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Three plant-based materials, namely water lettuce (WL), tarap peel (TP) and cempedak peel (CP), were used to investigate their potentials as adsorbents using acid blue 25 (AB25) dye as a model for acidic dye. The adsorbents were characterised using Fourier transform infrared spectroscopy, X-ray fluorescence and scanning electron microscope. Batch experiments involving parameters such as pH, temperature, contact time, and initial dye concentration were done to investigate the optimal conditions for the adsorption of AB25 onto the adsorbents. Thermodynamics study showed that the uptake of AB25 by the three adsorbents was feasible and endothermic in nature. Both the Langmuir and Freundlich isotherm models can be used to describe the adsorption process of AB25 onto WL and CP while pseudo-second-order fitted the kinetics data, suggesting that chemisorptions were majorly involved. The use of 0.1 M of NaOH showed the best results in regenerating of the WL, TP and CP's adsorption ability after AB25 treatment.

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A B S T R A C TPistia stratiotes L. (water lettuce or WL) was investigated for its potential as an effective low-cost biosorbent for the removal of methyl violet 2B (MV). Equilibrium isotherm for the adsorption of MV, fitted using six different isotherm models followed by error analyses, indicates that the maximum biosorption capacity (q max ) is 0.68 mmol g −1 (267.6 mg g −1 ) and that both the Langmuir and Sips isotherm models lead to good correlation with experimental data. Investigation on effects of pH, ionic strengths, and pre-treatment of the biosorbent on the extent of biosorption indicates the effect of these parameters on MV-biosorbent interaction. Kinetics of the interaction of MV and the biosorbent is fast with more than 50% dye being removed and follows the pseudo-second-order model.