Radiation-synthesized PVP-CMC/CNT biodegradable hydrogels for efficient dye removal

Methyl orange (MO) is classified as a recalcitrant and refractory xenobiotic, posing a significant threat to ecosystems due to its high toxicity and persistence. This highlights the urgent need for effective waste management. Biodegradable PVP-CMC hydrogel and PVP-CMC/CNT nanocomposite hydrogel were synthesized by copolymerization of carboxymethyl cellulose (CMC) and polyvinylpyrrolidone (PVP) via green gamma irradiation at 30 kGy, and 70:30 PVP: CMC, followed by incorporation of CNTs into the polymer matrix to prepare PVP-CMC/CNT. The biodegradation rates of the hydrogel and nanocomposite hydrogel are evaluated by quantifying weight loss in soil over 16 weeks. The biodegradation rates were 87 and 54.8% for the hydrogel and nanocomposite hydrogel, respectively. TGA shows that incorporating CNTs increases thermal stability and reduces overall PVP-CMC hydrogel breakdown by 30%. BET surface area increased to 5.653 m²/g upon CNT incorporation. The highest removal % was 82.5 and 94.7% at pH = 4, with pHpzc values of 7.9 and 8 for the hydrogel and the nanocomposite hydrogel, respectively. The PVP-CMC/CNT nanocomposite hydrogel achieved a maximum adsorption capacity (q_max) of 216 mg/g, demonstrating competitive performance compared to reported biopolymer-based adsorbents (typically 10-294 mg/g). Kinetic tests showed that the pseudo-second-order model best fit the adsorption process for the hydrogel and nanocomposite hydrogel, with R² values of 0.98, confirming chemisorption as the rate-limiting step. These findings demonstrate the development of a sustainable hydrogel for water purification.