1,720,992 research outputs found
Optical and conductive properties of as-synthesized organic-capped TiO 2 nanorods highly dispersible in polystyrene-block-poly(methyl methacrylate) diblock copolymer
No full textAs-synthesized organic-capped TiO2 nanorods were incorporated into polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer to achieve TiO2/PS-b-PMMA nanocomposites with enhanced optical and conductive properties. The specific surface chemistry of TiO2 nanorods derived from the colloidal synthetic approach allowed their prompt incorporation in the PS-b-PMMA block copolymer template up to 50 wt %, which resulted in films with an extended coverage of highly dispersed nanoparticles for contents higher than 30 wt %. At such high nanorod contents, the films fabricated by the prepared nanocomposites demonstrated enhanced optical properties. Atomic force microscopy investigation of the nanocomposite films showed a cylindrical morphology for low nanorod contents. Conversely, higher nanorod contents resulted upon removal of the organic component in the nanocomposites with UV treatment in overall nanorod coverage of the film surface with the concomitant formation of charge percolation paths, which led to noticeable conductivity values. EFM and PF-TUNA measurements confirmed the conductive properties of the composites at nanoscale, whereas semiconductor analyzer measurements provided their macroscale characterization. In addition, an increase in the UV-vis absorption was observed with the increase in the nanorod content along with a remarkable conductivity of the overall film. © 2014 American Chemical Society
Multifunctional TiO2/FexOy/Ag based nanocrystalline heterostructures for photocatalytic degradation of a recalcitrant pollutant
No full textThe photocatalytic degradation of pollutants is a key technological application for nanomaterials. Our work aims at developing a multifunctional nanocrystalline heterostructure based on TiO2nanorods, FexOyand Ag nanoparticles (NPs), TiO2NRs/FexOy/Ag, integrating in one nanostructure a visible light photoactive moiety (TiO2NRs/Ag) and a magnetic domain (FexOy), in order to address the photoactivity under visible light and the possibility of recovery and reuse the photocatalyst. The synthesis was carried by preparing first the TiO2NRs/FexOybased heterostructure and then growing Ag NPs with control on size. The resulting multidomain structures were characterized by FTIR and absorption spectroscopy, TEM and SEM microscopy, EDS and XRD analysis. The influence of the Ag NP domain and of its size on the photoactivity of the TiO2NRs/FexOy/Ag nanostructures under visible light were investigated in the photocatalytic degradation of the Nalidixic Acid, an antibiotic used as a model compound representative of recalcitrant pollutants. In the presence of the Ag domain a significant increase of the photoactivity with respect to TiO2NRs/FexOyheterostructures and to the commercially available TiO2P25 was observed. Such an enhanced photocatalytic efficiency was found dependent on the size of the Ag domain and explained taking into account the plasmonic properties and the different possible photoactivation mechanisms
Micropatterning of Plastic Nanocomposite Films: Effect of Au Nanoparticle Content
No full textThe fabrication of hierarchical architectures of colloidal nanoparticles (NPs) represents an increasingly relevant approach to obtain innovative mesoscale materials, thanks to the original size-dependent characteristics of the nanosized building blocks, as well as, the collective properties arising from their organization. Here, an unconventional patterning method, based on formation of "breath figures" (BF), has been used to fabricate highly ordered honeycomb structures in nanocomposite materials, obtained by blending pre-synthesized colloidal gold NPs (Au NPs) in a polymeric matrix. The cast nanocomposite solutions have successfully allowed the fabrication of highly regular microporous self standing films. Large scale iridescent and ordered micropatterns with an hexagonal symmetry have been prepared and the fundamental role of NPs in stabilizing the templating water droplets in BF formation has been demonstrated. The resulting structured arrays of NP decorated pores can have a great potential as efficient catalysts for chemical reactions, as well as, templates for fabrication of photonic and optoelectronic devices, sensors and membranes for separation and purification purposes
A combined size sorting strategy for monodisperse plasmonic nanostructures
No full textThe fabrication of highly monodisperse silica coated Au NPs by the microemulsion approach and the selection of the nanostructure morphology have been described. Several experimental conditions, synthetic parameters and post-preparative strategies such as reaction time, precursor concentration, size selection techniques and NP surface treatments have been suitably investigated in order to fabricate Au and Au@SiO2 NPs with peculiar and tuneable plasmonic properties that strongly depend on the specific size distribution and nanostructure morphology. In particular, size selected precipitation of oleylaminecapped Au NPs by antisolvent titration has successfully offered a strategy to discriminate and collect monodisperse fractions with different average size and narrow size distribution. Moreover, for the first time, a deep insight into the microemulsion mechanism for the silica shell growth has been provided, highlighting the critical role played by the density of oleylamine at the Au NP surface. Specifically the capping agent has been demonstrated to strongly determine the multiplicity of the core in the final Au@SiO2 nanostructures. Density gradient centrifugation has been finally performed to sort the achieved Au@SiO2 NPs with different morphologies, which was ultimately able to recover a significant fraction formed of two Au NPs in one silica shell. A systematic characterization of the Au and Au@SiO2 NPs has been carried out by complementary morphological and spectroscopic techniques. These deeply investigated materials, with tuneable plasmonic properties, have been proposed as versatile building blocks useful for the design and fabrication of plasmonic and photonic structures as well as metamaterials for device applications
Uniform TiO2/In2O3 surface films effective in bacterial inactivation under visible light
Full text linkThis study shows that the surface modification of TiO2 is an effective route to increase the TiO2 absorption in the visible region up to similar to 600 nm for photocatalytic applications. The In2O3 decorated TiO2 films on polyester obtained by reactive sputtering were shown to accelerate the Escherichia coli inactivation under actinic and simulated solar light. TiO2 sputtered films for 10 min inactivated bacteria within 300 min under actinic light. The inactivation time was reduced when using a TiO2 10 min-In2O3 10 s sample to 150 min when using actinic light and 90 min by simulated sunlight with 50 mW/cm(2) (one half of AM1). Thinner TiO2-In2O3 coatings led to faster bacterial inactivation compared to thicker TiO2-In2O3 layers due to the reverse diffusion of the generated charges. The increase in the optical absorption of the green coloured TiO2-In2O3 film was a function of the In2O3 loading as detected by diffuse reflectance spectroscopy (DRS). Evidence of the lack of TiO2 lattice doping by the sputtered In2O3 was found by X-ray diffraction spectroscopy (XRD). The deconvolution of TiO2 bands detected by X-ray photoelectron spectroscopy (XPS) revealed the existence of Ti4+/Ti3+ signals suggesting redox catalysis at the surface of the TiO2-In2O3. The photo-induced interfacial charge transfer (IFCT) between TiO2 and In2O3 can be accounted for by the band position potentials of both semiconductors. The faster kinetics of TiO2-In2O3 inducing E. coli inactivation with a higher quantum efficiency compared to TiO2 takes place in spite of the low intensity of the IFCT optical absorption bands >400 nm.GPA
Phase Transfer of CdS Nanocrystals Mediated by Heptamine beta-Cyclodextrin
No full textA fundamental and systematic study on the fabrication of a supramolecularly assembled nanostructure of an organic ligand-capped CdS nanocrystal (NC) and multiple heptamine beta-cyclodextrin ((NH2)(7)beta CD) molecules in aqueous solution has been here reported. The functionalization process of presynthesized hydrophobic CdS NCs by means of (NH2)(7)beta CD has been extensively investigated by using different spectroscopic and structural techniques, as a function of different experimental parameters, such as the composition and the concentration of CD, the concentration of CdS NCs, the nature of the NC surface capping ligand (oleic acid and octylamine), and the organic solvent. The formation of a complex based on the direct coordination of the (NH2)(7)beta CD amine groups at the NC surface has been demonstrated and found responsible for the CdS NC phase transfer process. The amine functional group in (NH2)(7)beta CD and the appropriate combination of pristine capping agent coordinating the NC surface and a suitable solvent have been found decisive for the success of the CdS NC phase transfer process. Furthermore, a layer-by-layer assembly experiment has indicated that the obtained (NH2)(7)beta CD functionalized CdS NCs are still able to perform the host guest chemistry. Thus, they offer a model of a nanoparticle-based material with molecular receptors, useful for bio applications
Biofunctionalization of Anisotropic Nanocrystalline Semiconductor-Magnetic Heterostructures
No full textAsymmetric binary nanocrystals (BNCs) formed by a spherical gamma-Fe(2)O(3) magnetic domain epitaxially grown onto a lateral facet of a rodlike anatase TiO(2) nanorod have been functionalized with PEG-terminated phospholipids, resulting in a micellar system that enables the BNC dispersion in aqueous solution. The further processability of the obtained water-soluble BNC including PEG lipid micelles and their use in bioconjugation experiments has been successfully demonstrated by covalently binding to bovine serum albumin (BSA). The whole process has also been preliminarily performed on spherical iron oxide nanocrystals (NCs) and TiO(2) nanorods (NRs), which form single structural units in the heterostructures. Each step has been thoroughly monitored by using optical, structural, and electrophoretic techniques. In addition, an investigation of the magnetic behavior of the iron oxide NCs and BNCs, before and after incorporation into PEG lipid micelles and subsequently bioconjugation, has been carried out, revealing that the magnetic characteristics are mostly retained. The proposed approach to achieving water-soluble anisotropic BNCs and their bioconjugates has a large potential in catalysis and biomedicine and offers key functional building blocks for biosensor applications
COLLOIDAL TiO2 NANORODS FOR PHOTOCATALYSIS: A FEMTOSECOND TRANSIENT ABSORPTION STUDY
No full textConcept: The excitation-dependent relaxation dynamics of charge carriers in anatase TiO2 nanorods (NRs) was investigated by femtosecond transient absorption spectroscopy. This technique is a widely known effective tool with unique capabilities for elucidating the electron-hole (e--h+) recombination dynamics of nanocrystals. Colloidal dispersions of such anisotropic nanocrystals were excited in the UV−vis range using three different pump wavelengths, i.e. above, close to, and below the direct band gap of anatase. We show that the ultrafast dynamics strongly depends on the excitation wavelength, and influences most of the processes contributing to the relaxation dynamics.
Motivations and objectives: TiO2 nanocrystals are successfully exploited in applications related to energy conversion, such as photocatalysis and photovoltaics, thanks to their ability to generate e--h+ pairs under proper lighting. In addition, the rod-like nanocrystal shape magnifies this effect, due to a larger surface/volume ratio and a higher number of active sites of interaction with the environment. The conversion efficiency is correlated to the lifetimes of e- and h+ before their recombination, which in turn are influenced by several factors. Excitation energy plays a major role, as it defines the initial potential of the carriers. An excitation-dependent investigation of the charge carrier dynamics is thus expected to provide major information crucial for understanding their reactivity and for further rationalizing their behavior in photocatalytic applications.
Results and discussion: TiO2 NRs were synthesized by a colloidal chemistry route and dispersed in an organic solvent, thanks to oleate ions coordinating the nanocrystal surfaces. We performed pump-probe experiments in a weak-excitation regime by pumping at 300, 350, and 430 nm and probing in a broadband spectral range extending from 450 to 750 nm. The temporal evolution of photoinduced absorption changes was found to be strongly dependent on the excitation conditions, both at short and long time delays. Nonetheless, the initial charge carriers trapping in surface defect states occurs very rapidly after the photogeneration in all investigated cases. The two distinct TA bands at 500 and 700 nm, typically attributed to trapped h+ and e- in anatase, are accessible only when TiO2 nanorods are photoexcited well above the band gap, while there is no evidence of such bands when excitation occurs close to or below the band gap. In such cases the observed
dynamics are attributed to excitonic states. This evidence is also supported by the persistence of a long-lasting TA contribution ascribable to such bound states
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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