Utilization of citric acid functionalized lignocellulosic biomass as a novel adsorbent for efficient removal of cationic dyes in single and multicomponent systems

Pennisetum glaucum (PG) is commonly known as “pearl millet”. The large amount of lignocelluloses biomass leftover from its harvest was used to make a green adsorbent that can substitute for other, more expensive adsorbents for water treatment. In this report, a novel citric acid (CA)—grafted PG based adsorbent was developed and employed for the efficient adsorption of three cationic dyes Crystal Violet (CV), Fuchsin Basic (FB), and Methylene Blue (MB) from their single and multicomponent systems. The effects of adsorption factors like pH, adsorbent dosage, contact time, and initial concentration of dye solution were studied, and the outcomes indicate that the current adsorbent is very efficient for the removal of cationic dye at neutral pH. Regression analysis revealed that the experimental data was well-suited to the second-order polynomial model with a coefficient of correlation (R²) value of 0.98 and a high Fisher F-value. The signal-to-noise ratio values i.e., 28.90 (CV), 32.75 (FB), and 34.79 (MB) indicate an adequate signal. The p-values for the lack of fit (0.4011 for CV, 0.4631 for FB, and 0.5728 for MB) confirmed the validity of the used models. Pseudo—2nd order and Langmuir isotherm models were the most compatible with the experimental results, giving chemisorptions and monolayer type adsorption with good values of maximum monolayer adsorption efficiency of 279.33, 135.68, and 133.57 mg/g for CV, FB, and MB dyes, respectively. The thermodynamic studies indicate that the negative values of ΔH (kJ/mol)—16.19 (CV),—23.15 (FB) and—13.87 (MB) show the exothermic adsorption process and the negative value of ΔS (J/molK)—20.89,—48.55,—31.22 for CV, FB and MB dyes indicated that the degree of randomness at the adsorbate-adsorbent interface decreased during adsorption. The cooperative and competitive effects of dyes in multicomponent solutions were studied using the modified Langmuir adsorption isotherm model. The outcome of this study indicates the competitive effect of counter adsorbates on the target dye, and this dye adsorption behavior was deeply explored by adsorption mechanisms. The adsorbent could be regenerated using acetone and hot water solution for up to five adsorption–desorption cycles. The synthesized CA—PG adsorbent has advantages such as ease of synthesis, cost-effectiveness, and being environmentally benign.