Removal of methylene blue from water by low-cost activated carbon prepared from tea waste: A study of adsorption isotherm and kinetics

Abstract Three different types of activated carbon were synthesized from tea-waste by chemical activation method using three activating agents - H3PO4 (H-AC), KOH (K-AC) and ZnCl2 (Z-AC) for analyzing the influence of activating agents on the physicochemical and adsorptive properties of materials. Energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectrometer (FT-IR), field emission scanning electron microscopy (FESEM), X-ray diffractometer (XRD), thermogravimetric analyzer (TGA), N2 gas adsorption-desorption analyzer, and point of zero charge (pHPZC) were employed for the characterization of the synthesized materials. Adsorption capacity of H-AC was found to be higher than those of K-AC and Z-AC, and methylene blue (MB) removal efficiency of H-AC was around 98% for the adsorbent dose of 0.15 g/L. The greater MB removal capacity of H-AC might be due its higher surface area and micropore volume than those of K-AC and Z-AC. The experimental data of batch equilibrium studies for H-AC and Z-AC fitted well with Freundlich isotherm model whereas MB sorption onto K-AC followed Langmuir isotherm. The adsorption kinetic data for all adsorbents followed pseudo-second order model. Intraparticle diffusion model indicated the influence of both external surface adsorption and intraparticle diffusion on adsorption mechanism.