Ruthenium deposited onto graphitic carbon modified with boron for the intensified photocatalytic production of benzaldehyde

Abstract

The selective oxidation of added-value aromatic alcohols into aldehydes of high interest via photocatalysis has been postulated as a green and competitive oxidative reaction at mild conditions. This work is focused on the design of a tertiary graphitic carbon nitride (g-C3N4) based photocatalysts competitive for the photocatalytic production of benzaldehyde in an aqueous solution. The polymeric g-C3N4 has been modified in an easy one-pot green synthesis scheme, with the incorporation of boron in the polymeric structure and the deposition of ruthenium nanoparticles. The Ru ratio within 0.5–4% was assessed. The photocatalysts were fully characterized (XRD, FTIR, XPS, N2 isotherms, DRS-UV–visible, and PL) and the photocatalytic activity was assessed in the oxidation of benzyl alcohol to benzaldehyde in an aqueous solution. The incorporation of boron enhanced the selectivity towards benzaldehyde due to enhanced separation charges suggested by the photoluminescence technique; whereas ruthenium improved the reaction rate of the alcohol, affecting negatively the selectivity though. The sample containing 1% of Ru was selected as the optimum in terms of selectivity. The relative contribution of the involved reactive oxidant species was assessed by chemical scavenger tests, highlighting the contribution of the photo-generated holes followed by O2•‾. The analysis of the band’s alignment of the g-C3N4 before the modification with boron and ruthenium supports the enhancement by rising the redox potential of the holes released in the valence band.