Adsorbents Derived from Plant Sources for Caffeine Removal: Current Research and Future Outlook

Pharmaceutical wastes, due to their recalcitrant nature, are emerging contaminants in wastewater that have been the focus of researchers and scientists. One pollutant of interest is caffeine, which is one of the most detected contaminants in a global context. Although commonly present in beverages such as coffee, caffeine can be harmful to both humans and animals when disposed of in water bodies. Current wastewater treatment approaches not only display ineffective results in removing the mentioned pollutant but also entail high financial costs in applying the treatment technology. Recent studies have revealed the potential of adsorbents derived from plant sources such as husks, fruit peels, and other plant fibers from biomass to effectively reduce caffeine concentrations in wastewater, with a removal efficiency in the range of 8.04 to 171.23 mg/g. Moreover, the adsorption phenomena exhibited a Langmuir isotherm model and pseudo-second-order kinetics. This review paper aims to systematically present and analyze the current literature and prospects of utilizing plant-based adsorbents in addressing the impact of caffeine on the environment. Specifically, the review will focus on the efficiency of said adsorbents in removing caffeine, considering the specific surface area, adsorbent dosage, pH level, maximum adsorption capacity, adsorption isotherms and kinetics, and the predicted optimum conditions for adsorption. The objective is to identify the most suitable adsorbents to be used in wastewater treatment plants. This study will serve as a valuable reference for future research.