Kinetic studies on the adsorption of phenol, 4-chlorophenol, and 2,4-dichlorophenol from water using activated carbons

This study uses rate parameters in pseudo-first-order (PFO) and pseudo-second-order (PSO) equations (k1 and k2qe, respectively) to judge the extent for approaching equilibrium in an adsorption process. Out of fifty-six systems collected from the literature, the adsorption processes with a k2qe value between 0.1 and 0.8 min−1 account for as much as 70% of the total. These are classified as fast processes. This work compares the validity of PFO and PSO equations for the adsorption of phenol, 4-chlorophenol (4-CP), and 2,4-dichlorophenol (2,4-DCP) on activated carbons prepared from pistachio shells at different NaOH/char ratios. The activated carbons, recognized as microporous materials, had a surface area ranging from 939 to 1936 m2/g. Findings show that the adsorption of phenol, 4-CP, and 2,4-DCP on activated carbons had a k2qe value of 0.15–0.58 min−1, reflecting the fast process. Evaluating the operating time by rate parameters revealed that k2qe was 1.6–1.8 times larger than k1. These findings demonstrate the significance of using an appropriate kinetic equation for adsorption process design.