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Abstract 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.

Diplazium esculentum, an edible fern, was investigated for its potential as a low-cost and effective biosorbent for the removal of toxic Brilliant green (BG) dye. Batch experiments were performed to investigate parameters such as contact time, ionic strength, kinetics, isotherm, and pH on the adsorption capacity. The Pakis adsorbent reached equilibrium within 2 h of contact time with BG dye, and of the five adsorption isotherm models tested, the Sips model gave the best fit with a maximum adsorption capacity (qmax) of 347.5 mg g-1. Kinetics study revealed that the pseudo-second-order model was best fitted to the experimental data, suggesting that chemisorption could be involved. Analyses of adsorption isotherm and kinetics were carried out using linear and nonlinear regressions and compared. ANOVA tests revealed a significant difference between the two methods of analyses for adsorption kinetics. The experimental data of both kinetics and isotherm fitted better when nonlinear regression was used, as compared to the corresponding linear regression analysis. The adsorbent maintained its effective adsorption of BG with varying pH solutions and salt concentrations. Treatment with 1.0 M NaOH of spent Pakis adsorbent could remove >80% BG dye even after five consecutive cycles. High adsorption capacity, relative stability, ability to be regenerated, and reused all lend support to the possible future application of Pakis as a potential low-cost adsorbent in wastewater treatment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Recent years have seen the rise in the use of leaf-based adsorbents to remove pollutants. Not only are leaves low-cost and abundant, but they also contain many compounds giving rise to various functional groups that could promote the adsorption process. This study focuses on the use of leaves of Dimocarpus longan ssp. malesianus var. malesianus, locally known as “mata kuching” and literally translated as “cat’s eyes”, as an adsorbent for the removal of toxic brilliant green (BG) dye. The mata kuching leaves (MKL) reached equilibrium when in contact with BG dye within 30 min. Its adsorption toward BG was not greatly affected by varying pH solutions or salt concentrations. Of the five models tested, the Sips model was the best fit for the adsorption isotherm data, giving a maximum adsorption capacity of 337.9 mg g–1. Adsorption process followed the pseudo-second-order kinetics and intraparticle diffusion was not the rate-controlling step. Regeneration and reuse of spent MKL were possible especially when treated with a base, maintaining almost 80% dye removal at the 5th consecutive cycle. With its many attractive features such as high adsorption capacity, short contact time, ability to be regenerated, relative stability under varying conditions, availability in abundance throughout the year, MKL, therefore, has potential application as a low-cost adsorbent in wastewater treatment. [ABSTRACT FROM AUTHOR]