Gamma Irradiation-Induced Synthesis of Dextrin/N-Vinylpyrrolidone Biohydrogel for High-Efficiency Adsorptive Removal of Nitrofurantoin and Methylene Blue from Aqueous Media

Biomedical pollutants, including pharmaceutical residues such as nitrofurantoin (NF) and medical dyes such as methylene blue (MB), are increasingly detected in surface water and wastewater, posing environmental and health concerns due to their durability and biological activity. In this study, dextrin/N-vinylpyrrolidone (Dex/NVP) biohydrogel was successfully synthesized by Co-60 gamma irradiation and evaluated as a green adsorbent for the removal of NF and MB from aqueous media. The optimized hydrogel, prepared with 5 wt% dextrin at an irradiation dose of 30 kGy, achieved a gel fraction of ≈ 90%. Structural (by FTIR and XRD), morphological(by SEM and AFM), and thermal (by TGA) characterization confirmed the successful formation of a porous, cross-linked hydrogel with a high swelling capacity (780–800%) and good thermal stability. Under the optimum adsorption conditions (pH 3.0, adsorbent dosage 0.05 g, and contact time 420 min), the hydrogel removed approximately 78% of NF and 98% of MB, with maximum Langmuir adsorption capacities of 40.93 and 42.51 mg g⁻¹, respectively. Adsorption kinetics followed the pseudo-second-order model, while the Langmuir isotherm provided the best fit, indicating monolayer adsorption on homogeneous active sites. Frontier molecular orbital analysis further supported the contribution of hydroxyl, carbonyl, and amide functional groups to the adsorption process. These findings demonstrate that the radiation-fabricated Dex/NVP biohydrogel is a sustainable and environmentally friendly adsorbent with promising potential for wastewater treatment applications.