Adsorption of herbicide [pendimethalin] onto activated carbons developed from date pits

ABSTRACT

Phosphoric acid-activated carbons PI and P2 were prepared by impregnating crushed date pits with 50 and 75 wt% phosphoric acid followed by carbonization at 500°C in limited air. Zinc chloride-activated carbons Zland Z2 were obtained by impregnating crushed date pits with 100 and 200 wt% zinc chloride followed by carbonization at 600°C in limited air. Steam-activated carbons SI and S2 were obtained by gasifying date pits carbonization product with steam at 950°C to burn-off s = 17 and 48%, respectively. The textural properties of the activated carbons were determined from nitrogen adsorption at 77K and the chemistry of their surfaces were characterized by measuring their surface pH and by determining their acid and base-neutralization capacities. The equilibrium adsorption of pendimethalin at 293, 300, 310 and 320K was studied using different system variables. Generally activated carbons exhibited high adsorption capacities towards pendimethalin. The adsorption data followed Freundlich and Langmuir models. The adsorption of this herbicide decreased with the rise of adsorption temperature and the small values of delta H indicated the loose bonding between adsorbate molecules and adsorbent surface. The negative values of entropy change delta S although small, indicated that the adsorption complex formed was stable