MnO₂ and MnO₂ blended with 1 and 2 weight percent of activated carbon (AC), MnO₂/AC1 and MnO₂/AC2 were synthesized through the sol–gel method. The pure chitosan (CS) films were cast in the form of films. Similarly, 5 weight% of each MnO₂, AC, MnO₂/AC1 and MnO₂/AC2 was intermingled with the CS to produce different films, such as CS-AC, CS-MnO₂, CS-MnO₂/AC1 and CS-MnO₂/AC2. Zero-valent Co NPs were then supported on these films through the chemical reduction method and expressed as CS@Co, CS-AC@Co, CS-MnO₂@Co, CS-MnO₂/AC1@Co and CS-MnO₂/AC2@Co NPs. All the catalysts were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques. The synthesized catalysts were used as a dip catalyst against the hydrogenation of 4-nitrophenol (4NP), and for the degradation of methyl orange (MO) and Congo red (CR) dyes. The k_app and R² values were deduced from pseudo-first-order kinetics for 4NP and MO and zero-order kinetics for CR dye. The k_app values of CS-AC@Co and CS-MnO₂/AC1@Co NPs for 4NP hydrogenation were higher than those for any other member of the series, at 1.14 × 10⁻¹ and 1.56 × 10⁻¹ min⁻¹ respectively. Similarly, the rate of CR degradation was highest with CS-AC@Co. The R² values for 4NP, MO and CR dyes were above 0.9, which indicated that the application of pseudo-first- and zero-order models were appropriate for this study. Furthermore, the antibacterial activity of all the catalysts was evaluated against Pseudomonas aeruginosa and Escherichia coli. The CS-AC@Co NPs exhibited the highest zone of inhibition compared to other catalysts against P. aeruginosa, while all the catalysts were inactive against E. coli. This study reveals that the catalyst can be used for the degradation of other pollutants and for microbial inhibition.

The development of a solid substrate for the support and stabilization of zero-valent metal nanoparticles (NPs) is the heart of the catalyst system. In the current embodiment, we have prepared solid support comprise of alginate-coated cellulose filter paper (Alg/FP) for the synthesis and stabilization of Co nanoparticles (NPs) named as Alg/FP@Co NPs. Furthermore, Alginate polymer was blended with 1 and 2 weight percent of CoNi NPs to make Alg-CoNi1/FP and Alg-CoNi2/FP, respectively. All these stabilizing matrixes were used as dip-catalyst for the degradation of azo dyes and reduction of 4-nitrophenol (4NP). The effect of initial dye concentration, amount of NaBH₄, and catalyst dosage was assessed for the degradation of Congo red (CR) dye by using Alg-CoNi2/FP@Co NPs. Results indicated that the highest k_app value (3.63 × 10⁻¹ min⁻¹) was exhibited by Alg-CoNi2/FP@Co NPs and lowest by Alg/FP@Co NPs against the discoloration of CR dye. Furthermore, it was concluded that Alg-CoNi2/FP@Co NPs exhibited strong catalyst activity against CR, and methyl orange dye (MO) degradation as well as 4NP reduction. Antibacterial activity of the prepared composites was also investigated and the highest l activity was shown by Alg-CoNi2/FP@Co NPs, which inhibit 2.5 cm zone of bacteria compared to other catalysts.