Highly ordered cubic mesoporous electrospun SiO2 nanofibers

Cubic (Im (3) over barm) mesoporous silica nanofibers were successfully prepared using a new F127-PVA-SiO2 tri-constituent assembly approach by the electrospinning technique. PVA was used to protect the F127 directed cubic micelles which usually deform during electrospinning. The preformed Au NPs can be loaded inside the mesopores of the nanofibers

Stable CdS QDs with intense broadband photoluminescence and high quantum yields

Aqueous synthesis of CdS quantum dots (QDs) using thiolactic acid (TLA) as a capping agent was reported. These QDs exhibited excellent colloidal and photostability over a span of 2 years and showed intense broadband and almost white photoluminescence suitable for solid state lighting devices. The photoluminescence (PL) property of the aqueous CdS QDs is optimized by adjusting various processing parameters. The highest quantum yield (QY) achieved for TLA capped CdS QDs of average size 3.5 nm was similar to 50%. Luminescence lifetime measurements of CdS-TLA QDs indicated longer lifetimes and a larger contribution of the surface-related emission, indicating removal of quenching defects. (C) 2011 Elsevier B.V. All rights reserved

Electrospun anatase TiO2 nanofibers with ordered mesoporosity

Anatase TiO2 nanofibers (200-300 nm in diameter) with 3-dimensionally (3D) ordered pore structure and high surface area were synthesized by electrospinning technique. The unique combination of partially acetylacetone chelated Ti-alkoxide, viscosity-controlling cum high positive charge balancing agent PVP and structure director F127 yielded nanofibers with ordered mesoporosity similar to the Pm (3) over barm structure. Dynamic heating of the fibers in the temperature range 350-540 degrees C and simultaneous XRD studies revealed that the amorphous to anatase transformation initiated at about 400 degrees C with the retention of 3D mesoporosity up to the final heat-treatment stage. TEM studies also confirmed this. During amorphous to anatase conversion, the surface area decreased from 165 (350 degrees C) to 90 m(2) g(-1) (540 degrees C). The crystalline mesoporous nanofibers showed enhanced photocatalytic activity with reusability

Transformation of Pd -> PdH(0.7) nanoparticles inside mesoporous Zr-modified SiO(2) films in ambient conditions

Pd nanoparticles were generated in situ in a mesoporous Zr-modified SiO(2) film and transformed into PdH(x) (x approximate to >0-0.7) nanoparticles by dipping in aqueous NaBH(4) solution in ambient conditions, and the adsorbed hydrogen can be released to regenerate the original Pd nanoparticles at 120 degrees C

TiO2 nanoparticles doped SiO2 films with ordered mesopore channels: a catalytic nanoreactor

Titanium dioxide (TiO2) incorporated ordered 2D hexagonal mesoporous silica (SiO2) films on a glass substrate were fabricated for use as a catalytic nanoreactor. Films were prepared using a tetraethyl orthosilicate (TEOS) derived SiO2 sol and a commercially available dispersion of TiO2 nanoparticles (NPs) in the presence of pluronic P123 as the structure directing agent. The effect of TiO2 doping (4-10 mol% with respect to the equivalent SiO2) into the ordered mesoporous SiO2 matrix was thoroughly investigated. The undoped SiO2 film showed a mesostructural transformation after heat-treatment at 350 degrees C whereas incorporation of TiO2 restricted such a transformation. Among all the TiO2 incorporated films, TEM showed that the 7 equivalent mol% TiO2 doped SiO2 film (ST-7) had an optimal composition which could retain the more organized 2D hexagonal (space group p(6)mm)-like mesostructures after heat-treatment. The catalytic activities of the TiO2 doped (4-10 mol%) films were investigated for the reduction of toxic KMnO4 in an aqueous medium. ST-7 film showed the maximum catalytic activity, as well as reusability. A TEM study on the resultant solution after KMnO4 reduction revealed the formation of MnO2 nanowires. It was understood that the embedded TiO2 NPs bonded SiO2 matrix increased the surface hydroxyl groups of the composite films resulting in the generation of acidic sites. The catalytic process can be explained by this enhanced surface acidity. The mesoporous channel of the ST-7 films with TiO2 doping can be used as a nanoreactor to form extremely thin MnO2 nanowires

Pd-Ni alloy nanoparticle doped mesoporous SiO2 film: the sacrificial role of Ni to resist Pd-oxidation in the C-C coupling reaction

A Pd-Ni alloy nanoparticle (NP) doped mesoporous SiO2 film was synthesized using a one pot inorganic-organic sol-gel process in the presence of structure director P123. Pure Pd and Ni NP containing films were also synthesized as controls. Overall a composition of 10 mol% metal (in the case of Pd-Ni, 5 mol% of each metal) and 90 equivalent mol% SiO2 was maintained in the heat-treated films. Grazing incidence X-ray diffraction and transmission electron microscopy studies of the final heat-treated Pd-Ni doped films revealed the (111) oriented growth of the Pd-Ni alloy NPs, with an average size of 5.3 nm, residing inside the mesopores of the SiO2 film. We performed the C-C coupling reaction employing the film-catalysts and the progress of the reaction was monitored using a fluorimeter. Overall, only the Pd-Ni alloy NP doped film showed good catalytic activity with excellent recyclability. It has been determined that the higher oxidising ability of metallic Ni restricted the oxidation of Pd in the Pd-Ni alloy catalyst under the reaction conditions, leading to the maintained reusability in consecutive cycles

Pd/Cu bimetallic nanoparticles embedded in macroporous ion-exchange resins: an excellent heterogeneous catalyst for the Sonogashira reaction

Cationic and macroporous amberlite resins with formate (HCOO-) as the counter anion (ARF) have been used to prepare a new class of heterogeneous Pd/Cu bimetallic composite nanoparticles (NPs) (Pd/Cu-ARF). The physicochemical characteristics of Pd/Cu-ARF were examined with the help of FTIR spectroscopy, X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and atomic absorption spectroscopy (AAS). XRD and TEM showed the existence of composite NPs made of metallic Pd, PdO and CuO. The TEM analysis revealed fairly uniform distributions of composite NPs of average size similar to 4.9 nm. The as-synthesized nanocomposite material (Pd/Cu-ARF) exhibited high catalytic activity in the Sonogashira cross-coupling reaction between aryl iodide and terminal alkynes. Heterogeneity of the catalytic activity was evidenced from different tests (hot-filtration and catalyst-poisoning experiments) and the recycling ability of the catalyst was examined for five consecutive runs without any significant loss of activity

Soft Chemical Fabrication of Iron-Based Thin Film Electrocatalyst for Water Oxidation under Neutral pH and Structure–Activity Tuning by Cerium Incorporation

Design of electrocatalysts for the fundamentally important oxygen evolution reaction can be greatly aided by systematic structure–activity tuning via composition variation. We have explored the iron–cerium system as they are the most abundant transition and rare earth metals, and also due to the mutualistic impact of their size and electronic attributes that can induce critical changes in the structure and electrochemical activity. Submicrometer thick films of a series of Fe­(III)–Ce­(III) phosphate­(oxyhydroxide) (FeCePH) are fabricated using a soft chemical strategy involving surfactant-aided assembly, spin-coating, and mild thermal annealing. FT-IR, Raman, and X-ray photoelectron spectroscopies, chemical analysis, X-ray diffraction, and electron microscopy reveal the systematic structural, electronic, and morphological variation, on tuning the iron–cerium composition. Nitrogen adsorption–desorption studies show the surface area increasing and pore size distribution shrinking with the cerium content, indicating its structure-directing role. The electrocatalysis of water oxidation by FeCePH films on FTO-coated glass is studied in neutral pH conditions. The overpotential and Tafel slope decrease with increasing cerium content, reaching minima at the optimal Fe:Ce ratio of 1:0.5; the turnover frequency shows a corresponding increase and maximum. The trends are explained on the basis of the structural changes in the films, and the coupling of Ce³⁺/Ce⁴⁺ with Fe³⁺/Fe⁴⁺ that leads to active state regeneration. This study presents a rational strategy to tune the efficiency of easily fabricated transition metal-based electrocatalyst thin films through rare earth metal incorporation; it should prove useful in the design of cost-effective catalysts for water oxidation

Electrospun ZrO2 nanofibers: precursor controlled mesopore ordering and evolution of garland-like nanocrystal arrays

We observed that the hydrolysis-condensation reaction of precursors makes a significant difference in constructing ordered mesopores in electrospun ZrO2 nanofibers. Transmission-SAXS studies confirm the generation of uniform clusters of size similar to 1.44 nm in the ZrOCl2 center dot 8H(2)O (inorganic salt) derived sol due to its relatively slow hydrolysis-condensation process. These initial -Zr-O-Zr- clusters acted as building blocks to form uniform 3D ordered cubic (Pm (3) over barm) mesopores in the presence of Pluronic F127 surfactant. In contrast, the commonly used Zr-alkoxide (zirconium n-propoxide) precursor, which is highly hydrolysable even after the use of a controlling agent, generates larger clusters with broad size distributions due to the uncontrolled hydrolysis-condensation of alkoxy groups. Accordingly, in the presence of F127, the alkoxide derived sol yielded disordered mesopores in the resultant fibers. XRD under dynamic heating conditions (up to 900 degrees C) and the corresponding TEM studies of the ZrOCl2 center dot 8H(2)O derived nanofibers confirmed the retention of mesopores even in the extremely thin nanofibers (diameter similar to 15-25 nm) after the amorphous to crystal phase transformation (cubic/tetragonal). An interesting morphological transformation has been observed in the nanofibers at 900 degrees C where the fibers have been uniformly segmented by distinct single nanocrystals (width similar to 15-65 nm) with mesopores. Further heat-treatment at 1100 degrees C made these segmented nanofibers nonporous, and a garland-like appearance with monoclinic nanocrystal arrays was formed