Name: preparation of silver-palladium alloyed nanoparticles for plasmonic catalysis under visible-light illumination
Uploaded: 2020-08-18T15:00:00
Description: Watch this Scientific Journal Video about Preparation of Silver-Palladium Alloyed Nanoparticles for Plasmonic Catalysis under Visible-Light Illumination at JoVE.com

This work was supported by the University of Helsinki and the Jane and Aatos Erkko Foundation. S.H. thanks Erasmus+ EU funds for the fellowship.

1. Synthesis of Ag-Pd/ZrO2 NPs 
NOTE: In this procedure, the Pd mol% in Ag-Pd corresponded to 1%, and the Ag-Pd loading on ZrO2 corresponded to 3 wt.%.
<ol>
	<li>Place 1 g of ZrO2 powder in a 250 mL beaker.</li>
	<li>Add 50 mL of an AgNO3 (aq) (0.0059 mol/L) and 9.71 mL of a K2PdCl4 (aq) (0.00031 mol/L) solutions to the beaker under vigorous magnetic stirring (500 rpm) at room temperature.</li>
	<li>Add 10 mL ...

<ol>
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The &#64257;ndings described in this method demonstrate that the intrinsic catalytic activity of Pd (or other catalytic but not plasmonic metal) can be signi&#64257;cantly enhanced by LSPR excitation via visible-light irradiation in bimetallic alloyed NPs35. In this case, Ag (or another plasmonic metal) is capable of harvesting energy from visible-light irradiation via LSPR excitation. The LSPR excitation leads to the formation of hot charge carriers (hot electrons and holes) and localized heating...

Among the several applications of metal nanoparticles (NPs), catalysis deserves special attention. Catalysis plays a central role in a sustainable future, contributing to less energy consumption, better utilization of raw materials, and enabling cleaner reaction conditions1,2,3,4. Thus, progress in catalysis can provide tools for enhancing the atomic efficiency of chemical processes, making them cleaner, more economically viable, and more environmentally friendly. Metal NPs encompassing silver (Ag), gold (Au) or copper (Cu) can display interesting optical properties in the visible range that arise from the unique way these systems interact with light at the nanoscale via the localized surface plasmon resonance (LSPR) excitation5,6,7,8. In these NPs, referred to as plasmonic NPs, the LSPR comprises the resonant interaction between the incident photons (from an incoming electromagnetic wave) with the collective motion of electrons5,6,7,8. This phenomenon takes place at a characteristic frequency which is dependent on the size, shape, composition, and dielectric constant of the environment9,10,11. For example, for Ag, Au, and Cu, these frequencies can range from the visible to the near-IR, opening up possibilities for the utilization of solar energy to excite their LSPR5,6,7,8,12,13.
Recently, it has been demonstrated that the LSPR excitation in plasmonic NPs can contribute to accelerate the rates and control the selectivity of molecular transformations5,14,15,16,17,18,19. This gave birth to a field called plasmonic catalysis, which focus on using energy from light to accelerate, drive, and/or control chemical transformations5,14,15,16,17,18,19. In this context, it has been established that the LSPR excitation in plasmonic NPs can lead to the formation of energetic hot electrons and holes, referred to as LSPR-excited hot carriers. These carriers can interact with adsorbed species through electronic or vibrational activation15,16. In addition to increased reaction rates, this process can also provide alternative reaction pathways not accessible via traditional thermochemically-driven processes, opening up new avenues for the control over reaction selectivity20,21,22,23,24,25. Importantly, it is worth noting that the plasmon decay can also lead to thermal dissipation, leading to a temperature increase in the vicinity of the NPs which can also contribute to speed up reaction rates15,16.
Due to these interesting features, plasmonic catalysis has been successfully employed towards a variety of molecular transformations18. Nevertheless, an important challenge remains. While plasmonic NPs such as Ag and Au display excellent optical properties in the visible and near-IR ranges, their catalytic properties are limited in terms of the scope of transformations. In other words, they do not display good catalytic properties for several of transformations. Additionally, metals that are important in catalysis, such as palladium (Pd) and platinum (Pt), do not support LSPR excitation in the visible or near-IR ranges. To bridge this gap, bimetallic NPs containing a plasmonic and catalytic metal represents an effective strategy20,26,27,28,29. In these systems, the plasmonic metal can be employed as an antenna to harvest energy from the light excitation through the LSPR, which is then used to drive, accelerate, and control molecular transformations at the catalytic metal. Therefore, this strategy enables us to extend plasmonic catalysis beyond traditional plasmonic metal NPs20,26,27,28,29.
This protocol describes the facile synthesis of bimetallic silver-palladium (Ag-Pd) alloyed NPs supported on ZrO2 (Ag-Pd/ZrO2) that can act as a plasmonic-catalytic system for plasmonic catalysis. The Ag-Pd/ZrO2 NPs were prepared by co-impregnation of the corresponding metal precursors on the ZrO2 support followed by simultaneous reduction30. This approach led to the formation of bimetallic NPs around 10 nm in size (diameter) directly at the surface of the ZrO2 support. The NPs were composed of 1 mol% of Pd to minimize the utilization of the catalytic metal while maximizing the optical properties of the resulting Ag-Pd NPs. A protocol for the application of the Ag-Pd/ZrO2 NPs in plasmonic catalysis was demonstrated for the reduction of nitrobenzene. We employed 425 nm LED illumination for the LSPR excitation. Gas chromatography was performed to monitor the conversion and selectivity of the reduction reaction under the dark and light irradiation conditions. LSPR excitation led to enhanced catalytic performance and control over selectivity in Ag-Pd/ZrO2 NPs relative to purely thermally driven conditions. The method described in this protocol is based on a simple photocatalytic reaction setup coupled with gas chromatography and can be adapted to a wide range of molecular transformations and NPs compositions. Thus, this method makes possible the characterization of photocatalytic activity, in terms of conversion and reaction selectivity, of different NPs and for a myriad of liquid-phase transformations. We believe this article will provide important guidelines and insights to both newcomers and more experienced scientists in the field.

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			<td height="42" style="height:42px;width:427px;">2-Propanol (anhydrous, 99.5%)</td>
			<td style="width:96px;">Sigma-Aldrich</td>
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			<td style="width:89px;">CAS Number 67-63-0</td>
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			<td height="42" style="height:42px;width:427px;">Azobenzene (98%)</td>
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			<td style="width:114px;">424633</td>
			<td style="width:89px;">CAS Number 103-33-3</td>
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			<td height="42" style="height:42px;width:427px;">Ethanol</td>
			<td style="width:96px;">Honeywell</td>
			<td style="width:114px;">32221</td>
			<td style="width:89px;">CAS Number 64-17-5</td>
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			<td height="42" style="height:42px;width:427px;">Hydrochloric acid (37%)</td>
			<td style="width:96px;">VWR</td>
			<td style="width:114px;">PRLSMC310066</td>
			<td style="width:89px;">CAS Number 7647-01-0</td>
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			<td height="42" style="height:42px;width:427px;">L-Lysine (crystallized, &#8805;98.0% (NT))</td>
			<td style="width:96px;">Sigma-Aldrich</td>
			<td style="width:114px;">62840</td>
			<td style="width:89px;">CAS Number 56-87-1</td>
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			<td height="42" style="height:42px;width:427px;">Nitric acid (65%)</td>
			<td style="width:96px;">Merck</td>
			<td style="width:114px;">100456</td>
			<td style="width:89px;">CAS Number 7697-37-2</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:427px;">Nitrobenzene</td>
			<td style="width:96px;">Sigma-Aldrich</td>
			<td style="width:114px;">8.06770</td>
			<td style="width:89px;">CAS Number 98-95-3</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:427px;">Potassium hydroxide</td>
			<td style="width:96px;">Fisher</td>
			<td style="width:114px;">10448990</td>
			<td style="width:89px;">CAS Number 1310-58-3</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:427px;">Potassium tetrachloropalladate (II) (98%)</td>
			<td style="width:96px;">Sigma-Aldrich</td>
			<td style="width:114px;">205796</td>
			<td style="width:89px;">CAS Number 10025-98-6</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:427px;">Silver nitrate (ACS reagent, &#8805;99.0%)</td>
			<td style="width:96px;">Sigma-Aldrich</td>
			<td style="width:114px;">209139</td>
			<td style="width:89px;">CAS Number 7761-88-8</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:427px;">Sodium borohydride (fine granular for synthesis)</td>
			<td style="width:96px;">Sigma-Aldrich</td>
			<td style="width:114px;">8.06373</td>
			<td style="width:89px;">CAS Number 16940-66-2</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:427px;">Zirconium (IV) oxide (nanopowder, &#60;100 nm particle size (TEM))</td>
			<td style="width:96px;">Sigma-Aldrich</td>
			<td style="width:114px;">544760</td>
			<td style="width:89px;">CAS Number 1314-23-4</td>
		</tr>
	</tbody>
</table>

preparation of silver-palladium alloyed nanoparticles for plasmonic catalysis under visible-light illumination

Localized surface plasmon resonance (LSPR) in plasmonic nanoparticles (NPs) can accelerate and control the selectivity of a variety of molecular transformations. This opens possibilities for the use of visible or near-IR light as a sustainable input to drive and control reactions when plasmonic nanoparticles supporting LSPR excitation in these ranges are employed as catalysts. Unfortunately, this is not the case for several catalytic metals such as palladium (Pd). One strategy to overcome this limitation is to employ bimetallic NPs containing plasmonic and catalytic metals. In this case, the LSPR excitation in the plasmonic metal can contribute to accelerate and control transformations driven by the catalytic component. The method reported herein focuses on the synthesis of bimetallic silver-palladium (Ag-Pd) NPs supported on ZrO2 (Ag-Pd/ZrO2) that acts as a plasmonic-catalytic system. The NPs were prepared by co-impregnation of corresponding metal precursors on the ZrO2 support followed by simultaneous reduction leading to the formation of bimetallic NPs directly on the ZrO2 support. The Ag-Pd/ZrO2 NPs were then used as plasmonic catalysts for the reduction of nitrobenzene under 425 nm illumination by LED lamps. Using gas chromatography (GC), the conversion and selectivity of the reduction reaction under the dark and light irradiation conditions can be monitored, demonstrating the enhanced catalytic performance and control over selectivity under LSPR excitation after alloying non-plasmonic Pd with plasmonic metal Ag. This technique can be adapted to a wide range of molecular transformations and NPs compositions, making it useful for the characterization of the plasmonic catalytic activity of different types of catalysis in terms of conversion and selectivity.

Figure 1A shows digital photographs of the solid samples containing the pure ZrO2 oxide (left) and the Ag-Pd/ZrO2 NPs (right). This change in color from white (in ZrO2) to brown (Ag-Pd/ZrO2) provides the initial qualitative evidence on the deposition of Ag-Pd NPs at the ZrO2 surface. Figure 1B shows the UV-visible absorption spectra from the Ag-Pd/ZrO2 NPs (blue trace) as well as ZrO2 (...

Watch this Scientific Journal Video about Preparation of Silver-Palladium Alloyed Nanoparticles for Plasmonic Catalysis under Visible-Light Illumination at JoVE.com

Preparation of Silver-Palladium Alloyed Nanoparticles for Plasmonic Catalysis under Visible-Light Illumination

Presented here is a protocol for the synthesis of silver-palladium (Ag-Pd) alloy nanoparticles (NPs) supported on ZrO2 (Ag-Pd/ZrO2). This system allows for harvesting energy from visible light irradiation to accelerate and control molecular transformations. This is illustrated by nitrobenzene reduction under light irradiation catalyzed by Ag-Pd/ZrO2 NPs.

Localized surface plasmon resonance (LSPR) in plasmonic nanoparticles (NPs) can accelerate and control the selectivity of a variety of molecular ...

This protocol represents the synthesis of silver palladium alloyed nanoparticles supported on zirconium dioxide. It facilitates the harvesting of energy from visible light irradiation to accelerate and control more light colored transformations. This method allows the matching of plasmonic and catalytic properties of a single line of particle to enable light trivalent transformations in catalytic metals that do not have plasmonic properties.This protocol can give insights into nanocatalysis, nanoparticle synthesis and supported catalyst synthesis. It can be applied to order molecular transformations in nanoparticle compositions. To fabricate silver palladium zirconium dioxide nanoparticles.Add 50 milliliters of silver nitrate and 9.71 milliliters of potassium tetrachloroplatinate to a 250 milliliter beaker containing one gram of zirconium dioxide. Mix the solutions under vigorous magnetic stirring at 500 revolutions per minute at room temperature for five minutes before adding 10 milliliters of lysine to the beaker. After 20 minutes, add 10 milliliters of a freshly prepared sodium borohydrid solution to the mixture drop wise at a rate of one milliliter per minute.Continue to stir the mixture for an additional 30 minutes at room temperature then allow the reaction to settle overnight. The next morning, split the suspension between several centrifuge tubes and separate the solids from the mixture by centrifugation. Carefully remove the supernatant and add 15 milliliters of deionized water to the tubes.Shake vigorously until the solid has been thoroughly dispersed placing the tubes in a vortex for one minute to fully resuspend the material as necessary. Repeat the centrifugation wash and resuspension two more times as demonstrated using 15 milliliters of deionized water for the second wash and ethanol for the third. After removing the ethanol from the last wash, dry the solid in a 60 degrees Celsius oven for 24 hours before characterizing the silver zirconium dioxide preparation by standard microscopy elemental and spectroscopic techniques.To produce silver zirconium dioxide nanoparticles add 50 milliliters of silver nitrate to a 250 milliliter beaker containing one gram of zirconium dioxide powder under vigorous magnetic stirring at room temperature, add 10 milliliters of lysine to the beaker and continue to stir the mixture for an additional 20 minutes. At the end of the incubation add 10 milliliters of freshly prepared sodium borohydride to the solution as demonstrated for a 30 minutes during incubation at room temperature. For separation and purification of the catalyst split the solution between several centrifuge tubes and collect the solids by centrifugation.Carefully remove the liquid phase and add 15 milliliters of deionized water to the tubes to allow a vigorous resuspension of the solids. Centrifuge the resulting solution for one additional wash with distilled water and one with ethanol as demonstrated. After removing the ethanol drive a solid in a 60 degrees Celsius oven for 24 hours before characterizing the silvers zirconium dioxide nanoparticles by a variety of standard microscopy elemental and spectroscopic techniques.To investigate the performance of the plasmonic catalyst under light illumination add 30 milligrams of catalyst to a 25 milliliter round bottom flask with a magnetic stir bar and add five milliliters of a 0.03 mole per liter nitrobenzene in isopropyl alcohol solution. Add 11.22 milligrams of potassium hydroxide powder to the flask and bubble this suspension with an argon flow for one minute to purge the reactor. Immediately after purging, place the sealed flask in a 70 degrees Celsius oil bath above a temperature controlled magnetic stirrer at 500 revolutions per minute.Use four LED lamps with a 427 nanometer wavelength and a 0.5 watts per square centimeter light intensity placed exactly seven centimeters away from the flask to irradiate the solution. And let the reaction proceed for 2.5 hours at 70 degrees Celsius under vigorous magnetic stirring. At the end of the incubation, turn off the lights and use a syringe and a needle to collect a one milliliter sample from the open reactor.Then strain the sample through a 0.45 micron filter into a glass chromatography vile to remove the catalyst particulate. To investigate the performance of the plasmonic catalyst in the absence of lighter radiation perform the analysis as just demonstrated but with the reaction container wrapped with aluminum foil to protect it from light. For gas chromatographic analysis prepare 10 milliliters of isopropyl alcohol solution containing approximately 30 millimoles per liter of nitrobenzene, 30 millimoles per liter of aniline and 30 millimoles per liter of azobenzene and run gas chromatography analysis on the solution according to standard protocols.The selected method should be able to separate the peaks corresponding to isopropyl alcohol, nitrobenzene, aniline and azobenzene in the minimum period of retention time as illustrated. Once the method has been selected prepare individual sets of solutions of 50, 25, 10, five and 2.5 millimolar nitrobenzene, aniline or azobenzene in isopropyl alcohol. Then run a gas chromatography analysis of each of the prepared solutions.Each chromatogram should present two peaks with the higher peak corresponding to isopropyl alcohol and the lower peak corresponding to nitrobenzene, aniline or azobenzene as appropriate. For each chromatogram note the retention time and peak area of each peak. Then plot the concentration versus peak area of each sample to trace the calibration curve to determine the concentration of each solvent.Zirconium dioxide does not display bans in the visible range and therefore should not contribute to any photocatalytic activity. A signal centered at 428 nanometers can be detected for the silvers zirconium dioxide nanoparticles while the silver palladium zirconium dioxide nanoparticles display a peak centered at 413 nanometers. It is difficult to identify silver palladium nanoparticles by scanning electron microscopy, but the formation of nanoparticles with a mean particle size of around 10 nanometers can be visualized by transmission electron microscopy.After the reaction the conversion and selectively for the formation of azobenzene and aniline can be measured by gas chromatography. In the absence of catalysts no nitrobenzene conversion is detected in the presence or absence of light illumination. For silver zirconium dioxide nanoparticles no conversion is detected in the dark while a 36%conversion is observed under LSPR excitation.A 56%selectivity toward azobenzene is also detected indicating that the silver alone can catalyze this reaction under LSPR excitation. For the bio metallic silver palladium zirconium dioxide nanoparticles no significant conversion is detected under dark conditions. Interestingly, under LSPR excitation the conversion is 63%with a 73%selectivity towards azobenzene, demonstrating the potential of the by metallic configuration to not only increase conversion under LSPR excitation but to also control reaction selectively.The reaction is catalytically driven by palladium and plus moronically enhanced by silver, under visible light irradiation. Therefore, controlling the nanoparticle synthesis and selecting the light wavelengths for catalysis are important. The catalytically active metal palladium and plasmonically active metal silver can be replaced with other types of possible combinations to target different types of organic reactions.

preparation-silver-palladium-alloyed-nanoparticles-for-plasmonic

Research

JoVE Journal

Chemistry

Gyroid Nickel Nanostructures from Diblock Copolymer Supramolecules

Nanoporous metal foams possess a unique combination of properties - they are catalytically active, thermally and electrically conductive, and furthermore, have high porosity, high surface-to-volume and strength-to-weight ratio. Unfortunately, common approaches for preparation of metallic nanostructures render materials with highly disordered architecture, which might have an adverse effect on their mechanical properties. Block copolymers have the ability to self-assemble into ordered nanostructures and can be applied as templates for the preparation of well-ordered metal nanofoams. Here we describe the application of a block copolymer-based supramolecular complex - polystyrene-block-poly(4-vinylpyridine)(pentadecylphenol) PS-b-P4VP(PDP) - as a precursor for well-ordered nickel nanofoam. The supramolecular complexes exhibit a phase behavior similar to conventional block copolymers and can self-assemble into the bicontinuous gyroid morphology with two PS networks placed in a P4VP(PDP) matrix. PDP can be dissolved in ethanol leading to the formation of a porous structure that can be backfilled with metal. Using electroless plating technique, nickel can be inserted into the template&#39;s channels. Finally, the remaining polymer can be removed via pyrolysis from the polymer/inorganic nanohybrid resulting in nanoporous nickel foam with inverse gyroid morphology.

This article describes the preparation of well-ordered nickel nanofoams via electroless metal deposition onto nanoporous templates obtained from self-assembled diblock copolymer based supramolecules.

Nanoporous metal foams possess a unique combination of properties - they are catalytically active, thermally and electrically conductive, and furthermore, ...

Preparation of Silica Nanoparticles Through Microwave-assisted Acid-catalysis

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle diameters ranging from 30-250 nm by varying the reaction conditions. Through the selection of a microwave compatible solvent, silicic acid precursor, catalyst, and microwave irradiation time, these microwave-assisted methods were capable of overcoming the previously reported shortcomings associated with synthesis of silica nanoparticles using microwave reactors. The siloxane precursor was hydrolyzed using the acid catalyst, HCl. Acetone, a low-tan &#948; solvent, mediates the condensation reactions and has minimal interaction with the electromagnetic field. Condensation reactions begin when the silicic acid precursor couples with the microwave radiation, leading to silica nanoparticle sol formation. The silica nanoparticles were characterized by dynamic light scattering data and scanning electron microscopy, which show the materials&#39; morphology and size to be dependent on the reaction conditions. Microwave-assisted reactions produce silica nanoparticles with roughened textured surfaces that are atypical for silica sols produced by St&#246;ber&#39;s methods, which have smooth surfaces.

Silica nanoparticles were prepared using acid-catalysis of a siloxane precursor and microwave-assisted synthetic techniques resulting in the controlled growth of nanomaterials ranging from 30-250 nm in diameter. The growth dynamics can be controlled by varying the initial silicic acid concentration, time of the reaction, and temperature of reaction.

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle ...

Synthesis of Immunotargeted Magneto-plasmonic Nanoclusters

Magnetic and plasmonic properties combined in a single nanoparticle provide a synergy that is advantageous in a number of biomedical applications including contrast enhancement in novel magnetomotive imaging modalities, simultaneous capture&#160;and detection of circulating tumor cells (CTCs),&#160;and multimodal molecular imaging combined with photothermal therapy of cancer cells. These applications have stimulated significant interest in development of protocols for synthesis of magneto-plasmonic nanoparticles with optical absorbance in the near-infrared (NIR) region and a strong magnetic moment. Here, we present a novel protocol for synthesis of such hybrid nanoparticles that is based on an oil-in-water microemulsion method. The unique feature of the protocol described herein is synthesis of magneto-plasmonic nanoparticles of various sizes from primary blocks which also have magneto-plasmonic characteristics. This approach yields nanoparticles with a high density of magnetic and plasmonic functionalities which are uniformly distributed throughout the nanoparticle volume. The hybrid nanoparticles can be easily functionalized by attaching antibodies through the Fc moiety leaving the Fab portion that is responsible for antigen binding available for targeting.

Here, we describe a protocol for synthesis of magneto-plasmonic nanoparticles with a strong magnetic moment and a strong near-infrared (NIR) absorbance. The protocol also includes antibody conjugation to the nanoparticles through the Fc moiety for various biomedical applications which require molecular specific targeting.

Magnetic and plasmonic properties combined in a single nanoparticle provide a synergy that is advantageous in a number of biomedical applications ...

Preparation and Characterization of SDF-1&#945;-Chitosan-Dextran Sulfate Nanoparticles

Chitosan (CS) and dextran sulfate (DS) are charged polysaccharides (glycans), which form polyelectrolyte complex-based nanoparticles when mixed under appropriate conditions. The glycan nanoparticles are useful carriers for protein factors, which facilitate the in vivo delivery of the proteins and sustain their retention in the targeted tissue. The glycan polyelectrolyte complexes are also ideal for protein delivery, as the incorporation is carried out in aqueous solution, which reduces the likelihood of inactivation of the proteins. Proteins with a heparin-binding site adhere to dextran sulfate readily, and are, in turn, stabilized by the binding. These particles are also less inflammatory and toxic when delivered in vivo. In the protocol described below, SDF-1&#945; (Stromal cell-derived factor-1&#945;), a stem cell homing factor, is first mixed and incubated with dextran sulfate. Chitosan is added to the mixture to form polyelectrolyte complexes, followed by zinc sulfate to stabilize the complexes with zinc bridges. The resultant SDF-1&#945;-DS-CS particles are measured for size (diameter) and surface charge (zeta potential). The amount of the incorporated SDF-1&#945; is determined, followed by measurements of its in vitro release rate and its chemotactic activity in a particle-bound form.

Preparation and Characterization of SDF-1&amp;#945;-Chitosan-Dextran Sulfate Nanoparticles

The objective of this protocol is to incorporate SDF-1&#945;, a stem cell homing factor, into dextran sulfate-chitosan nanoparticles. The resultant particles are measured for their size and zeta potential, as well as the content, activity, and in vitro release rate of SDF-1&#945; from the nanoparticles.

Chitosan (CS) and dextran sulfate (DS) are charged polysaccharides (glycans), which form polyelectrolyte complex-based nanoparticles when mixed under ...

A Simple Method for the Size Controlled Synthesis of Stable Oligomeric Clusters of Gold Nanoparticles under Ambient Conditions

Reducing dilute aqueous HAuCl4 with sodium thiocyanate (NaSCN) under alkaline conditions produces 2 to 3 nm diameter nanoparticles. Stable grape-like oligomeric clusters of these yellow nanoparticles of narrow size distribution are synthesized under ambient conditions via two methods. The delay-time method controls the number of subunits in the oligoclusters by varying the time between the addition of HAuCl4 to alkaline solution and the subsequent addition of reducing agent, NaSCN. The yellow oligoclusters produced range in size from ~3 to ~25 nm. This size range can be further extended by an add-on method utilizing hydroxylated gold chloride (Na+[Au(OH4-x)Clx]-) to auto-catalytically increase the number of subunits in the as-synthesized oligocluster nanoparticles, providing a total range of 3 nm to 70 nm. The crude oligocluster preparations display narrow size distributions and do not require further fractionation for most purposes. The oligoclusters formed can be concentrated &#62;300 fold without aggregation and the crude reaction mixtures remain stable for weeks without further processing. Because these oligomeric clusters can be concentrated before derivatization they allow expensive derivatizing agents to be used economically. In addition, we present two models by which predictions of particle size can be made with great accuracy.

We describe a simple method for producing highly stable oligomeric clusters of gold nanoparticles via the reduction of chloroauric acid (HAuCl4) with sodium thiocyanate (NaSCN). The oligoclusters have a narrow size distribution and can be produced with a wide range of sizes and surface coats.

Reducing dilute aqueous HAuCl4 with sodium thiocyanate (NaSCN) under alkaline conditions produces 2 to 3 nm diameter nanoparticles. Stable grape-like ...

Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst

A standardized technique for atom transfer radical polymerization of vinyl monomers using perylene as a visible-light photocatalyst is presented. The procedure is performed under an inert atmosphere using air- and water-exclusion techniques. The outcome of the polymerization is affected by the ratios of monomer, initiator, and catalyst used as well as the reaction concentration, solvent, and nature of the light source. Temporal control over the polymerization can be exercised by turning the visible light source off and on. Low dispersities of the resultant polymers as well as the ability to chain-extend to form block copolymers suggest control over the polymerization, while chain end-group analysis provides evidence supporting an atom-transfer radical polymerization mechanism.

A method for the atom transfer radical polymerization of functionalized vinyl monomers using perylene as a visible-light photocatalyst is described.

A standardized technique for atom transfer radical polymerization of vinyl monomers using perylene as a visible-light photocatalyst is presented. The ...

HKUST-1 as a Heterogeneous Catalyst for the Synthesis of Vanillin

Vanillin (4-hydoxy-3-methoxybenzaldehyde) is the main component of the extract of vanilla bean. The natural vanilla scent is a mixture of approximately 200 different odorant compounds in addition to vanillin. The natural extraction of vanillin (from the orchid Vanilla planifolia, Vanilla tahitiensis and Vanilla pompon) represents only 1% of the worldwide production and since this process is expensive and very long, the rest of the production of vanillin is synthesized. Many biotechnological approaches can be used for the synthesis of vanillin from lignin, phenolic stilbenes, isoeugenol, eugenol, guaicol, etc., with the disadvantage of harming the environment since these processes use strong oxidizing agents and toxic solvents. Thus, eco-friendly alternatives on the production of vanillin are very desirable and thus, under current investigation. Porous coordination polymers (PCPs) are a new class of highly crystalline materials that recently have been used for catalysis. HKUST-1 (Cu3(BTC)2(H2O)3, BTC = 1,3,5-benzene-tricarboxylate) is a very well known PCP which has been extensively studied as a heterogeneous catalyst. Here, we report a synthetic strategy for the production of vanillin by the oxidation of trans-ferulic acid using HKUST-1 as a catalyst.

The conversion of trans-ferulic acid to vanillin was achieved by heterogeneous catalysis. HKUST-1 was employed in this synthesis and the essential step in the catalytic process was the generation of unsaturated metal sites. Thus, when the catalyst was activated under vacuum, full vanillin conversion (yield of 95%) was obtained.

Vanillin (4-hydoxy-3-methoxybenzaldehyde) is the main component of the extract of vanilla bean. The natural vanilla scent is a mixture of approximately ...

Facile Synthesis of Worm-like Micelles by Visible Light Mediated Dispersion Polymerization Using Photoredox Catalyst

Presented herein is a protocol for the facile synthesis of worm-like micelles by visible light mediated dispersion polymerization. This approach begins with the synthesis of a hydrophilic poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) homopolymer using reversible addition-fragmentation chain-transfer (RAFT) polymerization. Under mild visible light irradiation (&#955; = 460 nm, 0.7 mW/cm2), this macro-chain transfer agent (macro-CTA) in the presence of a ruthenium based photoredox catalyst, Ru(bpy)3Cl2 can be chain extended with a second monomer to form a well-defined block copolymer in a process known as Photoinduced Electron Transfer RAFT (PET-RAFT). When PET-RAFT is used to chain extend POEGMA with benzyl methacrylate (BzMA) in ethanol (EtOH), polymeric nanoparticles with different morphologies are formed in situ according to a polymerization-induced self-assembly (PISA) mechanism. Self-assembly into nanoparticles presenting POEGMA chains at the corona and poly(benzyl methacrylate) (PBzMA) chains in the core occurs in situ due to the growing insolubility of the PBzMA block in ethanol. Interestingly, the formation of highly pure worm-like micelles can be readily monitored by observing the onset of a highly viscous gel in situ due to nanoparticle entanglements occurring during the polymerization. This process thereby allows for a more reproducible synthesis of worm-like micelles simply by monitoring the solution viscosity during the course of the polymerization. In addition, the light stimulus can be intermittently applied in an ON/OFF manner demonstrating temporal control over the nanoparticle morphology.

This article describes a process for producing polymeric self-assembled nanoparticles using visible light mediated dispersion polymerization. Using low energy visible light to control the polymerization allows for the reproducible formation of self-assembled worm-like micelles at high solids content.

Presented herein is a protocol for the facile synthesis of worm-like micelles by visible light mediated dispersion polymerization. This approach begins ...

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry

With this protocol, a well-defined singlesite silica-supported heterogeneous catalyst [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is designed and prepared according to the methodology developed by surface organometallic chemistry (SOMC). In this framework, catalytic cycles can be determined by isolating crucial intermediates. All air-sensitive materials are handled under inert atmosphere (using gloveboxes or a Schlenk line) or high vacuum lines (HVLs, &#60;10-5 mbar). The preparation of SiO2-700 (silica dehydroxylated at 700 &#176;C) and subsequent applications (the grafting of complexes and catalytic runs) requires the use of HVLs and double-Schlenk techniques. Several well-known characterization methods are used, such as Fourier-transform infrared spectroscopy (FTIR), elemental microanalysis, solid-state nuclear magnetic resonance spectroscopy (SSNMR), and state-of-the-art dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP-SENS). FTIR and elemental microanalysis permit scientists to establish the grafting and its stoichiometry. 1H and 13C SSNMR allows the structural determination of the hydrocarbon ligands coordination sphere. DNP SENS is an emerging powerful technique in solid characterization for the detection of poorly sensitive nuclei (15N, in our case). SiO2-700 is treated with about one equivalent of the metal precursor compared to the amount of surface silanol (0.30 mmol&#183;g-1) in pentane at room temperature. Then, volatiles are removed, and the powder samples are dried under dynamic high vacuum to afford the desired materials [(&#8801;Si-O-)Hf(&#951;2&#960;-MeNCH2)(&#951;1-NMe2)(&#951;1-HNMe2)]. After a thermal treatment under high vacuum, the grafted complex is converted into metal imido silica complex [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)]. [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] effectively promotes the metathesis of imines, using the combination of two imine substrates, N-(4-phenylbenzylidene)benzylamine, or N-(4-fluorobenzylidene)-4-fluoroaniline, with N-benzylidenetert-butylamine as substrates. A significantly lower conversion is observed with the blank runs; thus, the presence of the imido group in [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is correlated to the catalytic performance.

A new group IV metal catalyst for imine metathesis is prepared by grafting amine metal complex onto dehydroxylated silica. Surface metal fragments are characterized using FT-IR, elemental microanalysis, and solid-state NMR spectroscopy. Further dynamic nuclear polarization surface enhanced NMR spectroscopy experiments complement the determination of the coordination sphere.

With this protocol, a well-defined singlesite silica-supported heterogeneous catalyst [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is designed and prepared ...

Performing Spectroscopy on Plasmonic Nanoparticles with Transmission-Based Nomarski-Type Differential Interference Contrast Microscopy

Differential interference contrast (DIC) microscopy is a powerful imaging tool that is most commonly employed for imaging microscale objects using visible-range light. The purpose of this protocol is to detail a proven method for preparing plasmonic nanoparticle samples and performing single particle spectroscopy on them with DIC microscopy. Several important steps must be followed carefully in order to perform repeatable spectroscopy experiments. First, landmarks can be etched into the sample substrate, which aids in locating the sample surface and in tracking the region of interest during experiments. Next, the substrate must be properly cleaned of debris and contaminants that can otherwise hinder or obscure examination of the sample. Once a sample is properly prepared, the optical path of the microscope must be aligned, using Kohler Illumination. With a standard Nomarski style DIC microscope, rotation of the sample may be necessary, particularly when the plasmonic nanoparticles exhibit orientation-dependent optical properties. Because DIC microscopy has two inherent orthogonal polarization fields, the wavelength-dependent DIC contrast pattern reveals the orientation of rod-shaped plasmonic nanoparticles. Finally, data acquisition and data analyses must be carefully performed. It is common to represent DIC-based spectroscopy data as a contrast value, but it is also possible to present it as intensity data. In this demonstration of DIC for single particle spectroscopy, the focus is on spherical and rod-shaped gold nanoparticles.

The goal of this protocol is to detail a proven approach for the preparation of plasmonic nanoparticle samples and for performing single particle spectroscopy on them with differential interference contrast (DIC) microscopy.