Enhancing adsorption of crystal violet dye through simple base modification of leaf adsorbent: Isotherm, kinetics, and regeneration

Abstract

Dimorcarpus longan ssp. malesianus var. Malesianus (Mata Kuching) leaves (MKL) show a strong affinity toward crystal violet (CV), a commonly used industrial dye. Treatment of MKL with aqueous 1.0 M NaOH solution through stirring for 2.0 h, followed by washing and drying, enhances the adsorption of CV onto the modified adsorbent (NaOH-MKL), due to the conversion of acidic functional groups to the corresponding anionic forms leading to stronger Coulombic attractions. The performance of MKL and its modified NaOH-MKL toward CV dye adsorption indicates a strong attraction of both adsorbents. Strong adsorption of CV molecules to MKL and NaOH-MKL is evi-denced by changes in the Fourier transform infrared spectroscopic peaks and scanning electron microscopic images upon interaction with the adsorbate. The Sips isotherm, among the five adsorp-tion isotherm models used in this study, is suitable in explaining the interaction of both adsorbents with CV dye molecules. The maximum adsorption capacity (qmax ) of NaOH-MKL adsorbent toward CV is 391.7 mg g–1 under optimum conditions according to the Sips adsorption isotherm, which is 88% enhancement over the unmodified MKL with qmax of 208.1 mg g–1. Approach of CV dye molecules onto MKL/NaOH-MKL for adsorption is explained by the pseudo-second-order kinetics with an apparent rate constant of 6.108 g mmol–1 min–1, which is 72% increase over MKL. The superior nature of NaOH-MKL would make it an excellent sorbent for the removal of CV dye, which would thus have the potential for extrapolation toward real applications in the treatment of wastewater.