Spectroscopic monitoring of polyurethane-based nanocomposite as a potential catalyst for the reduction of dyes.

In this study, AgNPs-loaded polyurethane-sodium alginate (PU-S/Alg) composite polymers were prepared by precipitation polymerization and in-situ reduction method. Their catalytic potential was evaluated for the reduction of methyl orange (MO), brilliant blue (BB), Rhodamine B (RhB), 4-nitroaniline (4-NA), and 4-nitrophenol (4-NP). Successful preparation of samples was confirmed by UV-Visible spectrophotometry (UV-Visible), Fourier transform infrared (FTIR), and Scanning electron microscopy (SEM) analysis. During the catalytic study, the value of k_app for the reduction of MO in the presence of NaBH₄ and catalyst was found 0.488 min^-1 while, in the presence of NaBH₄ and catalyst alone, were found as 0.9 × 10^-4 and 0.8 × 10^-5 min^-1, respectively which indicates the role of catalyst in making the reaction speedy. The value of k_app for the reduction of BB, RhB, 4-NA, and 4-NP was found as 0.764, 0.475, 0.212 and 0.757 min^-1, respectively. Simultaneous reduction of dyes induced a decreased reaction completion time under the same reaction conditions. A slight increase in the value of k_app for the catalytic reduction of MO was also observed when reactions were performed in the presence of ionic media of different salts such as NaCl, KCl, CaCl_2, and MnCl₂. The rate of reduction of MO was increased with the increase in ionic strength of the medium. However, the presence of SDS (surfactant) in the reaction mixture induced the decreased activity of the catalyst and increased reaction completion time. The same value of k_app for the reduction of MO was observed in the case of freshly prepared and several days old nanocomposite catalyst. These results illustrate the stability and maintained catalytic potential of metal NPs for a prolonged time. Our reported catalyst also showed good potential for the treatment of dyes-polluted textile industry wastewater.