Characteristics of phosphate-ion adsorption on N-doped activated carbon derived from pinecones and urea

Abstract

Anion exchange resins are widely used to remove phosphates from water; however, they are expensive and cannot be efficiently reused. We have increased the quaternary nitrogen (N-Q) content in activated carbon by impregnating pinecones with urea and zinc chloride and activating it at 600 °C to improve its phosphate-ion adsorption capacity. The sample containing pinecone, urea, and zinc chloride in a 1 : 4 : 1 weight ratio (Ur4-1) adsorbed the largest amount of phosphate ions (0.29 mmol/g). As the weight ratio of urea increased, the N-Q content increased and the specific surface area of samples decreased. These findings indicated that the N-Q content has a larger effect on the phosphate-ion adsorption capacity of samples than on the specific surface area, which is often used as an indicator of the adsorption capacity of activated carbon. Ur4-1, with the largest N-Q content of 1.81 wt%, had the best phosphate-ion adsorption, and the amount it adsorbed at equilibrium pH (pH_e) 2–10 was investigated. Results indicated that Ur4-1 adsorbed higher amounts of phosphate ions (0.051 mmol/g) than the commercial anion exchange resin, IMAC HP555, at pH_e 3.