The authors would like to acknowledge the State of Washington for supporting this research through the University of Washington Clean Energy Institute Exploratory Fellowship Program, and National Science Foundation (NSF) Sustainable Energy Pathway (SEP) Award CHE-1230615.

Caution: Cadmium precursors are highly toxic and must be handled with great care. Wear proper protective equipment, use appropriate engineering controls and consult relevant materials safety data sheets (MSDS). In addition, the formation of nanoparticles may present additional hazards. The reactions described herein are conducted with a standard vacuum gas manifold, in order to conduct the experiments within an inert atmosphere. All chemicals were purchased commercially and used as received. This protocol is based upon a previously developed...

<ol>
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P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Semiconductor+Clusters,+Nanocrystals,+and+Quantum+Dots.">Semiconductor Clusters, Nanocrystals, and Quantum Dots.</a> Science. 271 (5251), 933-937 (1996).</li><li>Alivisatos, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Perspectives+on+the+Physical+Chemistry+of+Semiconductor+Nanocrystals.">Perspectives on the Physical Chemistry of Semiconductor Nanocrystals.</a> J. Phys. 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The authors disclose no competing financial interests.

We have developed a method to synthesize CdS nanoparticles within a sulfur copolymer matrix. This sulfur copolymer is composed of elemental sulfur and methylstyrene.5 An important feature of this method is that the copolymer can be used as both a high-temperature solvent and a sulfur source that reacts with a cadmium precursor to produce CdS nanoparticles in solution.5 The critical step in the procedure is the synthesis of the sulfur copolymer with a suitable ratio of methylstyrene and sulfur. The u...

Although proven useful for synthesis, conventional aliphatic ligands present a number of challenges for the implementation of nanoparticles in photonic and electrochemical devices. Aliphatic ligands are highly insulating, hydrophobic, and constitute a significant barrier to electrochemical surface reactions.1 Accordingly, several studies have developed ligand exchange and ligand stripping protocols that replace these aliphatic ligands with functional moieties or that strip away the ligands to reveal a bare nanoparticle surface.1-3 These reactions, however, pose several intrinsic problems. They significantly add to the complexity of the synthetic process, do not always go to completion, and can deteriorate the surface of the nanoparticles, which can in turn impose significant problems during device fabrication when using these techniques.4
We have developed a sulfur copolymer that can be used as both a high temperature solvent and sulfur source during the synthesis of CdS nanoparticles.5 This copolymer is based on a network copolymer developed by Chung et al. that uses elemental sulfur and 1,3-diisopropenylbenzene (DIB).6 In our case, a methylstyrene monomer is implemented instead of DIB. The methylstyrene monomer limits cross-linking reactions, which would otherwise produce a high molecular weight network copolymer.5,6 The presence of only one vinylic functional group on the methylstyrene monomer promotes the formation of oligomeric radicals once heated, which allows the sulfur copolymer to operate as a liquid solvent and sulfur source in parallel during the nanoparticle synthesis.5 Specifically, the sulfur polymer is produced by heating elemental sulfur to 150 &#176;C, which causes the S8 rings to transition into a linearly structured liquid sulfur diradical form. Next, methylstyrene is injected into the liquid sulfur in a 1:50 molar ratio of methylstyrene molecules to sulfur atoms.5 The methylstyrene double bond reacts with the sulfur chains to produce the copolymer, as presented in Figure 1.5 The sulfur copolymer is then cooled and the cadmium precursor is added. This mixture is then reheated to 200 &#176;C, during which, the sulfur copolymer melts and the nanoparticle nucleation and growth processes are initiated within the solution.5 A 20:1 molar ratio of sulfur to cadmium precursor is used, so that only some of the sulfur is consumed during the reaction.5 This copolymer stabilizes the nanoparticles by suspending them within a solid polymer matrix once the reaction has been terminated.5 The copolymer can be removed after the synthesis, resulting in the production of CdS nanoparticles that do not have organic coordinating ligands, as depicted in Figure 2.5
The synthetic method presented in this work is relatively simple in comparison with other methods presented in the literature.1-3,7 It is applicable for a diverse range of applications where traditional ligated nanoparticles have proven problematic or undesirable. This technique can open doors to higher throughput testing, where one batch of nanoparticles can be used to examine a complete spectrum of subsequent functionalizations without the need for complex and time consuming ligand stripping or exchange procedures.2,4,8,9 These unligated nanoparticles also offer opportunities to reduce the number of carbon defects commonly observed in printed nanoparticle devices, by eliminating the carbon source.10-16 This detailed protocol is intended to help others implement this new method and to help spur its active use in a variety of fields that will find it of particular significance.

<table>
	<tbody>
		<tr>
			<td>Sulfur (S8), 99.5%</td>
			<td>Sigma Aldrich</td>
			<td>84683</td>
			<td></td>
		</tr>
		<tr>
			<td>&#945;-methylstyrene, 99%</td>
			<td>Sigma Aldrich</td>
			<td>M80903</td>
			<td></td>
		</tr>
		<tr>
			<td>Cadmium acetylacetonate (Cd(acac)), 99.9%</td>
			<td>Sigma Aldrich</td>
			<td>517585</td>
			<td>Highly Toxic</td>
		</tr>
		<tr>
			<td>Chloroform (CHCl3), 99.5%</td>
			<td>Sigma Aldrich</td>
			<td>C2432</td>
			<td></td>
		</tr>
		<tr>
			<td>Hotplate / magnetic stirrer</td>
			<td>IKA RCT&#160;</td>
			<td>3810001</td>
			<td></td>
		</tr>
		<tr>
			<td>Temperature controller with probe and heating mantle</td>
			<td>Oakton Temp 9000</td>
			<td>WD-89800</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Beckman Coulter Allegra X-22</td>
			<td>392186</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge Tubes</td>
			<td>Thermo Scientific</td>
			<td>3114</td>
			<td>Teflon for resistance to chlorinated solvents</td>
		</tr>
		<tr>
			<td>TEM with attached EDS detector</td>
			<td>FEI Tecnai G2 F-20 with EDAX detector</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>TEM Sample Grid</td>
			<td>Ted Pella</td>
			<td>1824</td>
			<td>Ultrathin carbon film substrate with holey carbon support films on a 400 mesh copper grid</td>
		</tr>
		<tr>
			<td>XRD</td>
			<td>Bruker F-8 Focus Diffractometer</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Molybdenum coated soda lime glass substrates</td>
			<td></td>
			<td></td>
			<td>750 nm thick sputtered molybdenum layer</td>
		</tr>
		<tr>
			<td>Quartz Fluorescence Cuvettes</td>
			<td>Sigma Aldrich</td>
			<td>Z803073</td>
			<td>10 mm by 10 mm, 4 polished sides with screw top</td>
		</tr>
		<tr>
			<td>UV-Vis-NIR</td>
			<td>Perkin Elmer Lambda 1050 Spectrometer</td>
			<td></td>
			<td>With 3D WB Detector Module</td>
		</tr>
		<tr>
			<td>PL</td>
			<td>Horiba FL3-21tau Fluorescence Spectrophotometer</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

synthesis of ligand-free cds nanoparticles within a sulfur copolymer matrix

Aliphatic ligands are typically used during the synthesis of nanoparticles to help mediate their growth in addition to operating as high-temperature solvents. These coordinating ligands help solubilize and stabilize the nanoparticles while in solution, and can influence the resulting size and reactivity of the nanoparticles during their formation. Despite the ubiquity of using ligands during synthesis, the presence of aliphatic ligands on the nanoparticle surface can result in a number of problems during the end use of the nanoparticles, necessitating further ligand stripping or ligand exchange procedures. We have developed a way to synthesize cadmium sulfide (CdS) nanoparticles using a unique sulfur copolymer. This sulfur copolymer is primarily composed of elemental sulfur, which is a cheap and abundant material. The sulfur copolymer has the advantages of operating both as a high temperature solvent and as a sulfur source, which can react with a cadmium precursor during nanoparticle synthesis, resulting in the generation of ligand free CdS. During the reaction, only some of the copolymer is consumed to produce CdS, while the rest remains in the polymeric state, thereby producing a nanocomposite material. Once the reaction is finished, the copolymer stabilizes the nanoparticles within a solid polymeric matrix. The copolymer can then be removed before the nanoparticles are used, which produces nanoparticles that do not have organic coordinating ligands. This nascent synthesis technique presents a method to produce metal-sulfide nanoparticles for a wide variety of applications where the presence of organic ligands is not desired.

The TEM image in Figure 3a shows small CdS nanoparticles (3-4 nm) that have nucleated within the sulfur copolymer before the sulfur copolymer has been completely removed. The image in Figure 3a was acquired by taking an aliquot of the nanoparticle solution immediately after the solution reached 200 &#176;C. Figure 3b shows larger nanoparticles (7-10 nm) that have grown in solution for 30 min before the sulfur copolymer has been completely removed. Figure 3c</stro...

Watch this Scientific Journal Video about Synthesis of Ligand-free CdS Nanoparticles within a Sulfur Copolymer Matrix at JoVE.com

Synthesis of Ligand-free CdS Nanoparticles within a Sulfur Copolymer Matrix

Herein we present a method to synthesize ligand-free cadmium sulfide (CdS) nanoparticles based on a unique sulfur copolymer. The sulfur copolymer operates as a high temperature solvent and a sulfur source during the nanoparticle synthesis and stabilizes the nanoparticles after the reaction.

Aliphatic ligands are typically used during the synthesis of nanoparticles to help mediate their growth in addition to operating as high-temperature ...

The overall goal of this synthesis method is to use a sulfur copolymer to produce cadmium sulfide nanoparticles. This method can provide a route for researchers to develop new nanoparticle surface modification reactions. The main advantage of this technique is that it provides a way to easily synthesize nanoparticles that do not have conventional aliphatic ligands.This synthesis method is potentially useful in a range of fields where conventional nanoparticle ligands can be difficult to remove, exchange or block surface reactions. Demonstrating the procedure will be Trevor Martin, a graduate student from my laboratory. To prepare the molten elemental sulfur, place elemental sulfur in a 15 milliliter three-neck flask with an attached condenser and temperature probe.Perform pump and purge cycles with vacuum and nitrogen several times. Heat under nitrogen to 150 degrees Celsius with stirring. This will cause the sulfur to become a yellow-colored liquid.Once all of the sulfur has dissolved into the liquid, immediately inject alpha-methylstyrene into the solution. Heat the solution to 185 degrees Celsius with stirring at 500 RPM for 10 minutes. As the copolymer forms, the solution will change color from yellow to orange, finally producing a deep-red color.Remove the solution from the heat and cool to room temperature. As it cools, the copolymer will slowly crystallize to form an orange, rubbery solid. At this stage, the copolymer can be stored at room temperature for a subsequent synthesis, or it can be used immediately.Add cadmium acetylacetonate to the three-necked flask from the previous step so that the powder is placed evenly on top of the solid sulfur copolymer. Perform pump and purge cycles on the flask with nitrogen, and vacuum several times. It's important to ensure the cadmium precursor mixes into the liquid sulfur copolymer thoroughly and uniformly as soon as the polymer begins to melt so that the nanoparticle formation can begin homogeneously.Heat the solution to 200 degrees Celsius under nitrogen, with stirring. The sulfur copolymer will melt and mix with the cadmium precursor, allowing the nanoparticle nucleation and growth processes to begin. Allow the nanoparticles to grow for 30 minutes before removing the solution from the heat and cooling to room temperature.Once cooled, remove the solid nanocomposite from the flask, and store at room temperature. To remove the sulfur copolymer, place the 200 milligrams of nanocomposite in a 20 milliliter glass vial, and add 20 milliliters of chloroform. Place the vial in an ultrasonicator and sonicate for one hour to break up the nanocomposite and suspend the nanoparticles within the solution.Following sonication, separate the solution into two 30 milliliter centrifuge tubes, and add another 20 milliliters of chloroform to each. Centrifuge the solution at 8, 736 Gs for 15 minutes. Then, decant the sulfur copolymer from the centrifuge tubes, making sure not to disturb the settled nanonparticles.To isolate the settled nanoparticles, redisperse them by adding chloroform to each centrifuge tube and sonicating for 15 minutes. Repeat the centrifugation and redispersion three more times to ensure that all of the sulfur copolymer has been removed. Once all of the sulfur copolymer is removed, the decanted solution will no longer have an orange color.Collect the final nanoparticles by adding two milliliters of chloroform to each centrifuge tube. Combine the collected nanoparticles in one 20 milliliter glass vial. Place the glass vial under vacuum to remove all of the chloroform and to dry the nanoparticles.At this stage, determine the mass of the resulting nanoparticles. Compare this mass to the starting mass of the precursors to determine the yield of the reaction, using molar ratios of the starting material and product. To characterize the cadmium sulfide nanoparticles by transmission electron microscopy, or TEM, dilute 20 milligrams of the isolated nanoparticles in 20 milliliters of chloroform and ultrasonicate for one hour.Dilute this solution in chloroform and sonicate for 15 minutes. Drop the final solution onto an ultra-thin carbon-film substrate with Holey carbon support films on a 400-mesh copper TEM grid. Place the TEM grid in a glass vial.Hold the vial under vacuum overnight to remove any residual solvent from the sample. Once the drying is completed, acquire TEM images using a 200 kilovolt accelerating voltage, a spot size of three and an attached energy dispersive X-ray spectroscopy, or EDS detector. To characterize the cadmium sulfide nanoparticles by X-ray diffraction, dilute the isolated nanoparticles in chloroform at a concentration of 10 milligrams per milliliter.Then, clean the lipton(mumbles)coated sodalime glass substrates by sonicating in detergent, the ionized water, acetone and isopropyl alcohol for 10 minutes in each solvent. Finally, clean the substrates in an air plasma cleaner for 10 minutes prior to drop casting. Next, drop cast the solution onto the prepared substrates in seven microliter increments.Once the films have dried, acquire X-ray diffraction data. Collect data using 7, 000 data points at a scan rate of one data point per second, with a copper K-alpha X-ray source and an incident wavelength of 1.54059 angstroms. To characterize the cadmium sulfide nanoparticles by solution spectroscopy, disperse the isolated nanoparticles in chloroform at 0.1 milligram per milliliter and sonicate for 30 minutes.Then, place the samples in a sealed quartz cuvette. Prepare two additional samples for analysis by dispersing the nanocomposite as well as the sulfur copolymer in formamide both at one milligram per milliliter. Stir each dispersion at 700 RPM, and heat to 70 degrees Celsius to facilitate suspension of the material.Conduct optical absorbance measurements of all three samples using a spectrometer with a triple detector that extends across the ultraviolet, visible and near-infrared ranges. Finally, conduct photoluminescence measurements of all three samples using a fluorescence spectrophotometer with an excitation wavelength of 330 nanometers. Shown here is a TEM image showing three-to four-nanometer-sized cadmium sulfide nanoparticles forming within the sulfur copolymer at the beginning of the reaction.This TEM image shows aggregated nanoparticles once the copolymer has been removed. The inset shows the stoichiometry of the nanoparticles from EDS spectra. Shown here is the X-ray diffraction pattern for the isolated nanoparticles, which is consistent with the formation of cadmium sulfide.Here, spectroscopy data is shown for the isolated nanoparticles once the sulfur copolymer is removed. Once mastered, this nanoparticle synthesis can be completed in several hours. Don't forget that working with cadmium can be hazardous, and precautions such as wearing proper protective equipment should be taken while performing this procedure.After watching this video, you should have a good understanding of how to synthesize metal sulfide nanoparticles using a sulfur copolymer. We believe that this method will help provide a way to easily tune nanoparticle surface chemistry for a variety of applications.

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9.4K visualizações.  University of Washington. The overall goal of this synthesis method is to use a sulfur copolymer to produce cadmium sulfide nanoparticles. This method can provide a route for researchers to develop new nanoparticle surface modification reactions. The main advantage of this technique is that it provides a way to easily synthesize nanoparticles that do not have conventional aliphatic ligands.This synthesis method is potentially useful in a range of fields where conventional nanoparticle ligands can be difficult t...