Preparation of activated carbon from tobacco stalks using microwave assisted chemical activation for water purification

Abstract

Tobacco crop is an economically important crop. The remaining stalk after reaping the leaf however presents environmental pollution challenges. The carbonaceous nature of the stalk on the other hand makes it a promising precursor for activated carbon preparation. Optimization of the preparation of activated carbon using tobacco stalks and microwave heating was therefore studied. The prepared activated carbon was further applied as an adsorbent for methylene blue (MB) and lead removal from water. The optimized conditions for activated carbon preparation were a radiation power of 280 W for a period of six minutes having impregnated the precursor material with 30% ZnCl2 for 24 hours. The obtained activated carbon yield and iodine number were 49.43% and 1264.51 mg/g respectively. The activated carbon also had a point of zero charge of 5.81, BET surface area of 684.68 m2/g, pore volume of 0.4508 cm3/g with adsorption capacities of 123.45 mg/g and 39.06 mg/g for MB and lead respectively. The optimum conditions for lead adsorption were a pH of 6.5 with an adsorbent dosage of 0.15 g/50 mL at 250C while those for MB were a pH of 6.5 with an adsorbent dosage of 0.2 g/50 mL at 250C. The adsorption kinetics for both MB and lead followed the pseudo second order kinetic model with the intra-particle diffusion model suggesting a two-step adsorption mechanism. Experimental adsorption data for both MB and lead also fitted well within the Langmuir adsorption isotherm model. It can therefore be concluded that tobacco stalks can be turned into an economically important product through the production of activated carbon which performs well in comparison to other products produced from different precursor materials for lead and MB removal from water and waste water.