Authors: Cássio R. A. do Prado | Matheus Henrique de Oliveira Pessoa | Lucas da Silva dos Santos | Aline da Silva Xavier da Cruz | Luı́s R. Dinelli | André L. Bogado
Source: ACS Omega (article, 2024-06-14)
Field: Materials Science — Electronic, Optical and Magnetic Materials

The Self-Assembly of Cationic Metal Complexes on Gold Nanoparticle Surface This work aims to study the interaction between cationic metal complexes (M <i><sup>z</sup></i> <sup>+</sup>) and gold nanoparticles (AuNPs <i><sup>z-</sup></i> ). The M <i><sup>z</sup></i> <sup>+</sup> complexes were chosen from previous works described in the literature and were synthesized as defined. For example, they are as follows: <b>1</b> = [RuCl(dppb)(bipy)(py)](PF<sub>6</sub>); <b>2</b> = [RuCl(dppb)(bipy)(vpy)](PF<sub>6</sub>); <b>3</b> = [RuCl(dppb)(bipy)(mepy)](PF<sub>6</sub>); <b>4</b> = [RuCl(dppb)(bipy)(<i>t</i>bpy)](PF<sub>6</sub>); <b>5</b> = [RuCl<sub>2</sub>(dppb)(bipy)](PF<sub>6</sub>); <b>6</b> = [Fe(bipy)<sub>3</sub>]Cl<sub>2</sub>; <b>7</b> = [Ru(bipy)<sub>3</sub>](PF<sub>6</sub>)<sub>2</sub>; <b>8</b> = [TPyP{RuCl(dppb)(bipy)}<sub>4</sub>](PF<sub>6</sub>)<sub>4</sub>; and <b>9</b> = [RuCl(<i>p</i>-cymene)(Di<i>i</i>pmp)](PF<sub>6</sub>). The interactions between M <i><sup>z</sup></i> <sup>+</sup> and AuNPs <i><sup>z-</sup></i> were carried out using conductometry and UV-vis spectroscopy. These experiments allowed determination of kinetic parameters, revealing three different steps in the interaction process: induction time, flocculation, and agglomeration. The self-assembly between M <i><sup>z</sup></i> <sup>+</sup> and AuNPs <sup><i>z</i>-</sup> was investigated using three different models of binding site, namely, Langmuir or direct plot, Benesi-Hildebrand, and Scatchard. These models provide the fraction of total binding sites occupied (θ), the formation constant (<i>K</i> <sub>f</sub>), which is dependent on the temperature and geometric structure of each group of M <i><sup>z</sup></i> <sup>+</sup>, and the Gibbs free energy of reaction (Δ<i>G</i> <sub><i>r</i></sub> ), which was negative for each pair of M <i><sup>z</sup></i> <sup>+</sup> and AuNPs <i><sup>z-</sup></i> , revealing a spontaneous agglomeration process. The Hill coefficient (<i>n</i>) was 1 for almost all complexes, indicating that agglomeration is an independent process, except for <b>5</b>, where <i>n</i> = 2, suggesting a positive propensity to bind onto the AuNPs <i><sup>z-</sup></i> surface. The models have confirmed a noncovalent interaction between these species. The relative error in site binding does not show any variation with changes in the temperature, but a fine-tuning of the <i>n</i> value to 1.00 was observed with the increase of the temperature. Finally, the reduction reaction of the 4-nitrophenolate anion (4-NP<sup>-</sup>) by NaBH<sub>4</sub> catalyzed by AuNPs <i><sup>z-</sup></i> was used in the presence of M <i><sup>z</sup></i> <sup>+</sup> as an evaluation test to show how the M <i><sup>z</sup></i> <sup>+</sup> species will disturb the 4-NP<sup>-</sup> binding site on the surface of gold nanoparticles. Cationic polymerization ; Nanoparticle ; Metal ; Colloidal gold ; Nanotechnology ; Materials science ; Metallurgy ; Polymer chemistry Gold and Silver Nanoparticles Synthesis and Applications ; Nanomaterials for catalytic reactions ; Nanocluster Synthesis and Applications