Adsorption of methylene blue on adsorbents derived from Delonix Regia seed pods and Vigna Subterranea fruit hulls: a kinetic study

Abstract

Kinetics of methylene blue adsorption on adsorbents prepared from Delonix regia seed pods (DRSP) and Vigna subterranea fruit hulls (VSFH) were investigated. Characterization of the adsorbents indicates that the points of zero charge (PZC) of DRSP and VSFH are 5.30 and 4.80 respectively. Optimum removal efficiencies of methylene blue by DRSP and VSFH occurred at pH of 8.00 and 11.00 respectively. For both DRSP and VSFH, equilibrium was attained after 4 hours of agitation time, leading to over 80% removal of methylene blue at ionic strength of 0.4 M and beyond. Among the kinetic models tested, the experimental data fitted well to pseudo-second order model (?² = 0.996 for DRSP and ?² = 0.998 for VSFH), suggesting that the adsorption of methylene blue on DRSP and VSFH involves chemisorption. The study demonstrates that DRSP and VSFH can serve as alternative low-cost adsorbents for removing methylene blue from wastewater.