Conjugated polymers decorated lignocellulosic nanocomposites for malachite green contaminated water remediation

Abstract

Various novel conjugated polymer composites were synthesized via in situ chemical oxidative polymerization on lignocellulosic waste, notably Azadirachta indica sawdust. The composites, including Azadirachta indica/polyindole (AIS/PIn), Azadirachta indica/polyaniline (AIS/PAn), Azadirachta indica/polythiophene (AIS/PTh), and Azadirachta indica/polypyrrole (AIS/PPy), were investigated for their porous structure, ease of synthesis, unique adsorptive properties, and adjustable morphology. The synthesized composites were characterized using SEM/EDS, TEM/SAED, XRD, BET, TGA, and FTIR, revealing detailed insights into their structural and morphological features. The potential of these composites as efficient adsorbents for removing malachite green (MG) dye from water was a vital focus of this research. Batch experiments were conducted to assess the impact of various factors on adsorption, such as adsorbent/adsorbate contact time (0–280 min.), adsorbent dosage (0.4–20.0 g/L), initial adsorbate concentration (25–100 ppm), pH (2–13), and temperature (30–60 °C). The results indicate a remarkable removal efficiency of 89.98 % for MG with an initial concentration (Co) of 50 mg/L, achieved within 120 min using 0.4 g/L of AIS/PIn at a pH above 8.3. The Langmuir adsorption isotherm model provided the best fit for the experimental data, with maximum adsorption capacities of 384.61 mg g−1 for AIS/PIn, 344.82 mg g−1 for AIS/PAn, 277.77 mg g−1 for AIS/PTh, and 256.41 mg g−1 for AIS/PPy. This suggests monolayer adsorption. The adsorption kinetics conformed to a pseudo-second-order model, with the process being endothermic, feasible, and associated with positive entropy, thereby underlining its favorability and spontaneity. The desorption studies determined that 0.1 M HCl was the most effective desorbing agent compared to NaOH, NaCl, CH3COOH, and H2O. The spectral and effect of pH analyses suggested that the adsorption mechanisms might involve multiple interactions, prominently including electrostatic interactions, hydrogen bonding, π-π interactions, and n-π interactions. Based on the findings, it is submitted that the conjugated polymer decorated biomass composite adsorbents exhibit reasonable recyclability over multiple cycles, versatility, and potent efficacy as low-cost adsorbents for eliminating MG dye from aqueous systems.