A detailed analysis of the nature and photoinduced reactions of paramagnetic centers (PCs) in TiO2 based semiconductor nanoparticles has been performed, and energy diagrams of the investigated ...samples with the energy level positions in the band gap are determined using electron paramagnetic resonance (EPR) technique under illumination in situ. This study gives a new method for constructing the zone diagram of nanostructured semiconductors. N•, Ti3+, and Mo5+ PCs were detected in TiO2/MoO3 samples, and Ti3+ and V4+ centers were observed in the TiO2/MoO3:V2O5 one. The determined energy position of PCs in the band gap of nanostructured semiconductors are located from the valence band on 2.9 eV for Ti3+ ions, 2.7 eV for Mo5+ ions, 2.2 eV for V4+ PCs, and 1.4 eV below the bottom of the conduction band for N• radicals. The effect of illumination is reversible during a long time: approximately 24 h because of a separation of the photogenerated charge carriers just after excitation between different semiconductor oxide nanosized particles connected by nanoheterojunctions. These results can be useful for understanding the mechanism of photocatalytic reactions and further practical applications of the nanoheterojunction materials such as TiO2/MoO3 and TiO2/MoO3:V2O5 oxides.
We introduce a novel and versatile approach to the corrosion protection by use of “smart” laser-controllable coating. The main advantage of the proposed technique is that one could terminate the ...corrosion process by very intensive healing after an appearance of corrosion centers using local laser irradiation. It is also shown that by applying a polyelectrolyte shell with noble metal particles over the mesoporous titania and silica via layer-by-layer assembly it is possible to fabricate micro- and nanoscaled reservoirs, which, being incorporated into the zirconia−organosilica matrix, are responsible for the ability of laser-driven release of the loaded materials (e.g., corrosion inhibitor). Furthermore, the resultant films are highly adhesive and could be easily deposited onto different metallic substrates. Laser-mediated remote release of incorporated corrosion inhibitor (benzotriazole) from engineered mesoporous containers with silver nanoparticles in the container shell is observed in real time on single and multicontainer levels.
Titania is a widely used photocatalytic material possessing such advantages as low cost and high reactivity under the ultraviolet light illumination. However, the fast recombination of photoexcited ...charge carriers limits its application. Herein, we have synthesized original nanomaterials with mosaic structures that exhibited well-defined heterojunctions and new properties. Using SEM, XRD, EPR spectroscopy, photocatalytic measurements, and photoinduced pathphysiological activity of these photocatalysts, we studied the processes of charge carrier accumulation in TiO2/MoO3, TiO2/WO3, and TiO2/V2O5 under in situ UV illumination with emphasis on the charge exchange between energy levels of these nanosized semiconductors. It is shown that the accumulation of photoinduced charges occurs in two forms (i) filled electron traps corresponding to Ti4+/Ti3+ levels and (ii) Mo5+ centers, both forms contributing to the photoinduced biocide activity of the samples. This work demonstrates that light exposure of heterostructure photocatalysts with mosaic surfaces produces different types of charge-trapping centers capable of interacting with molecular oxygen yielding peroxo species, which provide long-life light-induced ”self-cleaning” behavior. Such photoaccumulating materials open new opportunities in developing light-driven self-sterilization structures exhibiting a prolonged bactericidal effect up to 10 h after stopping light exposure.
Metal oxide photocatalysts TiO
2
/MoO
3
and TiO
2
/MoO
3
:V
2
O
5
have been investigated by electron paramagnetic resonance (EPR) spectroscopy under in situ light excitation. Structural ...identification of all paramagnetic centers (PCs) recorded, such as surface and lattice Ti
3+
ions as well as Mo
5+
and V
4+
ions and nitrogen
14
N atoms containing the unpaired electron (“N
•
-radicals”), have been performed. The temperature behavior of PCs in the range of 30–300 K and photoinduced changes of EPR spectra under light irradiation have been investigated. The validity of the Curie law was confirmed for the PCs of such composite photocatalysts. A new original method of detection of charge carrier separation and accumulation is suggested using EPR-technique. It is shown that TiO
2
/MoO
3
and TiO
2
/MoO
3
:V
2
O
5
photocatalysts are capable to accumulate photogenerated charge providing fresh possibilities for practical applications in photocatalysis because these oxide heterostructures retaining oxidation activity for a long time (more than 5 h) under the dark conditions after illumination.
Graphical Abstract
Sonochemically formed metal capsules, which can protect a metal surface and release active compounds, are presented. The capsules are formed by modifying a metal surface into having a porous sponge ...layer; this layer is continuous with the bulk metal allowing for excellent adhesion. The porosity of the sponge layer and polyelectrolyte complexes allows active compounds to be stored and released depending on external stimuli. These porous capsules open up prospects in metal nanoengineering and surface protection as well as in encapsulation and polyelectrolyte applications.
In this review recent progress in photocatalysis on mesostructured systems, which behave as spatially confined micro- and nanoreactors, is presented. Mesoporous oxides and hybrid photocatalysts based ...on molecular-organized assemblies offer new possibilities of concentrating low reactant levels, controlling the reaction environment, separating photocatalyst and reaction products, and realizing host-guest catalysis of light-driven reactions. This allows one to organize the catalytic photolysis in an especially efficient way, to increase its selectivity, and to ensure another set of products as compared to photocatalysis in suspension of dispersed photocatalyst. Further increase in selectivity can be attained through functionalization of spatially confined photoreactors to impart them bio- or chemical recognition properties, to couple different photo- and redox-catalysts, and to create complicated hybrid microphotoreactors including those which mimic the natural photosynthetic centers.
Polyelectrolyte block copolymer micelles assembled thin film is switched in response to local photocatalytic reactions on titanium dioxide, resulting in a layer of variable height, stiffness in ...response to visible light irradiation. Preosteoblasts migrate toward stiffer side of the substrates.
Photocatalytic reactions on titanium dioxide in response to visible light irradiation are used to regulate polyelectrolyte block copolymer micelles assembled thin film. Irradiation results in change of film height, stiffness. Film can be switched in response to local irradiation. Preosteoblasts migrate toward stiffer side of the substrates.
A novel sonochemical method for formation of mesoporous metal sponges is developed. Systematic investigation of ultrasound effects on various types of metal particles reveals the cavitation-induced ...oxidation of metal surface and etching of metal matrix as main factors in the ultrasound-driven metal modification. Beyond the specific examples, the findings provide guidelines for expansion of the concept towards a broad variety of metal systems and allow development of the sonochemical approaches to manipulation of the metal surface and inner structure.
Front Cover: There are great prospects of conversion of energy of electromagnetic irradiation into pH gradients enabling also spatial regulation by localization of the irradiation spot onto a ...semiconductor titania surface to guide cells on a surface that promises many applications in biosciences, fundamental cell biology and microfluidics. Further details can be found in the article by Sviatlana A. Ulasevich, Nadzeya Brezhneva, Yulia Zhukova, Helmuth Möhwald, Peter Fratzl, Felix H. Schacher, Dmitry V. Sviridov, Daria V. Andreeva, Ekaterina V. Skorb on page 1422.
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