Highly ordered Periodic Mesoporous Organosilica material containing the ionic 4,4-bipyridinium group and decorated with palladium nanoparticles: A proposal for nanoreactor

Abstract

A Periodic Mesoporous Organosilica (PMO) containing the cationic 4,4-bipyridinium group, presenting 0.25 mmol g⁻¹ that corresponds to 11.5 w/w%, was successfully prepared. This material was designed to have the ionic group acting as anchoring agent of PdCl₄^2- anion complex, in a much lower amount than the available cationic sites (3 and 15 molar%). Subsequently, the palladium complex was in situ reduced to obtain stabilized palladium nanoparticles (PdNP). The ensemble of characterization results showed that the PMO material walls have a cylindrical morphology with hexagonal packing, generating well-ordered pores with a narrow size distribution and high surface area, even after being decorated with PdNP. This material is a candidate to be an efficient nanoreactor considering that it contains spatial uniformity in its chemical sites and confined environment. Aiming to evaluate the availability of palladium sites, the material was used as a catalyst in the reduction of p-nitrophenol model reaction. Although the catalyst of the present study has a comparable activity with other already reported systems, it presents the impressive lowest molar palladium/p-nitrophenol ratio found in literature.