فهرست نشریات علمی دسترسی آزاد ایران

The present work investigates the adsorption kinetics and pH-responsive behaviour of malachite green (MG) dye onto a novel pectin/poly(N-isopropylacrylamide-co-acrylic acid) nano-hydrogel synthesized via free-radical copolymerization. The nano-hydrogel was characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA), and BET surface area measurements. Batch adsorption experiments were conducted to evaluate the effects of adsorbent dosage (0.006–0.06 g), contact time (1–150 min), and solution pH (2–10) on MG removal efficiency. The optimum adsorbent weight was found to be 0.008 g, yielding an adsorption capacity of 596.04 mg/g with 95.37% removal efficiency. Kinetic analysis revealed that the pseudo-second-order model provided the best fit (R² ≈ 1.000; RMSE = 0.89 mg/g) with a calculated equilibrium capacity of 605.13 mg/g, suggesting chemisorption as the rate-controlling mechanism. The Weber–Morris intraparticle diffusion model indicated a two-stage process involving rapid surface adsorption followed by gradual pore diffusion. The point of zero charge (pHPZC) was determined at pH 4.2, explaining the enhanced adsorption capacity observed at higher pH values where the surface acquires a net negative charge. MG adsorption increased from 515.21 mg/g at pH 2 to 608.96 mg/g at pH 10, confirming electrostatic attraction as a dominant mechanism. Regeneration studies demonstrated that the nano-hydrogel retained 87.8% of its initial adsorption capacity after five adsorption–desorption cycles using 0.1 M HCl/50% ethanol eluent. Furthermore, the adsorbent maintained >79% removal efficiency in simulated industrial wastewater containing competing ions and organic co-contaminants.