Special attention has recently been paid to surface-defective titanium dioxide and black TiO₂ with advanced optical, electrical, and photocatalytic properties. Synthesis of these materials for photodegradation and mineralization of persistent organic pollutants in water, especially under visible radiation, presents interest from scientific and application points of view. Chemical reduction by heating a TiO₂ and NaBH₄ mixture at 350 °C successfully introduced Ti³⁺ defects and oxygen vacancies at the surface of TiO₂, with an increase in the photocatalytic degradation of amoxicillin—an antibiotic that is present in wastewater due to its intense use in human and animal medicine. Three TiO₂ samples were prepared at different annealing temperatures to control the ratio between anatase and rutile and were subjected to chemical reduction. Electron paramagnetic resonance investigations showed that the formation of surface Ti³⁺ defects in a high concentration occurred mainly in the anatase sample annealed at 400 °C, contributing to the bandgap reduction from 3.32 eV to 2.92 eV. The reduced band gap enhances visible light absorption and the efficiency of photocatalysis. The nanoparticles of ~90 m²/g specific surface area and 12 nm average size exhibit ~100% efficiency in the degradation of amoxicillin under simulated solar irradiation compared with pristine TiO₂. Mineralization of amoxicillin and by-products was over 75% after 48 h irradiation for the anatase sample, where the Ti³⁺ defects were present in a higher concentration at the catalyst’s surface.

The $K\beta$ x-ray spectra of the elements from Ca to Ge have been systematically investigated using a high-resolution antiparallel double-crystal x-ray spectrometer. Each $K{\beta }_{1,3}$ natural linewidth has been corrected using the instrumental function of this type of x-ray spectrometer, and the spin doublet energies have been obtained from the peak position values in $K{\beta }_{1,3}$ x-ray spectra. For all studied elements the corrected $K{\beta }_1$ x-ray lines FWHM increase linearly as a function of $Z$. However, for $K{\beta }_3$ x-ray lines this dependence is generally not linear in the case of $3d$ elements but increases from Sc to Co elements. It has been found that the contributions of satellite lines are considered to be $\left[KM\right]$ shake processes. Our theoretically predicted synthetic spectra of Ca, Mn, Cu, and Zn are in very good agreement with our high-resolution measurements, except in the case of Mn, due to the open-shell valence configuration effect (more than 7000 transitions for diagram lines and more than $100000$ transitions for satellite lines) and the influence of the complicated structure of the metallic Mn.

Bulk sensitive x-ray spectroscopy is performed to systematically study the effect of substitution on the valence transition in strongly correlated Yb compounds, such as ${\text{Y}}_{0.1}{\text{Yb}}_{0.9}{\text{InCu}}_4$, ${\text{YbInCu}}_4$, and ${\text{YbIn}}_{0.88}{\text{Ag}}_{0.12}{\text{Cu}}_4$, and is compared with complementary magnetic-susceptibility results. High-resolution x-ray absorption spectroscopy with partial fluorescence yields mode and resonant x-ray emission spectroscopy is used to measure the valency change as a function of temperature. The valency change determined from spectroscopy exactly follows the temperature evolution of the magnetic susceptibility. The results confirm first-order transitions in ${\text{Y}}_{0.1}{\text{Yb}}_{0.9}{\text{InCu}}_4$ and ${\text{YbInCu}}_4$, while ${\text{YbIn}}_{0.88}{\text{Ag}}_{0.12}{\text{Cu}}_4$ exhibits a continuous mixed-valence transition. The present results are in agreement with the mean-field Anderson lattice model theory of Goltsev and co-workers [Phys. Rev. B 63, 155109 (2001); J. Phys.: Condens. Matter 17, S813 (2005)], which includes the role of local deformations and Kondo volume collapse in the valence transition.