Effect of Multiply Twinned Ag(0) Nanoparticles on Photocatalytic Properties of TiO2 Nanosheets and TiO2 Nanostructured Thin Films.

Ag-decorated TiO2 nanostructured materials are promising photocatalysts. We used non-standard cryo-lyophilization and ArF laser ablation methods to produce TiO2 nanosheets and TiO2 nanostructured thin films decorated with Ag nanoparticles. Both methods have a common advantage in that they provide a single multiply twinned Ag(0) characterized by {111} twin boundaries. Advanced microscopy techniques and electron diffraction patterns revealed the formation of multiply twinned Ag(0) structures at elevated temperatures (500 °C and 800 °C). The photocatalytic activity was demonstrated by the efficient degradation of 4-chlorophenol and Total Organic Carbon removal using Ag-TiO2 nanosheets, because the multiply twinned Ag(0) served as an immobilized photocatalytically active center. Ag-TiO2 nanostructured thin films decorated with multiply twinned Ag(0) achieved improved photoelectrochemical water splitting due to the additional induction of a plasmonic effect. The photocatalytic properties of TiO2 nanosheets and TiO2 nanostructured thin films were correlated with the presence of defect-twinned structures formed from Ag(0) nanoparticles with a narrow size distribution, tuned to between 10 and 20 nm. This work opens up new possibilities for understanding the defects generated in Ag-TiO2 nanostructured materials and paves the way for connecting their morphology with their photocatalytic activity.

The Key Role of Tin (Sn) in Microstructure and Mechanical Properties of Ti2SnC (M2AX) Thin Nanocrystalline Films and Powdered Polycrystalline Samples.

Layered ternary Ti2SnC carbides have attracted significant attention because of their advantage as a M2AX phase to bridge the gap between properties of metals and ceramics. In this study, Ti2SnC materials were synthesized by two different methods-an unconventional low-energy ion facility (LEIF) based on Ar+ ion beam sputtering of the Ti, Sn, and C targets and sintering of a compressed mixture consisting of Ti, Sn, and C elemental powders up to 1250 °C. The Ti2SnC nanocrystalline thin films obtained by LEIF were irradiated by Ar+ ions with an energy of 30 keV to the fluence of 1.1015 cm-2 in order to examine their irradiation-induced resistivity. Quantitative structural analysis obtained by Cs-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) confirmed transition from ternary Ti2SnC to binary Ti0.98C carbide due to irradiation-induced ß-Sn surface segregation. The nanoindentation of Ti2SnC thin nanocrystalline films and Ti2SnC polycrystalline powders shows that irradiation did not affect significantly their mechanical properties when concerning their hardness (H) and Young's modulus (E). We highlighted the importance of the HAADF-STEM techniques to track atomic pathways clarifying the behavior of Sn atoms at the proximity of irradiation-induced nanoscale defects in Ti2SnC thin films.

Surface Properties of 1DTiO2 Microrods Modified with Copper (Cu) and Nanocavities.

This work deals with Cu-modified 1DTiO2 microrods (MRs) and their surface properties. The pristine lyophilized precursor Cu_1DTiO2, prepared by an environmentally friendly cryo-lyophilization method, was further annealed in the temperature interval from 500 to 950 °C. The microstructure of all samples was characterized by electron microscopy (SEM/EDS and HRTEM/SAED), X-ray powder diffraction (XRD), infrared spectroscopy, simultaneous DTA/TGA thermoanalytical measurement, and mass spectroscopy (MS). Special attention was paid to the surface structure and porosity. The 1D morphology of all annealed samples was preserved, but their surface roughness varied due to anatase-rutile phase transformation and the change of the nanocrystals habits due to nanocavities formation after releasing of confined ice-water. The introduction of 2 wt.% Cu as electronically active second species significantly reduced the direct bandgap of 1DTiO2 in comparison with undoped TiO2 and the standard Degussa TiO2_P25. All samples were tested for their UV absorption properties and H2 generation by PEC water splitting. We presented a detailed study on the surface characteristics of Cu doped 1DTiO2 MRs due to gain a better idea of their photocatalytic activity.

The relationship between microstructure and photocatalytic behavior in lanthanum-modified 2D TiO2 nanosheets upon annealing of a freeze-cast precursor.

Titanium dioxide modified with 3 wt% La was prepared via a green freeze-casting method, and its photocatalytic activity was tested in terms of its ability to degrade 4-chlorophenol (4-CP) and remove total organic carbon (TOC). Under annealing conditions, the freeze-cast precursor was transformed into an La-modified anatase with a well-defined 2D TiO2 nanosheet morphology. Rietveld refinement of the X-ray diffraction patterns confirmed the substitutional nature of the La cation that induced local structural variations and involved subtle ion displacement in the TiO2 lattice due to the ionic size effect. Despite nearly identical tetragonal structures, replacement of Ti with La alters the photocatalytic activity through a reduction in band gap energies and an increase in charge carrier mobility. Material annealed at 650 °C exhibited the highest photocatalytic performance and achieved efficient TOC removal. Upon annealing at 800 °C, nanoscale lanthanum-enriched regions were generated due to the diffusive migration of La cations and phase transition from anatase to rutile. The La3+ cation, acting as a structural promoter, supported 2D TiO2 growth with well controlled crystallite size, surface area and porosity. La3+ could be regarded as a potential electronic promoter that can reduce the band gap of 2D TiO2 nanosheets and can provide a signature of the electron transfer and carrier charge separation. Both methods, kinetics of degradation of 4-CP and TOC, provided similar results, revealing that the photocatalytic activity under UV light irradiation increased in the order 950C < 500 °C < 800 °C < 650 °C < TiO2-P25.

Synthesis of strongly fluorescent graphene quantum dots by cage-opening buckminsterfullerene.

Graphene quantum dots is a class of graphene nanomaterials with exceptional luminescence properties. Precise dimension control of graphene quantum dots produced by chemical synthesis methods is currently difficult to achieve and usually provides a range of sizes from 3 to 25 nm. In this work, fullerene C60 is used as starting material, due to its well-defined dimension, to produce very small graphene quantum dots (∼2-3 nm). Treatment of fullerene C60 with a mixture of strong acid and chemical oxidant induced the oxidation, cage-opening, and fragmentation processes of fullerene C60. The synthesized quantum dots were characterized and supported by LDI-TOF MS, TEM, XRD, XPS, AFM, STM, FTIR, DLS, Raman spectroscopy, and luminescence analyses. The quantum dots remained fully dispersed in aqueous suspension and exhibited strong luminescence properties, with the highest intensity at 460 nm under a 340 nm excitation wavelength. Further chemical treatments with hydrazine hydrate and hydroxylamine resulted in red- and blue-shift of the luminescence, respectively.

TiO2-graphene oxide nanocomposite as advanced photocatalytic materials.

BACKGROUND: Graphene oxide composites with photocatalysts may exhibit better properties than pure photocatalysts via improvement of their textural and electronic properties. RESULTS: TiO2-Graphene Oxide (TiO2 - GO) nanocomposite was prepared by thermal hydrolysis of suspension with graphene oxide (GO) nanosheets and titania peroxo-complex. The characterization of graphene oxide nanosheets was provided by using an atomic force microscope and Raman spectroscopy. The prepared nanocomposites samples were characterized by Brunauer-Emmett-Teller surface area and Barrett-Joiner-Halenda porosity, X-ray Diffraction, Infrared Spectroscopy, Raman Spectroscopy and Transmission Electron Microscopy. UV/VIS diffuse reflectance spectroscopy was employed to estimate band-gap energies. From the TiO2 - GO samples, a 300 µm thin layer on a piece of glass 10×15 cm was created. The photocatalytic activity of the prepared layers was assessed from the kinetics of the photocatalytic degradation of butane in the gas phase. CONCLUSIONS: The best photocatalytic activity under UV was observed for sample denoted TiGO_100 (k = 0.03012 h-1), while sample labeled TiGO_075 (k = 0.00774 h-1) demonstrated the best activity under visible light.

Brightly luminescent organically capped silicon nanocrystals fabricated at room temperature and atmospheric pressure.

Silicon nanocrystals are an extensively studied light-emitting material due to their inherent biocompatibility and compatibility with silicon-based technology. Although they might seem to fall behind their rival, namely, direct band gap based semiconductor nanocrystals, when it comes to the emission of light, room for improvement still lies in the exploitation of various surface passivations. In this paper, we report on an original way, taking place at room temperature and ambient pressure, to replace the silicon oxide shell of luminescent Si nanocrystals with capping involving organic residues. The modification of surface passivation is evidenced by both Fourier transform infrared spectroscopy and nuclear magnetic resonance measurements. In addition, single-nanocrystal spectroscopy reveals the occurrence of a systematic fine structure in the emission single spectra, which is connected with an intrinsic property of small nanocrystals since a very similar structure has recently been observed in specially passivated semiconductor CdZnSe nanoparticles. The organic capping also dramatically changes optical properties of Si nanocrystals (resulting ensemble photoluminescence quantum efficiency 20%, does not deteriorate, radiative lifetime 10 ns at 550 nm at room temperature). Optically clear colloidal dispersion of these nanocrystals thus exhibits properties fully comparable with direct band gap semiconductor nanoparticles.

Photocatalytic activity of boron-modified titania under UV and visible-light illumination.

Nanosized boron(III) oxide-doped titania was prepared by homogeneous hydrolysis of titanium oxo-sulfate with urea in aqueous solutions in the presence of amorphous boron. The prepared samples were annealing at 700 degrees C. The structure of as-prepared samples was characterized by X-ray powder diffraction (XRD) and selected area electron diffraction (SAED) and surface area (BET) and porosity determination (BJH). The morphology and microstructure characteristics were obtained by scanning electron microscopy (SEM) and high-resolution electron microscopy (HRTEM). The method of UV/vis diffuse reflectance spectroscopy was employed to estimate band gap energies of the boron-doped titania. The photoactivity of the prepared samples was assessed by the photocatalytic decomposition of Orange II dye in an aqueous slurry during irradiation at 365 and 400 nm wavelength. The prepared titania samples doped with boron(III) oxide showed better photocatalytic activity in comparison with the reference TiO(2) sample. These photocatalysts showed better photocatalytic performance under visible-light irradiation.

Zinc oxide prepared by homogeneous hydrolysis with thioacetamide, its destruction of warfare agents, and photocatalytic activity.

Zinc sulfide (ZnS) nanoparticles were prepared by homogeneous hydrolysis of zinc sulfate and thioacetamide (TAA) at 80 degrees C. After annealing at a temperature above 400 degrees C in oxygen atmosphere, zinc oxide (ZnO) nanoparticles were obtained. The ZnS and ZnO nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and Brunauer-Emmett-Teller (BET)/Barrett-Joyner-Halenda (BJH) methods were used for surface area and porosity determination. The photocatalytic activity of as-prepared zinc oxide samples was determined by decomposition of Orange II dye in aqueous solution under UV irradiation of 365 nm wavelength. Synthesized ZnO were evaluated for their non-photochemical degradation ability of chemical warfare agents to nontoxic products.

Electrolytic processes in various degrees of dispersion.

While following voltammetric behavior of ultrafine metallic powders, we realized that the results obtained with six metals (Al, Fe, Ni, Cu, Mo, and W) were providing us with material for treating the connection between electroactivity and the state of dispersion of matter. The electroactive species were metallic oxides formed spontaneously on surfaces of the metallic powder particles, and we could follow their electrochemical reactivity in the states of coarse and fine suspensions, colloids, and true solutions. Each state of dispersion can be characterized by a distinctive form of electroactivity, which we illustrated by experimental results with all six metals.

Analysis of earthy pigments in grounds of Baroque paintings.

Sixteen samples of orange-red and yellow Fe-oxide earthy pigments mainly from bole grounds of Baroque paintings were studied by elemental and phase analysis and voltammetry. Fe, K, and Ti content were found to be suitable for further classification of those earthy pigments. According to the chemical and phase composition the yellow grounds were natural yellow ochres formed by intense chemical weathering in a moderate climate. Very similar phase and elemental composition of part of the orange-red boles indicated their similar geological origin or even their formation by calcination of yellow ochres. Part of the orange-red boles differed significantly from the yellow boles, especially in their increased content of Ti, indicating their relation to end products of intense weathering, e.g. laterites formed in a tropical climate. Analogous materials with a correspondingly large Ti content are not currently commercially available and their geological origin (provenance) is not clear. In several orange-red boles the intentional addition of rather coarse-grained haematite to natural ochre by the painters was assumed on the basis of Fe oxide content and crystallinity.