Name: synthesis of bimetallic pt/sn-based nanoparticles in ionic liquids
Uploaded: 2018-08-23T13:30:00.000+00:00
Duration: 7 min 14 s
Description: Watch this Scientific Journal Video about Synthesis of Bimetallic Pt/Sn-based Nanoparticles in Ionic Liquids at JoVE.com

This work was supported by the German Science Foundation within the Priority Program (SPP1708) &#34;Material Synthesis near Room Temperature&#34; (projects BE 2243/3-1 and BE 2243/3-2). We further acknowledge Hermann K&#246;hler for experimental assistance as well as Dr. Christian K&#252;bel and Wu Wang for support with electron microscopy studies.

CAUTION: Please consult all relevant material safety data sheets before use. Several of the chemicals used in these syntheses are acutely toxic and carcinogenic. Nanomaterials may have additional hazards compared to their bulk counterpart. Please use all appropriate safety practices when performing a synthetic reaction including the use of engineering controls (fume hood, glove box) and personal protective equipment (safety glasses, gloves, lab coat, full length pants, closed-toe shoes). The following procedures involve standard, air-free handling Schlenk techniques using argon as an inert gas or the use of an anoxic glove box. Assemble all glass-to-glass joints carefully with Teflon ring seals or vacuum grease to avoid contact with air. Inspect all glassware for defects prior to use. Triethylborane is a pyrophoric liquid which burns in contact with air. Please take care of appropriate safety practices and handle in air-free conditions. Please employ all appropriate safety practices for the use of hydrogen and any equipment (autoclaves, gas burettes) under high pressure.
1. Preparation of the Reducing Agent
<ol>
	<li>Preparation of potassium triethylborohydride (K[BEt3H])
	<ol>
		<li>Suspend 34.5 g (0.873 mol) of potassium hydride in 400 mL of anhydrous tetrahydrofurane in a 1000 mL 3-neck round bottom Schlenk flask under argon atmosphere by using the Schlenk line and heat the flask to 50 &#176;C while stirring with a stir bar.</li>
		<li>With a syringe, add the 100 mL (0.71 mol) of triethylborane drop-wise (~1 drop/s) to the stirring suspension of potassium hydride in tetrahydrofurane.</li>
		<li>Cool the reaction mixture to -40 &#176;C and remove any excess of potassium hydride by filtration.</li>
		<li>Receive potassium triethylborohydride as a clear, colorless solution in tetrahydrofurane.</li>
	</ol>
	</li>
	<li>Preparation of methyltrioctylammonium triethylborohydride ([OMA][BEt3H])
	<ol>
		<li>Under argon atmosphere, dissolve 50 g (0.11 mol) of methyltrioctylammonium bromide in 100 mL of anhydrous tetrahydrofurane in a 500 mL 2-neck round bottom flask.</li>
		<li>At room temperature, add 100 mL of K[BEt3H] solution (1.5 M in tetrahydrofurane) to the solution of trioctylmethylammonium bromide in tetrahydrofurane.</li>
		<li>Stir for 3 h at room temperature with a stir bar, then cool to -40 &#176;C overnight.</li>
		<li>Remove potassium bromide via filtration of the cooled solution.</li>
		<li>Receive [OMA][BEt3H] as a clear solution in tetrahydrofurane.</li>
	</ol>
	</li>
</ol>
2. Treatment of Methyltrioctylammonium Bis(trifluoromethylsulfonyl)imide ([OMA][NTf2])
<ol>
	<li>Prior to use, dry and degas the [OMA][NTf2] in vacuum (10-3 mbar) at 70 &#176;C for 3 h and in vacuum (10-4 mbar) at room temperature for another 16 h.</li>
</ol>
3. Synthesis of Pt/Sn-based Nanoparticles
<ol>
	<li>Synthesis of Pt/Sn-based nanocrystals
	<ol>
		<li>In argon atmosphere, combine a total of 0.25 mmol of the two metal salt precursors. Adjust the molar ratio of the Pt2+ and Sn2+ precursors to 1:1 and 3:1 to achieve random alloy nanoparticles with different compositions:
		<ol>
			<li>For the synthesis of Pt/Sn nanoparticles (1:1 molar ratio of Pt:Sn precursor), suspend 33.2 mg of PtCl2 and 29.6 mg of Sn(ac)2 (or 23.7 mg of SnCl2, accordingly) in 4 mL of [OMA][NTf2] in a 100 mL Schlenk flask and stir with a stir bar at 60-80 &#176;C for 2-3 h under the vacuum line.</li>
			<li>For the synthesis of Pt/Sn samples (3:1 molar ratio of Pt:Sn precursor), suspend 49.9 mg of PtCl2 with 14.8 mg of Sn(ac)2 (or 11.9 mg of SnCl2, accordingly) in 4 mL of [OMA][NTf2] in a 100 mL Schlenk flask and stir with a stir bar at 60-80 &#176;C for 2-3 h under the vacuum line.</li>
		</ol>
		</li>
		<li>Place the suspension in an ultrasonic bath at room temperature for 1-2 h.</li>
		<li>At 60-80 &#176;C, rapidly inject 3 mL of [OMA][BEt3H] solution (1.23 M in tetrahydrofurane) with a 3 mL syringe to the metal salt precursors in [OMA][NTf2] whilst vigorously stirring. The rapid injection creates a sharp nucleation event, promoting a small size and narrow size distribution. Let the reaction proceed while stirring at 60-80 &#176;C for 2-3 h.</li>
		<li>Cool to room temperature and remove any volatile compounds in vacuum during a period of 0.5 h.</li>
		<li>Obtain the Pt/Sn-based particles as a highly stable colloidal sol in [OMA][NTf2].</li>
	</ol>
	</li>
	<li>Isolation of Pt/Sn-based nanocrystals
	<ol>
		<li>Precipitation of Pt/Sn-based nanocrystals
		<ol>
			<li>Add 3 mL of anhydrous acetonitrile or tetrahydrofurane to the solution to flocculate the nanocrystals. Transfer the suspension to a vial in the glove box, close the vial with a cap, and centrifuge for 15 min (4226 x g).</li>
			<li>Decant the solution. Discard the supernatant and wash the precipitate with anhydrous acetonitrile or tetrahydrofurane.</li>
			<li>Obtain the particles as a sticky powder containing the Pt/Sn nanoparticles in addition to some residual IL.</li>
			<li>Confirm the crystal structure and composition of the Pt/Sn-based nanocrystals by XRD analysis. A shift of the reflections towards lower Bragg angles indicates alloying of the platinum nanoparticles with tin. Estimate the particle size from XRD patterns with the Scherrer equation according to the following formula 
			<img alt="Equation 1" src="/files/ftp_upload/58058/58058eq1v3.jpg" /> 
			where Lhkl is the diameter (nm) of the Pd/Sn nanocrystal perpendicular to hkl, &#955; the wavelength (nm) (typically Cu K&#945; 0.154 nm), &#946; the peak width at half maximum, and&#160;&#952; the Bragg angle.</li>
			<li>Determine the metal content and the composition by ICP-AES. 
			NOTE: The composition of the particles can be tuned by changing both the nature of the metal precursors and the platinum to tin precursor ratio. Pt/Sn-based nanoparticles synthesized from platinum(II) chloride (PtCl2) and tin(II) acetate (Sn(ac)2) (Pt:Sn precursor ratio of 3:1 or 1:1), yield random alloy-type Pt/Sn nanoparticles. See reference for details [C. Dietrich, D. Schild, W. Wang, C. K&#252;bel, S. Behrens, Z. Anorg. Allg. Chem. 2017, 643, 120-129]25.</li>
		</ol>
		</li>
		<li>Extraction of Pt/Sn-based nanocrystals 
		NOTE: To transfer the nanoparticles from the IL into a conventional organic solvent (i.e., n-hexane), add 2 mL N-oleylsarcosine (10 wt.-% in hexane) and 2 mL of acetonitrile to 1 mL of the nanoparticle sol in the IL.
		<ol>
			<li>Add 2 mL N-oleylesarcosine in n-hexane (10 wt.-%) and 1 mL of anhydrous acetonitrile to the nanoparticle/IL sol to extract the nanocrystals in n-hexane. After shaking, monitor the phase transfer visually by both the decolorization of the IL phase and a black coloring of the n-hexane phase.</li>
			<li>Deposit a drop of the solution on a carbon-covered copper grid and analyze by transmission electron microscopy.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
4. Catalytic Testing
NOTE: For catalytic testing, use a semi-continuous autoclave reactor with a reactor equipped with a Teflon liner, a mechanical blowing stirrer (Teflon) and baffles (stainless steel) to achieve intimate mixing between the gas and the liquid phase, a thermocouple and a heating bath.
<ol>
	<li>Selective hydrogenation of &#945;,&#946;-unsaturated aldehydes
	<ol>
		<li>Add 2.2 mg (17 mmol) of cinnaic aldehyde (CAL) in 30 mL of anhydrous tetrahydrofurane under inert gas.</li>
		<li>In the anoxic glove box, combine with 1 mL of the nanoparticle solution.</li>
		<li>Place the reactor in the heating bath and pressurize with hydrogen. During catalytic experiments, keep the hydrogen pressure constant at 10 bar, while hydrogen is continuously supplied to the reactor via a 500 mL gas burette.</li>
		<li>Raise the temperature to 80 &#176;C. At 80&#176;C, start to stir using a blowing stirrer (1200 rpm). Load the reactor with hydrogen to start the reaction.</li>
		<li>Record the hydrogen consumption continuously based on the pressure drop in the gas burette. To determine catalytic activity and selectivity, take aliquots every 30 min.</li>
		<li>Analyze the reaction products by gas chromatography using a column (30m x 0.25mm, 0.25&#181;m film thickness).</li>
		<li>Calculate the turn over frequency (TOF), product selectivity (SCAOL [%]), and cinnamic alcohol (CAOL) yield ([%]) according to the following formulas 
		<img alt="Equation" src="/files/ftp_upload/58058/58058eq3v3.jpg" /> 
		&#160; &#160; 
		<img alt="Equation" src="/files/ftp_upload/58058/58058eq4v2.jpg" /> 
		&#160; &#160; 
		<img alt="Equation" src="/files/ftp_upload/58058/58058eq5v2.jpg" /> 
		where t is the reaction time (h), n0,CAL the initial amount of CAL (mol), nmetal/catalyst the amount of metal catalyst (mol), and Xt,CAL the conversion of CAL at time t (%). [CAOL], [HCAOL] and [HCAL] refer to the concentrations of cinnamic alcohol, hydrocinnamic alcohol and hydrocinnamic aldehyde (see reaction scheme Figure 2), respectively. 
		NOTE: For more details, also see reference 25.</li>
	</ol>
	</li>
</ol>

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We have nothing to disclose.

The metal salt precursors are carefully dissolved in [OMA][NTf2] by stirring the reaction mixture over night, followed by ultrasonication. This is an important step to achieve Pt/Sn nanoparticles of homogeneous composition and sizes. [OMA][BEt3H] (as a solution in tetrahydrofurane) is then rapidly injected with a syringe whilst vigorously stirring the viscous solution. Rapid injection and mixing of the two components is a prerequisite to achieve monodisperse and homogeneous nanoparticles and may limit the scale-up of the procedure. Successful nanoparticle formation may be monitored by the change in color from a yellowish to black solution. During this step, H2 is generated as a side product, and thus, the reduction step has to be performed in an argon stream to avoid pressurization of the reaction vessel. Contact with air and moisture has to be prevented during all steps of nanoparticle synthesis. The Pt/Sn nanoparticles are formed in the IL after the injection of the reducing agent, where IL cation and IL anion control both nucleation and growth processes25. As a result, very small nanoparticles are obtained which form an extraordinarily stable, colloidal sol in [OMA][NTf2]. This synthetic approach does not require the use of additional, strongly coordinating ligands and may be further employed to achieve small nanoparticles of various mono- and bimetallic compositions.
The sols in which the nanoparticles are immobilized in the IL are highly interesting in view of quasi-homogeneous catalytic applications. However, the isolation of the nanoparticles (e.g., for particle characterization) turns out to be quite challenging due to the high colloidal stability in the IL. The particles are isolated as a sticky powder by precipitation with tetrahydrofurane and successive centrifugation. This is a useful step with respect to nanoparticle characterization, e.g., by TEM or XRD analysis. Alternatively, the nanoparticles can be additionally functionalized and extracted to a conventional solvent, after adding a coordinating ligand (i.e., N-oleylsarcosine) in n-hexane and acetonitrile to the IL-based nanoparticle sol. The samples are then further treated like a conventional nanoparticle sol. In general, specific surface properties are typically required with respect to a certain biomedical or technical application of the nanoparticles. Due to the weak coordination of the particles to the surface, ILs can be replaced by other ligands easily. As a consequence, it&#39;s possible to engineer the surface properties based on the specific requirements of the application using the present synthetic procedure. Magnetic fluids based on small, superparamagnetic cobalt nanoparticles, e.g., are prepared in diverse aliphatic or aromatic carrier media (i.e., kerosene, AP201, or Edwards L9) following a similar procedure3,4. After nanoparticle extraction, the IL may be recycled and reused for nanoparticle synthesis.
TEM analysis of the particles is carried out by depositing a thin film of the nanoparticle sol on the TEM grid. Here, the decomposition of the IL in the electron beam and successive contamination of the TEM sample may represent a real challenge to image the small nanoparticles. Alternatively, the precipitated nanoparticles are deposited on the TEM grid and investigated by TEM analysis. In this case, the particles typically form highly aggregated structures. Figure 1a-d displays TEM images of the nanoparticles in the IL showing very small and regular nanoparticles of 2-3 nm diameter. For all samples, TEM-EDX analysis confirms the presence of both tin and platinum in the particles (Figure 1e).
In order to show the alloyed character and the random alloy-type structure of the nanoparticles, X-ray diffraction patterns are collected for the nanoparticle powders. The XRD patterns confirm the face centered cubic (fcc) and random alloy-type structure of the particles (Figure 1f). The random alloy structure is one of the most conventional forms in bimetallic nanoparticles, where the two elements are randomly (or nearly randomly) dispersed in the nanoparticles. For the Pt-Sn system, also the formation of some intermetallic compounds is known (i.e., PtSn, PtSn4, PtSn2, Pt2Sn3, and Pt3Sn)17,26. Ordered intermetallic and disordered random alloy structures may be distinguished by the presence and absence of additional diffraction patterns derived from superlattice structures. The fcc platinum phase has reflections at 40&#176;, 45&#176;, 68&#176;, and 82&#176; (2) corresponding to the (111), (200), (220), and (311) planes. For all Pt/Sn-based nanoparticles, the XRD pattern shows the four characteristic reflections of the fcc platinum phase. As compared to the positions of the reflections of the pure platinum reference, however, the reflections of the Pt/Sn-based nanoparticles are shifted to smaller Bragg angles. This shift to smaller Bragg angles indicates an increase of the lattice parameters by the insertion of the tin atoms into the fcc platinum lattice. In the XRD patterns, the reflections which are characteristic of the atomic ordering in the intermetallic phase (i.e., Pt3Sn) are not observed. This suggests the formation of an alloyed nanoparticle core with a random distribution of platinum and tin. The decrease of the PdCl2 to Sn(ac)2 precursor ratio from 3:1 to 1:1 additionally leads to small SnO2 nanoparticles in close contact to the random alloy-type Pt/Sn nanoparticles. SnO2 is formed by decomposition of the Sn(ac)2 precursor. If Sn(ac)2 is reacted with [OMA][BEt3H] under the same reaction conditions in the absence of the platinum precursor, SnO and SnO2 are obtained as major reaction products. If the Sn(ac)2 is replaced by tin(II)chloride (SnCl2) and reacted with [OMA][BEt3H] in the presence of the platinum precursor (PtCl2), exclusively amorphous particles are formed and no SnO2 is detected. The tin content in the nanoparticle core can be further analyzed if the lattice constants are determined via Rietveld analysis. According to Vegard&#39;s law, the lattice parameters increase linearly between the lattice parameters of the pure Pt nanoparticles (3.914 &#197;) and the Pt3Sn phase (4.004 &#197;). Following this approach, the tin in the crystalline nanoparticle core is calculated to 11% (i.e., for a PtCl2 / Sn(ac)2 precursor ratio of 3:1) and increases to 18 % (i.e., for a PtCl2 / Sn(ac)2 precursor ratio of 1:1). The overall tin content of 21% and 55%, respectively, is determined by ICP-AES analysis and thus, exceeds the amount of tin in the nanoparticle core. The higher overall tin content can be assigned to the additional formation of SnO2 (i.e., approximately 26%) and to some segregation of tin atoms on the nanoparticle surface. X-ray photoelectron spectra further confirm the presence of Pt0/Sn0 (i.e., for a PtCl2 to Sn(ac)2 precursor ratio of 3:1) and Pt0/Sn0 in combination with 20% SnO2 (i.e., for a PtCl2 to Sn(ac)2 precursor ratio of 1:1) in the Pt/Sn-based nanoparticles, which is consistent with the results of XRD analysis25. The peak broadening arises from Scherrer broadening due to finite crystal size. The size of the nanoparticles is calculated using the Scherrer equation for the Pt/Sn-based nanoparticles to 2.4 nm (i.e., Pt:Sn 1:1), 2.5 nm (i.e., Pt:Sn 3:1) and, for the Pt nanoparticle reference, to 2.7 nm, respectively, which is consistent with the results of TEM analysis.
The transformation of &#945;,&#946;-unsaturated aldehydes to unsaturated alcohols via selective hydrogenation is fundamental in catalytic chemistry and a critical step in the production of various fine chemicals25,27. Although thermodynamics favors the formation of the saturated aldehydes, the selectivity towards the formation of the unsaturated alcohols can be significantly increased on bimetallic Pt-based catalysts by tailoring their size, composition and their support material. The incorporation of an electropositive metal (e.g., Sn) into the platinum leads to the electronic modification of the Pt d band which lowers the binding energy for the C=C bond of the unsaturated aldehyde27. The electron-deficient Sn atoms may further act as Lewis acid adsorption sites for the carbonyl group28. Moreover, vacant oxygen sites in SnO2-x patches in close contact to Pt are also demonstrated to promote carbonyl adsorption and its subsequent hydrogenation by atomic hydrogen which is supplied via the nearby platinum sites29. Overall, these examples show that the catalytic performance of bimetallic Pt-based catalysts is governed by a complex set of factors. In this protocol, we use the hydrogenation of cinnamic aldehyde as a model reaction not only to probe the overall catalytic performance of the IL-stabilized nanoparticles but further to elucidate the effect of tin alloying on the activity and selectivity of the Pt nanoparticles. Figure 2 displays possible pathways and major reaction products in the hydrogenation of CAL. At first, the catalytic properties of the Pt reference nanoparticles are tested in the hydrogenation of CAL. In this case, the saturated aldehyde (i.e., HCAL) is obtained as the only reaction product after 3 h of reaction, and the CAL conversion XCAL is 5% (3 h) and 9% (22 h), accordingly. After alloying the Pt with Sn in the bimetallic nanoparticles, the product selectivity is clearly shifted towards the unsaturated alcohol (i.e., CAOL) (Figure 3). The selectivity SCAOL is 100 % (i.e., for particles synthesized by a molar PtCl2/Sn(ac)2 ratio of 1:1), 80 % (i.e., for particles synthesized by a molar PtCl2 / Sn(ac)2 ratio of 3:1), and 83 % (i.e., for particles synthesized by a molar PtCl2 / SnCl2 ratio of 1:1) after 3 h of reaction and thus, further influenced by the actual nanoparticle composition. The TOF decrease from 28 h-1 to 8 h-1 for the particles synthesized by a molar PtCl2 / Sn(ac)2 ratio of 3:1 and 1:1, respectively, and to 7 h-1 for the nanoparticles obtained using SnCl2 instead of Sn(ac)2 with a molar PtCl2/SnCl2 ratio of 1:1, accordingly. The CAL conversion XCAL is 25% (3h) and 84% (22h) for Pt/Sn-based nanoparticles (i.e., molar PtCl2 / Sn(ac)2 ratio 3:1) which leads to the highest yield in CAOL (YCAOL 20% (3 h)) among the nanoparticles investigated in this study. In order to evaluate the overall catalytic performance of the system, both aspects, i.e., catalytic selectivity and activity, need to be taken into account and thus, Pt/Sn nanoparticles prepared with an initial molar PtCl2/Sn(ac)2 ratio of 3:1 clearly outperformed all other Pt- and Pt/Sn-based particles investigated in our study in terms of cinnamic alcohol yield. Thus, the excellent catalytic performance in this case appears to be a consequence of the Sn doping of the Pt nanoparticles balancing activity and selectivity to cinnamic alcohol in the system. It has to be noted that the blank experiment using the same reaction conditions but without nanoparticle catalyst did not show any conversion of cinnamic aldehyde after 22 h of reaction.
We have demonstrated a synthetic procedure for controlling the preparation of small, Pt/Sn-based nanoparticles of random alloy-type structure by exploiting the beneficial physico-chemical properties of ILs. Similar co-precipitation approaches have already been applied to a wide range of bimetallic nanoparticles in conventional solvents, and we expect that the types of both random alloy and intermetallic nanoparticles that can be obtained by this approach will continue to expand. The nanoparticles reveal interesting catalytic properties in the catalytic hydrogenation of cinnamic aldehyde, and a significantly higher selectivity to the &#945;,&#946;-unsaturated cinnamic alcohol is achieved for the Pt/Sn-based nanoparticles.

ILs represent room-temperature molten salts of large organic cations with asymmetric substitution patterns. They are well known for their unusual physico-chemical properties. The IL properties can be tuned by different combinations of IL cations and anions, and by now, a plethora of ILs is commercially available. Recently, scientists started using ILs as reaction media for the synthesis of nanoparticle due to their modular and excellent solvent properties, low vapor pressure, high polarity and a wide electrochemical stability window1,2,3,4.
During the past decade, bimetallic nanoparticles have attracted considerable attention because they show multiple functionalities and prominent catalytic activity, selectivity as well as thermal and/or chemical stability over their monometallic counterparts5,6,7,8,9,10. Due to synergistic effects, modified electronic and/or geometric surface structures, high catalytic activities and selectivities may be achieved for chemical transformations even if one of the constituents is less or even inactive11. Although the controllable synthesis of nanoparticles has developed rapidly over the recent years, there is still a need for more accurate control over nucleation and growth stages for the synthesis of bimetallic nanocrystals. Since different metals are involved in bimetallic nanocrystals, the atomic distribution not only influences the final nanoparticle architecture but also the catalytic properties. The catalytic performance is highly sensitive to the nature of atomic ordering (i.e., random alloys vs intermetallic compound) even if the composition and stoichiometry are exactly identical. It is surprising, that, so far, the attractive properties of ILs are less explored for the controlled synthesis of bimetallic nanocatalysts12,13,14,15,16.
In this protocol, we will show how to exploit the unusual properties of ILs for the synthesis of bimetallic, random alloy-type nanoparticles. Here, very small nanoparticles with uniform sizes can be synthesized without the addition of auxiliary ligands at moderate reaction temperatures. Nucleation and growth processes are directly controlled by IL-inherent, weak cation/anion interactions. Several methods for Pt/Sn-based nanoparticles are known, however, these synthetic protocols typically involve either supports and/or stabilizing agents (i.e., rather strongly coordinating surfactants or ligands)17. Ligands/surfactants adsorbed on the nanoparticle surface may modify or even inhibit catalytic performance and often need to be successively removed (e.g., via thermal treatment) for catalytic application. This protocol yields IL-based nanoparticle sols of extraordinary high colloidal stability without the addition of such strongly coordinating ligands. Nanoparticles stabilized in ILs have revealed interesting properties as quasi-homogenous catalysts in a broad range of catalytic reactions18,19,20,21,22,23,24. In this protocol, the selective hydrogenation of an &#945;,&#946;-unsaturated aldehyde (i.e., cinnamic aldehyde) is described as a model reaction to probe the catalytic performance of the IL-stabilized nanoparticles and the influence of tin alloying on the catalytic activity and selectivity25.
This protocol is intended to elucidate the details of the experimental synthetic procedures and to help new practitioners in the field to avoid many common pitfalls associated with the synthesis of nanoparticles in ILs. The details of materials characterization is included in previous publication25.

<table><tbody><tr><td>Platinum(II) acetate (PtCl&lt;sub&gt;2&lt;/sub&gt;)</td><td>Acros</td><td>ACRO369670010</td><td>99%, anhydrous, toxic</td></tr><tr><td>Tin(II) acetate (Sn(ac)&lt;sub&gt;2&lt;/sub&gt;)</td><td>Strem</td><td>50-1975</td><td>99%</td></tr><tr><td>Tin(II) chloride (SnCl&lt;sub&gt;2&lt;/sub&gt;)</td><td>Sigma Aldrich</td><td>452335</td><td>98%; harmful</td></tr><tr><td>Methyltrioctylammonium&lt;br/&gt; bis(trifluoromethylsulfonyl) imide ([OMA][NTf&lt;sub&gt;2&lt;/sub&gt;])</td><td>IoLitec</td><td>IL-0017-HP</td><td>99 %; n.a.; H&lt;sub&gt;2&lt;/sub&gt;O &amp;lt; 100 ppm; halides &amp;lt; 100 ppm</td></tr><tr><td>Tetrahydrofurane</td><td>Sigma Aldrich</td><td>186562</td><td>99.9 %; anhydrous; carcinogenic</td></tr><tr><td>Acetonitrile</td><td>Sigma Aldrich</td><td>271004</td><td>99.8%; anhydrous; harmful</td></tr><tr><td>n-Hexane</td><td>Sigma Aldrich</td><td></td><td>95%, flammable, carcinogenic, toxic</td></tr><tr><td>(Trans)-cinnamaldehyde</td><td>Sigma Aldrich</td><td>14371-10-9</td><td>99%; irritant</td></tr><tr><td>Methyltrioctylammonium bromide</td><td>Sigma Aldrich</td><td>365718</td><td>97%; irritant</td></tr><tr><td>Potassium hydride (KH)</td><td>Sigma Aldrich</td><td>215813</td><td>30 wt.-% dispersion in mineral oil; corrosive</td></tr><tr><td>Triethylborane (B(Et)&lt;sub&gt;3&lt;/sub&gt;)</td><td>Witco</td><td>257192</td><td>95%; toxic, pyrophoric</td></tr><tr><td>N-oleylsarcosine (Korantin-SH)</td><td>BASF</td><td></td><td></td></tr><tr><td>H&lt;sub&gt;2&lt;/sub&gt;</td><td>Air Liquide</td><td></td><td>99.9 %, flammable</td></tr></tbody></table>

synthesis of bimetallic pt/sn-based nanoparticles in ionic liquids

We demonstrate a method for the synthesis of bimetallic nanoparticles consisting of Pt and Sn. A synthesis strategy is used in which the particular physico-chemical properties of ionic liquids (ILs) are exploited to control both nucleation and growth processes. The nanoparticles form colloidal sols of very high colloidal stability in the IL, which is particularly interesting in view of their use as quasi-homogeneous catalysts. Procedures for both nanoparticle extraction in conventional solvents and for nanoparticle precipitation are presented. The size, structure and composition of the synthesized nanocrystals are confirmed using inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDX). By this, we show that the nanocrystals are random-type alloy and of small (2-3 nm) size. The catalytic activity and selectivity in the hydrogenation of &#945;,&#946;-unsaturated aldehydes is tested in a semi-continuous batch-type reactor. In this context, the bimetallic Pt/Sn-based nanoparticles reveal a high selectivity towards the unsaturated alcohol.

XRD patterns and transmission electron microscopy (TEM) images are collected for the alloyed nanoparticles (Figure 1) and used to identify the size, phase and morphology of the nanostructures. Energy-dispersive X-ray spectroscopy (EDX) and ICP-AES are used to determine the elemental composition of the nanoparticles.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/58058/58058fig1.jpg" /> 
Figure 1. Representative TEM images with particle size distribution of random alloy-type Pt/Sn nanoparticles. The nanoparticles were prepared using platinum(II) chloride and tin(II) acetate precursors (a) in a molar Pt:Sn precursor ratio of 3:1 and (b,c) in a molar Pt:Sn precursor ratio of 1:1 and (d) using platinum(II) chloride and tin(II) chloride precursors in a molar Pt:Sn ratio of 1:1. (e) Representative energy-dispersive X-ray spectrum of the bimetallic Pt/Sn-based particles confirming the presence of both Sn and Pt. (Cu signals originate from the supporting Cu grid). (f) XRD patterns of Pt/Sn-based nanoparticles compared to Pt nanoparticle reference. <a href="https://www.jove.com/files/ftp_upload/58058/58058fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/58058/58058fig2.jpg" /> 
Figure 2. Schematic representation of the reaction pathways and major reaction products (i.e., cinnamic alcohol (CAOL), hydrocinnamic aldehyde (HCAL), and hydrocinnamic alcohol (HCAOL)) in the hydrogenation of cinnamic aldehyde (CAL). The selective hydrogenation of the carbonyl bond to the unsaturated alcohol is a critical step in the synthesis of various fine chemicals. By alloying Pt with Sn in Pt/Sn-based nanoparticles, the carbonyl bond may be selectively hydrogenated to yield the unsaturated alcohol (i.e., CAOL) as the main reaction product. <a href="https://www.jove.com/files/ftp_upload/58058/58058fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/58058/58058fig3.jpg" /> 
Figure 3. Time course of the conversion and selectivity in the catalytic hydrogenation of cinnamaldehyde (CAL) for the random alloy-type Pt/Sn nanoparticles which are prepared from platinum(II) chloride and tin(II) acetate in a Pt:Sn precursor ratio of (a) 1:1 and (b) 3:1 (reaction conditions: 80 &#176;C, 10 bar H2). Although the CAOL selectivity is lower for nanoparticles with a Pt:Sn precursor ratio of 3:1 (b), the enhanced CAL conversion results in a higher yield in CAOL. <a href="https://www.jove.com/files/ftp_upload/58058/58058fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Synthesis of Bimetallic Pt/Sn-based Nanoparticles in Ionic Liquids at JoVE.com

Synthesis of Bimetallic Pt/Sn-based Nanoparticles in Ionic Liquids

A protocol for the synthesis of bimetallic nanoparticles in ionic liquids and the procedure of their catalytic testing in the selective hydrogenation of unsaturated aldehydes are described.

We demonstrate a method for the synthesis of bimetallic nanoparticles consisting of Pt and Sn. A synthesis strategy is used in which the particular ...

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9.0K Views.  Karlsruhe Institute of Technology (KIT). A protocol for the synthesis of bimetallic nanoparticles in ionic liquids and the procedure of their catalytic testing in the selective hydrogenation of unsaturated aldehydes are described.

Video: Synthesis of Bimetallic Pt/Sn-based Nanoparticles in Ionic Liquids

Amide Coupling Reaction for the Synthesis of Bispyridine-based Ligands and Their Complexation to Platinum as Dinuclear Anticancer Agents

Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. Isonicotinic acid, or its derivatives, are coupled to variable length diaminoalkane chains under an inert atmosphere in anhydrous DMF or DMSO with the use of a weak base, triethylamine, and a coupling agent, 1-propylphosphonic anhydride. The products precipitate from solution upon formation or can be precipitated by the addition of water. If desired, the ligands can be further purified by recrystallization from hot water. Dinuclear platinum complex synthesis using the bispyridine ligands is done in hot water using transplatin. The most informative of the chemical characterization techniques to determine the structure and gross purity of both the bispyridine ligands and the final platinum complexes is 1H NMR with particular analysis of the aromatic region of the spectra (7-9 ppm). The platinum complexes have potential application as anticancer agents and the synthesis method can be modified to produce trinuclear and other multinuclear complexes with different hydrogen bonding functionality in the bridging ligand.

This protocol describes the use of amide coupling reactions of isonicotinic acid and diaminoalkanes to form bridging ligands suitable for use in the synthesis of multinuclear platinum complexes, which combine aspects of the anticancer drugs BBR3464 and picoplatin.

Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. ...

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The silica-encapsulated metal oxide nanoparticles are then carburized in a methane/hydrogen atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal carbide nanoparticles. During the carburization process, the silica shells prevent the sintering of adjacent carbide nanoparticles while also preventing the deposition of excess surface carbon. Alternatively, the silica-encapsulated metal oxide nanoparticles can be nitridized in an ammonia atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal nitride nanoparticles. By adjusting the reverse microemulsion parameters, the thickness of the silica shells, and the carburization/nitridation conditions, the transition metal carbide or nitride nanoparticles can be tuned to various sizes, compositions, and crystal phases. After carburization or nitridation, the silica shells are then removed using either a room-temperature aqueous ammonium bifluoride solution or a 0.1 to 0.5 M NaOH solution at 40-60 &#176;C. While the silica shells are dissolving, a high surface area support, such as carbon black, can be added to these solutions to obtain supported early transition metal carbide or nitride nanoparticles. If no high surface area support is added, then the nanoparticles can be stored as a nanodispersion or centrifuged to obtain a nanopowder.

A &#8220;removable ceramic coating method&#8221; is presented in visual format for the synthesis of non-sintered and metal-terminated monometallic and bimetallic early transition metal carbide and nitride nanoparticles with tunable sizes and crystal structures.

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The ...

Synthesis, Characterization, and Functionalization of Hybrid Au/CdS and Au/ZnS Core/Shell Nanoparticles

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large extinction coefficients which can be tuned across the visible spectrum. Research into the plasmonic enhancement of optical transitions has become popular, due to the possibility of altering and in some cases improving photo-absorption or emission properties of nearby chromophores such as molecular dyes or quantum dots. The electric field of the plasmon can couple with the excitation dipole of a chromophore, perturbing the electronic states involved in the transition and leading to increased absorption and emission rates. These enhancements can also be negated at close distances by energy transfer mechanism, making the spatial arrangement of the two species critical. Ultimately, enhancement of light harvesting efficiency in plasmonic solar cells could lead to thinner and, therefore, lower cost devices. The development of hybrid core/shell particles could offer a solution to this issue. The addition of a dielectric spacer between a gold nanoparticles and a chromophore is the proposed method to control the exciton plasmon coupling strength and thereby balance losses with the plasmonic gains. A detailed procedure for the coating of gold nanoparticles with CdS and ZnS semiconductor shells is presented. The nanoparticles show high uniformity with size control in both the core gold particles and shell species allowing for a more accurate investigation into the plasmonic enhancement of external chromophores.

The synthesis of uniform gold nanoparticles coated with semiconductor shells of CdS or ZnS is performed. The semiconductor coating is conducted by first depositing a silver sulfide shell and exchanging the silver cations for zinc or cadmium cations.

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large ...

Generation of Zerovalent Metal Core Nanoparticles Using n-(2-aminoethyl)-3-aminosilanetriol

In this work, a facile one-pot reaction for the formation of metal nanoparticles in a water solution through the use of n-(2-aminoethyl)-3-aminosilanetriol is presented. This compound can be used to effectively reduce and complex metal salts into metal core nanoparticles coated with the compound. By controlling the concentrations of salt and silane one is able to control reaction rates, particle size, and nanoparticle coating. The effects of these changes were characterized through transmission electron microscopy (TEM), UV-Vis spectrometry (UV-Vis), Nuclear Magnetic Resonance spectroscopy (NMR) and Fourier Transform Infrared spectroscopy (FTIR). A unique aspect to this reaction is that usually silanes hydrolyze and cross-link in water; however, in this system the silane is water-soluble and stable. It is known that silicon and amino moieties can form complexes with metal salts. The silicon is known to extend its coordination sphere to form penta- or hexa-coordinated species. Furthermore, the silanol group can undergo hydrolysis to form a Si-O-Si silica network, thereby transforming the metal nanoparticles into a functionalized nanocomposites.

Generation of Zerovalent Metal Core Nanoparticles Using n-2-aminoethyl-3-aminosilanetriol

A novel method for metal core nanoparticle synthesis using a water stable silanol is described.

In this work, a facile one-pot reaction for the formation of metal nanoparticles in a water solution through the use of ...

The Synthesis of [Sn10(Si(SiMe3)3)4]2- Using a Metastable Sn(I) Halide Solution Synthesized via a Co-condensation Technique

The number of well-characterized metalloid tin clusters, synthesized by applying the disproportionation of a metastable Sn(I) halide in the presence of a sterically demanding ligand, has increased in recent years. The metastable Sn(I) halide is synthesized at&#160;&#34;outer space conditions&#34; via the preparative co-condensation technique. Thereby, the subhalide is synthesized in an oven at high temperatures, around 1,300 &#176;C, and at reduced pressure by the reaction of elemental tin with hydrogen halide gas (e.g., HCl). The subhalide (e.g., SnCl) is trapped within a matrix of an inert solvent, like toluene at -196 &#176;C. Heating the solid matrix to -78 &#176;C gives a metastable solution of the subhalide. The metastable subhalide solution is highly reactive but can be stored at -78 &#176;C for several weeks. On heating the solution to room temperature, a disproportionation reaction occurs, leading to elemental tin and the corresponding dihalide. By applying bulky ligands like Si(SiMe3)3, the intermediate metalloid cluster compounds can be trapped before complete disproportionation to elemental tin. Hence, the reaction of a metastable Sn(I)Cl solution with Li-Si(SiMe3)3 gives [Sn10(Si(SiMe3)3)4]2- 1 as black crystals in high yield. 1 is formed via a complex reaction sequence including salt metathesis, disproportionation, and degradation of larger clusters. Further, 1 can be analyzed by various methods like NMR or single crystal X-ray structure analysis.

The Synthesis of [Sn10SiSiMe334]2- Using a Metastable SnI Halide Solution Synthesized via a Co-condensation Technique

The disproportionation reaction of a metastable Sn(I) chloride solution, obtained via the preparative co-condensation technique, is used for the synthesis of a metalloid tin cluster compound.

The number of well-characterized metalloid tin clusters, synthesized by applying the disproportionation of a metastable Sn(I) halide in the presence of a ...

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs within the interlayer space of semiconducting layered titania nanosheet (TNS) films was investigated here. Two types of intermediate films (i.e., TNS films containing methyl viologen (TNS/MV2+) and 2-ammoniumethanethiol (TNS/2-AET+)) were prepared. The two intermediate films were soaked in an aqueous tetrachloroauric(III) acid (HAuCl4) solution, whereby considerable amounts of Au(III) species were accommodated within the interlayer spaces of the TNS films. The two types of obtained films were then soaked in an aqueous sodium tetrahydroborate (NaBH4) solution, whereupon the color of the films immediately changed from colorless to purple, suggesting the formation of AuNPs within the TNS interlayer. When only TNS/MV2+ was used as the intermediate film, the color of the film gradually changed from metallic purple to dusty purple within 30 min, suggesting that aggregation of AuNPs had occurred. In contrast, this color change was suppressed by using the TNS/2-AET+ intermediate film, and the AuNPs were stabilized for over 4 months, as evidenced by the characteristic extinction (absorption and scattering) band from the AuNPs.

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Here, we present a protocol for the in situ synthesis of gold nanoparticles (AuNPs) within the interlayer space of layered titanate films without the aggregation of AuNPs. No spectral change was observed even after 4 months. The synthesized material has expected applications in catalysis, photo-catalysis, and the development of cost-effective plasmonic devices.

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Engineering

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Here we introduce experimental protocols for the real-time observation of a self-assembly process using liquid-cell transmission electron microscopy.

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Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance

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&#160; The protocol describes the synthesis and electrochemical testing of platinum-nickel nanowires. Nanowires were synthesized by the galvanic displacement of a nickel nanowire template. Post-synthesis processing, including hydrogen annealing, acid leaching, and oxygen annealing were used to optimize nanowire performance and durability in the oxygen reduction reaction.

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen ...

A Salt-Templated Synthesis Method for Porous Platinum-based Macrobeams and Macrotubes

The synthesis of high surface area porous noble metal nanomaterials generally relies on time consuming coalescence of pre-formed nanoparticles, followed by rinsing and supercritical drying steps, often resulting in mechanically fragile materials. Here, a method to synthesize nanostructured porous platinum-based macrotubes and macrobeams with a square cross section from insoluble salt needle templates is presented. The combination of oppositely charged platinum, palladium, and copper square planar ions results in the rapid formation of insoluble salt needles. Depending on the stoichiometric ratio of metal ions present in the salt-template and the choice of chemical reducing agent, either macrotubes or macrobeams form with a porous nanostructure comprised of either fused nanoparticles or nanofibrils. Elemental composition of the macrotubes and macrobeams, determined with x-ray diffractometry and x-ray photoelectron spectroscopy, is controlled by the stoichiometric ratio of metal ions present in the salt-template. Macrotubes and macrobeams may be pressed into free standing films, and the electrochemically active surface area is determined with electrochemical impedance spectroscopy and cyclic voltammetry. This synthesis method demonstrates a simple, relatively fast approach to achieve high-surface area platinum-based macrotubes and macrobeams with tunable nanostructure and elemental composition that may be pressed into free-standing films with no required binding materials.

A synthesis method to obtain porous platinum-based macrotubes and macrobeams with a square cross section through chemical reduction of insoluble salt-needle templates is presented.

The synthesis of high surface area porous noble metal nanomaterials generally relies on time consuming coalescence of pre-formed nanoparticles, followed ...

Catalytic Reactions at Amine-Stabilized and Ligand-Free Platinum Nanoparticles Supported on Titania During Hydrogenation of Alkenes and Aldehydes

Ligands like amines are used in the colloidal synthesis approach to protect platinum nanoparticles (Pt NP&#39;s) from agglomeration. Normally, ligands like amines are removed by diverse pre-treatment procedures before use in heterogeneous catalysis as amines are considered as a catalyst poison. However, a possible beneficial influence of these surface modifiers on hydrogenation reactions, which is known from spectator species on metal surfaces, is often neglected.
Therefore, amine-stabilized Pt nanoparticles supported by titania (P25) were used without any pre-treatment in order to elucidate a possible influence of the ligand in liquid phase hydrogenation reactions. The catalytic activity of amine-stabilized Pt nanoparticles of two different sizes was investigated in a double-walled stirring tank reactor at 69 &#176;C to 130 &#176;C and 1 atm hydrogen pressure. The conversion of cyclohexene to cyclohexane was determined by gas chromatography (GC) and was compared to ligand-free Pt particles. All catalysts were checked before and after reaction by transmission electron spectroscopy (TEM) and X-ray photoelectron spectroscopy (XPS) for possible changes in size, shape, and ligand shell. The hydrogenation of cyclohexene in liquid phase revealed a higher conversion for amine-stabilized Pt nanoparticles on titania than the ligand-free particles. The hydrogenation of 5-methylfurfural (5-MF) was chosen for a further test reaction, since the hydrogenation of &#945;, &#946;-unsaturated aldehydes is more complex and exhibits various reaction paths. However, XPS and infrared spectroscopy (IR) proved that 5-MF acts as catalyst poison at the given reaction conditions.

This protocol shows a convenient method for comparing the catalytic properties of supported platinum catalysts, synthesized by deposition of nanosized colloids or by impregnation. The hydrogenation of cyclohexene serves as a model reaction to determine the catalytic activity of the catalysts.

Ligands like amines are used in the colloidal synthesis approach to protect platinum nanoparticles (Pt NP&#39;s) from agglomeration. Normally, ligands ...

Synthesis of Bimetallic Pt/Sn-based Nanoparticles in Ionic Liquids

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A Salt-Templated Synthesis Method for Porous Platinum-based Macrobeams and Macrotubes

Catalytic Reactions at Amine-Stabilized and Ligand-Free Platinum Nanoparticles Supported on Titania During Hydrogenation of Alkenes and Aldehydes