Quick catalytic degradation of methylene blue using gellan gum-co-polymethacrylic acid hydrogel supported Ni-Cu bimetallic composite

• Synthesis of new bimetallic Ni-Cu composite hydrogel, [GG-co-PMAA]@Ni-Cu. • [GG-co-PMAA]@Ni-Cu demonstrating superior performance, achieving 99.74% dye removal very quickly under basic conditions. • Reusability tests showed that the bimetallic composites maintained high catalytic activity 87% over five consecutive cycles. • The synergistic effect of Ni and Cu nanoparticles enhancing the electron mobility and active sites for efficient performance. Water contamination, particularly by synthetic dyes, poses significant environmental and health risks. Among these, methylene blue (MB) is a common dye with persistent toxicity and resistance to degradation. In this study, we report the first-time development of a [gellan gum-co-polymethacrylic acid] ([GG-co-PMAA]) hydrogel-supported nickel–copper (Ni-Cu) bimetallic composite for the catalytic degradation of MB in the presence of sodium borohydride (NaBH 4 ). The hydrogel composites were synthesized using a free radical precipitation polymerization (FRPP) method, followed by in situ reduction of nickel (Ni 2+ ) and copper ions (Cu 2+ ) into their metallic forms. Characterization by FTIR, EDX, SEM, XRD, and BET confirmed successful incorporation of bimetallic nanoparticles and enhanced surface properties. The [GG-co-PMAA]@Ni-Cu composite demonstrated ultrafast and highly efficient dye degradation (99.74 % in 4 min at pH 9) , outperforming its monometallic and PMAA only counterparts. The composites followed pseudo-first-order kinetics with temperature dependent Arrhenius behavior, indicating an endothermic process. Thermodynamic analysis confirmed nonspontaneous but catalyst facilitated reduction. The catalyst retained 87 % efficiency after five cycles, proving good reusability. The superior performance is attributed to the synergistic effect of Ni and Cu and the pH responsive, biopolymer based hydrogel matrix, making it a promising and sustainable solution for wastewater treatment.