Adsorption isotherms, thermodynamics, and kinetics of activated carbon as adsorbent to water pollutants: a review

Abstract

Water pollutants, such as dyes and heavy metals, which cause various health and environmental problems, challenge researchers to investigate activated carbon-based adsorbents. These adsorbents are obtained from natural sources or waste, so they are environmentally friendly. The literature reveals that the adsorption capacities of activated carbons obtained from experiments, isotherm equations, and kinetic equations are relatively high but vary in value. The abundance of functional groups as active sites and the spread of pores or cavities on the adsorbent surface affect the efficiency of adsorption. This review aims to overview the adsorption isotherms, thermodynamic properties, and kinetic behaviors of several activated carbons from natural sources and waste. The maximum adsorption capacity of the dyes is in the range of 2.0–1169.25 mg∙g–1, while the maximum adsorption capacity of heavy metals is in the range of 0.488–312.5 mg∙g–1. The different adsorption mechanisms, the convenience of adsorption, adsorption energy, the spontaneity of adsorption, and the rate-determining step are described for each type of activated carbon. Therefore, specified information about their performances toward different water pollutants can be evaluated. Moreover, potential improvements in the performance of existing adsorbents can be gained through further research based on the findings of this review.