Mechanochemical hydroquinone regeneration promotes gold salt reduction in sub-stoichiometric conditions of the reducing agent

Author(s)

Xavier, Ismael P. L. ; Lemos, Laura L. ; de Melo, Eduardo C. ; Campos, Eduardo T. ; de Souza, Breno L. ; Faustino, Leandro A. ; Galante, Douglas ; de Oliveira, Paulo F. M.

• Document type: Journal article
• Source: Physical Chemistry Chemical Physics; v. 26, n. 15, p. 9-pg., 2024-03-26.

Abstract

Bottom-up mechanochemical synthesis (BUMS) has been demonstrated to be an efficient approach for the preparation of metal nanoparticles (NPs), protected by surface agents or anchored on solid supports. However, there are limitations, such as precise size and morphological control, due to a lack of knowledge about the mechanically induced processes of NP formation under milling. In this article, we further investigate the BUMS of AuNPs. Using SiO2 as a solid support, we studied the effect of typical reducing agents, namely NaBH4, l-ascorbic acid, and hydroquinone (HQ), on the conversion of a AuIII source. XANES showed that HQ is the strongest reducing agent under our experimental conditions, leading to the quantitative conversion of gold salt in a few minutes. Interestingly, even when HQ was used in sub-stoichiometric amounts, AuIII could be reduced to ratios higher than 85% after two minutes of milling. Investigations into the byproducts by 1H NMR and GC-FID/MS enabled the identification HQ regeneration and the formation of its derivatives. We mainly focused on benzoquinone (BQ), which is the product of the oxidation of HQ as it reduces the gold salt. We could demonstrate that HQ is regenerated from BQ exclusively under milling and acidic conditions. The regenerated HQ and other HQ-chlorinated molecules could then reduce gold-oxidized species, leading to higher conversions and economy of reactants. Our study highlights the intriguing and complex mechanisms of mechanochemical systems, in addition to fostering the atom and energy economy side of mechanochemical means to produce metal nanoparticles. The hydroquinone reducing agent is regenerated during the mechanochemical reduction of gold salt to form metal nanoparticles, and it remains active in the chemical reduction process even when used in sub-stoichiometric conditions. (AU)

• FAPESP's process: 23/01223-5 - Mechanochemistry as a tool in the preparation of multimetallic nanomaterials
• Grantee: Ismael Pinheiro Lucas Xavier
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• FAPESP's process: 22/04604-7 - Plasmonic contributions to N2 and CO2 co-electrolysis
• Grantee: Leandro Augusto Faustino
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 20/14955-6 - Designing the next generation of advanced multicomponent materials through mechanochemical synthesis
• Grantee: Paulo Filho Marques de Oliveira
• Support Opportunities: Research Grants - Young Investigators Grants
• FAPESP's process: 22/03996-9 - Study of milling parameters on the mechanochemical synthesis of Ag nanoparticles
• Grantee: Laura Libório Lemos
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• FAPESP's process: 19/09341-1 - Lithium-sulfur batteries: development of new generation of positive electrodes based on composites of MOFs/sulfur
• Grantee: Breno Luiz de Souza
• Support Opportunities: Scholarships in Brazil - Doctorate