Morphology and topography analysis of mesoporous titania templated by micrometric latex sphere arrays

In this work, mesoporous titania is prepared by templating latex sphere arrays with four different sphere diameters at the micrometric scale (phi > 1 mu m). The mesoporous titania homogeneously covers the latex spheres and substrate, forming a thin coating characterized by N-2 adsorption isotherm, small angle X-rays scattering, atomic force, field emission and transmission electronic microscopies. Mesoporous titania has been templated into different shapes such as hollow particles and monoliths according to the amount of sol used to fill the voids of the close packed latex spheres. Titania topography strongly depends on the adsorption of polymeric segments over latex spheres surface, which could be decreased by changing the dimensions of latex spheres (phi = 9.5 mu m) generating a lamellar architecture. Thus, micrometric latex sphere arrays can be used to achieve new surface patterns for mesoporous materials via a fast and inexpensive chemical route for construction of functional devices in different technological fields such as energy conversion, inclusion chemistry and biomaterials. (C) 2011 Elsevier Inc. All rights reserved.

Dually fluorescent silica nanoparticles

The cationic dyes 9-aminoacridine (9AA) and safranine (Sf) were entrapped into silica spheres of about 0.2 mu m diameter prepared by modified Stober method. The fluorescent materials are investigated by steady-state and time-resolved emission, in addition of confocal fluorescence microscopy. Silica particles containing 9-aminoacridine (SP9AA) and safranine (SPSf or both dyes (SPSf9AA) are emissive particles. When both dyes are present in the same particle but loaded in sequential stages 9AA emission is quenched as a consequence of energy transfer from 9AA (donor) to Sf (acceptor). This result suggests that particle growing processes where the acceptor is incorporated first into the core do not prevent donor/acceptor pairs to be close due to an overlay of the concentration gradients of both dyes in a radial core-shell like distribution. (C) 2010 Elsevier B.V. All rights reserved.

Shape Changes of Pt Nanoparticles Induced by Deposition on Mesoporous Silica

Polyvinylpyrollidone (PVP)-capped platinum nanoparticles (NPs) are found to change shape from spherical to flat when deposited on mesoporous silica substrates (SBA-15). Transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and extended X-ray absorption fine structure (EXAFS) analyses are used in these studies. The SAXS results indicate that, after deposition, the 2 nm NPs have an average gyration radius 22% larger than in solution, while the EXAFS measurements indicate a decrease in first neighbor co-ordination number from 9.3 to 7.4. The deformation of these small capped NPs is attributed to interactions with the surface of the SBA-15 support, as evidenced by X-ray absorption near-edge structure (XANES).

Raman and XRD study on brookite-anatase coexistence in cathodic electrosynthesized titania

Among the many methods developed for the synthesis of titanium dioxide, cathodic electrosynthesis has not received much attention because the resulting amorphous oxy-hydroxide matrix demands a further thermal annealing step to be transformed into crystalline titania. However, the possibility of filling deep recessed templates by the control of the solidliquid interface makes it a potentially suitable technique for the fabrication of porous scaffolds for photovoltaics and photocatalysis. Furthermore, a careful control of the crystallization process enables the growth of larger grains with lower density of grain boundaries, which act as electron traps that slow down electronic transport and promote charge recombination. In this report, well crystallized titania deposits were obtained by thermal annealing of amorphous deposits fabricated by cathodically assisted electrosynthesis on indium-tin oxide (ITO)substrates. The combined use of Raman spectroscopy and X-ray diffraction showed that the crystallization process is more intricate than previously assumed. It is shown that the amorphous matrix evolves into a rutile-free mixture of brookite and anatase at temperatures as low as 200 degrees C that persists up to 800 degrees C, when pure anatase dominates. The amount of brookite in the brookiteanatase mixture reaches a maximum at 400 degrees C. This very simple method for obtaining a brookiteanatase mixture and the ability to tune their proportions by thermal annealing is a promising alternative whose potential for solar cells and photocatalysis deserves a careful evaluation. Copyright (C) 2011 John Wiley & Sons, Ltd.

Immobilization of marine fungi on silica gel, silica xerogel and chitosan for biocatalytic reduction of ketones

The scanning electron microscopy (SEM) analysis showed that whole living hyphal of marine fungi Aspergillus sclerotiorum CBMAI 849 and Penicillium citrinum CBMAI 1186 were immobilized on support matrices of silica gel, silica xerogel and/or chitosan. P. citrinum immobilized on chitosan catalyzed the quantitative reduction of 1-(4-methoxyphenyl)-ethanone (1) to the enantiomer (S)-1-(4-methoxyphenyl)-ethanol (3b), with excellent enantioselectivity (ee > 99%, yield = 95%). Interestingly, ketone 1 was reduced with moderate selectivity and conversion to alcohol 3b (ee = 69%, c 40%) by the free mycelium of P. citrinum. This free mycelium of P. citrinum catalyzed the production of the (R)-alcohol 3a, the antipode of the alcohol produced by the immobilized cells. P. citrinum immobilized on chitosan also catalyzed the bioreduction of 2-chloro-1-phenylethanone (2) to 2-chloro-1-phenylethanol (4a,b), but in this case without optical selectivity. These results showed that biocatalytic reduction of ketones by immobilization hyphal of marine fungi depends on the xenobiotic substrate and the support matrix used. (c) 2012 Elsevier B.V. All rights reserved.

Structural and Luminescence Properties of Silica-Based Hybrids Containing New Silylated-Diketonato Europium(III) Complex

A new betadiketonate ligand displaying a trimethoxysilyl group as grafting function and a diketone moiety as complexing site (TTA-Si = 4,4,4-trifluoro-2-(3-trimethoxysilyl)propyl)-1-3-butanedione (C4H3S)COCH[(CH2)(3)Si(OCH3)(3)]COCF3) and its highly luminescent europium(III) complex [Eu(TTA-Si)(3)] have been synthesized and fully characterized. Luminescent silica-based hybrids have been prepared as well with this new complex grafted on the surface of dense silica nanoparticles (28 +/- 3 nm) or on mesoporous silica particles. The covalent bonding of Eu(TTA-Si)(3) inside the core of uniform silica nanoparticles (40 +/- 5 nm) was also achieved. Luminescence properties are discussed in relation to the europium chemical environment involved in each of the three hybrids. The general methodology proposed allowed high grafting ratios and overcame chelate release and tendency to agglomeration, and it could be applied to any silica matrix (in the core or at the surface, nanosized or not, dense or mesoporous) and therefore numerous applications such as luminescent markers and luminophors could be foreseen.

NIR luminescent Er3+/Yb3+ co-doped SiO2-ZrO2 nanostructured planar and channel waveguides: Optical and structural properties

Optical and structural properties of planar and channel waveguides based on sol gel Er3+ and Yb3+ co-doped SiO2-ZrO2 are reported. Microstructured channels with high homogeneous surface profile were written onto the surface of multilayered densified films deposited on SiO2/Si substrates by a femtosecond laser etching technique. The densification of the planar waveguides was evaluated from changes in the refractive index and thickness, with full densification being achieved at 900 degrees C after annealing from 23 up to 500 min, depending on the ZrO2 content Crystal nucleation and growth took place together with densification, thereby producing transparent glass ceramic planar waveguides containing rare earth-doped ZrO2 nanocrystals dispersed in a silica-based glassy host Low roughness and crack-free surface as well as high confinement coefficient were achieved for all the compositions. Enhanced NIR luminescence of the Er3+ ions was observed for the Yb3+- codoped planar waveguides, denoting an efficient energy transfer from the Yb3+ to the Er3+ ion. (C) 2012 Elsevier B.V. All rights reserved.

Enzymatic Solid-Phase Reactor Based on Silica Organofunctionalized with p-Phenylenediamine for Electrochemical Detection of Phenolic Compounds

A new biomaterial, based on silica organofunctionalized with p-phenylenediamine (p-PDA) and the enzyme peroxidase, was used in the development of an enzymatic solid-phase reactor. The analytical techniques used in the characterization showed that the organic ligand was incorporated into the silica matrix. Thus, the silica modified with p-PDA allowed the incorporation of peroxidase by the electrostatic interaction between the carboxylic groups present in the enzyme molecules and the amino groups attached to the silica. The enzymatic solid-phase reactor was used for chemical oxidation of phenols in 1, 4-benzoquinone that was then detected by chronoamperometry. The system allowed the analysis of hydroquinone with a detection limit of 83.6 nmol L-1. Thus, the new material has potential in the determination of phenolic compounds river water samples.

Broad combined orange-red emissions from Eu2+- and Eu3+-doped low-silica calcium aluminosilicate glass

In this paper, a broad combined orange-red emission from Eu2+- and Eu3+-doped low-silica calcium aluminosilicate (LSCAS) glass is reported. Spectroscopic results demonstrate that it is possible to tune the emission wavelength by changing the excitation wavelength in the UV-Vis region. The color coordinates for the emission spectra were calculated, and using the Commission Internationale de l'Eclairage 1931 and 1976 chromatic diagrams, it is possible to note that they are dependent on the excitation wavelength. In addition, the (u', v') color coordinates for the investigated LSCAS samples are close to the Planckian spectrum in the cold region between 2000 and 2600K. Our results show that the Eu:LSCAS system can be used in a white light phosphor when mixed in aggregate with phosphors using green-yellow luminescent ions. (c) 2012 Optical Society of America

Photo-induced electron transfer in supramolecular materials of titania nanostructures and cytochrome c

In the present paper, we report on the molecular interaction and photochemistry of TiO2 nanoparticles (NPs) and cytochrome c systems for understanding the effects of supramolecular organization and electron transfer by using two TiO2 structures: P25 TiO2 NPs and titanate nanotubes. The adsorption and reduction of cytochrome c heme iron promoted by photo-excited TiO2, arranged as P25 TiO2 NPs and as nanotubes, were characterized using electronic absorption spectroscopy, thermogravimetric analysis, and atomic force microscopy. In an aqueous buffered suspension (pH 8.0), the mass of cytochrome c adsorbed on the P25 TiO2 NP surface was 2.3 fold lower (0.75 mu g m(-2)) than that adsorbed on the titanate nanotubes (1.75 mu g m(-2)). Probably due to the high coverage of titanate nanotubes by adsorbed cytochrome c, the low amount of soluble remaining protein was not as efficiently photo-reduced by this nanostructure as it was by the P25 TiO2 NPs. Cytochrome c, which desorbed from both titanium materials, did not exhibit changes in its redox properties. In the presence of the TiO2 NPs, the photo-induced electron transfer from water to soluble cytochrome c heme iron was corroborated by the following findings: (i) identification by EPR of the hydroxyl radical production during the irradiation of an aqueous suspension of TiO2 NPs, (ii) impairment of a cytochrome c reduction by photo-excited TiO2 in the presence of dioxane, which affects the dielectric constant of the water, and (iii) change in the rate of TiO2-promoted cytochrome c reduction when water was replaced with D2O. The TiO2-promoted photo-reduction of cytochrome c was reverted by peroxides. Cytochrome c incorporated in the titanate nanotubes was also reversibly reduced under irradiation, as confirmed by EPR and UV-visible spectroscopy.

Self-Assembly of Poly(4-vynil-N-alkylpyridinium) Bromide onto Silica: Effect of Side-Chain Length on Structural Aspects at a Molecular Level

Self-assembly of poly(4-vynil-N-alkyl)pyridinium bromide with alkyl side chains of 2, 5, 7, 10, or 16 carbons from ethanolic solutions onto flat silica surfaces was studied by means of ellipsometry, atomic force microscopy (AFM), contact angle measurements, and sum-frequency generation (SFG) vibrational spectroscopy in the CH3 and CH2 stretch region. Ab initio quantum-chemical calculations on the N-alkylpyridinium side-group with restricted Hartree-Fock (RHF) method and 6-311G (d,p) basis set were C one to estimate the charge distribution along the pyridinium ring and the alkyl side-chain. SFG results showed that longer side chains promote the disorientation of the alkyl groups at the surface, corroborating with the contact angle values. AFM images revealed film homogeneity, regardless the alkyl side group. However, after 24 h contact with water, ringlike structures appeared on the film surfaces, when the polycation alkyl side chain had 7 or less carbons, and as the alkyl chain increased to 10 or 16 carbons, the films dewetted because the hydrophobic interactions prevailed over the electrostatic interactions between the pyridinium charged groups and the negatively charged SiO2 surface. Under acid conditions (HCl 0.1 mol.L-1), the film mean thickness values decreased up to 50% of original values when the alkyl side chains were ethyl or pentyl groups due to ion-pair disruption, but for longer groups they remained unchanged. Quantum-chemical optimization and Mulliken electron population showed that (i) from C2 to C15 the positive charge at the headgroup (HG) decreased 0.025, while the charge at combined HG + alpha-CH2 increased 0.037; and (ii) for C6 or longer, the alkyl side group presents a tilt in the geometry, moving away from the plane. Such effects summed up over the whole polymer chain give support to suggest that when the side chains are longer than 7 carbons, the hydrophobic interaction decreases film stability and increases acid resistance.

Design of a Dinuclear Nickel(II) Bioinspired Hydrolase to Bind Covalently to Silica Surfaces: Synthesis, Magnetism, and Reactivity Studies

Presented herein is the design of a dinuclear Ni-II synthetic hydrolase [Ni-2(HBPPAMFF)(mu-OAc)(2)(H2O)]-BPh4 (1) (H(2)BPPAMFF = 2-[(N-benzyl-N-2-pyridylmethylamine)]-4-methyl-6-[N-(2-pyridylmethyl)aminomethyl)])-4- methyl-6-formylphenol) to be covalently attached to silica surfaces, while maintaining its catalytic activity. An aldehyde-containing ligand (H(2)BPPAMFF) provides a reactive functional group that can serve as a cross-linking group to bind the complex to an organoalkoxysilane and later to the silica surfaces or directly to amino-modified surfaces. The dinuclear Ni-II complex covalently attached to the silica surfaces was fully characterized by different techniques. The catalytic turnover number (k(cat)) of the immobilized (NiNiII)-Ni-II catalyst in the hydrolysis of 2,4-bis(dinitrophenyl)phosphate is comparable to the homogeneous reaction; however, the catalyst interaction with the support enhanced the substrate to complex association constant, and consequently, the catalytic efficiency (E - k(cat)/K-M) and the supported catalyst can be reused for subsequent diester hydrolysis reactions.

Atomistic Study of Water Confined in Silica.

In this work, we have used a combined of atomistic simulation methods to explore the effects of confinement of water molecules between silica surfaces. Firstly, the mechanical properties of water severe confined (~3A) between two silica alpha-quartz was determined based on first principles calculations within the density functional theory (DFT). Simulated annealing methods were employed due to the complex potential energry surface, and the difficulties to avoid local minima. Our results suggest that much of the stiffness of the material (46%) remains, even after the insertion of a water monolayer in the silica. Secondly, in order to access typical time scales for confined systems, classical molecular dynamics was used to determine the dynamical properties of water confined in silica cylindrical pores, with diameters varying from 10 to 40A. in this case we have varied the passivation of the silica surface, from 13% to 100% of SiOH, and the other terminations being SiOH2 and SiOH3, the distribution of the different terminations was obtained with a Monte Carlo simulation. The simulations indicates a lowering of the diffusion coefficientes as the diameter decreases, due to the structuration of hydrogen bonds of water molecules; we have also obtained the density profiles of the confined water and the interfacial tension.