Dual functionality of iron oxide-doped Xanthan Gum Xanthate hydrogel nanocomposite for adsorption and photodegradation of toxic dyes in water

This study investigates the removal of methylene blue (MB) dye from water using a cost-effective, reusable, and efficient iron oxide-doped Xanthan-gum xanthate-based hydrogel nanocomposite (XNH@Fe3O4 NC). The nanocomposite was synthesized by doping optimized Xanthan-gum xanthate-based hydrogel (XNH; synthesised via free radical polymerization method) with Fe3O4 nanoparticles. Four synthesized hydrogel grades (XNH-1, XNH-2, XNH-3, and XNH-4) were evaluated based on their swelling ratio (SR), water retention percentage (%WRR), and point of zero charge (∆pHpzc) to identify the optimal grade for dye adsorption. XNH-3 exhibited the highest SR (268.19 g/g) and %WRR (92.03% at 65 °C) in distilled water, along with a negatively charged surface over a wider pH range, making it the most suitable for adsorption of MB dye. Consequently, XNH-3 was used to synthesise XNH-3@Fe3O4 NCs via the sol-gel method. The selectivity of Fe3O4 nanoparticles (NPs) is attributed to their magnetic properties, which allow for easy separation from the solution using an external magnetic field. Additionally, Fe3O4 NPs exhibit a low band gap between the valence band (VB) and conduction band (CB), facilitating electron transfer, thereby acting as a competent photocatalyst for the degradation of dye. The nanocomposite achieved a maximum MB removal of 97.9 (±1.0) % under optimal conditions i.e. (pH 7, temperature 25 °C, contact time 30 min, adsorbent dose 0.5 g/L and initial MB concentration 100 mg/L). The absorption process followed Langmuir isotherm model with adsorption capacity of 208.33 (±1.76) mg/g. Furthermore, the XNH-3@Fe3O4 NC demonstrated 87.56% degradation of MB dye under visible light photocatalysis.