Equilibrium modeling, kinetic and thermodynamic studies on the adsorption of Cr(VI) using activated carbon derived from matured tea leaves

A new porous carbon with high surface area of 1,313.41 m2 g−1 with pore volume 1.359 cm3 g−1 has been synthesized from matured tea leaves by chemical activation method using phosphoric acid. The carbon was found to be highly efficient for removal of Cr(VI) from aqueous solution. The effects of various parameters such as contact time, initial metal ion concentration, pH, temperature and amount of adsorbent on the extent of adsorption were studied. Langmuir, Freundlich and Temkin adsorption models were used to interpret the experimental data. The adsorption data were best fitted with Langmuir isotherm model. The adsorption capacity of Cr(VI) onto the activated carbon calculated from Langmuir isotherm was found to be 30.8 mg g−1 at pH 4.8 and temperature 303 K. The adsorption capacity increases from 25.36 to 32.04 mg g−1 with an increase in temperature from 303 to 323 K at initial Cr(VI) concentration of 60 mg L−1. The adsorption process followed a pseudo second order kinetic model. Thermodynamic parameters ΔH0 (28.6 KJ mol−1), ΔG0 at three different temperatures [(−0.145, −1.09, −2.04) KJ mol−1] and ΔS0 (94.87 J mol−1 K−1) were calculated. These values confirm the adsorption process to be endothermic and spontaneous in nature.