Redox Active Polyaniline-Chitosan Supported Nano Silver Composites with Tunable Surface Structure and Catalytic Activity

Surface and interface engineering of heterogeneous catalysts requires an understanding of structure-activity relationships to enhance catalytic activity and selectivity. Herein, we elaborate on the role of (bio)polymer supports on catalytic activity in polyaniline-chitosan nanocomposites (NCs) that contain Ag nanoparticles (Ag@PNI-(x)-CHT). These NCs can be tailored to enhance selectivity in reductive transformations of model dyes: methylene blue (MB) and p-nitrophenol (PNP). Adjusting the composition (x) of the (bio)polymer fraction is shown to regulate the catalyst structure, stability, activity, and selectivity. The findings herein underscore the critical role of chitosan content and surface modification in governing the interaction with the dye to yield improved catalyst performance and selectivity. The greater Langmuir binding affinity (K<inf>L</inf> = ∼68 L mmol⁻¹) and monolayer adsorption capacity (q<inf>m</inf> = 0.63 mmol.g⁻¹) of Ag@PNI-(25)-CHT with MB versus PNP reveal that modification of catalysts with chitosan led to surface accumulation of hydrophilic substrates onto the catalyst. Greater catalyst activity parallels the greater rate constant and values of K<inf>L</inf> between the catalyst with dyes, and higher q<inf>m</inf> values correlate with enhanced catalytic performance. The structure-property relationships reveal a unique reduction mechanism for MB over the PNP dye system, wherein polyaniline serves as the surface-active reduction site.