Self-assembled plasmonic templates produced by microwave annealing: applications to surface-enhanced Raman scattering

Perhaps the simplest method for creating metal nanoparticles on a substrate is by driving their self-assembly with the thermal annealing of a thin metal film. By properly tuning the annealing parameters one hopes to discover a recipe that allows the pre-determined design of the NP arrangement. However, thermal treatment is known for detrimental effects and is not really the manufacturer's route of choice when it comes to large-scale applications. An alternative method is the use of microwave annealing, a method that has never been applied for metal processing, due to the high reflectance of microwave radiation at the surface of a metal. However, in this work we challenge the widely used nanostructuring methods by proving the microwave's annealing ability to produce plasmonic templates, out of extremely thin metal films, by simply using a domestic microwave oven apparatus. We show that this process is generic and independent of the deposition method used for the metal and we further quantify the suitability of these plasmonic templates for use in surface-enhanced Raman scattering applications

Carbon Nanotubes Encapsulating Superconducting Single-Crystalline Tin Nanowires

Superconducting low dimensional systems are the natural choice for fast and sensitive infrared detection, because of their quantum nature and the low-noise, cryogenic operation environment. On the other hand, monochromatic and coherent electron beams, emitted from superconductors and carbon-based nanostructured materials, respectively, are significant for the development of electron optical systems such as electron microscopes and electron-beam nanofabrication systems. Here we describe for the first time a simple method which yields carbon nanotubes encapsulating single crystalline superconducting tin nanowires by employing the catalytic chemical vapor deposition method over solid tin dioxide. The superconducting tin nanowires, with diameters 15-35 nm, are covered with well-graphitized carbon walls and show, due to their reduced diameters, a critical magnetic field (Hc) more than 30 times higher than the value of bulk metallic tin.

Synthesis and characterization of ZnS nanosized semiconductor particles within mesoporous solids

ZnS semiconductor quantum dots have been synthesized using a method involving melt exchange reaction inside the pores of MCM-41 and subsequent reaction with H2S. The ZnS quantum dots-MCM-41 composite, which has been studied with XRD, EDS, and BET techniques, is shown to have retained within the pores the formed quantum dots, with a size distribution exhibiting a maximum nanoparticle diameter of ca. 1.8 nm. The structure and the sorption properties of the ZnS/MCM-41 composite have been studied by means of X-ray diffraction, Fourier transform infrared spectroscopy, and surface area measurements. All experimental data reveal that all the final composite products, containing up to 9.3 wt % ZnS as verified by EDS analysis, keep the basic structural characteristics of MCM-41 materials, without significant reduction of their active surface areas. The quantum dot optical properties have been studied with UV-vis, photoluminescence, and photoluminescence excitation spectroscopies providing evidence for the low-dimensional character of the ZnS semiconductor particles. © 2006 American Chemical Society

Mechanism of heavy metal uptake by a hybrid MCM-41 material: Surface complexation and EPR spectroscopic study

A novel hybrid MCM-41-based material was synthesized by incorporation of AEDTC [N-(2-aminoethyl)dithiocarbamate] in the MCM-41 pores. The derived MCM-41 ⊗ AEDTC material possesses high AEDTC loading 35% [w:w], and a well-defined array of regular mesopores with a specific surface area of 632 m2/g. Heavy metal, Cd, Pb, Cu, and Zn, uptake was studied in detail at physiological pH values 6-8, by a combination of analytical and electron paramagnetic resonance (EPR) spectroscopic techniques. The analytical data show a significant improvement, i.e., 200-500%, for Pb, Cu, and Zn uptake by the MCM-41 ⊗ AEDTC hybrid vs the unmodified MCM-41. In contrast, Cd shows an exceptional behavior: (a) Cd uptake by MCM-41 ⊗ AEDTC is very low. (b) Competitive metal uptake experiments reveal that Cd ions cause a characteristic inhibition of Cu or Pb uptake by the MCM-41 ⊗ AEDTC while Cd binding itself always remained low. The present findings are analyzed by a combination of surface complexation modeling and EPR spectroscopy. Accordingly, in the MCM-41 ⊗ AEDTC the sulfur atoms of AEDTC provide strong binding sites for metal binding, with a stoichiometry [SAEDTC]:[Metal] = 1:1. Cd inhibits accessibility of Cu or Pb ions in the AEDTC sites. © 2009 Elsevier Inc. All rights reserved

Synthesis and characterization of hybrid MCM-41 materials for heavy metal adsorption

A small dithiocarbamate molecule, N-(2-Aminoethyl)dithiocarbamate, was synthesized, characterized and afterwards used to modify and activate the surfaces of MCM-41 materials. The structure and the surface charge properties of the starting and the novel organic-inorganic hybrid mesoporous materials were studied by means of powder X-ray diffraction, Fourier transform infrared spectroscopy, DTA/TG thermal analyses, surface area measurements and potentiometric acid-base titrations. The hybrid materials retained the regular hexagonal arrangement of cylindrical pores which is the characteristic of the MCM-41 solids, while a high content (2.57 mmol/g) of the organic molecules in the final products was achieved. Despite the high concentration of the dithiocarbamate molecules in the pores of the hybrid MCM-41 materials, final solids retained high specific surface areas (632 m2/g) indicating a homogenous incorporation of the small organic molecules in the pores. A surface complexation model was developed to explain the results of the potentiometric titrations and to describe the surface charge and H-binding properties of the starting and final hybrid materials. These materials are promising heavy metal adsorbents due to the presence of the effective dithiocarbamate groups and the low pH value (3.2) of the point of zero charge. © 2009 Elsevier Inc. All rights reserved

Hybrid [polysulfone-Zero Valent Iron] membranes: Synthesis, characterization and application for As^III remediation

Hybrid polysulfone membranes decorated with Zero Valent Iron (ZVI) nanoparticles were prepared and evaluated for AsIII uptake. The hybrid polysulfone/ZVI membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM), mercury intrusion porosity measurements, thermal gravimetric analysis (TGA) and differential thermal analysis (DTA). The membranes are characterized by a macroporous structure with ZVI particles dispersed both inside the pores as well as at their surface. Electron Paramagnetic Resonance (EPR) spectroscopy reveals that the surface sulfide groups of polysulfone are readily accessible by extrinsic CuII cations. Moreover the polysulfone/ZVI membranes have a considerable electron-donating capacity to surface-adsorbed atoms, thus they are able to reduce CuII to CuI, and inhibit oxidation of ZVI from Fe0 to Fe3+. As a result, the Zero Valent Iron particles are stabilized against oxidation by ambient air and show appreciable AsIII adsorption capacity (26.6mgg-1). This renders them a significant stability, thus they can be reused at least four times for AsIII adsorption with a loss less than 1% of their As-uptake capacity. Based on a theoretical Surface Complexation Model we provide a consistent interfacial/structural picture that describes quantitatively all observed phenomena

Efficient and Rapid Photocatalytic Reduction of Hexavalent Chromium Achieved by a Phloroglucinol-Derived Microporous Polymeric Organic Framework Solid

A microporous polymeric organic framework (POF) based on phloroglucinol (phlo-POF) was for the first time evaluated on photoreduction and removal processes of hexavalent chromium (Cr6+) from aqueous solutions. The phlo-POF synthesis was based on reaction of phloroglucinol and terephthalaldehyde under hydrothermal conditions. Structural and chemical characterization was performed using UV-vis-NIR diffuse reflectance spectroscopy (DRS), FT-infrared spectroscopy, and thermogravimetric methods, while surface area analysis was employed to determine other physical and surface properties. Batch experiments were conducted on contaminated water to determine the rate and extent of Cr6+ removal and its immobilization by the phlo-POF material. The kinetic studies showed a rapid removal of Cr6+ ions from the water in the presence of the phlo-POF, best described by the zero-order kinetic model. The efficiency of the material with UV-C irradiation on Cr6+ reduction was compared with a well-studied material, the Degussa P-25 TiO2 catalyst, and found to be ∼200% higher. Cycle experiments verify the successful reuse of the phlo-POF photocatalyst for at least ten times for Cr6+ reduction

Low-temperature synthesis and characterization of gallium nitride quantum dots in ordered mesoporous silica

Semiconducting gallium nitride (GaN) quantum dots (QDs) were synthesized at low temperatures (650 °C), using ammonia flow without any organogallium precursor compound, assisted and controlled by an ordered mesoporous silica MCM-41 as host matrix. The final materials exhibit an intense blue shift of the band gap energy compared to the three-dimensional (3D) GaN. MCM-41 hosted GaN QD synthesis is also reported from pyrolysis of an organic precursor, tris(dimethylamido)gallium(III), at 365 °C under ammonia flow, with the largest band gap blue shift reported for such synthesized GaN of 0.6 eV. The QDs, involving inorganic precursor, exhibit an average X-ray diffraction estimated diameter of 12.6 Å and crystallize in the zinc blende lattice with cubic symmetry (β-GaN), whereas the hexagonal system is thermodynamically preferred. QDs, based on organic precursor, have hexagonal symmetry (α-GaN, wurtzite structure) with an average diameter of 20.6 Å. Spectroscopic and structural characterization of the QD-MCM composites showed the successful synthesis of well-defined distributions of QDs, exhibiting luminescence at high energies in the UV region and in some cases defect luminescence, depending on the specific synthetic route. © 2011 American Chemical Society

Naphthalene-based periodic nanoporous organosilicas: II. Hydrogen and methane adsorption and physicochemical study

Novel Periodic Nanoporous Organosilicas (PNOs) synthesized by direct co-condensation of tetraethylorthosilicate and triethoxy(naphthalen-1-yl)silane (as described in detail in part I) were evaluated for their hydrogen and methane storage ability. The naphthalene-based PNO materials exhibit regular hexagonal arrangement of uniform pores, high naphthalene content up to 17 wt.%, specific surface areas above 1000 m 2/g and pore size distributions in the microporous/mesoporous boundary. Methane and hydrogen storage properties, at different temperatures, have been investigated for these samples by Sievert-type apparatus. The samples exhibit a reversible methane/hydrogen surface excess adsorption capacity, with measured maximum uptake of up to 5.27 wt.% at 298 K and 3.5 MPa and 2.05 wt.% at 77 K and 4.3 MPa respectively. The analysis of the obtained isotherm curves by Tth equation shows high grade of surface homogeneity of the samples. Total storage capacities were also estimated. For methane a maximum 41.6 v/v at 298 K and 3.5 MPa was found, while for hydrogen a maximum 15.8 g/L at 77 K and 4.3 MPa was calculated. © 2012 Elsevier Inc. All rights reserved

Nanoscale zero-valent iron supported on mesoporous silica: Characterization and reactivity for Cr(VI) removal from aqueous solution

MCM-41-supported nanoscale zero-valent iron (nZVI) was sytnhesized by impregnating the mesoporous silica martix with ferric chloride, followed by chemical reduction with NaHB4. The samples were studied with a combination of characterization techniques such as powder X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) and Mössbauer spectroscopy, N2 adsorption measurements, transmission electron microscopy (TEM), magnetization measurements, and thermal analysis methods. The experimental data revealed development of nanoscale zero-valent iron particles with an elliptical shape and a maximum size of ~80nm, which were randomly distributed and immobilized on the mesoporous silica surface. Surface area measurements showed that the porous MCM-41 host matrix maintains its hexagonal mesoporous order structure and exhibits a considerable high surface area (609m2/g). Mössbauer and magnetization measurements confirmed the presence of core-shell iron nanoparticles composed of a ferromagnetic metallic core and an oxide/hydroxide shell. The kinetic studies demonstrated a rapid removal of Cr(VI) ions from the aqueous solutions in the presence of these stabilized nZVI particles on MCM-41, and a considerably increased reduction capacity per unit mass of material in comparison to that of unsupported nZVI. The results also indicate a highly pH-dependent reduction efficiency of the material, whereas their kinetics was described by a pseudo-first order kinetic model. © 2013 Elsevier B.V