Supported Gold Nanoparticles for Alcohols Oxidation in Continuous-Flow Heterogeneous Systems

Gold nanoparticles (AuNPs) were anchored on alkynyl carbamate-functionalized support materials having the suitable features for application as catalysts in continuous-flow packed bed reactors. The functionalization step was carried out by grafting with the di-functional organosilane [3-(2-propynylcarbamate)propyl]triethoxysilane (PPTEOS) three commercial micrometer-sized oxide supports, i.e. silica, alumina, and titania. The alkynyl-carbamate moieties were capable to straightforwardly reduce the gold precursor HAuCl4 yielding the supported AuNPs systems Au/SiO2@Yne, Au/Al2O3@Yne, and Au/TiO2@Yne. A comparison among the three materials revealed that silica allowed the highest organic functionalization (12 wt%) as well as the highest gold loading (3.7 wt%). Moreover, TEM investigation showed only for Au/SiO2@Yne the presence of homogeneously distributed, spherically shaped AuNPs (av. diameter 15 nm). Au/SiO2@Yne is an efficient catalyst, both in batch and flow conditions, in the oxidation of a large variety of alcohols, using H2O2 as oxidizing agent, at a temperature of 90 \ub0C. Furthermore, under flow conditions, the catalyst worked for over 50 h without any significant decrease in the catalytic activity. The catalytic activity of the three catalysts was evaluated and compared in the oxidation of 1-phenylethanol as a model substrate. We found that the flow approach plays a strategic role in preserving the physical and chemical integrity of the solid catalysts during its use, with remarkable consequences for the reaction conversion (from 2% in batch to 80 % in flow) in the case of Au/TiO2@Yne

Morphological and electrochemical characterization of TiO2 blocking layers in Dye Sensitized Solar Cells

In recent years much attention has been paid to dye-sensitized solar cells due to their low cost and wide applicability. The modest efficiencies achieved by these devices are caused by several phenomena, including electronic losses due to parasitic electronic reactions. One of the most common way to reduce the electronic losses is to introduce a compact layer of conductive material (blocking layer) between the transparent conductive substrate and the sensitized semiconductor film. Aim of this work was to asses the correlation between the most common deposition processes (spin coating and dip coating) and the morphological and electrochemical properties of the blocking layers produced by them. The blocking layer of TiO2 was prepared on FTO glass, and the results obtained with the conventional dip coating were compared with the ones coming from spin coating of two different solutions of TiCl4 (50 mM). The TiO2 films obtained were deeply characterized in particular from the electrochemical point of view in order to assess the best conditions needed to obtain an efficient blocking layer. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used to understand the electrochemical behavior of the blocking layer (BL

Propargyl carbamate-functionalized Cu(II)-metal organic framework after reaction with chloroauric acid: An x-ray photoelectron spectroscopy data record

A copper-containing metal organic framework was prepared using the new organic linker 5-(2-{[(prop-2-yn-1-yloxy)carbonyl]-amino} ethoxy)isophthalic acid [1,3-H2YBDC (where Y = alkYne and BDC = Benzene DiCarboxylate)] and functionalized with gold particles by reaction with HAuCl4 under thermal treatment in methanol. The resulting system was investigated by complementary techniques to obtain information on its structure and morphology. In the present work, x-ray photoelectron spectroscopy (XPS) was employed to analyze the chemical composition of a representative specimen. Besides wide scan spectra, data obtained by the analysis of the C 1s, O 1s, N 1s, Cu 2p, and Au 4f signals are presented and critically discussed. The results highlight the reduction of Au(III) to mostly Au(I) species. Overall, the data presented herein may act as useful guidelines for the eventual tailoring of material properties and their possible implementation toward functional applications in heterogeneous catalysis

Gold nanoparticles supported on functionalized silica as catalysts for alkyne hydroamination: A chemico-physical insight

Highly stable gold nanoparticles anchored on propynylcarbamate-functionalized silica (Au/SiO2@Yne) have been efficiently utilized for the heterogeneous hydroamination of phenylacetylene with aniline under different reaction conditions. In order to ascertain the eventual influence of surface silanol groups on the system activity and selectivity tailored modifications of Au/SiO2@Yne catalysts were pursued according to two different strategies, involving respectively functionalization with trimethylethoxysilane (Au/SiO2@Yne-TMS) or post-treatment with triethylamine (Au/SiO2@Yne-NEt3). The prepared materials were analysed by several complementary techniques such as Solid State NMR (SS NMR), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD). A comparison of the resulting catalytic activities with that of the pristine Au/SiO2@Yne revealed a significant improvement for Au/SiO2@Yne-NEt3 in terms of both conversion and selectivity. Recycling and stability studies showed a catalytic activity decrease after the first run, due to the formation of polyphenylacetylene (PPhA) oligomers shielding the active sites. PPhA removal by sonication in acetone fully restored the catalytic activity and empowered the system with a good operational stability, a very crucial issue in view of eventual practical applications

Effectiveness of Snail Slime in the Green Synthesis of Silver Nanoparticles

The development of green, low cost and sustainable synthetic routes to produce metal nanoparticles is of outmost importance, as these materials fulfill large scale applications in a number of different areas. Herein, snail slime extracted from Helix Aspersa snails was successfully employed both as bio-reducing agent of silver nitrate and as bio-stabilizer of the obtained nanoparticles. Several trials were carried out by varying temperature, the volume of snail slime and the silver nitrate concentration to find the best biogenic pathway to produce silver nanoparticles. The best results were obtained when the synthesis was performed at room temperature and neutral pH. UV-Visible Spectroscopy, SEM-TEM and FTIR were used for a detailed characterization of the nanoparticles. The obtained nanoparticles are spherical, with mean diameters measured from TEM images ranging from 15 to 30 nm and stable over time. The role of proteins and glycoproteins in the biogenic production of silver nanoparticles was elucidated. Infrared spectra clearly showed the presence of proteins all around the silver core. The macromolecular shell is also responsible of the effectiveness of the synthesized AgNPs to inhibit Gram positive and Gram negative bacterial growth

Determination of sugars in atmospheric aerosols by hydrophilic interaction liquid chromatography-mass spectrometry

Sugar and Sugar alcohol are indicative compounds in the environmental aerosol which make them really important. The concentration of sugar and sugar alcohol reveal biogenic and anthropogenic information such as climate, air quality, wood consumption, the activity of plantation and pollution. The conventional analysis methods of sugar and sugar alcohol are reverse phase High Performance Liquid Chromatography–Mass Spectrometry (HPLC-MS/MS), and Gas Chromatography-Mass Spectrometry (GC-MS/MS). However, both of them have some limitations due to the sugar and sugar alcohol aerosol sample which are not easy to analyze. For reverse phase HPLC-MS/MS, the separation of analytes is not satisfied. For the GC-MS/MS, the derivatization process requires extra work and the derivatization compound is not stable. Besides, the matrix effect from the aerosol sample is a significant challenge which needs to be solved. Hence, the hydrophilic interaction chromatography (HILIC) and the Solid Phase Extraction (SPE) are introduced. The retention factors of HILIC column are the hydrophilic partition, the hydrogen bonding, and the electrostatic interactions. Polar stationary phase is used in HILIC mode, and the highly organic solvent is employed in mobile phase. Hence, a stagnant aqueous-rich layer is generated in HILIC mode, which can separate sugars and sugar alcohol efficiently. Furthermore, the interference and the matrix effect are solved by SPE. The development and the optimization of SPE-HILIC-MS/MS method for sugars were done in the experimental part. Eventually, the real environmental aerosol was analyzed by the optimized parameters and methods. The sugars and sugar alcohols were analyzed successfully from atmospheric aerosol samples

Actuatable Membranes based on Polypyrrole-Coated Vertically Aligned Nanostructures

Nanoporous membranes are an enabling technology in a wide variety of applications because of their ability to efficiently and selectively separate molecules. A great deal of effort is concentrated on developing methods of externally controlling membrane selectivity and on integrating the membranes within multi-scale systems. In this dissertation, synthetic nanoporous membranes that fit the described needs are constructed from vertically aligned nanostructures. Vertically aligned carbon nanofibers and anisotropically etched silicon posts are aligned perpendicular to the substrate and act as obstacles to material flow parallel to the surface. The distances between the outer edges of the nanostructures define the pores of the membranes. Transport through the membranes is controlled by physically selecting species as they pass between the vertically aligned nanostructures. Membrane properties such as permeability and porosity are specified by defining the spatial locations of the membrane components. Subsequent physical and chemical modification of the nanostructures enables further tuning of pore sizes and opens up new methods to controllably modulate the permeability of the membranes. In this dissertation, permeability is externally controlled by electrochemical actuation of the conductive polymer, polypyrrole. Vertically aligned membrane components are coated with the actuatable polymer. Upon electrochemical reduction, the polypyrrole coatings swell in volume, increasing the diameters of the membrane components and decreasing the pore sizes of the membranes. Modulating the physical size of the membrane pores enables size selective transport of species and gating of the nanoscale pores

Supported gold nanoparticles catalysts for organic transformations

The research work described in this thesis concerns the synthesis, characterisation and study of the catalytic activity of supported gold nanoparticles (AuNPs) immobilised on various oxide supports, i.e. silica (SiO2), alumina (Al2O3), titania (TiO2) and magnetite (Fe3O4), previously functionalised with [3-(2-propynylcarbamate)propyl]triethoxysilane (PPTEOS). The alkynyl-carbamate moieties anchored on the support were capable of straightforwardly reducing the gold precursor chloroauric acid (HAuCl4) to afford Au/OS@Yne (OS = Oxide Support, Yne = organic functionalisation), without the need of additional reducing or stabilising agents. The resulting materials were characterised by means of several complementary techniques, such as thermogravimetric analysis (TGA), atomic absorption spectroscopy (AAS), transmission electron microscopy (TEM), solid state NMR spectroscopy (SS NMR) and x-rays photoelectron spectroscopy (XPS), in order to investigate their structural and chemical properties. Furthermore, the catalytic activity of the obtained Au/OS@Yne was evaluated first in the oxidation of alcohols and then in the hydroamination of alkynes. Finally, during a six months stay at the Karl-Franzens University of Graz, a second research work was carried out, concerning the study of metal organic frameworks biocomposites

Nanoparticelle d'oro supportate su silice funzionalizzata: Sintesi, caratterizzazione e catalisi.

Sono stati sintetizzati catalizzatori eterogenei di oro supportati su silice funzionalizzata. Le specifiche funzionalità condensate sulla superficie del supporto sono in grado di ridurre HAuCl4, producendo nanoparticelle d’oro metalliche sferiche e stabilizzate sulla superficie, senza l’aggiunta di agenti riducenti e stabilizzanti. I catalizzatori sono attivi per la reazione di riduzione del 4-nitrofenolo (4-NP) a 4-amminofenolo (4-AP)

Silica-Supported Gold Nanoparticles: Synthesis, Characterization and Reactivity

The main aim of this work was the synthesis and applications of functionalized-silica-supported gold nanoparticles. The silica-anchored functionalities employed, e.g. amine, alkynyl carbamate and sulfide moieties, possess a notable affinity with gold, so that they could be able to capture the gold precursor, to spontaneously reduce it (possibly at room temperature), and to stabilize the resulting gold nanoparticles. These new materials, potentially suitable for heterogeneous catalysis applications, could represent a breakthrough among the “green” synthesis of supported gold nanoparticles, since they would circumvent the addition of extra reducing agent and stabilizers, also allowing concomitant absorption of the active catalyst particles on the support immediately after spontaneous formation of gold nanoparticles. In chapter 4 of this thesis is also presented the work developed during a seven-months Marco Polo fellowship stay at the University of Lille (France), regarding nanoparticles nucleation and growth inside a microfluidic system and the study of the corresponding mechanism by in situ XANES spectroscopy. Finally, studies regarding the reparation and reactivity of gold decorated nanodiamonds are also described. Various methods of characterization have been used, such as ultraviolet-visible spectroscopy (UV-Vis), Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS), X-ray Fluorescence (XRF), Field Emission Gun Scanning Electron Microscopy (SEM-FEG), X-ray Photoionization (XPS), X ray Absorption Spectroscopy (XAS)