Successful immobilization of lanthanides doped TiO2 on inert foam for repeatable hydrogen generation from aqueous ammonia

We describe the successful possibility of the immobilization of a photocatalyst on foam, which is beneficial from a practical point of view. An immobilized photocatalyst is possible for use in a continuous experiment and can be easily separated from the reactor after the reaction concludes. Parent TiO2, La/TiO2, and Nd/TiO2 photocatalysts (containing 0.1 wt.% of lanthanide) were prepared by the sol-gel method and immobilized on Al2O3/SiO2 foam (VUKOPOR A) by the dip-coating method. The photocatalysts were investigated for the photocatalytic hydrogen generation from an aqueous ammonia solution under UVA light (365 nm). The evolution of hydrogen was compared with photolysis, which was limited to zero. The higher hydrogen generation was observed in the presence of 0.1 wt.% La/TiO2 than in 0.1 wt.% Nd/TiO2. This is, besides other things, related to the higher level of the conduction band, which was observed for 0.1 wt.% La/TiO2. The higher conduction band's position is more effective for hydrogen production from ammonia decomposition.Web of Science135art. no. 125

Investigation of catalytic activation of peroxydisulfate on cu-doped mesoporous silica-based particles (Cu-BMS) for efficient degradation of methylene blue

The Cu-doped mesoporous silica-based particles (Cu-BMS) were prepared using an evaporation-induced self-assembly sol-gel procedure as a heterogeneous catalyst for the activation of peroxydisulfate (PDS). The formation of well-organized mesoporous structures with amorphous nature and high surface area of 286 m²/g was demonstrated. The catalytic activity of Cu-BMS in the degradation of Methylene Blue (MB) and the effects of operating parameters, including Cu-BMS dosage, initial PDS amount, initial MB concentration, temperature and initial pH, were investigated in details. The Cu-BMS demonstrated a remarkable catalytic activity (93.5% degradation efficiency within 60 min) and good stability

Graphitic carbon nitride for photocatalytic air treatment

Graphitic carbon nitride (g-C3N4) is a conjugated polymer, which recently drew a lot of attention as a metal-free and UV and visible light responsive photocatalyst in the field of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability and earth-abundant nature. In the present work, bulk g-C(3)N(4)was synthesized by thermal decomposition of melamine. This material was further exfoliated by thermal treatment. S-doped samples were prepared from thiourea or further treatment of exfoliated g-C(3)N(4)by mesylchloride. Synthesized materials were applied for photocatalytic removal of air pollutants (acetaldehyde and NOx) according to the ISO 22197 and ISO 22197-1 methodology. The efficiency of acetaldehyde removal under UV irradiation was negligible for all g-C(3)N(4)samples. This can be explained by the fact that g-C(3)N(4)under irradiation does not directly form hydroxyl radicals, which are the primary oxidation species in acetaldehyde oxidation. It was proved by electron paramagnetic resonance (EPR) spectroscopy that the dominant species formed on the irradiated surface of g-C(3)N(4)was the superoxide radical. Its production was responsible for a very high NO(x)removal efficiency not only under UV irradiation (which was comparable with that of TiO2), but also under visible irradiation.Web of Science1313art. no. 303

Investigation of catalytic activation of peroxydisulfate on cu-doped mesoporous silica-based particles (Cu-BMS) for efficient degradation of methylene blue

The Cu-doped mesoporous silica-based particles (Cu-BMS) were prepared using an evaporation-induced self-assembly sol-gel procedure as a heterogeneous catalyst for the activation of peroxydisulfate (PDS). The formation of well-organized mesoporous structures with amorphous nature and high surface area of 286 m2/g was demonstrated. The catalytic activity of Cu-BMS in the degradation of Methylene Blue (MB) and the effects of operating parameters, including Cu-BMS dosage, initial PDS amount, initial MB concentration, temperature and initial pH, were investigated in details. The Cu-BMS demonstrated a remarkable catalytic activity (93.5% degradation efficiency within 60 min) and good stability.Alexander Dubček University of Trenčín; Centre for Functional and Surface Functionalized Glass; Vedecká Grantová Agentúra MŠVVaŠ SR a SAV, VEGA, (1/0064/21); Horizon 2020, (739566); Univerzita Tomáše Bati ve Zlíně, UTBEuropean Union [739566]; Scientific Grant Agency of the Slovak Republic [VEGA 1/0064/21

Radical Intermediates in Photoinduced Reactions on TiO2 (An EPR Spin Trapping Study)

The radical intermediates formed upon UVA irradiation of titanium dioxide suspensions in aqueous and non-aqueous environments were investigated applying the EPR spin trapping technique. The results showed that the generation of reactive species and their consecutive reactions are influenced by the solvent properties (e.g., polarity, solubility of molecular oxygen, rate constant for the reaction of hydroxyl radicals with the solvent). The formation of hydroxyl radicals, evidenced as the corresponding spin-adducts, dominated in the irradiated TiO2 aqueous suspensions. The addition of 17O-enriched water caused changes in the EPR spectra reflecting the interaction of an unpaired electron with the 17O nucleus. The photoexcitation of TiO2 in non-aqueous solvents (dimethylsulfoxide, acetonitrile, methanol and ethanol) in the presence of 5,5-dimethyl-1-pyrroline N-oxide spin trap displayed a stabilization of the superoxide radical anions generated via electron transfer reaction to molecular oxygen, and various oxygen- and carbon-centered radicals from the solvents were generated. The character and origin of the carbon-centered spin-adducts was confirmed using nitroso spin trapping agents

Fused-Ring Derivatives of Quinoxalines: Spectroscopic Characterization and Photoinduced Processes Investigated by EPR Spin Trapping Technique

10-Ethyl-7-oxo-7,10-dihydropyrido[2,3-f]quinoxaline derivatives, synthesized as promising biologically/photobiologically active compounds were characterized by UV/vis, FT-IR and fluorescent spectroscopy. Photoinduced processes of these derivatives were studied by EPR spectroscopy, monitoring in situ the generation of reactive intermediates upon UVA (λmax = 365 nm) irradiation. The formation of reactive oxygen species and further oxygen- and carbon-centered radical intermediates was detected and possible reaction routes were suggested. To quantify the investigated processes, the quantum yields of the superoxide radical anion spin-adduct and 4-oxo-2,2,6,6-tetramethylpiperidine N-oxyl generation were determined, reflecting the activation of molecular oxygen by the excited state of the quinoxaline derivative

EPR Investigations of G-C3N4/TiO2 Nanocomposites

The g-C3N4/TiO2 nanopowders prepared by the annealing of melamine and TiO2 P25 at 550 °C were investigated under dark and upon UV or visible-light photoactivation using X- and Q-band electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra of powders monitored at room temperature and 100 K showed the impact of the initial loading ratio of melamine/TiO2 on the character of paramagnetic centers observed. For the photocatalysts synthesized using a lower titania content, the paramagnetic signals characteristic for the g-C3N4/TiO2 nanocomposites were already found before exposure. The samples annealed using the higher TiO2 loading revealed the photoinduced generation of paramagnetic nitrogen bulk centers (g-tensor components g1 = 2.005, g2 = 2.004, g3 = 2.003 and hyperfine couplings from the nitrogen A1 = 0.23 mT, A2 = 0.44 mT, A3 = 3.23 mT) typical for N-doped TiO2. The ability of photocatalysts to generate reactive oxygen species (ROS) upon in situ UV or visible-light photoexcitation was tested in water or dimethyl sulfoxide by EPR spin trapping using 5,5-dimethyl 1-pyrroline N-oxide. The results obtained reflect the differences in photocatalyst nanostructures caused by the differing initial ratio of melamine/TiO2; the photocatalyst prepared by the high-temperature treatment of melamine/TiO2 wt. ratio of 1:3 revealed an adequate photoactivity in both spectral regions

Synthesis and Herbicidal Activity of New Hydrazide and Hydrazonoyl Derivatives

Three new hydrazide and five new hydrazonoyl derivatives were synthesized. The chemical structures of these compounds were confirmed by 1H-NMR, IR spectroscopy and elemental analysis. The prepared compounds were tested for their activity to inhibit photosynthetic electron transport in spinach chloroplasts and growth of the green algae Chlorella vulgaris. IC50 values of these compounds varied in wide range, from a strong to no inhibitory effect. EPR spectroscopy showed that the active compounds interfered with intermediates Z•/D•, which are localized on the donor side of photosystem II. Fluorescence spectroscopy suggested that the mechanism of inhibitory action of the prepared compounds possibly involves interactions with aromatic amino acids present in photosynthetic proteins

Photoinduced reactive species in interfacial charge transfer complex between TiO2 and taxifolin: DFT and EPR study

The TiO2-based interfacial charge transfer (ICT) complex with taxifolin (dihydroquercetin), a polyphenol with pronounced antioxidant ability, displays light absorption in the visible spectral range. The extent of the red absorption shift, obtained using the density functional theory (DFT) calculations on a cluster model that mimics the ICT complex, is in excellent agreement with spectroscopic measurements. The reactive paramagnetic species generated in the dispersed pristine and surface-modified TiO2 powders with taxifolin upon excitation with ultraviolet and visible light were identified by indirect electron paramagnetic resonance (EPR) spectroscopy techniques. The spin trapping and spin scavenging revealed the differences between the behavior of the pristine and surface-modified TiO2 powders with taxifolin before and upon excitation. On one side, the TiO2-based ICT complex with taxifolin efficiently scavenges reactive oxygen species by the taxifolin’s hydroxyl groups and, on the other side, the promotion of electrons from the ground state of taxifolin to the conduction band of TiO2 takes place under visible light excitation

Photocatalytic hydrogen production from methanol over Nd/TiO2

Nd modified TiO2 photocatalysts containing 0.15-1.5 wt.% of Nd (wt.% Nd determined by XRF) as well as parent TiO2 were investigated for the photocatalytic oxidation of CH3OH. The photocatalysts were prepared by the common sol-gel method followed by thermal treatment. The textural, structural and electronic properties of all synthesized photocatalysts were characterized by nitrogen physisorption, powder X-ray diffraction, X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, Raman spectrometry, DR UV-vis spectroscopy, electron paramagnetic resonance spectroscopy and photo-electrochemical measurements. It was revealed that all materials show comparable band gap energy and phase composition. However, the addition of different amounts of Nd in the range of 0.15-1.5 wt.% significantly affected the TiO2 crystallite size, the specific surface area, the amount of surface 0 species and subsequently also the photocurrent response. The positive role of neodymium was proved at its very low loading, i.e. for Nd/TiO2 with 0.15 wt.% Nd which exhibited the highest photocatalytic activity. The photocatalytic activity was promoted by both increasing crystallite size of TiO2 and decreasing amount of surface O species.Web of Science366special issue645