Copper nanoparticles synthesis in hybrid mesoporous thin films: Controlling oxidation state and catalytic performance through pore chemistry

Abstract

The room temperature synthesis of copper (Cu) nanoparticles (NPs) supported within SiO 2 mesoporous thin films (MTF) modified with either COOH or NH 2 functional groups is reported. The functional groups present in the MTF surface acted as adsorption sites for Cu (II) ions, which were afterwards reduced to Cu NPs in presence of sodium borohydride at room temperature. The oxidation state of the copper NPs, corroborated by X-ray Photoelectron Spectroscopy and Electron Energy Loss Spectroscopy, was strongly dependent on the functional group present in the pores of the MTF and on the number of adsorption/reduction (A/R) cycles applied for NPs loading. Metallic Cu (0) NPs were obtained in MTFs displaying COOH groups applying 10 A/R cycles while NPs with higher oxidation state were as well present after 20 A/R cycles. For MTF functionalized with NH 2 groups the copper is present as Cu (I) and Cu(II) in the NPs but no Cu (0) can be detected. The MTF-Cu(CuOx) composite materials were tested as catalysts for the reduction of 4-nitrophenol in the presence of NaBH 4 . Catalytic activity of composite materials depends on the oxidation state of Cu NPs, being more active those samples containing Cu (0) NPs, synthesized from COOH functionalized MTFs.

Size-Controlled Transformation of Cu2O into Zero Valent Copper within the Matrix of Anion Exchangers via Green Chemical Reduction

“…In order to protect CuNPs against their sticking and oxidation, surface-active agents, such as surfactants, dissolved polymers, and organic ligands (known as capping agents), can be used in aqueous media as dispersants and surface modifiers to yield highly stable, well-dispersed particles [13,16,17]. Another promising strategy concerning the stability of CuNPs is their immobilization on supporting solid materials, both of natural origin (cellulose, cotton, paper, chitosan, carbon active) and synthetic polymers (zeolite, graphene oxide, cation exchangers) [18][19][20][21][22][23].…”

Revisiting carboxylic group functionalization of silica sol–gel materials

“…72 Based on this approach, Bordoni and coworkers employed PRTEA to modify vinyltrimethoxysilane (VTMS) with several thiocarboxylic acids and functionalized SiO 2 SBA-15 mesoporous powders with the carboxylic silanes by postgrafting (Scheme 4). 56,58,[74][75][76][77] Successful modification of VTMS was easily followed from the 1 H-NMR spectra of the crude reaction given the (a) absence of the typical deshielded resonance of vinyl protons at large d (d B 6.5-5.8 ppm) from VTMS and (b) presence of a signal at high fields (d B 0.9 ppm) from the CH 2 bonded to Si after the formation of a thioether bond (Fig. 2).…”