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

• Published in: Desalination and water treatment 2021-03, Vol.215, p.194-208
• Main Authors: Priyantha, Namal, Romzi, Amal Asheeba, Chan, Chin Mei, Lim, Linda B.L.
• Format: Article
• Language: English
• Subjects: Adsorption isotherm; Base modified leaf adsorbent; Crystal violet cationic dye; Kinetics; Regeneration
• ISSN: 1944-3986; 1944-3986
• DOI: 10.5004/dwt.2021.26758

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 evidenced 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 adsorption 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.