Aquatic plant, Ipomoea aquatica, as a potential low-cost adsorbent for the effective removal of toxic methyl violet 2B dye

Abstract

Abstract Ipomoea aquatica (IA) was investigated for its potential as a low-cost adsorbent to remove toxic methyl violet 2B (MV2B) dye in aqueous solutions. Optimising parameters such as the effects of contact time, medium pH and ionic strength (using NaCl, NaNO3, KCl and KNO3) were investigated. The results indicated that 150 min were sufficient for the adsorption to reach an equilibrium state and no adjustment of pH medium was necessary. Batch adsorption experiments such as adsorption isotherm, thermodynamics and kinetics were investigated and the experimental isotherm data were fitted to six isotherm models, namely Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Redlich-Peterson and Sips, with the latter being the best-fit isotherm model showing maximum adsorption capacity (q max) of 267.9 mg g−1. Thermodynamics studies indicated adsorption of MV2B to be exothermic in nature, occurring spontaneously. The kinetics was best described by the pseudo-second-order model. Regeneration of IA pointed to its reusability, maintaining high adsorption capacity even up until Cycle 5 when treated with acid (HCl) and base (NaOH). Functional groups such as hydroxyl and amine groups which could be involved in the adsorption of MV2B were determined using FTIR spectroscopy, and the point of zero charge of IA was found to be at pH 6.81.

Keywords

• Water spinach adsorbent
• Cationic methyl violet dye
• Adsorption isotherm
• Kinetics
• Thermodynamics
• Regeneration