Exploring the gellan gum effect on the catalytic performance of [gellan gum–co-poly(methacrylic acid)]@Ni–Cu composites toward methylene blue reduction

This study investigates the effect of gellan gum (GG) content on the catalytic performance of GG–co-poly(methacrylic acid) hydrogels embedded with Ni–Cu nanoparticles. Composites with 2.5%, 5%, and 7.5% GG were synthesized and evaluated for the reductive degradation of methylene blue (MB) under varying pH, temperature, and initial dye concentration. The composites were characterized by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), Energy-dispersive x-ray spectroscopy (EDX), Scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) surface area analyzer. FTIR confirmed successful GG–PMAA copolymerization and effective complexation of Ni–Cu ions within the hydrogel network. XRD, SEM, and EDX analyses demonstrated that the GM–NC/5 composite exhibits enhanced crystallinity, uniform Ni–Cu nanoparticle dispersion, and optimal metal loading, whereas lower or higher GG contents resulted in less favorable structures. BET/BJH results further revealed that the 5% GG composite possesses the highest surface area (10.26 m2 g−1) and pore volume, while excessive GG loading led to pore collapse and reduced accessibility. Among the tested composites, the 5% GG formulation, gellan gum–co-poly(methacrylic acid) acid based Ni–Cu bimetallic composite (GM–NC/5) exhibited the highest activity (99.74% ± 1.99 MB degradation at pH 9 in 4 min) due to its optimal network structure. Kinetic studies indicated pseudo first order behavior, while thermodynamic analysis using Arrhenius and Eyring equations revealed low activation energies (15.61–19.42 kJ·mol–1), endothermic enthalpies, and negative entropy changes. At lower MB concentrations (3 ppm), GM–NC/5 achieved rapid degradation, removing 97.89% ± 1.95 within 4 min (k = 2.3 min–1), indicating highly efficient catalytic performance. Recyclability tests showed that the 5% GG composite retained 87% ± 2.61 activity after five cycles, outperforming the 2.5% and 7.5% GG formulations (GM–NC/2.5 and GM–NC/7.5). These results demonstrate that composites with optimized GG content are highly efficient, stable, and reusable catalysts for wastewater treatment applications.