Nanocrystalline materials based on titanium dioxide possess unique properties, including photocatalytic and antibacterial activities. Despite many approaches have already been utilized to fabricate and characterize pure and doped TiO₂, a systematic description of its nanostructured samples depending on the synthesis method has not been presented yet. In this study, we shed new light on the process–structure relationships of nanocrystalline TiO₂-based powders fabricated by extraction–pyrolytic, hydrothermal, and sol–gel techniques. The comprehensive analysis of the fabricated nanocrystalline TiO₂-based powders with different anatase/rutile phase content is performed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The hydrothermal and sol–gel methods are also used to grow TiO₂ particles doped with Cu and Er-Yb. The correlation between synthesis parameters (pyrolysis and annealing temperature) and properties of the produced materials is studied. Particular attention is paid to Raman spectroscopy and the detailed comparison of our obtained data with existing experimental and theoretical studies.

This study reveals a significant improvement in surface-enhanced Raman scattering (SERS) activity of Ag/ZrO₂ substrates covered with a few-layer graphene preliminary exposed to ultraviolet (UV) light. The SERS-active substrates are formed by the “silver mirror” deposition of Ag nanoparticles on annealed zirconia blocks. The film composed of ~3 graphene layers is grown on copper foil by a chemical vapor deposition and then wet-transferred to the SERS-active substrates. The graphene-free Ag/ZrO₂ samples are found to provide an enhancement of the Raman scattering from rhodamine 6G (R6G) at a micromolar concentration, which is associated with combined effects from the surface plasmon resonance in the Ag nanoparticles and a charge transfer facilitated by zirconium dioxide. It is revealed that the SERS signal from the analyte molecules can be suppressed by a UV exposure of the Ag/ZrO₂ samples due to photocatalytic activity of the wide band gap semiconductor. However, if the samples are covered with a few-layer graphene (Gr/Ag/ZrO₂) it prevents the dye molecule decomposition upon the UV treatment and improves SERS activity of the substrates. The 365 nm treatment leads to a 40% increase in the 10^–6 M R6G SERS spectrum intensity, while the 254 nm irradiation causes it to rise by 47%, which is explained by different responses from the surface and bulk zirconia crystals to the short and long UV wavelengths. This enhancement is attributed to the distinct responses of surface and in-depth zirconia crystals to varied UV wavelengths and underscores the pivotal role of graphene as a protective and enhancing layer.

Surface-enhanced Raman scattering (SERS) spectroscopy is used to investigate a composition of wash swabs from the Cu-TiO₂/TiO₂-modified filters with disinfecting ability. Macroporous Si chips coated with conformal 800 nm thick Ni layer and Ag particles (Ag/Ni) are engineered to act as SERS-active substrates. Such substrates are characterized by a moderate reflection band in the visible range and provide an improved heat dissipation from contaminants in wash swabs during SERS study. This prevents thermal-induced destruction of analyzing media for reliable assessment of its composition. The anatase Cu-TiO₂ and TiO₂ nanoparticles are synthesized using the sol-gel method and characterized via Raman spectroscopy and X-ray diffractometry. The filters are modified with Cu-TiO₂/TiO₂ nanoparticles and embedded in three-valve facial masks that are worn by a volunteer to breathe for 4 h. Comparative SERS analysis of the filters shows that they slightly destroy chemical bonds in the molecules constituting airborne contaminations upon ceiling day lights, which can be associated with Cu-TiO₂ photocatalytic activity. The filters additionally exposed to near-ultraviolet light prominently decrease the intensity of Raman signatures of airborne contaminant due to the presence of pure TiO₂.

In this study, we developed a filtering material for facial masks, which is capable of trapping and subsequent inactivation of bacteria under white light emitting diodes (LED) or sunlight irradiation. Such a functionality is achieved via the modification of the composite membrane based on porous polymer with photocatalytic (TiO₂) and plasmonic (Ag) nanoparticles. The porous polymer is produced by means of a computer numerical control machine, which rolls a photoresist/thermoplastic mixture into a ~20-µm-thick membrane followed by its thermal/ultraviolet (UV) hardening and porosification. TiO₂ nanoparticles are prepared by hydrothermal and sol-gel techniques. Colloidal synthesis is utilized to fabricate Ag nanoparticles. The TiO₂ photocatalytic activity under UV excitation as well as a photothermal effect generated by plasmonic Ag nanoparticles subjected to LED irradiation are studied by the assessment of methylene blue (MB) decomposition. We demonstrate that, in contrast to the filter of the standard facial medical mask, the polymer membrane modified with spray-coated TiO₂ and Ag nanoparticles prevents the penetration of bacillus subtilis from its top to bottom side and significantly inhibits bacterial growth when exposed to LED or sunlight.