Revealing the Role of Electrostatics in Gold-Nanoparticle-Catalyzed Reduction of Charged Substrates

The potency of electrostatic effects arising from nanoparticle (NP) surface in Au-NP-catalyzed reduction of charged substrates are presented. The electrostatic potential around Au NPs is controlled by varying the nature of ligands and ionic strength of the medium. Favorable interactions arising from the attraction between oppositely charged Au NP and substrates results in the channeling of substrates to the NP surface, which in turn enhances the catalytic reduction. The positively charged ([+]) Au NP outperformed other NP systems despite having comparable or even lower surface area for adsorption, proving the exclusivity of electrostatics in catalysis. At least an order of magnitude higher concentration of negatively charged ([−]) Au NP is required to compete with the catalytic activity of [+] Au NP

Regulation of Interparticle Forces Reveals Controlled Aggregation in Charged Nanoparticles

The ability to control interparticle forces not only improves the existing nanoparticle (NP) functionalities but paves the way for newer properties as well. A proof of concept in this direction is presented here, wherein the regulation of interparticle forcesrevealing controlled aggregationhas been successfully translated into the trapping and scavenging of toxic ions. A perfect balance between the attractive and repulsive forces is achieved by tuning the [+] and [−] ligands on the surface of heterogeneously charged metal NPs. The NP–ion aggregates are stable for ∼2 days, with a visible color change (Δλ_max = 12–15 nm), which makes them available for scavenging from the site of action. The incorporation of “<i>potent</i>” forces like repulsions, rather than a mere dilution of attractive forces, is necessary to ensure the formation of controlled aggregates. The net surface charge of NPs is conveniently modified to trap ions irrespective of their charge and binding strength. More importantly, the regulation of interparticle forces imparts a new function of selectivity toward trapping of toxic ions in a carboxylate functionalized NP system. Thus, the present work introduces a conceptually unprecedented approach to impart long-term stability (∼2 days) to NP–ion aggregates by controlling the interparticle forces