Photoelectrochemical and EPR features of polymeric C3N4 and O-modified C3N4 employed for selective photocatalytic oxidation of alcohols to aldehydes

Abstract

Four different C3N4 specimens have been prepared, a bulk one (MCN), a thermally etched (MCN-TE), a solid prepared by hydrothermally treating MCN with H2O2 (MCN-H2O2) and a polymeric carbon nitride-hydrogen peroxide adduct (MCN-TE-H2O2). Photoelectrochemical studies revealed that MCN-TE represented the best material in terms of band gap energy and photoconductivity, 2 whereas MCN-H2O2 was defective and evidenced a poor mobility of carriers. EPR studies showed a maximum generation of reactive oxygen species irradiating the MCN-TE sample. The photocatalytic activity of these materials in the selective oxidation of three different alcohols to the corresponding aldehydes, both under UV and natural solar light, showed that the highest conversion was obtained in the presence of the MCN-TE sample, whereas the most selective was MCN-TE-H2O2. Under solar light irradiation the performances of the powders were generally better than those carried under UV light. The characterization of the C3N4-based materials well justified their photocatalytic activity, where the pristine C3N4 materials were more active but less selective than those prepared in the presence of H2O2.

Effect of Substituents on Partial Photocatalytic Oxidation of Aromatic Alcohols Assisted by Polymeric C3N4

“…[35] Moreover, the 1 H-13 C CPMAS and 1 H, 13 C MAS solid state NMR data suggested the formation of hydrogen bonds between NHx moieties and H2O2, and TPD-MS measurements confirmed the evolution of molecular O2 while heating the PCN-H2O2 adduct in an inert atmosphere indicating on the decomposition of hydrogen peroxide contained in the sample. The EPR study reported by Marcì et al [37] showed a signal at about 2.02 g-value earlier assigned to peroxo groups in titanium silicalite, [38] additionally confirming the presence of bonded H2O2 in the PCN-H2O2 material. Henceforth, based on these experimental results a theoretical model demonstrating that the H2O2 in TEO is bonded to the non-condensed carbon nitride species by strong hydrogen bonding was proposed.…”

Modification of Graphitic Carbon Nitride with Hydrogen Peroxide

“…One of the procedures used for the GCN doping with oxygen is the formation of oxygen functional groups by the treatment of already prepared GCN with H 2 O 2 [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. Hydrogen peroxide was also hypothesized to create some defects in the GCN structure [ 25 ]. The treatment with H 2 O 2 is easy but interpretation of the results is not unambiguous.…”

“…The treatment with H 2 O 2 is easy but interpretation of the results is not unambiguous. Oxygen functional groups, such as N-O [ 22 ] and N-C-O [ 22 , 24 , 25 , 26 ], were supposed to be formed in the GCN structure. Other authors observed the formation of C-O-C [ 23 ] and C-OH groups [ 23 , 27 ] as well.…”

A 3D Hierarchical Pancake-Like Porous Carbon Nitride for Highly Enhanced Visible-Light Photocatalytic H2 Evolution

“…Compared with BCN, the PPCN edge shows apparent blue shift, indicating the increase in band gap of semiconductors caused by the quantum confinement effect. The bandgaps for PPCN and BCN were 2.97 and 2.80 eV according to the Kubelka-Munk function [61] (Figure 4b). Consequently, the enlarged bandgap of PPCN would endow the photo-induced electrons and holes with relatively stronger redox abilities toward photocatalytic reactions.…”