Bonding of gold nanoclusters to oxygen vacancies on rutile TiO2(110)

Through an interplay between scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we show that bridging oxygen vacancies are the active nucleation sites for Au clusters on the rutile TiO2(110) surface. We find that a direct correlation exists between a decrease in density of vacancies and the amount of Au deposited. From the DFT calculations we find that the oxygen vacancy is indeed the strongest Au binding site. We show both experimentally and theoretically that a single oxygen vacancy can bind 3 Au atoms on average. In view of the presented results, a new growth model for the TiO2(110) system involving vacancy-cluster complex diffusion is presented

Doped Framework Iron Hydroxyl Phosphate as Photocatalyst for Hydrogen Production from Water/Methanol Mixtures

[EN] In the search for novel photocatalysts for hydrogen production and with the alpha-Fe2O3 photoelectrocatalyst as a recent precedent, we report herein the preparation, semiconductor properties and photocatalytic activity of metal-doped (0.1-5 wt.-% loading) iron hydroxyl phosphate (FeP). X-ray diffraction analyses of FeP samples subjected to extended photocatalytic irradiation showed the stability of this framework phosphate under photocatalytic conditions. Doping increased the photocatalytic efficiency of FeP for all dopants, with the optimal doping level between 0.1 and 1%. Under the optimized conditions (Cr at 1% doping), the photocatalytic activity of FeP reached a hydrogen production rate of 35.82 mu molg(Fe)(-1) in the absence of platinum as co-catalyst. The conduction flat band potential was estimated by photocurrent measurements or impedance spectroscopy to be 0.1 eV versus NHE and the charge carrier density 2.6 x 10(20) carriers cm(-3). Transient absorption spectroscopy revealed a transient species decaying on the microsecond time-scale characterized by a broad band spanning 300-750 nm. This transient was attributed to the charge-separated state. These results are promising for the development of novel photocatalytic materials based on framework metal phosphate.Financial support by the Spanish Ministry of Economy and Competitiveness (MEC) (Severo Ochoa and CTQ20212-32315) and the Generalidad Valenciana (Prometeo 2012/014) is gratefully acknowledged. M. S. thanks the Spanish Consejo Superior de Investigaciones Cientificas (CSIC) and Technical University of Valencia for a postgraduate scholarship.Serra, M.; García Baldoví, H.; Alvaro Rodríguez, MM.; García Gómez, H. (2015). Doped Framework Iron Hydroxyl Phosphate as Photocatalyst for Hydrogen Production from Water/Methanol Mixtures. European Journal of Inorganic Chemistry. 2015(25):4237-4243. https://doi.org/10.1002/ejic.201500629S42374243201525Amao, Y. (2011). Solar Fuel Production Based on the Artificial Photosynthesis System. ChemCatChem, 3(3), 458-474. doi:10.1002/cctc.201000293Centi, G., & Perathoner, S. (2010). Towards Solar Fuels from Water and CO2. ChemSusChem, 3(2), 195-208. doi:10.1002/cssc.200900289Gust, D., Moore, T. A., & Moore, A. L. (2009). Solar Fuels via Artificial Photosynthesis. Accounts of Chemical Research, 42(12), 1890-1898. doi:10.1021/ar900209bHammarström, L. (2009). Artificial Photosynthesis and Solar Fuels. Accounts of Chemical Research, 42(12), 1859-1860. doi:10.1021/ar900267kSerpone, N., Lawless, D., & Terzian, R. (1992). Solar fuels: Status and perspectives. Solar Energy, 49(4), 221-234. doi:10.1016/0038-092x(92)90001-qAbbott, D. (2010). Keeping the Energy Debate Clean: How Do We Supply the World’s Energy Needs? Proceedings of the IEEE, 98(1), 42-66. doi:10.1109/jproc.2009.2035162Dunn, S. (2002). Hydrogen futures: toward a sustainable energy system. International Journal of Hydrogen Energy, 27(3), 235-264. doi:10.1016/s0360-3199(01)00131-8Kamat, P. V. (2007). Meeting the Clean Energy Demand:  Nanostructure Architectures for Solar Energy Conversion. The Journal of Physical Chemistry C, 111(7), 2834-2860. doi:10.1021/jp066952uLewis, N. S., & Nocera, D. G. (2006). Powering the planet: Chemical challenges in solar energy utilization. Proceedings of the National Academy of Sciences, 103(43), 15729-15735. doi:10.1073/pnas.0603395103Bard, A. J., & Fox, M. A. (1995). Artificial Photosynthesis: Solar Splitting of Water to Hydrogen and Oxygen. Accounts of Chemical Research, 28(3), 141-145. doi:10.1021/ar00051a007Bensaid, S., Centi, G., Garrone, E., Perathoner, S., & Saracco, G. (2012). Towards Artificial Leaves for Solar Hydrogen and Fuels from Carbon Dioxide. ChemSusChem, 5(3), 500-521. doi:10.1002/cssc.201100661Chen, X., Shen, S., Guo, L., & Mao, S. S. (2010). Semiconductor-based Photocatalytic Hydrogen Generation. Chemical Reviews, 110(11), 6503-6570. doi:10.1021/cr1001645Crabtree, G. W., Dresselhaus, M. S., & Buchanan, M. V. (2004). The Hydrogen Economy. Physics Today, 57(12), 39-44. doi:10.1063/1.1878333Graetzel, M. (1981). Artificial photosynthesis: water cleavage into hydrogen and oxygen by visible light. Accounts of Chemical Research, 14(12), 376-384. doi:10.1021/ar00072a003Ni, M., Leung, M. K. H., Leung, D. Y. C., & Sumathy, K. (2007). A review and recent developments in photocatalytic water-splitting using TiO2 for hydrogen production. Renewable and Sustainable Energy Reviews, 11(3), 401-425. doi:10.1016/j.rser.2005.01.009NOWOTNY, J., SORRELL, C., SHEPPARD, L., & BAK, T. (2005). Solar-hydrogen: Environmentally safe fuel for the future. International Journal of Hydrogen Energy, 30(5), 521-544. doi:10.1016/j.ijhydene.2004.06.012Bahnemann, D. W. (2000). Current challenges in photocatalysis: Improved photocatalysts and appropriate photoreactor engineering. Research on Chemical Intermediates, 26(2), 207-220. doi:10.1163/156856700x00255Fox, M. A., & Dulay, M. T. (1993). Heterogeneous photocatalysis. Chemical Reviews, 93(1), 341-357. doi:10.1021/cr00017a016FUJISHIMA, A., ZHANG, X., & TRYK, D. (2008). TiO2 photocatalysis and related surface phenomena. Surface Science Reports, 63(12), 515-582. doi:10.1016/j.surfrep.2008.10.001Herrmann, J.-M. (1999). Heterogeneous photocatalysis: fundamentals and applications to the removal of various types of aqueous pollutants. Catalysis Today, 53(1), 115-129. doi:10.1016/s0920-5861(99)00107-8Linsebigler, A. L., Lu, G., & Yates, J. T. (1995). Photocatalysis on TiO2 Surfaces: Principles, Mechanisms, and Selected Results. Chemical Reviews, 95(3), 735-758. doi:10.1021/cr00035a013Mills, A., & Le Hunte, S. (1997). An overview of semiconductor photocatalysis. Journal of Photochemistry and Photobiology A: Chemistry, 108(1), 1-35. doi:10.1016/s1010-6030(97)00118-4Beermann, N., Vayssieres, L., Lindquist, S.-E., & Hagfeldt, A. (2000). Photoelectrochemical Studies of Oriented Nanorod Thin Films of Hematite. Journal of The Electrochemical Society, 147(7), 2456. doi:10.1149/1.1393553Bjoerksten, U., Moser, J., & Graetzel, M. (1994). Photoelectrochemical Studies on Nanocrystalline Hematite Films. Chemistry of Materials, 6(6), 858-863. doi:10.1021/cm00042a026Hu, Y.-S., Kleiman-Shwarsctein, A., Forman, A. J., Hazen, D., Park, J.-N., & McFarland, E. W. (2008). Pt-Doped α-Fe2O3Thin Films Active for Photoelectrochemical Water Splitting. Chemistry of Materials, 20(12), 3803-3805. doi:10.1021/cm800144qKay, A., Cesar, I., & Grätzel, M. (2006). New Benchmark for Water Photooxidation by Nanostructured α-Fe2O3Films. Journal of the American Chemical Society, 128(49), 15714-15721. doi:10.1021/ja064380lSivula, K., Le Formal, F., & Grätzel, M. (2011). Solar Water Splitting: Progress Using Hematite (α-Fe2O3) Photoelectrodes. ChemSusChem, 4(4), 432-449. doi:10.1002/cssc.201000416Sivula, K., Zboril, R., Le Formal, F., Robert, R., Weidenkaff, A., Tucek, J., … Grätzel, M. (2010). Photoelectrochemical Water Splitting with Mesoporous Hematite Prepared by a Solution-Based Colloidal Approach. Journal of the American Chemical Society, 132(21), 7436-7444. doi:10.1021/ja101564fGrätzel, M. (2001). Photoelectrochemical cells. Nature, 414(6861), 338-344. doi:10.1038/35104607Wang, X., Pang, H., Zhao, S., Shao, W., Yan, B., Li, X., … Du, W. (2013). Ferric Phosphate Hydroxide Microcrystals for Highly Efficient Visible-Light-Driven Photocatalysts. ChemPhysChem, 14(11), 2518-2524. doi:10.1002/cphc.201300331Song, Y., Zavalij, P. Y., Chernova, N. A., Suzuki, M., & Whittingham, M. S. (2003). Comparison of one-, two-, and three-dimensional iron phosphates containing ethylenediamine. Journal of Solid State Chemistry, 175(1), 63-71. doi:10.1016/s0022-4596(03)00144-0Song, Y., Zavalij, P. Y., Chernova, N. A., & Whittingham, M. S. (2005). Synthesis, Crystal Structure, and Electrochemical and Magnetic Study of New Iron (III) Hydroxyl-Phosphates, Isostructural with Lipscombite. Chemistry of Materials, 17(5), 1139-1147. doi:10.1021/cm049406

Enhanced Photocatalytic H2 Production in Core–Shell Engineered Rutile TiO2

The authors thank the Major Basic Research Program, Ministry of Science and Technology of China (2014CB239401), NSFC (Nos. 51422210, 51572266, 51561130157, 51172243, 51521091). GL thanks Newton Advanced FellowshipA rationally designed crystalline Ti3+ core/amorphous Ti4+ shell configuration can reverse the population disparity between holes and electrons reaching the surface of microsized rutile TiO2 photocatalyst, thus significantly enhancing its photocatalytic activity by two orders of magnitude in terms of the hydrogen production rate under the irradiation of UV–vis light.PostprintPeer reviewe

Water-Gated Charge Doping of Graphene Induced by Mica Substrates

We report on the existence of water-gated charge doping of graphene deposited on atomically flat mica substrates. Molecular films of water in units of ~0.4 nm-thick bilayers were found to be present in regions of the interface of graphene/mica hetero-stacks prepared by micromechanical exfoliation of kish graphite. The spectral variation of the G and 2D bands, as visualized by Raman mapping, shows that mica substrates induce strong p-type doping in graphene, with hole densities of $(9 \pm 2) \times 1012 cm${-2}$. The ultrathin water films, however, effectively block interfacial charge transfer, rendering graphene significantly less hole-doped. Scanning Kelvin probe microscopy independently confirmed a water-gated modulation of the Fermi level by 0.35 eV, in agreement with the optically determined hole density. The manipulation of the electronic properties of graphene demonstrated in this study should serve as a useful tool in realizing future graphene applications.Comment: 15 pages, 4 figures; Nano Letters, accepted (2012

Porous TiO2 thin film-based photocatalytic windows for an enhanced operation of optofluidic microreactors in CO2 conversion

Using a photocatalytic window can simplify the design of an optofluidic microreactor, providing also a more straightforward operation. Therefore, the development of TiO2 coatings on glass substrates seems appealing, although a priori they would imply a reduced accessible area compared with supported nanoparticle systems. Considering this potential drawback, we have developed an endurable photocatalytic window consisting on an inner protective SiO2 layer and an outer mesoporous anatase layer with enhanced surface area and nanoscopic crystallite size (9–16 nm) supported on a glass substrate. The designed photocatalytic windows are active in the CO2-to-methanol photocatalytic transformation, with maximum methanol yield (0.52 μmol·h-1·cm-2) for greatest porosity values and minimum crystallite size. Compared with benchmark supported nanoparticle systems, the nanoscopic thickness of the coatings allowed to save photoactive material using only 11–22 μg·cm-2, while its robustness prevented the leaching of active material, thus avoiding the decay of performance at long working periods.The authors gratefully acknowledge the financial support from the Basque Government (PIBA18/14; IT1291-19), the Spanish Ministry of Science and Innovation (MICINN projects: PID2019-104050RA-I00 and PID2019-108028GB-C21), the European Union’s Horizon 2020 research and innovation program (grant agreement No 792103 SOLWARIS) and the Ramón y Cajal programme (RYC-2015-17080). Technical and human support provided by SGIker (UPV/EHU, MICINN, GV/EJ, and ESF) is also acknowledged

Photodeposition as a facile route to tunable Pt photocatalysts for hydrogen production:on the role of methanol

Photodeposition of H2PtCl6 in the presence of methanol promotes the formation of highly dispersed, metallic Pt nanoparticles over titania, likely via capture of photogenerated holes by the alcohol to produce an excess of surface electrons for substrate-mediated transfer to Pt complexes, resulting in a high density of surface nucleation sites for Pt reduction. Photocatalytic hydrogen production from water is proportional to the surface density of Pt metal co-catalyst, and hence photodeposition in the presence of high methanol concentrations affords a facile route to optimising photocatalyst design and highlights the importance of tuning co-catalyst properties in photocatalysis

Small Polarons in Transition Metal Oxides

The formation of polarons is a pervasive phenomenon in transition metal oxide compounds, with a strong impact on the physical properties and functionalities of the hosting materials. In its original formulation the polaron problem considers a single charge carrier in a polar crystal interacting with its surrounding lattice. Depending on the spatial extension of the polaron quasiparticle, originating from the coupling between the excess charge and the phonon field, one speaks of small or large polarons. This chapter discusses the modeling of small polarons in real materials, with a particular focus on the archetypal polaron material TiO2. After an introductory part, surveying the fundamental theoretical and experimental aspects of the physics of polarons, the chapter examines how to model small polarons using first principles schemes in order to predict, understand and interpret a variety of polaron properties in bulk phases and surfaces. Following the spirit of this handbook, different types of computational procedures and prescriptions are presented with specific instructions on the setup required to model polaron effects.Comment: 36 pages, 12 figure

Growth behavior of titanium dioxide thin films at different precursor temperatures

The hydrophilic TiO2 films were successfully deposited on slide glass substrates using titanium tetraisopropoxide as a single precursor without carriers or bubbling gases by a metal-organic chemical vapor deposition method. The TiO2 films were employed by scanning electron microscopy, Fourier transform infrared spectrometry, UV-Visible [UV-Vis] spectroscopy, X-ray diffraction, contact angle measurement, and atomic force microscopy. The temperature of the substrate was 500°C, and the temperatures of the precursor were kept at 75°C (sample A) and 60°C (sample B) during the TiO2 film growth. The TiO2 films were characterized by contact angle measurement and UV-Vis spectroscopy. Sample B has a very low contact angle of almost zero due to a superhydrophilic TiO2 surface, and transmittance is 76.85% at the range of 400 to 700 nm, so this condition is very optimal for hydrophilic TiO2 film deposition. However, when the temperature of the precursor is lower than 50°C or higher than 75°C, TiO2 could not be deposited on the substrate and a cloudy TiO2 film was formed due to the increase of surface roughness, respectively

UV-stable paper coated with APTES-modified P25 TiO2 nanoparticles

In order to inhibit the photocatalytic degradation of organic material supports induced by small titania (TiO2) nanoparticles, highly photocatalytically active, commercially available P25-TiO2 nanoparticles were first modified with a thin layer of (3-aminopropyl) triethoxysilane (APTES), which were then deposited and fixed onto the surface of paper samples via a simple, dip-coating process in water at room temperature. The resultant APTES-modified P25 TiO2 nanoparticle-coated paper samples exhibit much greater stability to UV-illumination than uncoated blank reference paper. Very little, or no, photo-degradation in terms of brightness and whiteness, respectively, of the P25-TiO2-nanoparticle-treated paper is observed. There are many other potential applications for this Green Chemistry approach to protect cellulosic fibres from UV-bleaching in sunlight and to protect their whiteness and maintain their brightness