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Novel mono- and bimetallic nanoparticles (MNPs and BNPs) decorated surface of perovskite-type KTaO3 photocatalysts were successfully synthesized by hydrothermal reaction of KTaO3 followed by photodeposition of MNPs/BNPs. The effect of noble metal type (MNPs = Au, Ag, Pt, Pd, Rh, Ru or BNPs = Au/Pt, Ag/Pd, Rh/Ru), amount of metal precursor (0.5, 1.0, 1.5 or 2.0 wt%) as well as photoreduction method (simultaneous (both) or subsequent (seq) deposition of two metals) on the physicochemical and photocatalytic properties of MNPs- and BNPs-KTaO3 have been investigated. All as-prepared photocatalysts were subsequently characterized by UV–Vis diffuse reflectance spectroscopy (DRS), Brunauer-Emmett-Teller (BET) specific surface area and pore size distribution measurement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (PXRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) emission spectroscopy. The crystal structure was performed using visualization for electronic and structural analysis (VESTA). The photocatalytic activity under Vis light irradiation was estimated in phenol degradation in aqueous phase and toluene removal in gas phase, while under UV–Vis light irradiation was measured amount of H2 generation from formic acid solution. The absorption properties of O2 and H2O molecules on KTaO3(1 0 0) surface supported by Au or Au/Pt NPs was also investigated using density-functional theory (DFT). The experimental results show that, both MNPs-KTaO3 and BNPs-KTaO3 exhibit greatly enhanced pollutant decomposition efficiency under Vis light irradiation and highly improved H2 production under UV–Vis light irradiation compared with pristine KTaO3. MNPs deposition on KTaO3 surface effects by disperse metal particle size ranging from 11 nm (Ru NPs) to 112 nm (Au NPs). Simultaneous addition of Au/Pt precursors results in formation of agglomerated larger metal nanoparticles (50–100 nm) on KTaO3 surface than subsequent deposition of Au/Pt with composition of concentrated smaller metal nanoparticles (>50 nm) on KTaO3 surface. The 0.5 Au/1.5 Pt-KTaO3_both and 2.0 Rh-KTaO3 reveal the highest Vis-induced activity among prepared samples in aqueous phase (14.75% of phenol decomposition after 90 min of irradiation) and gas phase (41.98% of toluene removal after 60 min of irradiation), respectively. The theoretical calculations confirmed that adsorption energy of O2 and H2O molecules was increased after loading of Au or Au/Pt NPs on KTaO3(1 0 0) surface. Control tests with scavengers show that O2 − radical is significantly involved in phenol oxidation under Vis light irradiation, which proposed mechanism is based on direct electron transfer from MNPs/BNPs to conduction band of KTaO3. The highest amount of H2 evaluation is obtained also by 0.5 Au/1.5 Pt-KTaO3_both after 240 min of UV–Vis light irradiation (76.53 µmol/min), which is eleven times higher than for pristine KTaO3 (6.69 µmol/min). Moreover, the most photocatalytic samples for each model reaction present good repeatability and stability after subsequent three cycles. Summarized, MNPs- and BNPs-KTaO3 are promising material in advanced applications of photocatalysis.

Novel rare earth-doped K2Ta2O6 (RE-K2Ta2O6) photocatalysts were successfully synthesized by one-step hydrothermal method. The effect of dopant type (RE = Y, Yb, Ho, Pr, Er) and amount of rare earth precursor (2, 4, 8 and 10 mol%) on the physicochemical and photocatalytic properties of RE-K2Ta2O6 have been investigated. All as-prepared materials were subsequently characterized by UV–vis diffuse reflectance spectroscopy (DRS), Brunauer-Emmett-Teller (BET) specific surface area measurement, scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, mass magnetic susceptometry and photoluminescence (PL) emission spectroscopy. The photocatalytic activity under UV–vis light irradiation was estimated in phenol degradation in aqueous phase, toluene removal in gas phase and H2 generation from formic acid solution. The experimental results show that, novel RE-K2Ta2O6 exhibits greatly improved degradation efficiency under UV–vis light irradiation compared with pristine K2Ta2O6. The Er-K2Ta2O6 and Pr-K2Ta2O6, obtained by introducing of 2 mol% of RE ions during synthesis, reveal the highest photocatalytic activity among prepared samples in aqueous phase (33% of phenol decomposition after 90 min of irradiation) and gas phase (45% of toluene removal after 60 min of irradiation), respectively. Moreover, both photocatalysts present good stability after subsequent three cycles. The active species trapping test shows that OH and O2 − radicals are significantly involved in phenol oxidation under UV–vis light irradiation. The amount of H2 evolution increases with increasing addition of Er dopant into K2Ta2O6 lattice. The highest H2 production is obtained for 10 mol% Er-K2Ta2O6 after 240 min of UV–vis light irradiation (15.40 μmol/min). Enhanced photoactivity performance can be attributed to incorporation of RE ions at K+ lattice site in RE-K2Ta2O6, probably leading to formation of new RE 4f states below the conduction band of K2Ta2O6 structure. To investigate the localization of RE ions in K2Ta2O6 structure, the band structure and partial density of the states (PDOS) have been investigated. Computer simulations were performed using plane-wave based Vienna ab-initio simulation package (VASP) with the generalized gradient approximation (GGA) by Perdew-Burke-Ernzerhof (PBE). Moreover, inclusion of RE ions in K2Ta2O6 causes predominance pyrochlore phase formation over perovskite in regular cubic structure. Summarized, RE-doped K2Ta2O6 is promising material in photocatalytic degradation of organic pollutants and H2 generation processes. Our work may provide valuable information for rare earth doping semiconductor with improved photocatalytic performance.

One of the challenges in the field of heterogeneous photocatalysis is the development of new type of photoactive materials activated by low-power and low-cost irradiation sources, and to understand the mechanism of photocatalytic reaction in the presence of those materials. Photocatalysis based on Er-TiO2 has become an attractive process to remove contaminants from aquatic environments. Unfortunately, there is no available literature presenting the systematic experimental and theoretical study of the effects of erbium ions on the photocatalytic activity of TiO2 and visible light excitation mechanism of this system. Accordingly, to obtain solar-responsive photocatalysts, nanostructured Er-TiO2 was prepared via hydrothermal method. The physicochemical characterization of samples indicate that modified photocatalysts contain both doped erbium and the surface adsorbed erbium species (e.g., Er2O3, Er(OH)x). Predicted electronic structures of Er-doped TiO2 indicate that the formation of new Er-4f states within the band gap region of TiO2 might be crucial for observed photocatalytic effects towards Vis response. However, the up-conversion process is not responsible for Vis activity and efficient O2 − generation. Moreover, Er modification of TiO2 results in an inhibition of the growth of titania crystallites, and thus an increase in the specific surface area, which are also beneficial for an efficient degradation of pollutants.

Bismuth tungstate (Bi2WO6) can work as a photocatalyst but suffers from rapid recombination of photogenerated charge carriers. Herein, density functional theory (DFT) simulations revealed that the formation of a thermodynamically stable AgInS2(112)/Bi2WO6(010) heterojunction could promote charge separation and enhance the photoactivity of Bi2WO6. To confirm these theoretical predictions, a new type of photocatalysts in the form of Bi2WO6 flower-like microspheres decorated with different amounts of AgInS2 quantum dots (QDs) was obtained using a three-step procedure. The optimized system, obtained by embedding 1 wt% AgInS2 QDs on a Bi2WO6 matrix, possessed an enhanced photocatalytic activity for both phenol degradation and water splitting under visible light irradiation (λ > 420 nm), as well as good reusability and stability during prolonged storage. Finally, DFT calculations of the adsorption energies of reagents (O2, H2O, and H2 molecules) on Bi2WO6 and AgInS2/Bi2WO6 surfaces showed that the surface of the AgInS2(112)/Bi2WO6(010) interface was more active, allowing this system to strongly interact with surrounding species such as H2, O2, and H2O and thereby inducing photocatalytic oxidation of OH– to •OH, reduction of O2 to O2•– or reduction of H+ to H2.

We have studied computationally the CdF 2 crystal doped with Al, Ga, In, Sc and Y impurities, using the density-functional theory and the ultrasoft pseudopotential method. In particular, we focus on the bistability behavior of the dopants. The formation energies, ionization levels and spatial configurations are calculated. For bistable donor configurations (DX centers), the overlap populations and energy barriers are also estimated. The results obtained for the DX centers associated with Ga and In atoms in the negative charge state are in a good agreement with previous works. We predict the existence of bistability in the case of the Sc-doped CdF 2 . In all the investigated cases for the DX centers we find an antibonding state between the impurity and the nearest Cd atoms.

Hole self-trapping in technologically important BaTiO 3 and SrTiO 3 crystals is studied using a quantum-chemical method developed for periodic systems, e.g., crystals. The computations are carried out in the self-consistent-field manner using the embedded molecular cluster model. The possibility of spontaneous hole self-trapping is estimated by employing an analytical procedure based on the energetical favourability principle. Our results support the self-trapping of radiation-induced hole in BaTiO 3 crystals while such an outcome is not predicted for SrTiO 3 crystals. Computational results are discussed in the light of available experimental data on light-induced absorption spectra measurements in BaTiO 3 crystals.