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Applied cutting-edge electronic structure and phonon simulations provide a reliable knowledge about the stability of perovskite structures and their electronic properties, which are crucial for des...

The design of an active, stable and efficient photocatalyst that is able to be used for hydrogen production is of great interest nowadays. Therefore, four methods of AgTaO3 perovskite synthesis, such as hydrothermal, solvothermal, sol-gel and solid state reactions, were proposed in this study to identify the one with the highest hydrogen generation efficiency by the water splitting reaction. The comprehensive results clearly show that the solid state reaction (SSR) led to the obtainment of a sample with an almost seven times higher photocatalytic activity than the other methods. Furthermore, four ionic liquids, all possessing nitrogen in the form of organic cations (two imidazoliums with different anions, ammonium and tetrazolium), were used for the first time to prepare composites consisting of AgTaO3 modified with IL and Pt, simultaneously. The effect of the ionic liquids (ILs) and Pt nanoparticles&rsquo, presence on the structure, morphology, optical properties, elemental composition and the effectiveness of the hydrogen generation was investigated and discussed. The morphology investigation revealed that the AgTaO3 photocatalysts with the application of [OMIM]-cation based ILs created smaller granules (&lt, 500 nm), whereas [TBA] [Cl] and [TPTZ] [Cl] ILs caused the formation of larger particles (up to 2 &mu, m). We found that various ILs used for the synthesis did not improve the photocatalytic activity of the obtained samples in comparison with pristine AgTaO3. It was detected that the compound with the highest ability for hydrogen generation under UV-Vis irradiation was the AgTaO3_0.2% Pt (248.5 &mu, mol∙g&minus, 1), having an almost 13 times higher efficiency in comparison with the non-modified pristine sample. It is evidenced that the enhanced photocatalytic activity of modified composites originated mainly from the presence of the platinum particles. The mechanism of photocatalytic H2 production under UV-Vis light irradiation in the presence of an AgTaO3_IL_Pt composite in the water splitting reaction was also proposed.

Novel visible light responsive materials for water splitting are essential for the efficient conversion of solar energy into hydrogen bond energy. Among other semiconductors, gadolinium orthovanadate has appropriate conduction and valence band edges positioned to split water molecules and a narrow band gap that allows the use of visible light for hydrogen generation. Thus, we present here that hydrogen evolution under visible light (λ > 420 nm) could be accomplished using hierarchical 3D GdVO4 particles, obtained by a simple, one pot hydrothermal synthesis. We found that applying various reaction components, such as EDTA-Na2 and EDTA, and adjusting the pH of the solution allow one to tune the shape of GdVO4 (such as short nanowires, long nanowires, short nanorods, long nanorods, nanoparticles and spheres – all having a tetragonal crystal structure) as well as optical and photocatalytic properties. The highest ability to photocatalytically split methanol solution into hydrogen under UV-Vis irradiation was detected for the long nanowire sample (42 μmol h−1), having almost 11 times higher efficiency in comparison with the weakest sample – short nanowires. In addition, GdVO4 spheres generated H2 more than 2 times (5.75 μmol h−1) in comparison with the short nanorod sample (2.5 μmol h−1) under visible light excitation. Photostable in three-hour work cycles, long nanowires and spheres were even able to generate hydrogen from pure water, reaching values of 17 and 3 μmol under UV-Vis and Vis light, respectively.

A series of novel ZnO quantum dots modified with rare earth metals was successfully prepared by a simple sol-gel approach. The effects of types (Eu, Er, Tb, Yb, Ho, La) and amounts (from 0.09 to 0.45 mmol) of lanthanides on the optical properties, structural characterization and photocatalytic activity of ZnO/RE QDs were systematically investigated. The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) with energy dispersive X-ray analysis (EDX) and UV–Vis diffuse reflectance spectroscopy were used to characterize surface properties, while photoluminescence (PL) emission spectroscopy and UV–Vis-driven degradation of phenol in aqueous phase were applied to understand optical and photocatalytic properties. The experiments demonstrated that generally modification of ZnO QDs by lanthanides resulted in increase of photoactivity while photoluminesce decrease at the same moment. The highest photocatalytic activity among all obtained nanomaterials and the lowest photoluminescence quantum yield among ZnO/Er photocatalysts were observed for ZnO QDs modified with 0.09 mmol of erbium. Increased photocatalytic activity has been shown in successive samples: ZnO/0.09_Er > ZnO/0.18_Eu > ZnO/0.09_La > ZnO/0.27_Er > ZnO/0.18_Tb > pristine ZnO QDs. The experimental results were supported by calculations based on density functional theory (DFT) which revealed atomic and electronic structure of Er/La modified ZnO QDs.

In this study, we report a novel method of BaZrO3 and SrZrO3 surface modification by two different types of quantum dots (QDs, Cu2O and Bi2O3), which improved the photocatalytic performance of the obtained materials under UV-Vis light irradiation. Pristine BaZrO3 and SrZrO3 were prepared by the hydrothermal method. The deposition of Cu2O- and Bi2O3-QDs was carried out by chemical reduction. The morphology of the nanoparticles was estimated based on microscopic analysis (SEM, TEM). The perovskite structure and phase composition of polycrystals were confirmed by X-ray powder diffraction analysis (XRD). The elemental surface composition and the chemical character of detected elements were identified by X-ray photoelectron spectroscopy (XPS). The absorption ability and luminescence properties of nanocomposites were investigated by UV–Vis diffuse-reflectance spectroscopy (DRS UV-Vis) and luminescence spectroscopy. The influence of Cu2O/Bi2O3-QDs modification on the photocatalytic activity of BaZrO3 and SrZrO3 was evaluated by the phenol photodegradation process in the liquid phase under UV-Vis and toluene degradation in the gas phase under Vis irradiation. The highest photoactivity under UV-Vis light was observed for BaZrO3/1% Cu2O/33% Bi2O3 and SrZrO3/1% Cu2O/33% Bi2O3 samples. Research also demonstrated that single-type QD deposition (Cu2O or Bi2O3) on the zirconate surface decreases the photoactivity in comparison with pristine zirconates. The mechanism of photocatalytic activity of the obtained nanocomposites was investigated by the formation of hydroxyl radicals under UV-Vis irradiation in the presence of terephthalic acid.

Titanium dioxide can present advantages when coupled with ozonation. Moreover, the catalytic ozonation can be enhanced by radiation. The main disadvantage of this technology is the use of a suspended catalyst entailing a separation step. Thus, catalytic ozonation was analysed using supported TiO2 nanotubes prepared by anodization at different voltages. The effect of different radiation sources on the catalytic ozonation of parabens was tested. The increase on voltage preparation led to plates with higher surface areas from 60 to 280 cm2. However, this did not improve the parabens mixture degradation during UVA photocatalytic ozonation. The use of sunlight radiation allows a significant reduction in terms of time necessary for total parabens degradation from 15 to 10 min. However, the amount of ozone required doubles. Catalytic ozonation presents worst results than single ozonation. This means that molecular ozone is the main responsible for degradation. No dissolved ozone was detected at the experiments with supported nanotubes which could mean that it was adsorbed on the catalysts surface decreasing the degradation rates. The presence of municipal wastewaters as matrix inhibited parabens degradation for both single and catalytic ozonation, mainly due to the trapping ozone effect. In fact, for the TOD of 4.5 mg/L it was just possible to remove about 80% of parabens when MWW compared to 100% when UP was used. Even so, the presence of supported nanotubes during ozonation seems to be required to reduce the toxicity of the resultant treated effluent. In fact, the wastewater luminescence inhibition decreased (from 100 to 43%) and germination index increased (from 7 to 97%) with catalytic ozonation which may enable treated water reuse.

Novel visible light responsive materials for water splitting are essential for the efficient conversion of solar energy into hydrogen bond energy. Among other semiconductors, gadolinium orthovanadate has appropriate conduction and valence band edges positioned to split water molecules and a narrow band gap that allows the use of visible light for hydrogen generation. Thus, we present here that hydrogen evolution under visible light (λ420 nm) could be accomplished using hierarchical 3D GdVO