|Monday, July 18|
Crystallization of Gold Ultrasmall Icosahedral Nanoparticles: Growth Mechanism Study using Microfluidic Chips
* Ezgi Yildirim, Université de Toulouse, Laboratoire de Physique et Chimie des Nano-Objets(LPCNO) INSA, CNRS, UPS, France
Raj Kumar Ramamoorthy, Université de Toulouse, Laboratoire de Physique et Chimie des Nano-Objets(LPCNO) INSA, CNRS, UPS, France
Lise-Marie Lacroix, Université de Toulouse, Laboratoire de Physique et Chimie des Nano-Objets(LPCNO) INSA, CNRS, UPS, France
Pierre Roblin, Laboratoire de Génie Chimique, Université de Toulouse, CNRS, INP, UPS Toulouse, France
Isaac Rodriguez-Ruiz, Laboratoire de Génie Chimique, Université de Toulouse, CNRS, INP, UPS Toulouse, France
Sébastien Teychené, Laboratoire de Génie Chimique, Université de Toulouse, CNRS, INP, UPS Toulouse, France
Guillaume Viau, Université de Toulouse, Laboratoire de Physique et Chimie des Nano-Objets(LPCNO) INSA, CNRS, UPS, France
Ultrasmall gold nanospheres find applications in fields ranging from catalysis to biotechnology, but to meet the efficiency requirements, a unique control of the size and the shape and the crystalline structure is needed. In order to produce properly the desired nanoparticles (NPs), the nucleation and growth mechanisms should be understood properly. The synthesis of ultrasmall gold NPs consists in the reduction of HAuCl4.3H2O by silane reducing agents (tri-isopropylsilane (TIPS) or triethylsilane (TES)) in presence of oleylamine (OY) in organic solvent.Though fairly simple to carry out, this reaction offers a great control over the NP shape and atomic structure varying the different experimental parameters: temperature, OY concentration and reducing agent concentrations and nature. With the stoichiometric ratio OY/Au = 2.5, monodisperse particles with a diameter of 2 nm and an icosahedral structure were rapidly obtained. To follow the formation of the nanoparticles at very short times (down to 300 µs) we have used a dedicated microfluidic set-up with an efficient mixer. In-situ time resolved small angle X-ray scattering and X-ray absorption measurements were performed at synchrotron facilities and revealed a non-classical nucleation mechanism with the presence of prenucleation clusters. A competition was then observed between the direct reduction of the PNCs to yield monodisperse 2nm NPs and the stabilization of an Au(I) complex which then favors the growth of larger fcc-like particles. To favour monodisperse NPs, fast reaction should be reached, increasing the reaction temperature (40°C vs 25°C) or the strength of the reducing agent (TES vs TIPS). Recently, we have shown that the monodisperse icosahedral NPs are perfect starting points to get controlled decahedra after an aging process under mild conditions (95°C, 26h).
Improved Size-Tunable Synthesis of Gold Nanorods through the Control of the Key Silver Intermediate Solubility
* Jun Zhu, McGill University , Canada
R. Bruce Lennox, McGill University, Canada
Gold nanorods have attracted considerable research interest due to their unique shape-dependent optical properties originated from surface plasmonic resonance (SPR) phenomenon. The seed-mediated protocol developed by Murphy and El-Sayed group,1,2 has emerged as the standard method for nanorod synthesis. Using the seed mediated method, silver additives can be used to adjust the LSPR of AuNR up to 900 nm. Understanding the role of silver ions is thus particularly useful for mechanism researches. The role of silver ions in seed-mediated gold nanorod (AuNR) syntheses has been investigated and the key silver intermediate which controls the AuNR aspect ratio (AR) was identified to be a CTA-Ag-Br complex. The CTA-Ag-Br complex has a characteristic UV absorption peak which enables an in situ spectroscopy study of the roles the silver has in AuNR formation. Previous assumptions have held that silver is only involved in the symmetry breaking of the seed growth step. However, this is the case only a small fraction of the silver present is involved in the process, whereas the AuNR aspect ratio (AR) can be controlled by varying the Ag:Au ratio. The current work however provides direct experimental evidence for the first time that the silver intermediate is consumed at the same rate as gold nanorod growth. The silver intermediate also plays an important role during the AuNR growth step and becomes a size-limiting reagent due to its limited solubility. However, addition of a limited quantity of acetonitrile (2% v/v) leads to a significant increase in the solubility of the silver intermediate, leading to AuNR with a greater range of characteristic AR values. The LSPR of the resulting AuNR can be increased from 880 nm (AR = 4.5) to 1200 nm (AR = 8). This work provides new insight into the mechanism of seed-mediated growth of AuNRs as well as the synthesis of AuNRs having a greater AR range (1.5 - 8) using the same seed-mediated growth method.
Quantifying surface ligands for NHC stabilized gold nanoparticles by NMR
* Francois Ribot, Sorbonne Universite / CNRS - LCMCP, France
Alexandre Porcheron, Sorbonne Universite / CNRS - LCMCP & IPCM, France
Louis Fensterbank, Sorbonne Universite / CNRS - IPCM, France
A NMR based methodology has been developed to quantify the ligand surface coverage in N-heterocyclic carbene (NHC) stabilized gold nanoparticles. This approach allows one to analyse nanoparticles that are stabilized by two different NHC and determine the relative proportion of each ligand.
Seed-mediated Synthesis of Gold Nano-Earbuds
* Debashree Roy, IISER Pune, India
One dimensional (1D) nanostructures are of fundamental interest as well as promising for practical applications in the realm of biological imaging in the second near-infrared (NIR-II) region. Among the various 1D nanostructures, Au nanorods remain extensively investigated due to their well-defined shape anisotropy giving rise to aspect ratio (AR) dependent and widely tunable longitudinal surface plasmon resonance (LSPR). Substantial efforts have been put forward in recent times to develop synthetic protocols to extend the tunability of their LSPR into the near-infrared regime. These synthetic protocols were marred by either tedious multistep processes, long reaction duration or low yield, apart from the inability to maintain the dimension under 100 nm for the Au NRs to be useful for biological imaging. Herein, a new morphology, Au nano-earbud (NEB), has been introduced to the existing library of anisotropic 1D Au nanostructures, by employing a binary surfactant mixture of CTAC (cetyltrimethylammonium chloride) and BDAC (benzyldimethylhexadecylammonium chloride) and using TA (tannic acid) as a mild reducing agent in the versatile seed-mediated synthesis. These as-synthesized Au NEBs are monodispersed, structurally uniform, and single crystalline whose aspect ratios could be tuned over a wide range (7-19) resulting in broadly tunable plasmon resonance peaks (LSPR tuned beyond 1200 nm) while maintaining the sub-100 nm dimension. The role of the key chemical parameters, which were instrumental behind the tunable ARs of Au NEBs, have also been studied to investigate the growth and formation of this unique morphology. Additionally, the Au NEBs exhibit three distinct plasmonic peaks, rather uncommon for 1D nanostructures, attributed to the bulbous ends as well as the high AR of the structure from theoretical calculations solving the Maxwell’s equations with finite element method.
Surfactant-free fully inorganic fluorescent gold atom clusters synthesized by laser fragmentation in liquids
* Christoph Rehbock, University of Duisburg-Essen, Technical Chemistry I, Germany
Anna Rosa Ziefuß, University of Duisburg-Essen, Technical Chemistry I, Germany
Stephan Barcikowski, University of Duisburg-Essen, Technical Chemistry I, Germany
In this study we present an entirely new class of fully inorganic gold atom clusters (AuAC) available by laser fragmentation in liquids (LFL). We used LFL on plasmonic gold nanoparticles to obtain AuAC in an advanced liquid jet reactor and show to what extent the adjustment of the incident fluence as well as the addition of anions at micromolar salinity allows to significantly increase the yield of AuAC with diameters < 3 nm following a one step, one pulse fragmentation mechanism. The optical properties of the obtained AuAC are studied using UV-Vis spectroscopy as well as time-resolved fluorescence spectroscopy. The clusters show a distinctive UV fluorescence with two distinctive emission maxima associated with surface-based and core-based transition states. Finally, we observed that charging the AuAC surface by addition of hydroxide anions (alkaline pH) has a pronounced impact on the emission intensity, which verifies a clear impact of charge transfer effects on the AuAC´s electronic structure.