Hexacyanoferrate (III) reduction by electron transfer induced by plasmonic catalysis on gold nanoparticles

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Plasmonic NPs supported on photocatalytic substrates

TiO 2 is a very efficient photocatalyst due to its strong oxidation capacity, high photochemical and biological stability and low cost. Since the discovery of photoinduced decomposition of water on a TiO 2 electrode, TiO 2 based photocatalysts have attracted wide attention 69 The limitation in TiO 2 application, results from low quantum yield due to fast charge carriers (electron/hole e –/h+) recombination and its activation only under UV irradiation because of the value of its band gap (3.2 eV for anatase and 3.0 eV for rutile). UV light constitutes only about 3 4 % of the solar spectrum impin ging on the Earth’s surface, therefore modification of titania to extent its absorption to visible domain and to enhance its activity is a very active area of research. Surface modification with noble metal (platinum, palladium, silver, gold) nanoparticles (NPs) can result in enhancement of the photo conversion quantum yield and may allow the extension of the light absorption of wide band gap semiconductors to the visible light. In particular, plasmonic photocatalysts have appeared as a very promising way t o induce a photocatalytic activity of TiO 2 in the visible range .
Different studies report on modification of TiO photocatalytic app lications: water depollution and hydrogen production.

Türkevich synthesis of spherical gold nanoparticles in solution

Spherical gold nanoparticles can be prepared by several methods (chemical, photochemical and radiolytic, and physical methods (cf. Chapter I).
We have chosen the Türkevich method for gold nanoparticles synthesis, as it allows us to work in an aqueous medium with controlled pH at room temperature. This method is based on the reduction of AuIII complexes [AuCl4]- by citrate ions, which act as reducing and stabilizing agents.
Türkevich method is probably one of the most basic and reproducible method for synthesis of Au NPs. J. Türkevich et al. [1] first published this method in 1951, and then G. Frens [2] developed this method, and added the parameter of gold-to-reductant ratio to well control the nanoparticle size. Indeed, citrate ions reduce AuIII into Au0 (Figure II-1) and simultaneously stabilize the formed Au nanoparticles via electrostatic weak-bonds. Because citrate is a weak reducing agent, the gold salt solution is heated and generally boiled [3]. The synthesis of Au-NPs@Citrate starts by boiling a gold salt aqueous solution, then sodium citrate (a solution containing 1% in mass) is added as a reducing and stabilizing agent (Figure II-2).

Transmission Electron Microscopy (TEM)

Transmission Electron Microscopy (TEM) is a powerful imaging tool for the characterization of morphology, lattice coordinates, and distribution of nanostructures. TEM is used to observe the size, shape and morphology of nanoparticles. It probes the internal structure of solids in order to give us an idea about the morphology of the material. When the accelerating electrons are focused on the grid containing the sample, part of the electrons is transmitted by the sample while a part of them are scattered. The electromagnetic lenses in the TEM machine focuses the transmitted electrons into an image or a diffraction pattern and provides us with insight about the sample under observation. The electron diffraction, observed by TEM provides us with the Fourier transform reconstruction. In TEM apparatus, the sample is illuminated using multiple electron beams confined in a high vacuum space, and the transmitted beam makes the image magnified from about fifty to over one million times (Figure II-3). In principle, contrast of the TEM image arises because of the differences in electron density of the elements constituting the sample under investigation. Transmission electronic microscopy (TEM) observations were performed with a JEOL JEM 100 CXII TEM instrument operated at an accelerating voltage of 100 kV and a JEOL JEM 2011 operated at 200 kV. Prior to observations, a few droplets of the metal nanostructure solution were deposited and dried on carbon-coated copper TEM grids under N2 flow. The images were collected using a CCD camera. These characterizations were done in collaboration with Patricia Beaunier, LRS (Sorbonne Université).

X-Ray Photoelectron Spectroscopy (XPS)

X-ray photoelectron spectroscopy (XPS) is a surface-sensitive spectroscopic technique providing information concerning the elemental composition as well as the chemical state of the elements present at the surface. XPS spectra are obtained by irradiating a material with a beam of X-rays (the X-ray sources usually employed consist of an Al / Kα = 1486.6 eV or Mg / Kα = 1253.6 eV anodes) in vacuum while simultaneously measuring the kinetic energy and number of electrons that escape from roughly the first 5 to 10 nm of the material being analyzed. The measured kinetic energy (Ek) can be converted into the atomic core level binding energy (EB), relative to the Fermi level of the sample using the formula: EB = Esource- Ek.

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Gas Chromatography coupled with Mass Spectroscopy

Gas Chromatography coupled with mass spectroscopy (GC-MS) is considered as an important analytical tool for natural products analysis, volatile organic compounds, active medical materials and pollutants. GC-MS offers an in-depth knowledge of the sample components as it allows to detect their masses along with their chemical structure.
For example, when analyzing volatile organic compounds (VOC), target analytes are extracted by mixing the sample with water and purge with inert gas (Argon gas in our studies) into an airtight chamber, this is known as purging. Purge-Trap technic is widely used in many petrochemical industries [8]. The trap is a column of adsorbent material at ambient temperature that holds the compounds by returning them to the liquid phase. The trap is then heated and the sample compounds are introduced to the GC-MS column via a volatiles interface, which is a split inlet system. Purge and trap gas chromatography-mass spectrometry system (P&T GC-MS) is particularly suited to volatile organic compounds (VOCs).

Table of contents :

General introduction
Chapter I: State of the art
I- Metal nanoparticles in history and nowadays
II- Synthesis of metal nanoparticles
II-1- Physical methods for synthesis of metal nanoparticles
II-1-1- Magnetron sputtering
II-1-2- Laser vaporization or ablation
II-2- Chemical methods for synthesis of metal nanoparticles
II-2-1- Türkevich synthesis of gold nanoparticles
II-2-2- Deposition-Precipitation Method
II-3- Synthesis of metal nanoparticles by radiolysis
III- Properties of metal nanoparticles and applications
III-1- Catalytic properties
III-2- Optical properties
III-3- Biological applications
IV- Catalysis assisted by plasmon of metal nanoparticles
IV-1- Plasmon assisted catalysis with non-supported metal nanoparticles:
IV-2- Plasmon assisted catalysis via supported metal nanoparticles
IV-3- Plasmonic NPs supported on photocatalytic substrates
V- Conclusion
Chapter II: Experimental setups, materials and methods
I- Synthesis of metal nanoparticles and nanostructures
I-1- Türkevich synthesis of spherical gold nanoparticles in solution
I-2- Synthesis of Palladium Nanoflowers
II- Characterization techniques of the metal nanostructures
II-1- UV–Visible absorption spectroscopy
II-2- Transmission Electron Microscopy (TEM)
II-3- X-Ray Photoelectron Spectroscopy (XPS)
III- Analytical methods
III-1- Electrospray Ionization Mass Spectrometry
III-2- Gas Chromatography coupled with Mass Spectroscopy
III-3- Surface Raman Enhanced Spectroscopy (SERS)
IV- Irradiation setups
IV-1- Xenon Lamp equipped with a longpass filter
IV-2- Homemade LED-based cylindrical photochemical reactor
IV-3- Continuous green laser excitation
V- Chemicals
Chapter III: Degradation of para-nitrothiophenol by plasmon exciation of gold nanoparticles
I- Introduction
II- Sample preparations and irradiation
III- Degradation of pNTP followed by UV-visible spectroscopy
IV- Characterizations of the formed products
IV-1- Analysis of the supernatant
IV-1-1- ESI-MS spectra of known compounds
IV-1-1- ESI-MS spectra of the irradiated solutions
IV-2- SERS analysis of the AuNPs surface
V- Discussion
VI- Conclusion
Chapter IV: Hexacyanoferrate (III) reduction by electron transfer induced by plasmonic catalysis on gold nanoparticles
I- Introduction
II- Experimental details
III- Reduction of hexacyanoferrate in the presence of sodium thiosulfate
III-1- Irradiation using LEDs at 520 nm
III-2- Irradiation using a Xe lamp equipped with a 450 nm optical cutoff filter
IV- Reduction of hexacyanoferrate in the absence of sodium thiosulfate
IV-1- Irradiation using LEDs at λ = 520 nm
IV-2- Irradiation using a Xe lamp equipped with a 450 nm optical cutoff filter
IV-3- Effect of stabilizing agent of the Au-NPs
V- Discussion
VI- Conclusions
Chapter V: Plasmonic catalysis for Suzuki-Miyaura cross-coupling reaction using Palladium nanoflowers
I- Introduction
II- Pd nanoflowers as catalysts
III- Catalytic study of the Suzuki-Miyaura cross coupling reactions
III-1- Experimental details
III-2- Reaction between iodobenzene and phenylboric acid
III-3- Reactions between other haloarenes and phenylboric acid
III-4- Proposed mechanism
IV- Pd nanoflowers after catalysis
V- Conclusion
Conclusion and perspectives
Annex: Gas phase oxidation of CO to CO2 assisted by plasmon of gold nanoparticles
I- Synthesis of gold nanoparticles on support
I-1- Deposition-Precipitation (DP) with urea
I-2- Synthesis after impregnation of gold ions on silica (SiO2) substrate
II- Oxidation of CO
II-1- Reactor
II-2- Results
II-3- Perspectives
Résumé de thèse
Summary of thesis

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