Effect of carbonization/activation temperature on benzene adsorption by potassium carbonate activated corncob biochar

As a new kind of carbonaceous adsorbent, biochar has a good function of controlling VOCs. A series of biochar (BCx) and potassium carbonate activated biochar (KBC-x-y) were pre-pared from corncob for benzene adsorption. Thermogravimetric analysis, nitrogen adsorption-desorption, scanning electron microscopy (SEM) and elemental analysis (EA) were used to char-acterize the pyrolytic properties, specific surface area, pore volume and pore size, surface mor-phology and atomic percentage of the biochar (mass) samples. The effects of carboniza-tion/activation temperature on benzene adsorption were investigated by adsorption experiments. The results show that the specific surface area of biochar modified by potassium carbonate is up to 576.76 m²/g, the pore volume is 0.325 m³/g, and the maximum adsorption capacity of benzene is up to 82.51 mg/g (2.9 times higher than that of unmodified biochar). The carbonization temperature and adsorption capacity show a trend of normal distribution. The adsorption capacity increases with the increase of carbonization temperature, but the high carbonization temperature above 800 ℃ will lead to the clogging of pores, decrease in number, decrease in specific surface area and decrease in adsorption capacity. The adsorption capacity of biochar shows the same trend with the activation temperature under low/high carbonization temperature. After high-temperature carbonization (800 ℃), the optimum activation temperature is 400 ℃ (KBC-800-400). If the activation temperature is too high, it will lead to the fracture of micropore wall and the sintering effect of volatiles, thus reducing the adsorption capacity. Lower activation temperature fails to make K₂CO₃ fully react on the carbon surface. After low-temperature carbonization (400 ℃), the optimal activation temperature is (800 ℃). The adsorption performance of low-temperature carbonized high-temperature activated biochar (KBC-400-800) is better than that of high-temperature carbonized low-temperature activated biochar (KBC-800-400). It is possibly because the higher activation temperature facilitates the involvement of potassium carbonate in the reaction of the activation process in the case of low temperature car-bonization.