Preparation and characterization of a new nanocomposite, Genista Scorpius fibers/Poly (diallyldimethylammonium chloride)/zero valent silver: Application to the catalytic reduction of hazardous azo dyes in water

Biomass residues constitute a source of polymeric fibers, chemicals, biofuels, nanocomposites, etc. Their versatile physico-chemical characteristics and their aptitude to be chemically functionalized justify their employment in several domains. In the present study, Genista Scorpius fibers were used as a starting cellulosic substrate, functionalized with Poly (diallyldimethylammonium chloride), and zero valent silver nanoparticles. Several analytical methods including, SEM, FTIR, XRD, and TGA/DTG were used to analyze the chemical composition, morphological features, crystallinity, and thermal behavior of the studied samples. SEM analysis displayed the wide dispersion of the zero valent silver nanoparticles onto Genista surface. The XRD peaks observed at 2 thetas = 30.8°, 38.5°, and 44.2° confirmed the presence of zero valent silver nanoparticles onto the functionalized fibers surface. Highest residual masses were observed for the functionalized Genista fibers (46.46 %-50.04 %) compared to virgin fibers (17.37 %). The nanocomposites were more thermally stable than the virgin material. The nanocomposites were further investigated, as catalysts, for the catalytic reduction of Eriochrome Black T and Naphthol blue black B in aqueous suspension using sodium borohydride (NaBH₄) as a reducing agent. Several experimental conditions influencing the catalytic reduction including NaBH₄ concentration, initial dyes concentrations, time of reaction, and bath temperature were discussed. Eriochrome and Naphthol solutions were completely decolorized under the following optimum conditions: time = 8 min, pH = 6, NaBH₄ =1 M, C₀ = 40 mg/L, and T = 50 °C. The catalytic degradation of the azo dye solutions was analyzed using, zero-, first- and second-order reaction kinetics. The calculated activation energies were equal to 58.53 kj mol⁻¹ and 57.47 kj mol⁻¹ for Eriochrome and Naphthol solutions, respectively. These small values confirmed the efficiency of the use of the prepared nanocomposites in water purification.