Azolla pinnata: An Efficient Low Cost Material for Removal of Methyl Violet 2B by Using Adsorption Method

Abstract

Azolla pinnata (AP), a floating aquatic macrophyte, was studied as a potential adsorbent for the removal of methyl violet (MV) in a batch adsorption system. Surface characterisation, effects of particle size, adsorbent dosage, pH, ionic strength and pre-treatments of adsorbent were carried out. The study of the effects of pH and ionic strength suggested that electronic interaction and hydrophobic–hydrophobic interaction might be the major forces of dye interaction. Pseudo 2nd order kinetic model best-fitted the kinetic data indicating that the adsorption process may be controlled by chemical process. The Weber–Morris and Boyd models were used for describing the diffusion mechanism which showed that intraparticle diffusion was not the rate limiting step, and film diffusion or in combination of other mechanisms might be in control. Isotherm modelling showed that the Langmuir model best-fitted the experimental data with q m of 194.2 mg g−1 at 25 °C and 323.4 mg g−1 at 65 °C. Thermodynamic studies showed that the adsorption process is endothermic, spontaneous and with significant change to the internal structure of adsorbent. The estimated activation energy by Arrhenius equation is 54.8 kJ mol−1, which indicates that the adsorption process may be controlled by chemical process. Adsorbent regenerated using NaOH displayed retention of high adsorption capability almost similar to fresh adsorbent even after five consecutive cycles. Ability to regenerate coupled with good adsorption capability suggests that AP has great potential to be utilised as a low-cost adsorbent for the removal of MV in real life application.