Eco-Friendly Dye Remediation Using a Rice Husk-Derived Activated Carbon–PAMPS Hydrogel Composite

The persistent discharge of synthetic dyes into water bodies presents a critical environmental challenge due to their toxicity, non-biodegradability, and aesthetic pollution. This study explores an eco-friendly approach to dye remediation using a composite hydrogel synthesized from rice husk-derived activated carbon (RH-AC) embedded within a poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) matrix. Rice husk, an abundant agricultural waste, was converted to activated carbon (AC) through pyrolysis followed by KOH activation, yielding AC with high surface functionality. The material was characterized using attenuated total reflectance infrared spectroscopy (ATR-IR), powder X-ray diffraction (PXRD), Raman spectroscopy, field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HR-TEM), thermogravimetric analysis (TGA), and differential thermal analysis (DTA). The PAMPS/AC hydrogel composite was synthesized via free-radical polymerization. The composite exhibits high adsorption efficiencies for various synthetic dyes over a 24 h period, achieving 87% for Methylene Blue (MB), 86% for Eosin B (EB), and 76% for Rhodamine B (RhB). The high removal performance is attributed to strong π–π stacking interactions, electrostatic attractions, and enhanced molecular diffusion within the hydrogel network. The synergistic effects between three critical independent variables including AMPS wt % (5–15 wt %), RH-AC wt % (5–15 wt %), adsorbent dose (5–20 mg), and dye removal efficiency (%) were statistically studied and optimized. Kinetic models suggest that adsorption follows pseudo-second-order kinetics and Langmuir adsorption isotherms as high regression was obtained (R2-value <0.94). This PAMPS/AC composite offers a sustainable, recyclable, and cost-effective solution for industrial wastewater treatment applications.