Search

Keggin H3PW12O40 (PW12) and Wells-Dawson H6P2W18O60 (P2W18) heteropolyacids (HPAs) are photo(catalysts) for various acid-promoted and redox catalytic reactions. Their activity increases if they are deposited on certain supports as metal oxides or carbon materials. Although the surface area and acid-base interactions of the HPAs with supports are considered as key factors for the performance of the binary material, the role of the local structure changes in the HPAs upon their immobilization on solids must be also of primary importance, directly affecting both acidity and photoredox properties. Here, the (photo)catalytic performance of Keggin and Wells-Dawson heteropolytungstates supported on boron nitride (BN) and two types of carbon nitride (C3N4) in the gas-solid 2-propanol dehydration to propene has been studied. Apart from characterizing the materials by a set of conventional laboratory-scale structural and physical-chemical techniques, an insight into the variations of the local structure of supported HPAs is provided by means of X-ray absorption spectroscopy (XAS), and their influence on the supported HPAs (photo)catalytic activity is discussed. The irradiation with UV light increased the activity of both heteropolytungstates with respect to the catalytic experiments. The apparent activation energy calculated for the photo-assisted process resulted always lower with respect to that obtained for the catalytic one alone. Moreover, the materials that showed the highest apparent turnover frequency (TOF) were those in which the HPAs were impregnated on graphitic C3N4 or on BN and, in particular, the highest TOF values were observed at the highest temperature for the PW12/BN and P2W18/BN samples. Interestingly, the highest activity of HPAs supported on BN seems to be due to the stabilization of the W octahedral coordination, according to the XAS data., LFL is grateful to progetto di Ricerca ARS01_00637 Energie per l’Ambiente-TARANTO (PNR 2015-2020) for financial support. IK acknowledges support by Spanish MINECO (MAT2016-78155-C2-1-R), Gobierno del Principado de Asturias (GRUPIN-ID2018-170) and the Alexander von Humboldt Foundation through the Humboldt Research Fellowship. S.V.-R. and J.I.P. acknowledge financial support from the Spanish Ministerio de Ciencia, Innovación y Universidades (MCIU), the Spanish Agencia Estatal de Investigación and European Regional Development Fund (ERDF) through project RTI2018-100832B-I00, and partial funding by Plan de Ciencia, Tecnología e Innovación (PCTI) 2013-2017 del Principado de Asturias and the ERDF (project IDI/2018/000233). A.S acknowledges financial support from the MCIU through the projects MAT2017-86540-C4-1-R and RTI2018-095303-A-C52 and from the Comunidad de Madrid for an “Atracción de Talento Investigador” contract (No. 2017t2/IND5395). The European Synchrotron (ESRF), MCIU and Consejo Superior de Investigaciones Científicas (CSIC) are also acknowledged for the provision of synchrotron radiation facilities. We also thank the BM25-SpLine staff for the technical support beyond their duties.

Selective photooxidation of aromatic alcohols to corresponding aldehydes is a widely used model reaction for evaluation of performance of heterogeneous photocatalysts. A chief example is the photocatalytic production of hydrogen peroxide via reduction of dioxygen with concomitant photooxidation of benzyl alcohol to benzaldehyde. Although it has long been known that photoexcitation of benzaldehyde under UV light yields reactive benzaldehyde radicals capable of oxidizing substrates such as benzyl alcohol, it was assumed that such autocatalytic processes cannot be initiated under visible light irradiation. Herein we demonstrate the ability of benzaldehyde to promote auto-photocatalytic oxidation of benzyl alcohol and produce large quantities of H2O2 in solvent-free (no water) or biphasic (with water) systems even under nominally solar-simulated visible light (>420 nm cutoff filter) irradiation. While these results open up broader prospects for the use of benzaldehyde in visible light-driven photocatalysis as exemplified by the ability of benzaldehyde to photocatalyze H2O2 production even in the presence of alternative electron donors (e.g., ethanol), they also shed some critical light on the plethora of research reports on photocatalytic H2O2 production in which benzyl alcohol was employed as electron donor. Since the autocatalytic pathway based on the photocatalytic activity of benzaldehyde formed during photocatalysis under such conditions cannot be neglected, the interpretations of photocatalytic performance are likely contentious and distorted in such reports. We conclude that the use of benzyl alcohol as a model electron donor in photocatalytic studies should be definitely discouraged, and highlight the importance of carrying out simple check protocols for excluding similar issues when using alternative substrates.

This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Projektnummer 364549901 – TRR 234 CataLight [Projects A5, B6, B7, C2, C3 and Z2] and BE 5102/5-1. We acknowledge also support by Spanish Ministerio de Ciencia e Innovación (PID2020-113558RB-C41)., Mitoraj, D., Krivtsov, I., Li, C., Rajagopal, A., Im, C., Adler, C., Köble, K., Khainakova, O., Hniopek, J., Neumann, C., Turchanin, A., da Silva, I., Schmitt, M., Leiter, R., Lehnert, T., Popp, J., Kaiser, U., Jacob, T., Streb, C., Dietzek, B., Beranek, R.

Light-driven production of hydrogen peroxide via selective dioxygen reduction is an attractive “green” alternative to the conventionally used anthraquinone process. One of the most promising classes of photocatalytic materials for this conversion that excels by high selectivity, chemical stability and low cost is represented by polymeric carbon nitrides, and particularly by various types of poly(heptazine imide) (PHI), i.e., ionic variants of carbon nitride. A crucial challenge highlighted by recent studies is the problem of separation of formed H2O2 from the reaction medium and especially from the suspended photocatalyst particles since photocatalytically generated H2O2 can undergo light-driven decomposition, as well as disproportionation on the surface of the photocatalyst in the dark. Herein, we report an elegant solution to this problem by implementing a biphasic reaction system in which the hydrophobic photocatalyst oxidizes a lipophilic electron donor in the organic phase, while the produced H2O2 is instantaneously extracted into the aqueous layer. To this end, we have achieved an effective hydrophobization of ionic carbon nitride (PHI) nanoparticles in the form of a composite with alkylated silica. The hydrophobized composite effectively photocatalyzes the reduction of dioxygen to H2O2 with concurrent oxidation of a model fatty alcohol (1-octanol) in the organic phase under visible light irradiation (406 nm LED), and enables, at the same time, facile separation of the high-value H2O2/water mixture from the reaction medium at H2O2 concentrations (~0.12 M) that are unprecedentedly high for light-driven systems reported in the literature. Notably, fatty alcohols are readily available from vegetable waxes and as pulping sub-products, and the products of their partial oxidation represent a valuable feedstock for the synthesis of pharmaceuticals and cosmetic products. This work thus showcases a rational design of a high-performance photocatalytic system for H2O2 production that enables easy separation of the product from electron donors and its recovery at high concentrations, and paves the way for sustainable and economically viable light-driven H2O2 production from easily available feedstock.

The unique optical and photoredox properties of heptazine-based polymeric carbon nitride (PCN) materials make them promising semiconductors for driving various productive photocatalytic conversions. However, their typical absorption onset at ca. 430-450 nm is still far from optimum for efficient sunlight harvesting. Despite many reports of successful attempts to extend the light absorption range of PCNs, the determination of the structural features responsible for the red shift of the light absorption edge beyond 450 nm has often been obstructed by the highly disordered structure of PCNs and/or low content of the moieties responsible for changes in optical and electronic properties. In this work, we implement a high-temperature (900 °C) treatment procedure for turning the conventional melamine-derived yellow PCN into a red carbon nitride. This approach preserves the typical PCN structure but incorporates a new functionality that promotes visible light absorption. A detailed characterization of the prepared material reveals that partial heptazine fragmentation accompanied by de-ammonification leads to the formation of azo-groups in the red PCN, a chromophore moiety whose role in shifting the optical absorption edge of PCNs has been overlooked so far. These azo moieties can be activated under visible-light (470 nm) for H

This file contains a set of input structures for simulations.

In spite of the enormous promise that polymeric carbon nitride (PCN) materials hold for various applications, the fabrication of high-quality, binder-free PCN films and electrodes has been a largely elusive goal to date. Here, we tackle this challenge by devising, for the first time, a water-based sol−gel approach that enables facile preparation of thin films based on poly(heptazine imide) (PHI), a polymer belonging to the PCN family. The sol−gel process capitalizes on the use of a water-soluble PHI precursor that allows formation of a non-covalent hydrogel. The hydrogel can be deposited on conductive substrates, resulting in formation of mechanically stable polymeric thin layers. The resulting photoanodes exhibit unprecedented photoelectrochemical (PEC) performance in alcohol reforming and highly selective (∼100 %) conversions with very high photocurrents (>0.25 mA cm−2 under 2 sun) down to, This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)–Projektnummer 364549901–TRR 234 [Projects B6, B7, C2, C4 and Z2] and BE 5102/5-1. C.N and A.T. acknowledge financial support of the DFG through the project TU 149/8-2 “Towards photo-active membranes for artificial photosynthesis” as well as the DFG through a research infrastructure grant INST 275/257-1 FUGG. S.G.G. acknowledges support by Spanish MINECO (MAT2016-78155-C2-1-R) and Gobierno del Principado de Asturias (GRUPIN-ID2018-170). L.d.S.G. acknowledges Juan de la Cierva Formación scholarship. I.K. acknowledges the support of the Alexander von Humboldt Foundation through the Humboldt Research Fellowship. Open access funding enabled and organized by Projekt DEAL.

Ultrafast transient absorption anisotropy spectroscopy (TAA) reveals the orientational dynamics of light-induced excitations in a water soluble poly(heptazine imide). The results provide insights into the fast charge transfer processes in the material.

Detailed understanding of the structural and photophysical properties of polymeric carbon nitride (PCN) materials is of critical importance to derive future material optimization strategies towards more desirable optical properties and more photocatalytically active materials. However, the wide range of structural motifs found in synthesized PCNs complicates atomistic simulations that rely on well defined models. Performing hybrid DFT studies, we systematically investigate formation energy trends and optical properties of PCNs as a function of dimensionality, going from molecular oligomers over periodic sheet models to stacked crystals. Thermochemical calculations that take into account vibrational enthalpy and entropy contributions predict that a mixture of structural motifs including the melon string structure, poly(heptazine imide), and g-C3N4 motifs is stable under typical synthetic conditions. The degree of lateral condensation as well as stacking can reduce the bandgap while out-of-plane corrugation of the material increases both stability and the optical gap. The key result of this work is that already small domains of strongly condensed PCN are calculated to give rise to favorable optical properties. This result reconciles conflicting literature reports indicating that the thermodynamically favorable melon motif has a too large bandgap compared to experiments, while the g-C3N4 structure, for which bandgap calculations are in better agreement with experiments, does not agree with measured chemical compositions of PCNs. Finally, we postulate a new computational model for carbon nitride materials that encompasses the most important structural motifs and shows a bandgap of ca. 2.9 eV.

Ionic carbon nitrides based on poly(heptazine imides) (PHI) are intriguing materials with possible applications in photocatalysis and energy storage. In this work, effective photodoping and unusually fast charge extraction times in binder‐free PHI photoanodes are demonstrated. These results establish a strong rationale for the use of PHI films in various applications, such as bias‐free photoelectrochemistry or photobatteries. Ionic carbon nitrides based on poly(heptazine imides) (PHI) represent a vigorously studied class of materials with possible applications in photocatalysis and energy storage. Herein, for the first time, the photogenerated charge dynamics in highly stable and binder‐free PHI photoanodes using in operando transient photocurrents and spectroelectrochemical photoinduced absorption measurements is studied. It is discovered that light‐induced accumulation of long‐lived trapped electrons within the PHI film leads to effective photodoping of the PHI film, resulting in a significant improvement of photocurrent response due to more efficient electron transport. While photodoping is previously reported for various semiconductors, it has not been shown before for carbon nitride materials. Furthermore, it is found that the extraction kinetics of untrapped electrons are remarkably fast in these PHI photoanodes, with electron extraction times (ms) comparable to those measured for commonly employed metal oxide semiconductors. These results shed light on the excellent performance of PHI photoanodes in alcohol photoreforming, including very negative photocurrent onset, outstanding fill factor, and the possibility to operate under zero‐bias conditions. More generally, the here reported photodoping effect and fast electron extraction in PHI photoanodes establish a strong rationale for the use of PHI films in various applications, such as bias‐free photoelectrochemistry or photobatteries., publishedVersion

Solar hydrogen evolution from water is a necessary step to overcome the challenges of rising energy demand and associated environmental concerns. Low-cost photocatalytic architectures based on polymeric light absorbers coupled to highly efficient molecular catalysts might represent an attractive platform to address this issue. However, to-date, our mechanistic knowledge of these systems is still largely underdeveloped. In this study, a molecular molybdenum sulfide hydrogen evolving catalyst, [Mo3S13]2–, is loaded onto polymeric carbon nitride (CNx) photoabsorber by impregnation. The resulting composite shows enhanced photocatalytic activity for hydrogen evolution compared to pristine CNx under monochromatic visible light (l = 420 nm) irradiation in the presence of sacrificial reducing agents. The light-driven dynamics of excitons and charges involved in hydrogen evolution catalysis were studied by a combination of spectroscopic (steady-state and time-resolved photoluminescence, femtosecond time-resolved transient absorption) and photoelectrochemical (open-circuit photopotential transients) methods. We demonstrate that the molecular molybdenum sulfide catalyst, at optimum loading (10 wt% nominal), improves the charge separation in the CNx absorber by facilitating the depopulation of emissive (band-edge) or non-emissive (shallow trap) states, followed by an effectively catalyzed transfer of electrons from the charge-separated state (deep trap) to protons in the solution. The results provide important insights into the complex interplay between polymeric light absorbers and molecular redox catalysts, indicating that the electron transfer to the catalyst occurs on relatively longer (nanosecond – seconds) time scale, as the catalyst had no impact on the ultrafast (sub-nanosecond) photoinduced kinetics in the CNx. These findings are of crucial importance for further development of soft-matter based architectures for solar fuels production.

Heptazine‐based polymeric carbon nitrides (PCN) are promising photocatalysts for light‐driven redox transformations. However, their activity is hampered by low surface area resulting in low concentration of accessible active sites. Herein, we report a bottom‐up preparation of PCN nanoparticles with a narrow size distribution (ca. 10±3 nm), which are fully soluble in water showing no gelation or precipitation over several months. They allow photocatalysis to be carried out under quasi‐homogeneous conditions. The superior performance of water‐soluble PCN, compared to conventional solid PCN, is shown in photocatalytic H2O2 production via reduction of oxygen accompanied by highly selective photooxidation of 4‐methoxybenzyl alcohol and benzyl alcohol or lignocellulose‐derived feedstock (ethanol, glycerol, glucose). The dissolved photocatalyst can be easily recovered and re‐dissolved by simple modulation of the ionic strength of the medium, without any loss of activity and selectivity., This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—Projektnummer 364549901—TRR 234 [Projects B6, B7, C3 and Z2] and BE 5102/3‐1. We acknowledge also support by Spanish MINECO (MAT2016‐78155‐C2‐1‐R) and Gobierno del Principado de Asturias (GRUPIN‐ID2018‐170), and the project CICECO‐Aveiro Institute of Materials, FCT Ref. UID/CTM/50011/2019, financed by national funds through the FCT/MCTES. L.M., M.S., and M.I. also acknowledge the National NMR Network (PTNMR), partially supported by Infrastructure Project N° 022161, and FCT/MCTES for funding (Project PTDC/QEQ‐QAN/6373/2014). B.K. acknowledges the University of Iceland Research Fund for support through a PhD fellowship. Computational resources were provided by the state of Baden‐Württemberg through bwHPC and the German Science Foundation (DFG) under Grant No. INST 40/467‐1 FUGG. C.N. and A.T. acknowledge financial support of the DFG through the project TU 149/8‐2 “Towards photo‐active membranes for artificial photosynthesis” as well as the DFG through a research infrastructure grant INST 275/257‐1 FUGG. I.K. acknowledges the support of the Alexander von Humboldt Foundation through the Humboldt Research Fellowship.

Charge accumulation in photoactive molecules and materials holds great promise in solar energy conversion as it allows for decoupling solar‐driven charging from (dark) redox reactions. In this contribution, light‐driven charge accumulation was investigated for a recently reported novel water‐soluble carbon nitride [K,Na‐poly(heptazine imide); K,Na‐PHI] photocatalyst, which exhibits excellent activity and stability in highly selective photocatalytic oxidation of alcohols and concurrent reduction of dioxygen to H2O2 under quasi‐homogeneous conditions. An excellent charge storage ability of the K,Na‐PHI material was demonstrated, showing an optimal density of accumulated electrons (32.2 μmol of electrons per gram) in the presence of 10 vol % MeOH as a sacrificial electron donor. The long‐lived electrons accumulated under anaerobic conditions as K,Na‐PHI.− radical ions were utilized in interfacial electron transfer to O2 or methyl viologen in a subsequent dark reaction. Ultrafast time‐resolved spectroscopy was employed to reveal the kinetics of charge‐carrier recombination and methanol oxidation. Geminate recombination of electrons and holes within approximately 100 ps was followed by trap‐assisted recombination. The presence of methanol as a sacrificial electron donor accelerated the decay of the transient absorption signal when a static sample was used. This behavior was ascribed to the faster charge recombination in the presence of the radical anions generated after hole extraction. The work suggests that photodriven electron storage in the water‐soluble carbon nitride is enabled by localized trap states, and highlights the importance of the effective electron donor for creating long‐lived photo‐generated carbon nitride radicals., Taking a (very) quick look: A water‐soluble carbon nitride reveals excellent storage capacity for photogenerated charges. The photoinduced dynamics in this high‐performance water‐soluble carbon nitride photocatalyst are investigated by ultrafast time‐resolved spectroscopy.

Solar hydrogen evolution from water is a necessary step to overcome the challenges of rising energy demand and associated environmental concerns. Low-cost photocatalytic architectures based on polymeric light absorbers coupled to highly efficient molecular catalysts might represent an attractive platform to address this issue. However, to-date, our mechanistic knowledge of these systems is still largely underdeveloped. In this study, a molecular molybdenum sulfide hydrogen evolving catalyst, [Mo3S13]2–, is loaded onto polymeric carbon nitride (CNx) photoabsorber by impregnation. The resulting composite shows enhanced photocatalytic activity for hydrogen evolution compared to pristine CNx under monochromatic visible light (l = 420 nm) irradiation in the presence of sacrificial reducing agents. The light-driven dynamics of excitons and charges involved in hydrogen evolution catalysis were studied by a combination of spectroscopic (steady-state and time-resolved photoluminescence, femtosecond time-resolved transient absorption) and photoelectrochemical (open-circuit photopotential transients) methods. We demonstrate that the molecular molybdenum sulfide catalyst, at optimum loading (10 wt% nominal), improves the charge separation in the CNx absorber by facilitating the depopulation of emissive (band-edge) or non-emissive (shallow trap) states, followed by an effectively catalyzed transfer of electrons from the charge-separated state (deep trap) to protons in the solution. The results provide important insights into the complex interplay between polymeric light absorbers and molecular redox catalysts, indicating that the electron transfer to the catalyst occurs on relatively longer (nanosecond – seconds) time scale, as the catalyst had no impact on the ultrafast (sub-nanosecond) photoinduced kinetics in the CNx. These findings are of crucial importance for further development of soft-matter based architectures for solar fuels production.

Well-defined anatase TiO

Well-defined anatase TiO2 crystals with co-exposed {101} and {001} facets represent a promising platform for fundamental studies in photocatalysis and for the development of novel photocatalytic systems exhibiting higher than usual quantum efficiencies. Herein, we present protocols enabling the photoreductive deposition of Pt nanoparticles onto anatase TiO2 micro-sized (1-3 mm) crystals prepared by hydrothermal growth in fluoride-containing solutions to be carried out either facet-selectively (on {101} facets only) or facet non-selectively (on both {101} and {001} facets). The photocatalytic behavior of resulting photocatalysts is studied using investigations of oxidative photodegradation of a test pollutant (4-chlorophenol, 4-CP), photocurrent measurements, and kinetic analysis of the open-circuit photopotential decay. We demonstrate that the deposition of Pt nanoparticles effectively triggers the photocatalytic degradation of 4-CP at anatase crystals which are otherwise completely inactive. The role of Pt in triggering the photocatalysis is demonstrated to consist chiefly in the catalytic enhancement of the reaction rate of oxygen reduction by photogenerated electrons. Only platinized {101} facets contribute to photocatalysis, whereas the {001} facets, in the literature often referred to as “highly reactive”, are even after platinization completely inactive, most likely due to (1 × 4) surface reconstruction upon the heat treatment necessary to decrease the amount of surface fluorides. Based on our results, we highlight the eminent role of efficient surface catalysis for effective charge separation, and provide specific design rules for further development of photocatalysts with high quantum efficiencies.

The affinity of biomolecules, such as peptides and proteins, with inorganic surfaces, is a fundamental topic in biotechnology and bionanotechnology. Amino acids are often used as “model” bits of peptides or proteins for studying their properties in different environments and/or developing functional surfaces. Despite great demand for knowledge about amino acid interactions with metal oxide surfaces, studies on the issue represent a fragmentary picture. In this paper, we describe amino acid adsorption on nanocrystalline anatase systematically at uniform conditions. Analysis of the Gibbs free adsorption energy indicated how the aliphatic, aromatic, polar, and charged side chain groups affect the binding affinity of the amino acids. Thermodynamic features of the L-amino acid adsorption receive thorough interpretation with calculated molecular descriptors. Theoretical modelling shows that amino acids complex with TiO2 nanoparticles as zwitterions via ammonium group., This work was financially supported by the Russian Foundation for Basic Research (grant no. 15-03-07834-a). I.K. acknowledge the financial support from Spanish MINECO (CTQ2014-52956-C3-1-R and MAT2016-78155-C2-1-R).

Polymeric carbon nitride-hydrogen peroxide adduct (PCN-H2O2) has been prepared, thoroughly characterised and its application for selective photocatalytic conversion of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxaldehyde (FDC) in aqueous suspension has been studied. The PCN-H2O2 adduct is stable in aqueous suspension under UV and solar irradiation up to 100 °C. It is also stable up to 200 °C if heated in air, while at temperatures close to 300 °C its decomposition takes place. Based on the obtained characterisation data it has been proposed that H2O2 attaches to the non-polymerised carbon nitride species and to the heptazine nitrogen atoms, thus producing strong hydrogen bonding within the PCN-H2O2 adduct. The blockage of the surface amino-groups in PCN-H2O2 by H2O2 hinders the interaction of HMF with these sites, which are responsible for unselective substrate conversion. PCN-H2O2, although being less active, possesses a superior selectivity in natural solar light assisted oxidation of HMF to FDC reaching 80% with respect to its thermally etched PCN counterpart, which gives rise to a 40–50% selectivity. We believe that the exceptional performance of the applied photocatalyst in the selective photocatalytic conversion of HMF to a high added value FDC in a green solvent under natural illumination makes a significant contribution to the development of environmentally friendly technologies for biomass valorisation.

A set of bare and P-doped graphitic carbon nitride (g-C3N4) photocatalysts has been prepared by thermal condensation of melamine, urea or thiourea. For the sake of comparison, a g-C3N4 sample obtained in the presence of cyanuric acid and thermally exfoliated C3N4 powders were also studied. The materials were physicochemically characterized and their photocatalytic activity was studied for the selective oxidation of benzyl alcohol (BA), 4-methoxy benzyl alcohol (4-MBA) and piperonyl alcohol (PA) in water suspension both under UV and visible light irradiation. The influence of the type and position of the substituents on conversion and selectivity to aldehyde was remarkable. The presence of P in the C3N4 material improved the selectivity of the reaction towards the aldehyde., University of Oviedo thanks for financial support Spanish MINECO (MAT2013-40950-R, CTQ2014-52956-C3-1-R and MAT2016-78155- C2-1-R) grants. I.K. is grateful for financial support of the Ministry of Education and Science of the Russian Federation (grant No 4.9722.2017/8.9)

The Keggin heteropolyacid (HPA), H3PW12O40 (PW12) has been supported on commercial boron nitride (BN) and two types of home prepared carbon nitride (C3N4). The supported PW12 was used in the gas-solid (photo)catalytic 2-propanol dehydration reaction to give propene at atmospheric pressure and temperatures in the range 70–120 °C and resulted more active than the pristine PW12. Reaction rate increased by increasing the temperature. Noticeably, the propene formation rate was higher by irradiating the catalytic system. The PW12/BN material resulted more active than PW12/C3N4. The acidity of the HPA cluster accounts for the catalytic role, whereas both the acidity and the redox properties of the HPA species were responsible for the increase of the reaction rate in the photo-assisted catalytic reaction.

[EN] Keggin [PW12O40]3– and Wells–Dawson [P2W18O62]6– heteropolyanions are nanosized transition-metal-oxygen clusters belonging to the heteropolyacids (HPAs) family. They are widely used as catalysts due to their high Brønsted acidity, and their dispersion on solid supports favors the accessibility to their acid sites generally increasing the catalytic activity. A series of binary materials composed of Keggin or Wells–Dawson HPAs and SiO2, TiO2, and ZrO2 have been prepared by impregnation or solvothermal methods. Remarkable differences have been found in the catalytic activities among the unsupported and supported HPAs. These differences have been correlated in the past to the structural changes of the HPAs due to the cluster–support interaction, which is different depending on preparation methodologies of the binary material. In the present work, the modes of interaction between the two types of HPA, Keggin and Wells–Dawson, and various supports have been studied by X-ray absorption spectroscopy. The obtained data have been compared to the characterization of the same materials reported before by using different bulk and surface physicochemical techniques. The characterization results were then used to correlate the interaction modes between the HPAs and the supports with the catalytic performances reported for 2-propanol dehydration to propene and for propene hydration to 2-propanol. The results reveal that the deposition of HPA by impregnation or solvothermal treatment may cause distortions in the H3PW12O40 cluster structure depending on the presence of stronger (TiO2 and ZrO2) or weaker (SiO2) basic sites in the support, respectively. Moreover, the type of preparation method affects the structure and acidic properties of the supported HPAs. In particular, during the preparation of TiO2 and ZrO2 with HPA by in situ solvothermal method, the reaction of the HPA with the products of metal alkoxides hydrolysis occurs with consequent destruction of the Keggin structure. Therefore, the catalytic activity of such materials is poor. These modifications, in addition to the bulk and surface features of the supported HPAs, affected the catalytic 2-propanol dehydration to a significant extent. On the contrary, the propene hydration was less influenced, probably, due to the propene nonpolar nature., I.K. acknowledges the financial support from Spanish MINECO (MAT2016-78155-C2-1-R), Gobierno del Principado de Asturias (GRUPIN-ID2018-170), and Ministry of Education and Science of the Russian Federation (grant No. 4.9722.2017/8.9). L.F.L. is grateful to progetto di Ricerca ARS01_00637 Energie per l′Ambiente-TARANTO (PNR 2015-2020) for financial support. The authors acknowledge The European Synchrotron (The ESRF), MINECO, and CSIC for the provision of measurements using the BM25-SpLine beamline. They also thank the BM25-SpLine staff for the technical support beyond their duties.

Hydrolysis products of aqueous yttrium nitrates obtained by sol-gel method at room temperature, under atmospheric pressure without any templates and structure directing agents were investigated by thermal analysis combined with mass spectrometry of thermolysis products, XRD and scanning electron microscope with elemental EDS analyzer. Formation of yttrium hydroxonitrocarbonates with various ratio depending on synthesis conditions was found. The samples obtained at 8.5 pH with hydrolysis time at least 40 min using ammonia water solution have the least quantity of impurities and demonstrates the most visible layered morphology. The most explicit layered morphology and the least amount of impurities were revealed in the samples obtained at 8.5 pH with hydrolysis time at least 40 min using ammonia water solution as a hydrolytic agent.

In the present work we scrutinize the effect of substituents in the phenyl ring of the benzyl alcohol on its photo-oxidation to the corresponding benzaldehyde driven by polymeric carbon nitride photocatalyst in aqueous medium. It has been established that electron donating (ED) substituents in para- and ortho-position with respect to the CH2OH-group promote the reactivity of the substrate without compromising the selectivity towards benzaldehyde formation, maintaining it in the range of 84–98 %, if compared to the unsubstituted molecule. The same observation is true for meta-substituted benzyl alcohol with an electron withdrawing (EW) group. On the other hand, the presence of ED-group in meta-position or EW-group in para-position with respect to the CH2OH-group reduces the reactivity as well as the selectivity towards the aldehyde production, resulting in the values of selectivity ranging from 40 to 80 %. Quantum chemical calculations have allowed to establish that the reactivity correlates with the positive charge on the benzylic carbon in benzyl alcohol cation intermediate, while the selectivity, most probably, is conditioned by a negative charge on the carbon atoms in the phenyl ring being a target for an electrophile attack. The modification of the polymeric C3N4 photocatalyst with H2O2 reduces the unselective benzyl alcohol oxidation, thus favouring the higher selectivity towards benzaldehyde production.

The effect of Eu doping of ceria nanocubes on the morphology, oxidation state of deposited Au particles and their activity in CO oxidation was studied. The decisive role of doping of ceria support with Eu in the sintering of deposited Au nanoparticles has been established and discussed for the first time. The redispersion of gold nanoparticles is responsible for the formation of small, ca. ~1 nm Au nanoclusters, and as a consequence the increase of the number of active sites participating in CO-oxidation reaction.

The commercialization of oxygen-related energy storage/conversion devices, for instance metal-air batteries or fuel cells, is highly dependent on development of low-cost, high performance electrocatalysts for oxygen reduction/oxygen evolution reactions (ORR and OER). In the present study, we employed Co-ZIF-9 as a sacrificial precursor to synthesize highly efficient bifunctional ORR/OER electrocatalysts through tuning the pyrolysis temperature and Fe-doping of the zeolitic imidazolate framework. The synthesized samples were characterized extensively using X-ray photoelectron spectroscopy (XPS), X-ray diffraction, elemental CHN and ICP analyses, and Fourier transform infrared (FTIR) spectroscopy as well as scanning (SEM) and transmission (TEM) electron microscopies. It has been found that the Fe-doping can significantly affect the electrocatalytic activity of the product through improving the number of transferred electrons. The ZIF-9_Fe3_Pyrol exhibited excellent electrocatalytic activity towards ORR (Eonset = 0.90 V vs. RHE) and OER (Eonset = 1.55 V vs. RHE), much better than other evaluated catalysts and comparable to the commercial PtRuC bifunctional catalyst. Moreover, the ZIF-9_Fe3_Pyrol sample outperformed the precious PtRuC catalyst with very little decay in ORR and OER activity over long continuous operation. The ZIF-9_Fe3_Pyrol exhibited excellent performance as a cathode catalyst in rechargeable Zn-air batteries, superior to the one assembled with the state-of-the-art catalyst.

Four different C 3 N 4 specimens have been prepared, a bulk one (MCN), a thermally etched (MCN-TE), a solid prepared by hydrothermally treating MCN with H 2 O 2 (MCN-H 2 O 2 ) and a polymeric carbon nitride-hydrogen peroxide adduct (MCN-TE-H 2 O 2 ). The principal aim of this work was to correlate the capability of the prepared material to generate reactive oxygen species (ROS), under irradiation, with their photocatalytic activities in terms of conversion and selectivity for partial oxidation reactions. Photoelectrochemical studies revealed that MCN-TE represented the best material in terms of photoconductivity, whereas MCN-H 2 O 2 was defective and evidenced a poor mobility of carriers. EPR studies showed a maximum generation of reactive oxygen species irradiating the MCN-TE sample. The photocatalytic activity of these materials in the selective oxidation of three different alcohols to the corresponding aldehydes, both under UV and natural solar light, showed that the highest conversion was obtained in the presence of the MCN-TE sample, whereas the most selective one was MCN-TE-H 2 O 2 . Under solar light irradiation the performances of the powders were generally better than those under UV light. The characterization of the C 3 N 4 -based materials well justified their photocatalytic activity. The pristine C 3 N 4 materials were more active but less selective than those prepared in the presence of H 2 O 2 .

The affinity of biomolecules, such as peptides and proteins, with inorganic surfaces, is a fundamental topic in biotechnology and bionanotechnology. Amino acids are often used as "model" bits of peptides or proteins for studying their properties in different environments and/or developing functional surfaces. Despite great demand for knowledge about amino acid interactions with metal oxide surfaces, studies on the issue represent a fragmentary picture. In this paper, we describe amino acid adsorption on nanocrystalline anatase systematically at uniform conditions. Analysis of the Gibbs free adsorption energy indicated how the aliphatic, aromatic, polar, and charged side chain groups affect the binding affinity of the amino acids. Thermodynamic features of the l-amino acid adsorption receive thorough interpretation with calculated molecular descriptors. Theoretical modeling shows that amino acids complex with TiO

Composite microporous SiO2-TiO2 spheres and micro/mesoporous TiO2 spheres were prepared via the template-free two-step synthetic route using aqueous peroxotitanate solution and tetraethyl orthosilicate (TEOS) as precursors. Both the composite SiO2-TiO2 and pure TiO2 spheres prepared by the solvent-exchange method were initially non-porous, but the applied reflux treatment in water-ethanol suspension successfully transformed them into microporous materials with high apparent surface areas approaching 500 m2·g− 1 and the micropore volume of 0.17 cm3·g− 1, while maintaining the same morphology. The prepared composites retained high values of pore volume and specific surface area up to 400 °C of thermal treatment temperature. The crystallization of TiO2 into the anatase phase in the mixed oxide occurred only at 700 °C, that process was also accompanied by the significant reduction of pore volume, as well as apparent surface area values. The prepared materials were tested as adsorbents for the lead(II) removal; they demonstrated high adsorption capacities, reaching 340 mg(Pb2 +)·g− 1. Moreover, the mixed silica-titania oxide was found to be more efficient adsorbent at low pH values., South Ural State University is grateful forfinancial support of theMinistry of Education and Science of the Russian Federation (grant No16.2674.2014/K). University of Oviedo gratefully acknowledgesfi-nancial support from the Spanish MINECO (MAT2013-40950-R andMAT2016-78155-C2-1-R). Igor Krivtsov thanks for the support theRussian Foundation for Basic Research 16-29-10757-ofi.

This work reports a study on the reactivity of polymeric carbon nitride (PCN) and PCN-H2O2 adduct samples for sunlight photocatalytic selective oxidation reactions. The characterization of these materials was reported in a previous paper where the reactivity towards the partial oxidation of 5-hydroxymethylfurfural (HMF) was studied by using two different laboratory scale photoreactors; one irradiated by UV lamps and the other one by natural sunlight. In the present study it has been confirmed the effectiveness of these C3N4 based materials for the selective partial oxidation of HMF to FDC (2,5-furandicarboxaldehyde) in aqueous medium in a pilot plant photoreactor irradiated by natural sunlight. The reactivity results and, in particular, the selectivity to FDC formation have been very encouraging, mostly by considering that the reaction was carried out in water. Moreover, they are comparable with those obtained in the laboratory scale photoreactors irradiated by both UV lamps and natural sunlight. Interestingly, the pristine PCN sample has shown a higher HMF conversion with respect to that of the PCN-H2O2 adduct, but the last one is more selective to the FDC formation. A kinetic study indicates that the pseudo-first-order rate constant of HMF oxidation is higher in the case of pristine photocatalyst and that the equilibrium adsorption constants of HMF is higher in the case of PCN-H2O2 adduct catalyst. Finally, the partial oxidation of two aromatic alcohols, i.e. benzyl alcohol (BA) and 4-methoxy benzyl alcohol (4-MBA) to benzaldehyde (BAL) and 4-methoxy benzaldehyde (4-MBAL), respectively, has also been studied.

Magnetite (Fe3O4) nanoparticles modified with a nonionic surfactant, Triton X-100, have been applied for magnetic solid-phase extraction of organochlorine pesticides (OCPs) from a water medium. The magnetic core-shell nanoparticles decorated with layers of silica and Triton X-100 have been prepared through a step-by-step technique. The synthesized materials were thoroughly characterized using transmission electron microscopy, powder X-ray diffraction analysis, nitrogen physisorption, elemental analysis, and vibrating sample magnetometry. The synthesized solids were tested for the preconcentration of OCPs present in water for their subsequent analysis by gas chromatography coupled with mass spectrometry. The proposed method has demonstrated a good linearity ( R 2 > 0.9915) in the range of 1–10 000 ng·kg−1, with a relative standard deviation of less than 11.7%. The preconcentration factors obtained under the optimal conditions were in the range of 2362–10593 for 100 mL of sample solution.

A new solvent-exchange technique to prepare anatase nanoparticles with exceptional thermal stability and photocatalytic activity is described here. The process of preparation is accomplished by using organic solvents to precipitate hydrous titania particles from a basic aqueous medium containing a titanium peroxo complex. Undoped titanium dioxide formed via a solvent exchange method has unprecedented thermal stability against transformation to the rutile phase, as opposed to TiO2 prepared by the common method of the gelation of an aqueous titanium peroxo complex. On the basis of X-ray thermodiffraction experiments, it has been established that the thermal treatment at 1000 °C of the titania prepared by ethanol precipitation contains 100% pure anatase phase. The stabilization of anatase is induced by the high defectiveness of the TiO2 nanostructure, which is evidenced from band-gap energy estimation, PXRD and HRTEM studies. The prepared TiO2 nanoparticles show an outstanding photocatalytic activity comparable to the commercial Aeroxide P25 photocatalyst in the UV-assisted decomposition of methylene blue., We gratefully acknowledge financial support from the Spanish MINECO (MAT2013-40950-R, CTQ2011-29272-C04-02, and Técnicos de Infraestructuras Científico-Tecnológicas grants PTA2011-4903-I to Z.A. and PTA2011-4950-I to S.A.K.), the Government of the Principality of Asturias (Severo Ochoa PhD grant BP-14-029 to M. I.) and FEDER. South Ural State University acknowledges financial support of The Ministry of Education and Science of the Russian Federation Grant no. 16.2674.2014/K.

Extended X-ray absorption fine structure (EXAFS) investigation of the oxygen-rich titania formed via the thermal treatment of N-doped TiO has revealed that the removal of N-dopants is responsible for the creation of defect sites in the titanium environment, thus triggering at high temperatures (500-800 °C) the capture of atmospheric oxygen followed by its diffusion toward the vacant sites and formation of interstitial oxygen species. The effect of the dopants on Ti coordination number and Ti-O and Ti-N bond distances has been estimated. The photocatalytic p-cresol degradation tests have demonstrated that the interband states formed by the N-dopants contribute to a greater extent to the visible-light activity than the oxygen interstitials do. However, under the UV irradiation the oxygen-rich titania shows higher efficiency in the pollutant degradation, while the N-dopants in N-TiO play the role of recombination sites. The presence of the surface nitrogen species in TiO is highly beneficial for the application in partial photooxidation reactions, where N-TiO demonstrates a superior selectivity of 5-hydroxymethyl furfural (HMF) oxidation to 2,5-furandicarboxaldehyde (FDC). Thus, this work underlines the importance of a rational design of nonmetal doped titania for photocatalytic degradation and partial oxidation applications, and it establishes the role of bulk defects and surface dopants on the TiO photooxidation performance., This work was financially supported by Spanish MINECO (MAT2013-40950-R, MAT2016-78155-C2-1-R, and CTQ2014-52956-C3-1-R), Gobierno del Principado de Asturias (GRUPIN14-060 and GRUPIN14-078), FEDER and South Ural State University thanks for the support the Ministry of Education and Science of the Russian Federation (grant No 16.2674.2014/K)., MINECO/ICTI2013-2016/MAT2016-78155-C2-1-R

Detailed investigation of thermal and structural properties of mixed SiO2/TiO2 xerogels prepared via the method based on application of a precursor containing peroxo titanic acid and oligomeric silica and by the conventional co-precipitation technique has been presented. Formation of oxide phases from the xerogels prepared via the peroxo method and the co-precipitation of inorganic salts has been studied by TG/DSC, FTIR and in situ powder XRD techniques. The co-precipitation method provides higher degree of molecular homogeneity of the composite oxide, while in the case of the peroxo route segregation of the oxides takes place. The silica–titania samples prepared by the co-precipitation method include anatase phase, which is stable up to 1000 °C, while TiO2 in the mixed oxide synthesized by the peroxo method transits to rutile at temperatures near 800 °C. The presented data give no evidence for formation of Si O O Ti peroxo bridges in the xerogels prepared via the peroxo method. Peroxo groups in the silica–titania xerogels synthesized via the peroxo-method have been found to be more stable in silica–rich samples, compared to pure titania. Thus, these materials hold promise for application as catalysts in oxidation reactions and photocatalysis.

We propose in this manuscript a new peroxo-mediated procedure for preparing magnesia-zirconia mixed oxides, with Mg/Zr molar ratio between 1 and 3, with enhanced distribution of basic sites. The mixed magnesia-zirconia oxides have been prepared from the gelled complex by Pechini-type method. The MgO-ZrO 2 materials have been characterized and used as catalysts for acetone aldol condensation. The proposed preparation method provides a high degree of molecular homogeneity and favours the formation of magnesia-stabilized zirconia phase. Acetone gas-phase self-condensation was carried out over these catalysts as model reaction requiring the presence of basic sites. The condensation yields diacetone alcohol and mesityl oxide as mean C6 products, and phorones, isophorones and mesitylene as C9 products. In comparison to Mg-Zr oxide prepared by co-precipitation, these new materials present better conversions and higher selectivity to linear dimers and trimers (as mesitylene), whereas the selectivity for isophorones is significantly lower. © 2014 Elsevier B.V., This work was supported by the Spanish Government (contract CTQ2011-29272-C04-02).

The composite silica-zirconia xerogels have been prepared via sol–gel method using zirconium oxychloride, oxynitrate, acetate and sodium silicate as the precursors. The prepared materials have been characterized using FTIR, TG/DTA, EDX and surface area analyses. It has been established that surface area of silica-zirconia xerogels significantly depends on the zirconium source, but phase transitions and structural features of the xerogels seem to be unaffected by the choice of the zirconia precursor. Prepared xerogels increase the activity of chiral inductor in the asymmetric Biginelli reaction. The anion of the zirconium salt adsorbed on the surface of the synthesized material and the presence of Si–O–Zr heterolinkages determines the reaction yield. The highest chemo- and enantioselectivity towards formation of ee isomer have been provided by the catalyst prepared from zirconium oxychloride.

Two series of the composite silica-zirconia xerogels with various SiO2/ZrO2 molar ratios have been prepared by the “acidic” and “basic” precipitation methods. It has been established that the ways of synthesis have significant effect on surface area, morphological and thermal properties of the xerogels. In addition, the segregation processes in dependence on post-synthetic treatment have been examined in the gels with various molar compositions. Optimal molar composition for each synthetic route in terms of the phase segregation stability of the composite SiO2–ZrO2 xerogels has been proposed.

The unprecedented ability of g-C3N4 to chemoselectively photo-oxidise the methyl group of 2-(4-methylphenoxy)ethanol instead of the easily oxidised oxyethanol fragment has been demonstrated. When g-C3N4 is treated with H2O2, its selectivity enhances due to the blocking of surface sites responsible for the adsorption and the subsequent oxidation of the oxyethanol substituent., This work was financially supported by Spanish MINECO (MAT2013-40950-R, CTQ2014-52956-C3-1-R and MAT2016-78155-C2-1-R), Gobierno del Principado de Asturias (GRUPIN14-060, GRUPIN14-078), Severo Ochoa PhD grant BP-14-029 to MI, and FEDER. EB is grateful to the Ministry of Education and Science of the Russian Federation (grant 4.1157.2017/PP) for financing the computational studies. IK is thankful to the Ministry of Education and Science of the Russian Federation (grant no. 4.9722.2017/8.9)

Graphitic carbon nitride assisted partial photocatalytic oxidation of 5-hydroxymethyl-2-furfural (HMF) in aqueous medium was investigated. Different carbon nitride precursors were considered, being melamine the one yielding the most efficient photocatalyst. The obtained 30% selectivity of HMF oxidation to 2,5-furandicarboxaldehyde (FDC) is higher than those reported up to now. A further thermal exfoliation of the g-C3N4 samples showed under artificial light irradiation both an enhanced photocatalytic activity in conversion of HMF, and selectivity (ca. 42–45%) to FDC. The performance of the catalysts increased when the experiments were carried out under real outdoor illumination, reaching 50% of selectivity versus FDC formation at 40% of HMF conversion. The utilization of radical scavengers revealed that O2− was the main reactive species responsible for HMF oxidation to FDC. The photocatalytic test carried out under natural solar irradiation resulted in higher yields of FDC compared to that observed in the laboratory UV irradiated set-up, thus demonstrating the applicability of the exfoliated carbon nitride material in real-life conditions., University of Oviedo gratefully acknowledges financial support from the MINECO (MAT2013-40950-R), FEDER-FICyT (GRUPIN14-060) and CTQ2014-52956-C3-1-R. IK thanks for the support the Ministry of Education and Science of the Russian Federation (grant No 16.2674.2014/K).

The photocatalytic TiO2-assisted decomposition of 2-(4-methylphenoxy)ethanol (MPET) in aqueous solution has been studied for the first time. The intermediate compounds of MPET photodegradation have been also determined. A toxic p-cresol is formed in significant quantities during the photocatalytic reaction. A solvent-exchange approach for a template-free preparation of spherical TiO2 particles has been described, which is based solely on precipitation of hydrous titania from aqueous titanium peroxo complex by using organic solvents. The proposed method favours the formation of spherical titania particles with a mean size varying from 50 to 260 nm depending on the choice of solvent. The procedure for converting nonporous titania spheres into mesoporous material maintaining the same spherical morphology has been developed. The synthesized TiO2 spheres demonstrate a degree of MPET photo-degradation close to that of the commercial titania Aeroxide P25, besides being successfully recovered and reused for four reaction cycles without loss of photocatalytic activity. The effectiveness of the commercial Aeroxide P25 in MPET photodegradation, on the other hand, suffers 10-time drop during the third reaction cycle, which is attributed to its poor recoverability because the photocatalyst is composed of small particles of 20 nm size., We gratefully acknowledge financial support from the Spanish MINECO (MAT2016-78155-C2-1-R, MAT2013-40950-R, CTQ2011-29272-C04-02), and the Government of the Principality of Asturias (GRUPIN14-060; GRUPIN14-078; and “Severo Ochoa” PhD grantBP-14-029 to M.I.) and FEDER. South Ural State University acknowledges financial support from Ministry of Education and Science of the Russian Federation (grant No 16.2674.2014/K). IK is grateful for the support by Act 211 Government of the Russian Federation, contract № 02.A03.21.0011.

Gels were prepared via sol-gel method by addition of zirconium oxychloride solution into sodium metasilicate (SZ) and sodium metasilicate solution into zirconium oxychloride (ZS) at varying final pH. Si/Zr molar ratio equaled 1/1. Synthesized gels were dried with calcium chloride until they reached a constant mass. SEM and nitrogen adsorption analysis have shown that SZ gels have surface area 175-200 m 2 g -1, consist of 20-30 nm grains. ZS samples have surface area about 1 m 2 g -1, consist of grains smaller than 10 nm. Thermal and X-ray phase analysis have shown that transition of amorphous ZrO 2 to crystalline form shifts from 430 to 850-870 °C for SZ gels. Unlike zirconia gels phase transitions that proceed in order: "amorphous (430 °C) - tetragonal (800 °C) - monoclinic (1,000 °C) phases", themonoclinic phase inZSgels appears immediately after transition from amorphous to crystalline state; the tetragonal phase in SZ samples is stable until 1,000 °C. © Akadémiai Kiadó, Budapest, Hungary 2012.

Composite silica–titania spherical particles, from the nanometer to submicron size, have been synthesized via a new template-free method, being achieved by the reaction of aqueous titanium peroxo complex with TEOS (tetraethylorthosilicate) in aliphatic alcohols. The choice of the solvent greatly affects the growth of silica–titania particles. It has been established that size of the spheres increases as carbon chain length of alcohol extends (from methanol to n-propanol). The nanometer size SiO2–TiO2 spheres with mean diameter of about 50 nm are formed in the methanol solution, while n-propanol promotes particle growth up to 400 nm. The synthesized composites retain amorphous structure up to 500 °C due to the formation of Si–O–Ti heterolinkages, whose presence has been confirmed by FTIR and XPS studies., South Ural State University is grateful for financial support of the Ministry of Education and Science of the Russian Federation (grant No 16.2674.2014/K). University of Oviedo gratefully acknowledges financial support from the MINECO (MAT2013-40950-R) and FEDER-FICyT (GRUPIN14-060). IK thanks for the support the Russian Foundation for Basic Research13-03-12188-ofi.

A new completely inorganic method of preparation of silica–titania photocatalyst has been described. It has been established that the addition of silica promotes crystallinity of TiO2 anatase phase. Relative crystallinity and TiO2 crystal size in the silica–titania particles increase with the silica content until SiO2/TiO2 molar ratio of 0.9, but at higher molar ratios they start to decrease. The single-source precursor containing peroxo titanic (PTA) and silicic acids has been proved to be responsible for high crystallinity of TiO2 encapsulated into amorphous silica. It has been proposed that peroxo groups enhance rapid formation of crystalline titania seeds, while silica controls their growth. It has been concluded from the TEM that the most morphologically uniform anatase crystallites covered with SiO2 particles are prepared at SiO2/TiO2 molar ratio of 0.4. This sample, according to 29Si NMR, also shows the high content of hydroxylated silica Q3 and Q2 groups, and it is the most photocatalytically active in UV-assisted decomposition of methylene blue among the tested materials. It has been determined that the increase in the amount of the condensed Q4 silica in the mixed oxides leads to the decrease in photocatalytic performance of the material, despite its better crystallinity. High crystallinity, low degree of incorporation of Ti atoms in SiO2 in the mixed oxide and adsorption of methylene blue in the vicinity of photoactive sites on the hydroxylated silica have been considered as the main factors determining the high degradation degree of methylene blue in the presence of silica–titania., South Ural State University acknowledges financial support of The Ministry of Education and Science of the Russian Federation Grant No 16.2674.2014/K. The study is also carried out within grants of Spanish MINECO (MAT2013-40950-R; CTQ2011-29272-C04-02). Marina Ilkaeva thanks the government of the Principality of Asturias for a Ph.D. fellowship (Severo Ochoa programm) BP 14-029.

et al., The preparation procedure of silica-titania composite oxide using novel solution/sol single precursor containing titanium peroxocomplex and silicic acid has been described. Pechini-type sol-gel process has been used to prepare oxides from the aqueous precursor. Some structural, morphological and textural characteristics of the prepared material have been presented. Composite SiO 2/TiO2 has high surface area (c.a. 300 m2/g), and it is composed of anatase nanoparticles with the mean diameter of 5 nm embedded in amorphous silica, then TiO2 prepared via similar method is presented as a mixture of anatase and rutile phases. The proposed synthetic procedure meets the requirements of "green chemistry". © 2013 Springer Science+Business Media New York., The study is carried out within the Federal Goal-oriented Program "Scientific and scientific pedagogical personnel of innovative Russia" for 2009–2013, Gov. contract No. 14.132.21.1449, and a grant of Russian Ministry of Education No. 01201255647. Oviedo University team thanks the financial support from FEDER and MINECO (MAT2010-15094).