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Abstract Upconversion nanoparticles (UCNPs) are a promising nanoplatform for bioreagent formation for in vivo imaging, which emit UV and blue light under the action of near-infrared radiation, providing deep tissue penetration and maintaining a high signal-to-noise ratio. In the case of solid tumor visualization, the UCNP surface functionalization is required to ensure a long circulation time, biocompatibility, and non-toxicity. The effective UCNP accumulation in the solid tumors is determined by the disturbed architecture of the vascular network and lymphatic drainage. This work demonstrates an approach to the UCNP biofunctionalization with endogenous polysialic acid for in vivo bioreagent formation. Bioreagents possess a low level of nonspecific protein adsorption and macrophage uptake, which allow the prolongation of the circulation time in the bloodstream up to 3 h. This leads to an intense photoluminescent signal in the tumor.

In the late 1990s, the unique possibilities application of inorganic nanocrystals with anti-Stokes photoluminescence were demonstrated. In a fairly short period, a significant breakthrough has been achieved in this field due to the development of new and modification of existing methods for the synthesis of these nanomaterials, and the expansion of understanding of the photophysical processes occurring in nanocrystals. The interest from the scientific community is due to the exceptional luminescence properties of upconversion nanomaterials, which can convert photons of the near-infrared spectrum to radiation in the visible and UV ranges. This multiquantum process takes place under low-intensity excitation, which largely determines the use of this class of nanomaterials in high-tech fields, including biotechnology, photochemistry, medicine, solar energy, nanosensorics, etc. The goals of this review are to consider the mechanisms of anti-Stokes luminescence, to analyze the synthesis methods, and to demonstrate the applications of fluoride upconversion nanomaterials, in which they have formed a stable scientific and technological niche.

A procedure has been proposed for the preparation of capsules with shells composed of titanium dioxide nanoparticles and polymers via the formation of Pickering emulsions (colloidosomes) followed by layer-by-layer deposition of polyelectrolytes. The feasibility of stabilizing oil droplets of emulsions by spontaneous adsorption of partly hydrophobized nanoparticles of anatase-form titanium dioxide at the oil/water interface has been studied. Conditions have been determined for the formation of stable colloidosomes and the subsequent layer-by-layer deposition of oppositely charged polyelectrolytes onto their surfaces. It has been shown that hydrophobic dyes may be encapsulated using the procedure developed for the preparation of the capsules. The photocatalytic activity of TiO2 particles occurring in the shell has been demonstrated by the example of degradation of Nile red which is incorporated in the oil core of a capsule.

The adsorption ability of titanium dioxide samples with nanoscale anatase prepared by the sulfate method and Degussa (Evonik) P25, Hombfine N, and Hombikate UV-100 commercial agents with different compositions and characteristics to extract Nb(V) and Ta(V) ions from a model aqueous system has been investigated for the first time. It is established that the degree of sorption R (%) depends on the sorption conditions and the nature of analyte. It is demonstrated that the degree of sorption of Nb(V) ions in the presence of all samples is the highest (Rmax = 99.9%) for Degussa P25, except for the peroxide-modified samples on which the maximum sorption of Ta(V) ions with Rmax = 99.9% has been attained.

Nanoparticulate anatase and η-TiO2 prepared via a sulfate route have been shown (using powder X-ray diffraction, scanning electron microscopy, X-ray microanalysis, and IR spectroscopy) to differ in micro- and nanoparticle size and elemental composition. The degree of As(V), V(V), and Bi(III) extraction from aqueous solutions (for the last element, a content below its maximum allowable concentration has been reached) using nanoparticulate titania adsorbents depends on their composition, crystal structure, crystallinity, and microstructure. The synthesized anatase and η-TiO2 powders are shown to be potentially attractive carriers of PdCl2-CuCl2/TiO2 catalysts for low-temperature carbon monoxide oxidation in air.

Samples containing anatase and η-TiO2 nanoparticles have been prepared from titanyl sulfate solutions and characterized by X-ray diffraction, transmission electron microscopy, and electron diffraction. Unit-cell parameters of η-TiO2 have been proposed that do not rule out a relationship between the anatase and η-TiO2 structures. The samples containing anatase and η-TiO2 differ in crystallite size and specific surface area and consist of agglomerates of particles of various sizes covered with an amorphous layer. We have studied the effect of synthesis conditions on the ability to prepare a particular titania polymorph with various functional characteristics.