2 Results and discussion 2.1 FTIR spectra of p(NIPAM-co-MAA) microgels The catalytic activity of Ni-p(NIPAM-co-MAA) and Co-p(NIPAM-co-MAA) hybrid microgels was compared with each other. We also studied the effect of catalyst dosages on the value of the apparent rate constant ( k app) of 4-NP. UV-Visible spectrophotometry was used to investigate the catalytic activity of hybrid microgels for the reduction of 4-NP. FTIR analysis and DLS studies were used for the structural and responsiveness characterization of p(NIPAM-co-MAA) microgels, respectively. Ni and Co nanoparticles were fabricated inside p(NIPAM-co-MAA) microgels by in situ reduction of metallic salts (NiSO 4♶H 2 O, CoCl 2♶H 2 O) in aqueous medium. In this work, we synthesized p(NIPAM-co-MAA) microgels in aqueous medium. Ni and Co nanoparticles fabricated in p(NIPAM-co-MAA) microgels have not been reported yet. (44) for the catalytic reduction of 4-NP. Nickel-poly(acrylic acid) hybrid spherical polyelectrolyte brushes were used by Zhu et al. (25, 41) studied the catalytic reduction of ortho-nitrophenol (2-NP) and 4-NP by using nickel-poly(2-acrylamido-2-methyl-1-propansulfonic acid) and cobalt-poly(2-acrylamido-2-methyl-1-propansulfonic acid) hybrid microgels. (42) used nickel-iron oxide-(3-aminopropyl)triethoxysilane-poly(4-vinylpyridine) hybrid microgels for the catalytic reduction of nitriles. To the best of our knowledge, no researcher has yet studied the catalysis of p-nitrophenol (4-NP) by using Co and Ni nanoparticles fabricated in poly( N-isopropylacrylamide-co-methacrylic acid) hybrid microgels. Hybrid microgels are extensively used as catalysts for the reduction of nitroarenes (4, 25, 41), nitriles (aliphatic and aromatic) (42) and coupling reactions (43). Contrary to this, there are some coinage metal-based nanoparticles easily fix the nanoparticles within microgels. The catalytic applications of nanoparticles of expensive metals such as gold (1, 12), silver (2, 3, 13), platinum (14–16) and palladium (17–20) are mostly studied because they are stable under different environmental conditions and do not oxidize to their oxides easily. They are enormously used in the field of catalysis (1–5), magnetic resonance imaging (6), environmental remediation (7), medicine (8, 9), cosmetics (10) and biosensing (11) due to their quantum size-related properties. Metal nanoparticles have been the subject of much research in recent years. The nickel-based hybrid system was found to be five times more efficient as a catalyst compared to the cobalt-based hybrid system for the reduction of 4-NP to 4-AP in aqueous medium. The value of apparent rate constant of reaction was found to change linearly with catalyst dosage. The catalytic activity of hybrid microgels for the reduction of p-nitrophenol (4-NP) to p-aminophenol (4-AP) was investigated by UV-visible spectrophotometery. DLS studies revealed that the hydrodynamic radius of these microgels increased with the increase in pH of the medium at 25☌. The pH sensitivity of these copolymer microgels was studied using dynamic light scattering technique (DLS). Fourier transform infrared spectroscopy was used to characterize these microgels. Then, nickel and cobalt nanoparticles were fabricated within these microgels by in situ reduction of metal ions using sodium borohydride (NaBH 4) as a reducing agent. In this research work, multi-responsive poly( N-isopropylacrylamide-co-methacrylic acid) copolymer microgels were synthesized via emulsion polymerization in aqueous medium.
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