Short-term variability of macro- and trace elements in Elymus repens L. and Urtica dioica L.

Abstract Background: The main aim of the research was to study short-term changes in the concentrations of elements in two widely distributed plant species, couch grass and nettle and in the rhizosphere soil of the plants. Methods: The sampling of plants and soil was carried out on three dates: 3, 10, and 25 May 2021. On each day of sampling, the plants and soil were collected three times: at 9:00, 14:00, and 19:00. The ICP-OES and ICP-MS analytical techniques were used for determination of elements in the plant and soil samples. The Raman spectroscopy was applied to study variations in the organic compounds. Results: The concentrations of both macro-nutrients and trace elements in plants varied greatly over daytime on all dates of sampling. The differences between concentrations of many elements in the plants collected at different times during a day were statistically significant. There were also statistically significant differences between concentrations of some elements (Na, Mg, P, K, Fe, Ba) in the plants collected on different dates. The relative intensity of diffuse luminescence of the rhizosphere soil of couch grass and nettle was different during daytime and also differed between the soils taken from roots of the two plant species, especially in the beginning of May. Conclusions: The experimental data indicates that the daily variations of the element concentrations in plants might be a result of multiple effects of various factors. The differences in the daily element variations in the couch grass and nettle growing in the same site and collected simultaneously might be due to the fact that these plants belong to different clades. The diurnal fluctuations (that also include regular changes in the element concentrations in plants) can be different for monocotyledons (couch grass) and dicotyledons (nettle). New experimental findings on short-term variations in the concentrations of macro-nutrients and trace elements can help to gain a new insight into accumulation of the elements in different plant species and also be useful in agricultural practice

Ti-Modified Hydroxyapatites: Synthesis, Crystal Chemistry, and Photocatalytic Activity

The structural nature of photocatalytic properties of hydroxyapatites (HAp) synthesized from Ti-containing media (of Ti-modified hydroxyapatites) needs clarification. We synthesized hydroxyapatites from Ti-containing water solutions under various conditions and studied the received powder precipitations (before and after calcination at a temperature of 700 °C for 6 h) by a wide set of methods: powder X-ray diffraction (PXRD); vibrational, energy-dispersive X-ray, X-ray photoelectron, and diffuse reflectance spectroscopy; scanning electron microscopy, and gas phase photocatalytic activity tests. Analyzing the variations of unit cell parameters, we have proved that titanium is able to incorporate into the hydroxyapatite lattice in amounts of up to ∼10 wt % depending on synthesis conditions. At low concentrations (Ti/Ca ≤ 0.16), Ti4+ ions incorporate predominantly to the P site of hydroxyapatite structure. At higher concentrations (0.16 ≤ Ti/Ca ≤ 0.28), additional Ti4+ ions incorporate Ca sites. Besides, a significant share of titanium forms predominantly amorphous impurity phases, which transform into crystalline TiO2 (anatase and rutile) upon calcination and are often undetectable by PXRD. The presence of crystalline titanium oxides (anatase and rutile) has a crucial effect on photocatalytic activity of calcined Ti-modified hydroxyapatites. Synthesized HAp/TiO2 compositions are biocompatible heterostructured materials with photocatalytic activity comparable to that of commercial photocatalysts and could be recommended for medical–biological applications