Production of highly effective adsorbent from tea waste, and its adsorption behaviors and characteristics for the removal of Rhodamine B

Abstract

ABSTRACT The use of biowaste as an adsorbent for the removal of contaminants in wastewater with the adsorption process is very environmentally friendly, highly efficient, and economic. For this purpose, the hydrochar of tea waste (HTW) was obtained by hydrothermal treatment of the tea waste (TW), and then the active carbon of tea waste (ACTW) was obtained with the activation of KOH. The SEM, FTIR, BET, and pHzpc analyses were used in the characterisation of the adsorbent. The adsorption experiments were performed on the removal of Rhodamine B (RhB). For the adsorption isotherm studies, the Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models were used, and it was determined that the most suitable model was the Freundlich isotherm with R2 = 0.992 and maximum adsorption capacity was 1666.7 mg/g. For the adsorption kinetic studies, the pseudo-first-order, pseudo-second-order, Elovich, and intra-particle diffusion models were used, and it was determined that the most suitable model was the pseudo-second-order with R2 = 0.999. With the analysis of thermodynamic parameters, it was obtained that the adsorption process was spontaneous (ΔG°≤ −9,025 kJ/mol) and endothermic (ΔH° = 22.447 kJ/mol). Lastly, it was found that the activation energy of the adsorption process was 16.95 kJ/mol, which indicates that it is physical sorption, and the rate constant of adsorption was 0.052 g/mg s. As a result, it was understood that the biomass-based ACTW can be used as an effective adsorbent and is a suitable adsorbent for the removal of RhB.