2/g, 2.778 ml/g, and 2.32 nm, respectively, under optimum conditions. The activated carbon and char were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. FTIR showed that the chemical groups of the activated carbon had changed, and SEM revealed that the activated carbon had lots of small, irregular pores on its surface. The inner structure of the activated carbon under the optimum preparation conditions is viewed by the TEM.