EPR investigations of polymeric and H2O2 -modified C3N4 -based photocatalysts

The C3N4 -based nanopowders prepared by thermal condensation of melamine (MCN) with subsequent thermal etching (MCN-TE) and H2O2 -treatment were investigated by Q- and X-band EPR spectroscopy in dark and upon in situ UVA or visible-light exposure. Lorentzian signal at g = 2.003, more pronounced in the case of the thermally etched material, dominates EPR spectra of MCN and MCN-TE. More complex spectra were found for H2O2 -treated photocatalysts revealing the presence of signals attributed to the radicals produced via H2O2 interaction with C/N sites in the C3N4 polymeric network. The X-band spectra monitored upon in situ irradiation of the C3N4 -based photocatalysts evidenced the intensity growth of the single line at g = 2.0033 indicating the photoinduced generation of electrons in localized paramagnetic states with the Curie dependence on temperature in the temperature range 100–180 K. The response towards UV or visible-light exposure was significantly limited in the case of H2O2 -treated photocatalysts. EPR spin trapping experiments performed in aqueous suspensions demonstrated the formation of HO2[rad] and HO [rad] spin-adducts, and the increased stability of the primary photogenerated O2 javax.xml.bind.JAXBElement@3a251187 – in aprotic media was well documented by the irradiation of the photocatalysts in the dimethylsulfoxide/water mixed solvent. The highest activities in the production of the non-persistent radical species spin-adducts were found for the thermally etched and pristine photocatalysts, confirming the negative effect of H2O2 -treatment

Methacrylated Quinizarin Derivatives for Visible-Light Mediated Photopolymerization: Promising Applications in 3D-Printing Biosourced Materials under LED@405 nm

The high initiating properties of mono- (Q-1Ac) and dimethacrylated (Q-2Ac) quinizarin derivatives under visible-light irradiation are reported here. Associated with various co-initiators, such as iodonium salt (electron acceptor), an amine derivative (electron donor), or thiol cross-linker (H-donor), the quinizarin-derived photosensitizers lead to high conversions by radical photopolymerization in laminate or under air. Mechanisms of photoinitiation were deeply investigated by fluorescence, laser flash photolysis (LFP) and electron paramagnetic resonance (EPR) experiments. The use of soybean oil acrylate (SOA) as biobased monomer leads to highly cross-linked materials under visible-light, with comparable mechanical properties than UV-induced ones previously described in literature. Copolymerization of the photosensitizer (PS) with the polymer matrix not only prevents leakage, but also ensures antiadhesion properties of SOA materials against Staphylococcus aureus (S. aureus) under visible-light activation. Finally, complex 3D biobased structures are successfully obtained by 3D-printing under visible-light irradiation (LED@405 nm), opening opportunities to design photoinduced biosourced materials

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

Four different C 3 N 4 specimens have been prepared, a bulk one (MCN), a thermally etched (MCN-TE), a solid prepared by hydrothermally treating MCN with H 2 O 2 (MCN-H 2 O 2 ) and a polymeric carbon nitride-hydrogen peroxide adduct (MCN-TE-H 2 O 2 ). The principal aim of this work was to correlate the capability of the prepared material to generate reactive oxygen species (ROS), under irradiation, with their photocatalytic activities in terms of conversion and selectivity for partial oxidation reactions. Photoelectrochemical studies revealed that MCN-TE represented the best material in terms of photoconductivity, whereas MCN-H 2 O 2 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 one was MCN-TE-H 2 O 2 . Under solar light irradiation the performances of the powders were generally better than those under UV light. The characterization of the C 3 N 4 -based materials well justified their photocatalytic activity. The pristine C 3 N 4 materials were more active but less selective than those prepared in the presence of H 2 O 2