Smart stimuli responsive pNIPAM-co-AAc@Ag/Au bimetallic hybrids: Tunable catalytic activity by varying Ag/Au molar ratio

We report synthesis of Ag/Au bimetallic nanoparticles within a stimuli-responsive pNIPAM-co-AAc microgel matrix using seed-mediated growth strategy. By systematically varying the Au³⁺ precursor, we obtained a series of nanohybrids (MG-Ag/Au 1–9) with tunable Ag/Au molar ratios. The COO⁻ groups of the microgel facilitated stabilization of Ag/Au bimetallic NPs, enabling colloidal stability of the nanohybrids. Our UV–vis and XRD analysis confirmed formation of heterostructured Ag and Au domains rather than homogeneous alloys. Catalytic activity of these bimetallic nanocomposites was evaluated with a borohydride mediated (BH₄⁻) model reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) which shows a significant trend of gradual increase and then rapid decrease in K_app while gradually decreasing Ag/Au molar ratio. pNIPAM-co-AAc @Ag/Au 6 showed a remarkable K_app of 4.519 min⁻¹, outperforming many previously reported similar bimetallic systems. Furthermore, it showcased increased catalytic efficiency compared to their monometallic counterparts i.e. ∼8.5-fold higher than pNIPAM-co-AAc@Ag and ∼27-fold higher than pNIPAM-co-AAc@Au. In-silico molecular docking studies demonstrated binding energy of −0.57, −0.94 and −1.55 kcal/mol for BH₄⁻-NIPAM, 4-NP-COO^- and 4-NP-NIPAM. This work highlights the importance of bimetallic compositional tuning inside microgel matrix in developing efficient nanocatalysts for future applications.