Eco-friendly sunlight driven photocatalytic remediation of water pollutants using N-doped NiO integrated into a guar gum-agar polymeric network.

Hydrogel based photocatalysts with strong photocatalytic and adsorption capacities have promising future in wastewater treatment. Herein, a novel nitrogen doped NiO/guargum agar-agar nanocomposite hydrogel (GGAA@N-NiO) was synthesized via facile co-precipitation and in-situ methods. Characterization using relevant tools confirmed successful inclusion of N-NiO in the hydrogel-matrix. The higher zeta-potential of GGAA@N-NiO (-23.4) than N-NiO (-16.3) confirms the greater stability. The average crystallite size for NiO (7.82 nm) and N-NiO (4.38 nm) was calculated using the Scherrer equation and, NiO (5.7 nm) and N-NiO (2.31 nm) using WH plot. FESEM image, showed particle size of N-NiO 79.4 nm. Band gaps 2.70 eV, 2.75 eV, and 3.03 eV for GGAA@N-NiO, N-NiO, and NiO, respectively, were calculated using Kubelka Munk plots. The lower PL intensity of GGAA@N-NiO indicates a suppressed electron-hole (e/h) recombination rate, which reflects its enhanced photocatalytic activity. GGAA@N-NiO achieved 95.3 % removal of benzyl butyl phthalate (BBP) and 94.6 % removal of para-cresol (PC) within 240 min under optimized conditions (i.e. pH ∼7.0; catalyst-dose: 1.5 g/L with BBP and 1.0 g/L with PC, pollutant-concentration: 20 ppm for BBP and, 50 ppm for PC). The removal followed first-order-kinetics and Langmuir-isotherm, with OH radicals exhibiting a dominant role in the photocatalytic-removal process. GC-MS analysis confirmed the degradation of BBP and PC into safer metabolites. The nanocomposite was reusable over six cycles, demonstrating stability. This study offers cost-effective and highly-efficient approach to developing stable hydrogel-supported photocatalysts for water-remediation.