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Carbon-modified TiO2 using a sol–gel method (TiO2/CSG) and mechanochemical treatment (TiO2/CMC) was obtained. X-ray powder diffraction (XRD), scanning electron microscopy with an integrated system for electron microprobe analysis (SEM, EDX), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS), Infrared (IR) and Ultraviolet–visible (UV–Vis) spectroscopy were applied for the powders characterization. The presence of a hysteresis loop in the nitrogen ad(de)sorption isotherms for the synthesized samples proved their mesoporous structure. XRD analysis revealed the anatase and rutile phase in TiO2SG with a size of 10 and 7 nm, respectively, and only anatase phase (15–16 nm) for all TiO2/CSG samples modified by a sol–gel method was observed. Carbon additives to TiO2 did not lead to significant shifts in the peaks of bond energies of Ti 2p, O 1s and C 1s levels. The powders TiO2/CSG had additional bands in IR-spectra which are characteristic bonds of carbon with oxygen unlike the TiO2/CMC samples. It was found that modification of titanium dioxide with carbon by a sol–gel method leads to the band gap narrowing. Photocatalytic activity of the synthesized samples was investigated in H2 photoproduction and Rifampicinum (RF) photodestruction. The TiO2/CSG samples showed higher photocatalytic activity in both reactions compared to TiO2/CMC. The correlation between the RF photocatalytic degradation degree and RF adsorption was demonstrated. The reusability of the powders in RF photodegradation was checked. [ABSTRACT FROM AUTHOR]

The nanocomposites based on TiO2 doped with sulfur (S/TiO2), carbon (C/TiO2), carbon and sulfur (S/C/TiO2) have been obtained. The powders were characterized by XRD, XPS, BET, SEM, EDX, TEM and UV-VIS spectroscopy. EDX and XPS spectroscopies prove that titanium dioxide powder includes only Ti and O elements, composites C/TiO2 include the elements Ti, O, C, composites S/TiO2 - Ti, O, S and composites C/S/TiO2 - Ti, O, C, and S. XRD analysis revealed the phase of anatase in all composites, rutile phase appeared with increasing of sulfur amount in sulfur-containing powders. It has been found that the composites consist of roundish agglomerates in the range of 5–30 μm. Sulfur additives decrease grain growth of titanium dioxide particles from 14 to 9–10 nm in S/TiO2 composites, carbon leads to increase in particle size from 14 to 19 nm, simultaneous modification of titanium dioxide by carbon and sulfur leads to the formation of particles with sizes of 7–8 nm. Analysis of nitrogen sorption–desorption isotherms for all synthesized samples has shown the presence of a hysteresis loop which is the evidence for mesoporous structure of the powders. The isotherms correspond to type IV of IUPAC classification for mesoporous materials with H1 type for C/TiO2 and H2 type for S/TiO2, and C/S/TiO2 of hysteresis loop. The modification of TiO2 by carbon and sulfur leads to increase of the specific surface area (of about 1.8 times in the case of C/TiO2, about 3.3 times for S/TiO2 and about 4.7 times for C/S/TiO2), pore volume and decrease of pore radius compared with TiO2. Absorption spectra of the nanocomposites showed a bathochromic shift as compared with the absorption band of pure TiO2. It has been found that modification leads to band gap narrowing. Nanocomposite samples showed higher photocatalytic activity in the destruction of safranine T under UV and visible irradiation compared to pure TiO2. It may be related to the participation of dopants in the inhibition of electron-hole recombination, prolongation of charges lifetime, increasing efficiency of interfacial charge separation and formation of doping electronic states. [ABSTRACT FROM AUTHOR]

Nanoscale composite materials based on cerium, barium titanate and titanium dioxide were synthesized by thermal hydrolysis. The obtained individual TiO2, BaTiO3 and as-synthesized Ce/xBaTiO3/TiO2 semiconductive nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive spectrometry, transmission electron microscopy, nitrogen adsorption–desorption, UV–vis diffuse reflectance spectroscopy, and Fourier transform infrared spectroscopy. The structural investigations revealed that all prepared powders were nanocrystalline with an average crystallite size within the range of 5–17 nm. Analysis of nitrogen adsorption–desorption isotherms for the synthesized nanocomposites showed the presence of a hysteresis loop, which is evidence for the mesoporous structure of the powders. The photocatalytic degradation of the model pollutants (Safranine T and Rhodamine B) was carried out under UV irradiation. Ce/xBaTiO3/TiO2 nanocomposites showed higher photocatalytic activity compared to pure TiO2 and BaTiO3 as well as BaTiO3/TiO2. An increase of the amount of BaTiO3 in Ce/xBaTiO3/TiO2 samples by more than 12% reduces the photocatalytic activity of nanocomposites while doping of BaTiO3/TiO2 samples with cerium increases their photoactivity. [ABSTRACT FROM AUTHOR]

A comparative analysis was carried out on the photocatalytic properties of nanocomposites derived from anatase and carbon obtained by two different reactions in the decomposition of Safranin T. Compared with samples obtained by mechanochemical modification of titanium dioxide by carbon, the nanocomposites obtained by the sol-gel method in the presence of carbon particles are more effective photocatalysts for this reaction due to narrowing of the band gap and the appearance of additional (defective) absorption in the visible spectral range. The effects of the pH of the solution, the extent of substrate adsorption, and the concentrations of the photocatalyst and substrate on the rate of decomposition of this dye were studied. [ABSTRACT FROM AUTHOR]

The aim of our work was to prepare nanoscale composites based on TiO2 and carbon photocatalytically active under UV and visible irradiation in the destruction of safranin T. The samples were characterized by XRD, BET, SEM, UV-Vis and IR spectroscopy. X-ray analysis revealed photocatalytically active phase of anatase in all the composites. The powders consist of roundish agglomerates, crystallite size in agglomerates is 15 nm. Analysis of nitrogen sorption- desorption isotherms for the samples show the presence of a hysteresis loop which is the evidence for mesoporous structure. Vibrational spectra of the composites reveal the following bands: near 700 cm−1 corresponding to the Ti-O stretching vibration; around 3407 cm-1 attributed to the surface-adsorbed H2O; at 1628 cm-1 which is referred to deformational vibrations in adsorbed water, and around 1300-1500 cm-1 corresponding to carbon-oxygen bonds. Absorption spectra of nanocomposites show a bathochromic shift as compared with those of TiO2. Modification of TiO2 with carbon leads to band gap narrowing of composites, as well as to emerging of additional energy levels in the band gap of TiO2 with energies of 3.12-3.14 eV under valence band; that leads to sensitizing of C/TiO2 composites to visible irradiation. Nanocomposites show higher photocatalytic activity compared to pure TiO2. It may be connected with the participation of carbon in the inhibition of electron-hole recombination, prolongation of charge lifetime, increasing of efficiency of interfacial charge separation from TiO2 to carbon and formation of doping electronic states inside the TiO2 band gap. [ABSTRACT FROM AUTHOR]

Mesoporous samples of rutile with particle sizes from 14 to 21 nm modified with CN were obtained. They are characterized by the presence of an absorption band in the visible region and by increased photocatalytic activity in the degradation of safranin T and rhodamine under the influence of visible and UV light. The effects of the pH of the medium, the CN content of the photocatalyst, and the concentration of the latter on the rate of the degradation reactions of the dyes were investigated. [ABSTRACT FROM AUTHOR]

A method for producing mesoporous titania modified with barium titanate has been developed. As the proportion of barium titanate in the samples increases, the specific surface area and average pore volume and radius decrease. The modified materials exhibit photocatalytic and sorption activity with respect to the Safranin T dye and the dichromate anion. The rate constants of photocatalytic reactions increase with an increase in the amount of the adsorbate. [ABSTRACT FROM AUTHOR]

We have prepared nanodimensional mesoporous titanium–zinc oxide composites consisting of anatase, rutile, and zincite. The pore volume and specific surface of the samples increase with increasing zincite content, while the pore radius decreases. The titanium–zinc oxide nanocomposites display greater photocatalytic activity than ZnO or TiO2 and the rate constants for the decomposition of substrates increase with their increasing adsorption. [ABSTRACT FROM AUTHOR]

The effect of the concentration of disperse titanium-containing oxide photocatalysts on the decomposition of safranine in aqueous solution was studied. The observed decomposition rate constant of safranine increases with increasing catalyst content in the solution and reaches a maximum at catalyst concentration ≤3 g/L, after which this constant no longer depends on the catalyst content. The plateau for the rate constant results from light scattering and narrowing of the reaction space due to increased optical density of the solution. An increase in the specific catalyst surface is observed in the region of a rising rate constant with increasing catalyst concentration, while no such dependence is found in the plateau region. [ABSTRACT FROM AUTHOR]

The photocatalytic degradation of dyes at the nanosized sulfides of transition metals in aqueous solutions was investigated. The rate of degradation increases with decrease in the synthesis temperature of the nanoparticles and with the addition of alcohol. The substitution of Cd2+ cations by Ag+ or Cu2+ leads to a decrease in the photoactivity of the CdS, while substitution by In3+ leads to an increase. The substitution of Ni2+ and Co2+ cations in the corresponding sulfides by Cd2+ leads to an increase in the rate of degradation. [ABSTRACT FROM AUTHOR]

It is known that titanium dioxide as photocatalyst has significant drawback - limited absorption spectrum in the ultraviolet region makes it impossible to use solar energy. To expands the absorption spectrum of TiO2, the doping of impurities (metal, non-metal, etc.) were used. They affected the electronic structure and spectral characteristics of TiO2. The aim of our work was to investigate the influence of tin impurities on spectral characteristics of titanium dioxide using experimental and theoretical methods. The TiO2 powders modified by different amount of tin (Sn/TiO2) were synthesized by sol-gel method. The samples were characterized by SEM, EDX, FT-IR and UV-VIS spectroscopy. It has been found that Sn/TiO2 consists of fragmented agglomerates in the range of 5–10 μm. EDX spectroscopy proved that powders include TiO2 and Sn elements. Modification of titanium dioxide with tin led to band gap narrowing of samples, which explains by insertion of Sn atoms into crystal lattice of titanium dioxide, because Ti4+ and Sn4+ ions radii are close. The band gap values increased with increasing of tin content. The work also analyzes the vibrational spectra of Sn/TiO2 both experimentally and theoretically. In order to interpret the results obtained, quantum chemical calculations on the spatial and electronic structures of cluster models of titanium dioxide (anatase) with inserted tin atoms using the density functional theory B3LYP method and the basis set 6-31G (d, p) were carried out and the corresponding FT-IR spectra have been simulated. By comparing the experimental and theoretical results, the influence has been analyzed of the number and arrangement of impurity tin atoms in clusters on the observed IR spectra of the samples. This makes it possible to forgive the most probable structural motives of titanium dioxide particles doped with tin atoms, as well as to establish the fact of the presence of tin atoms in the samples. Based on the comparison of the IR spectra of samples with different numbers of tin atoms, it is possible to quantify their composition. [ABSTRACT FROM AUTHOR]

Abstract: The effect of nanocrystalline TiO2 doping with transition metal cations (Cu2+, Fe3+, Co2+, Cr3+) on their optical absorption and photocatalytic properties was investigated. The obtained metal-doped TiO2 samples were characterized by X-ray diffraction, scanning electron microscopy, and UV–vis absorption spectroscopy. It is shown that doping effect on anatase (A) and rutile (R) properties is quite different, being much stronger and complicated on A than on R. Contrary to doped R, doped A revealed a significant red shift of the absorption edge along with the band gap narrowing. Photocatalytic activity of anatase increases upon doping in the order: AR/Co>R/Cu>R/Fe>R/Cr, indicating the inhibitory effect of impurity cations. This fact correlates with the decrease in the UV absorption of the doped rutile in the region of the Hg-lamp irradiation at 4.88eV. [Copyright &y& Elsevier]

Abstract: Nanocrystalline titanium–manganese mixed oxides (TMMO) with Mn content of 13–16at.% were first synthesized by manganese hydroxide precipitation on anatase or rutile particles. The structure, morphology and chemical composition of the samples were characterized using XRD, SEM, EDS and XRF methods showing that the synthesized mixed oxides are polydisperse materials of different phase compositions containing TiO2, Mn2O3 and MnTiO3. The defect structure and phase formation of the prepared compounds were characterized by FTIR, FT-FIR, FT-Raman spectroscopies. UV–vis absorption spectra were investigated in 2.4–6.0eV region and revealed that compared with pure TiO2 the presence of manganese oxides results in an increase of the absorption intensity and significant red shift of the TMMO absorption edge. Photocatalytic activity of pure TiO2, Mn2+-doped TiO2 and TMMO during the photocatalytic decomposition of the safranine dye under UV irradiation was studied. A great improvement of photocatalytic activity is registered for Mn2+-doped TiO2 (anatase and rutile), and rutile-based TMMO sample. [ABSTRACT FROM AUTHOR]

Molecular interactions between pyridine molecules and titanium dioxide particles of different crystalline modifications (anatase and rutile) have been investigated by IR spectroscopy. Analysis of spectral data allowed to suggest possible mechanisms of these interactions and make some conclusions about TiO2 surface state and active centers. Anatase surface has active centers of both Lewis and Brønsted types (LAC and BAC), with which pyridine interacts via coordination bonding or by the creation of pyridinium-ion (PyH+). Rutile samples have only LAC on their surface, and this does not depend on thermal treatment. Also, pyridine can form hydrogen bonds with hydroxyl groups of TiO2 surface and adsorbed water molecules in these heterogeneous systems. There are at least two types of non-equivalent OH-groups with different bonding enthalpies. Their amount and enthalpy depend on the crystalline modification of TiO2, thermal treatment, and change after loading TiO2 particles into pyridine. [Copyright &y& Elsevier]