Application of Microgel-Based Copper Oxide Nanocomposites in Catalytic Reduction of Congo Red

Abstract

Congo Red (CR) is a synthetic azo dye widely used in the textile industry because of its strong coloring properties. Despite its industrial importance, it offers serious environmental challenges due to poor biodegradability and potential toxicity. The dye can persist in aquatic ecosystems, posing risks to living organisms. This persistence and toxicity highlight the need for safer alternatives and better management practices. In the present research work, the catalytic performance of a previously reported microgel-based copper oxide (M@CuO) nanocomposite was evaluated for the reduction of Congo Red dye in aqueous medium using sodium borohydride (NaBH4) as a reducing agent. The nanocomposite, consisting of CuO nanoparticles uniformly embedded within a quater polymeric microgel matrix (based on N,N-dimethylacrylamide, styrene, N-hydroxymethylacrylamide, and methacrylic acid as monomers), provides a high surface area and improved dispersion of active catalytic sites. Further, the kinetics of the reduction reactions have been studied using ultraviolet–visible spectroscopy. M@CuO nanocomposite with NaBH4 showed better catalytic efficiency, reaching 92.11% reduction of CR dye with the corresponding apparent rate constant of 11.9 × 10-2 min?¹.

Introduction

The text investigates the catalytic reduction of Congo Red (CR) dye, a persistent and toxic azo dye, using a microgel-stabilized copper oxide (M@CuO) nanocomposite. CR is chemically stable and resistant to biodegradation, posing environmental and health hazards. Traditional dye-removal methods like adsorption, membrane separation, and advanced oxidation have limitations, while nanocatalytic approaches offer rapid, efficient, and cost-effective alternatives.

The M@CuO nanocomposite is synthesized via a hydrothermal method, incorporating CuO nanoparticles into a crosslinked polymer microgel network. This structure prevents nanoparticle aggregation, enhances dispersion, and improves catalytic activity. In the presence of sodium borohydride (NaBH?) as a reducing agent, the nanocomposite facilitates electron transfer from BH?? ions to CR molecules, breaking azo bonds and decolorizing the dye.

Catalytic experiments demonstrate that increasing either the amount of nanocomposite or NaBH? concentration improves reduction efficiency. Using 8–12 mg of M@CuO with 0.2 mL of NaBH?, CR reduction ranged from 59% to 87.5% in 21 minutes. With 0.2–0.4 mL of NaBH? and 8 mg of catalyst, reduction increased from 59% to 92% in the same time. Kinetic studies indicate that the reaction follows pseudo-first-order kinetics, with higher catalyst or reducing-agent concentrations accelerating the process.

Overall, the study shows that microgel-stabilized CuO nanocomposites are effective, stable, and potentially reusable catalysts for rapid degradation of dye-contaminated wastewater.

Conclusion

This research paper demonstrates that the microgel-based copper oxide (M@CuO) nanocomposite is an efficient and robust catalyst for the reduction of cango red dye in aqueous media using sodium borohydride (NaBH4). The polymeric microgel matrix effectively stabilizes the CuO nanoparticles, providing high surface area and enhanced dispersion of active sites, which facilitates rapid electron transfer from BH?? ions to CR molecules. Catalytic tests revealed that increasing either the amount of nanocomposite or the concentration of NaBH4 significantly improves the cango red dye reduction efficiency, achieving up to 92.11% decolorization within 21 minutes, with a corresponding apparent rate constant of 11.9 × 10-2 min?¹. The M@CuO nanocomposite showed strong catalytic activity for the reduction of CR dye using NaBH4. Increasing either the amount of nanocomposite or the concentration of NaBH4 improved the reduction efficiency and reaction rate. The reaction followed pseudo-first-order kinetics, and the apparent rate constant increased with higher catalyst and reducing agent amounts. Overall, the M@CuO nanocomposite demonstrated good catalytic performance and potential for wastewater treatment applications.

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Copyright

Copyright © 2026 Anmol Kumar, Shubhangi Pandey , Krishna Kumar, Kranthikumar Tungala. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.