Physically (CO2) activated hydrochars from hickory and peanut hull: preparation, characterization, and sorption of methylene blue, lead, copper, and cadmium

The effects of CO2 activation temperature (600-900 degrees C) and time (1 and 2 h) on the physicochemical and sorptive characteristics of hickory and peanut hull hydrochars were investigated. The extent of burn-off increased with increasing activation times and temperatures, and ranged from 34-54% and 28-50% for activated hydrochars (AHCs), respectively. The surface area and pore volume of the AHCs also increased with activation time and temperature and were much higher than those of their corresponding nonactivated parent hydrochars. In general, the physical activation improved the ability of all AHCs to sorb methylene blue, lead (Pb2+), copper (Cu2+), and cadmium (Cd2+) from aqueous solutions. AHCs created at 900 degrees C had the best sorption ability, and the highest sorption rate was usually observed in 900 degrees C 2 h AHCs. The sorption of methylene blue and the three heavy metals was strongly correlated with AHC surface area, suggesting that the adsorption occurred via site-specific interactions.