Chitin-cl-poly (acrylamide-co-guar gum) – Nickel oxide-Zirconium phosphate nanocomposite hydrogel as miniature adsorptional-photocatalysts units for removal of Tetracycline

This study introduces the development and evaluation of a novel Chitin-cl-poly (acrylamide-co-guar gum)-Nickel oxide-Zirconium phosphate nanocomposite hydrogel (Ch-cl-poly (AA-co-GG)-NZHC) for efficient removal of tetracycline from wastewater through combined adsorptional-photocatalytic processes. The synthesis of NiO, NiO-ZrP composite, and the hydrogel composite was carefully optimized, and structural analyses using XRD, FTIR, XPS, FE-SEM, and TEM confirmed their successful formation and morphological features. The Ch-cl-poly (AA-co-GG)-NZHC demonstrated exceptional tetracycline removal efficiency, achieving 41.84 % through adsorption, 86.64 % through adsorption followed by photocatalysis, and an impressive 94.89 % through adsorptional-photocatalysis. Kinetic studies revealed pseudo-first-order degradation behavior with a maximum rate constant of 0.0339 min⁻¹ for the nanocomposite hydrogel. Optimal removal efficiency was achieved at a tetracycline concentration of 10 ppm, catalyst dosage of 40 mg, and pH 9–12. Radical participation was confirmed via scavenging-based experiments, hydroxyl (OH^•) and superoxide (^•O₂⁻) radicals served as dominant factor in degradation process. LC-MS analysis identified multiple degradation pathways, involving dehydroxylation, decarboxylation, and ring-opening reactions, leading to complete mineralization into CO₂ and H₂O. Reusability studies demonstrated the hydrogel's stability, maintaining 75.19 % efficiency after five cycles. The neutral surface charge of the composite at pH 9 favoured tetracycline adsorption and subsequent photocatalytic degradation. These findings highlight the synergistic interaction of hydrogel components and nanomaterials, making the Ch-cl-poly (AA-co-GG)-NZHC a promising candidate for sustainable wastewater treatment and environmental remediation applications, particularly in addressing pharmaceutical contamination in water sources.