Department of Chemistry

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Author: search.filters.author.Rao, AnishSubject: search.filters.subject.Nanoparticles

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    Revealing the role of electrostatics in gold-nanoparticle-catalyzed reduction of charged substrates
    (ACS, 2017-09) Rao, Anish
    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.
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    Emergence of selectivity in inherently nonselective gold nanoparticles through preferential breaking of interparticle interactions
    (2018-10) Rao, Anish
    We demonstrate a fundamentally unique identification strategy to impart selectivity to a traditionally and inherently nonselective carboxylate-functionalized gold-nanoparticles ([-] AuNPs), without the aid of any analyte specific ligands. The common practice is to use the ability of divalent ions to trigger the aggregation process in a kinetically trapped dispersed solution of [-] AuNPs. Aggregation of NPs being a thermodynamically favourable process will result in a uniform and nonselective turn-off response from most of the strongly binding divalent ions. Our approach is to use the abilities of various divalent ions to break a thermodynamically stable inter-nanoparticle precipitates containing [+] and [-] AuNPs (nanoionic precipitates), as the means of identification. Importantly both [+] and [-] AuNPs, independently, were ‘blind’ in terms of selectivity towards divalent ions. Remarkably, a hybrid-system composed of such nonselective nanoparticles was able to discriminate between the hard-to-distinguish pair of Pb2+ and Cd2+ ions. The rationale is that only the strongest of strongly binding ions will be able to break the interactions between the NP precipitates (thermodynamically stable state) and re-disperse them back in solution (kinetically trapped state). This is in stark contrast with the conventional idea of forming an interaction between NPs and divalent ions, with the help of analyte-specific ligands.