Photoaccumulating nanoheterostructures based on titanium dioxide

Nanoheterostructures based on titanium dioxide synthesized by the sol–gel technique are studied. Microscopy, X-ray diffraction, optical spectroscopy, and electron-spin resonance techniques are used. All the investigated samples are characterized by a large specific surface area ($\sim$ 100 m$^2$ per 1 g substance). It is established that the main types of radicals in the obtained structures are N$^\bullet$, Ti$^{3+}$, Mo$^{5+}$, V$^{4+}$ и W$^{5+}$, depending on the composition of the samples. It is shown that nanoheterostructures consisting of several metal oxides have a high photocatalytic activity in the visible spectral region and the ability to accumulate photogenerated charge carriers. As a result, catalytic reactions in the samples continue even after illumination is turned off. A correlation is found between the rate of photocatalysis, the absorption spectra in the visible region, and the concentration of radicals in the studied structures. The results can be used to develop energy-efficient catalytic devices based on nanoheterostructures consisting of titanium, molybdenum, tungsten, and vanadium nanooxides in various combinations which operate under periodic illumination in the visible spectral range.