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 synthetic method, which we recently described elsewhere.5
1. Sulfur Copolymer Synthesis
<ol>
	<li>Preparation of Molten Elemental Sulfur
	<ol>
		<li>Place elemental sulfur (4 g, 124.8 mmol, S8, 99.5%) in a 50 ml three neck flask with an attached condenser and temperature probe. Perform pump and purge cycles with vacuum and nitrogen several times.</li>
		<li>Heat under nitrogen to 150 &#176;C with stirring, which will cause the sulfur to become a yellow colored liquid.</li>
	</ol>
	</li>
	<li>Preparation of Sulfur Copolymer
	<ol>
		<li>Once all of the sulfur has dissolved into the liquid, immediately inject &#945;-methylstyrene (330 &#181;l, 2.5 mmol, 99%) into the solution.</li>
		<li>Heat solution to 185 &#176;C with stirring at 500 rpm for 10 min. As the copolymer forms, the solution will change color from yellow to orange, finally producing a deep red color.</li>
		<li>Remove the solution from 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.</li>
	</ol>
	</li>
</ol>
2. CdS Nanoparticle Synthesis
<ol>
	<li>Add cadmium acetylacetonate (Cd(acac), 900 mg, 2.9 mmol 99.9%) to the three neck flask from the previous step, so that the powder is placed evenly on top of the solid sulfur copolymer (4.0 g, 116 mmol).</li>
	<li>Perform pump and purge cycles on the flask with nitrogen and vacuum several times.</li>
	<li>Heat the solution to 200 &#176;C under nitrogen with stirring. The sulfur copolymer will melt and mix with the cadmium precursor, and the nanoparticle nucleation and growth processes will begin.</li>
	<li>Allow the nanoparticles to grow for 30 min. 
	Note: Varying the reaction time will influence the growth of the nanoparticles, so it is possible to tune the final size of the nanoparticles.5 A 30 min reaction time will with a size range of 7-10 nm.5</li>
	<li>Remove the solution from heat and allow to cool to room temperature.</li>
	<li>Once cooled, remove the solid nanocomposite from the flask and store at room temperature.</li>
</ol>
3. Remove the Sulfur Copolymer and Isolate the Nanoparticles&#160;
<ol>
	<li>Removal of the Sulfur Copolymer
	<ol>
		<li>Place the nanocomposite (200 mg) in a 20 ml glass vial and add chloroform (20 ml).</li>
		<li>Place the vial in an ultrasonicator and sonicate for 1 hr, to break up the nanocomposite and suspend the nanoparticles within the solution.</li>
		<li>Separate the solution into two 30 ml centrifuge tubes and add another 20 ml of chloroform to each.</li>
		<li>Centrifuge the solution at 8,736 x g (relative centrifugal force) for 15 min.</li>
		<li>Decant the sulfur copolymer from the centrifuge tubes, making sure to not disturb the settled nanoparticles.</li>
	</ol>
	</li>
	<li>Isolation of the Nanoparticles
	<ol>
		<li>Re-disperse the settled nanoparticles by adding chloroform to each centrifuge tube (30 ml) and sonicate for 15 min.</li>
		<li>Repeat the steps described in sections 3.1.4, 3.1.5 and 3.2.1 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.</li>
		<li>Collect the final nanoparticles by adding chloroform (2 ml) to each centrifuge tube.</li>
		<li>Combine the collected nanoparticles in one 20 ml glass vial (4 ml solution total) and place the glass vial under vacuum to remove all of the chloroform and to dry the nanoparticles. At this stage, the mass of the resulting nanoparticles can be determined and compared to the starting mass of the precursors in order to determine the yield of the reaction using molar ratios of the starting material and product.</li>
	</ol>
	</li>
</ol>
4. Characterize the CdS Nanoparticles
<ol>
	<li>Transmission Electron Microscopy
	<ol>
		<li>Dilute the isolated nanoparticles (20 mg) in chloroform (20 ml) and ultrasonicate for 1 hr.</li>
		<li>Dilute this solution in chloroform (5 drops/5 ml) and sonicate for 15 min.</li>
		<li>Drop the final solution onto an ultrathin carbon film substrate with holey carbon support films on a 400 mesh copper Transmission Electron Microscopy (TEM) grid.</li>
		<li>Place the TEM grid in a glass vial and hold under vacuum overnight, to remove any residual solvent from the sample.</li>
		<li>Once the drying is completed, acquire TEM images using a 200 kV accelerating voltage, a spot size of 3 and an attached Energy Dispersive X-ray Spectroscopy (EDS) detector.</li>
	</ol>
	</li>
	<li>X-ray Diffraction&#160;
	<ol>
		<li>Dilute the isolated nanoparticles in chloroform (10 mg/ml).</li>
		<li>Clean molybdenum coated soda lime glass substrates (1 cm2) by sonicating in detergent, deionized water, acetone and isopropyl alcohol, each for 10 min. Finally, clean the substrates in an air plasma cleaner for 10 min prior to drop casting.</li>
		<li>Drop cast the solution from 4.2.1 onto the substrates from 4.2.2 in 7 &#181;l increments.</li>
		<li>Once the films have dried, acquire X-ray Diffraction (XRD) data. Collect data using 7,000 data points at a scan rate of 1 data point per second with a Cu-K&#945; X-ray source and an incident wavelength of 1.54059 &#197;.</li>
	</ol>
	</li>
	<li>Solution Spectroscopy
	<ol>
		<li>Disperse the isolated nanoparticles (0.1 mg/ml) in chloroform and sonicate for 30 min and place samples in a sealed quartz cuvette.</li>
		<li>Disperse the nanocomposite from section 2.6 and the sulfur copolymer from section 1.2.3 in formamide (1 mg/ml), stir at 700 rpm, and heat to 70 &#176;C to facilitate suspension of the material.</li>
		<li>Acquire photoluminescence (PL) and absorbance spectra for all three samples. Conduct optical absorbance measurements using a spectrometer with a triple detector that extends across the ultraviolet, visible and near infrared ranges (UV-Vis-NIR). Conduct PL measurements using a fluorescence spectrophotometer with an excitation wavelength of 330 nm. 
		NOTE: The specific protocol for characterizing nanoparticles using the techniques discussed in sections 4.1.5, 4.2.4, and 4.3.2 varies widely depending on the nature of the specific equipment used, so we present only general characterization parameters here. The interested reader is directed to several review papers for more information regarding using these analysis techniques for CdS nanoparticles.17-19</li>
	</ol>
	</li>
</ol>

<ol><li>Rosen, E. L., Buonsanti, R., Llordes, A., Sawvel, A. M., Milliron, D. J., Helms, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Exceptionally+Mild+Reactive+Stripping+of+Native+Ligands+from+Nanocrystal+Surfaces+by+Using+Meerwein%27s+Salt%5BTitle%5D)+AND+%22Angew.+Chemie+Int.+Ed%22%5BJournal%5D)">Exceptionally Mild Reactive Stripping of Native Ligands from Nanocrystal Surfaces by Using Meerwein's Salt.</a> Angew. Chemie Int. Ed. 51 (3), 684-689 (2012).</li>
<li>Anderson, N. C., Hendricks, M. P., Choi, J. J., Owen, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ligand+exchange+and+the+stoichiometry+of+metal+chalcogenide+nanocrystals%3A+spectroscopic+observation+of+facile+metal-carboxylate+displacement+and+binding%5BTitle%5D)+AND+%22J.+Am.+Chem.+Soc%22%5BJournal%5D)">Ligand exchange and the stoichiometry of metal chalcogenide nanocrystals: spectroscopic observation of facile metal-carboxylate displacement and binding.</a> J. Am. Chem. Soc. 135 (49), 18536-18548 (2013).</li>
<li>Owen, J. S., Park, J., Trudeau, P. E., Alivisatos, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Reaction+chemistry+and+ligand+exchange+at+cadmium-selenide+nanocrystal+surfaces%5BTitle%5D)+AND+%22J.+Am.+Chem.+Soc%22%5BJournal%5D)">Reaction chemistry and ligand exchange at cadmium-selenide nanocrystal surfaces.</a> J. Am. Chem. Soc. 130 (37), 12279-12281 (2008).</li>
<li>Lokteva, I., Radychev, N., Witt, F., Borchert, H., Parisi, J., Kolny-Olesiak, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Surface+Treatment+of+CdSe+Nanoparticles+for+Application+in+Hybrid+Solar+Cells%3A+The+Effect+of+Multiple+Ligand+Exchange+with+Pyridine%5BTitle%5D)+AND+%22J.+Phys.+Chem.+C%22%5BJournal%5D)">Surface Treatment of CdSe Nanoparticles for Application in Hybrid Solar Cells: The Effect of Multiple Ligand Exchange with Pyridine.</a> J. Phys. Chem. C. 114 (29), 12784-12791 (2010).</li>
<li>Martin, T. R., Mazzio, K. A., Hillhouse, H. W., Luscombe, C. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Sulfur+copolymer+for+the+direct+synthesis+of+ligand-free+CdS+nanoparticles%5BTitle%5D)+AND+%22Chem.+Commun%22%5BJournal%5D)">Sulfur copolymer for the direct synthesis of ligand-free CdS nanoparticles.</a> Chem. Commun. 51 (56), 11244-11247 (2015).</li>
<li>Chung, W. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+use+of+elemental+sulfur+as+an+alternative+feedstock+for+polymeric+materials%5BTitle%5D)+AND+%22Nat.+Chem%22%5BJournal%5D)">The use of elemental sulfur as an alternative feedstock for polymeric materials.</a> Nat. Chem. 5 (6), 518-524 (2013).</li>
<li>Nag, A., Kovalenko, M. V., Lee, J. -S., Liu, W., Spokoyny, B., Talapin, D. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Metal-free+Inorganic+Ligands+for+Colloidal+Nanocrystals+S2-%2C+HS-%2C+Se2-%2C+HSe-%2C+Te2-%2C+HTe-%2C+TeS32-%2C+OH-%2C+and+NH2-+as+Surface%5BTitle%5D)+AND+%22J.+Am.+Chem.+Soc%22%5BJournal%5D)">Metal-free Inorganic Ligands for Colloidal Nanocrystals S2-, HS-, Se2-, HSe-, Te2-, HTe-, TeS32-, OH-, and NH2- as Surface.</a> J. Am. Chem. Soc. 133 (27), 10612-10620 (2011).</li>
<li>Dong, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+generalized+ligand-exchange+strategy+enabling+sequential+surface+functionalization+of+colloidal+nanocrystals%5BTitle%5D)+AND+%22J.+Am.+Chem.+Soc%22%5BJournal%5D)">A generalized ligand-exchange strategy enabling sequential surface functionalization of colloidal nanocrystals.</a> J. Am. Chem. Soc. 133 (4), 998-1006 (2011).</li>
<li>Cossairt, B. M., Juhas, P., Billinge, S., Owen, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Tuning+the+Surface+Structure+and+Optical+Properties+of+CdSe+Clusters+Using+Coordination+Chemistry%5BTitle%5D)+AND+%22J.+Phys.+Chem.+Lett%22%5BJournal%5D)">Tuning the Surface Structure and Optical Properties of CdSe Clusters Using Coordination Chemistry.</a> J. Phys. Chem. Lett. 2 (4), 3075-3080 (2011).</li>
<li>Lee, E., Park, S. J., Cho, J. W., Gwak, J., Oh, M. -K., Min, B. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Nearly+carbon-free+printable+CIGS+thin+films+for+solar+cell+applications%5BTitle%5D)+AND+%22Sol.+Energy+Mater.+Sol.+Cells%22%5BJournal%5D)">Nearly carbon-free printable CIGS thin films for solar cell applications.</a> Sol. Energy Mater. Sol. Cells. 95 (10), 2928-2932 (2011).</li>
<li>Bucherl, C. N., Oleson, K. R., Hillhouse, H. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Thin+film+solar+cells+from+sintered+nanocrystals%5BTitle%5D)+AND+%22Curr.+Opin.+Chem.+Eng%22%5BJournal%5D)">Thin film solar cells from sintered nanocrystals.</a> Curr. Opin. Chem. Eng. 2 (2), 168-177 (2013).</li>
<li>Cai, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Nanoparticle-induced+grain+growth+of+carbon-free+solution-processed+CuIn%28S%2CSe%292+solar+cell+with+6%25+efficiency%5BTitle%5D)+AND+%22ACS+Appl.+Mater.+Inter%22%5BJournal%5D)">Nanoparticle-induced grain growth of carbon-free solution-processed CuIn(S,Se)2 solar cell with 6% efficiency.</a> ACS Appl. Mater. Inter. 5 (5), 1533-1537 (2013).</li>
<li>Zhou, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((CZTS+nanocrystals%3A+a+promising+approach+for+next+generation+thin+film+photovoltaics%5BTitle%5D)+AND+%22Energy+Environ.+Sci%22%5BJournal%5D)">CZTS nanocrystals: a promising approach for next generation thin film photovoltaics.</a> Energy Environ. Sci. 6 (10), 2822-2838 (2013).</li>
<li>Polizzotti, A., Repins, I. L., Noufi, R., Wei, S. -H., Mitzi, D. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+state+and+future+prospects+of+kesterite+photovoltaics%5BTitle%5D)+AND+%22Energy+Environ.+Sci%22%5BJournal%5D)">The state and future prospects of kesterite photovoltaics.</a> Energy Environ. Sci. 6 (11), 3171-3182 (2013).</li>
<li>Suehiro, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Solution-Processed+Cu2ZnSnS4+Nanocrystal+Solar+Cells%3A+Efficient+Stripping+of+Surface+Insulating+Layers+using+Alkylating+Agents%5BTitle%5D)+AND+%22J.+Phys.+Chem.+C%22%5BJournal%5D)">Solution-Processed Cu2ZnSnS4 Nanocrystal Solar Cells: Efficient Stripping of Surface Insulating Layers using Alkylating Agents.</a> J. Phys. Chem. C. 118 (2), 804-810 (2013).</li>
<li>Graeser, B. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Synthesis+of+%28CuInS2%290.5%28ZnS%290.5+Alloy+Nanocrystals+and+Their+Use+for+the+Fabrication+of+Solar+Cells+via+Selenization%5BTitle%5D)+AND+%22Chem.+Mater%22%5BJournal%5D)">Synthesis of (CuInS2)0.5(ZnS)0.5 Alloy Nanocrystals and Their Use for the Fabrication of Solar Cells via Selenization.</a> Chem. Mater. 26 (14), 4060-4063 (2014).</li>
<li>Yin, Y., Alivisatos, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Colloidal+nanocrystal+synthesis+and+the+organic-inorganic+interface%5BTitle%5D)+AND+%22Nature%22%5BJournal%5D)">Colloidal nanocrystal synthesis and the organic-inorganic interface.</a> Nature. 437 (7059), 664-670 (2005).</li>
<li>Alivisatos, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Semiconductor+Clusters%2C+Nanocrystals%2C+and+Quantum+Dots%5BTitle%5D)+AND+%22Science%22%5BJournal%5D)">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/pubmed?term=((Perspectives+on+the+Physical+Chemistry+of+Semiconductor+Nanocrystals%5BTitle%5D)+AND+%22J.+Phys.+Chem%22%5BJournal%5D)">Perspectives on the Physical Chemistry of Semiconductor Nanocrystals.</a> J. Phys. Chem. 100 (95), 13226-13239 (1996).</li>
<li>Xiao, Q., Xiao, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Surface-defect-states+photoluminescence+in+CdS+nanocrystals+prepared+by+one-step+aqueous+synthesis+method%5BTitle%5D)+AND+%22Appl.+Surf.+Sci%22%5BJournal%5D)">Surface-defect-states photoluminescence in CdS nanocrystals prepared by one-step aqueous synthesis method.</a> Appl. Surf. Sci. 255 (16), 7111-7114 (2009).</li>
<li>Zhang, J. Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Interfacial+Charge+Carrier+Dynamics+of+Colloidal+Semiconductor+Nanoparticles%5BTitle%5D)+AND+%22J.+Phys.+Chem.+B%22%5BJournal%5D)">Interfacial Charge Carrier Dynamics of Colloidal Semiconductor Nanoparticles.</a> J. Phys. Chem. B. 104 (31), 7239-7253 (2000).</li>
<li>Joswig, J. -O., Springborg, M., Seifert, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Structural+and+Electronic+Properties+of+Cadmium+Sulfide+Clusters%5BTitle%5D)+AND+%22J.+Phys.+Chem.+B%22%5BJournal%5D)">Structural and Electronic Properties of Cadmium Sulfide Clusters.</a> J. Phys. Chem. B. 104 (12), 2617-2622 (2000).</li>
<li>Unni, C., Philip, D., Gopchandran, K. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Studies+on+optical+absorption+and+photoluminescence+of+thioglycerol-stabilized+CdS+quantum+dots%5BTitle%5D)+AND+%22Spectrochim.+Acta.+A.+Mol.+Biomol.+Spectrosc%22%5BJournal%5D)">Studies on optical absorption and photoluminescence of thioglycerol-stabilized CdS quantum dots.</a> Spectrochim. Acta. A. Mol. Biomol. Spectrosc. 71 (4), 1402-1407 (2008).</li>
</ol>

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 (S&lt;sub&gt;8&lt;/sub&gt;), 99.5%</td><td>Sigma Aldrich</td><td>84683</td><td></td></tr><tr><td>&amp;alpha;-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 (CHCl&lt;sub&gt;3&lt;/sub&gt;), 99.5%</td><td>Sigma Aldrich</td><td>C2432</td><td></td></tr><tr><td>Hotplate / magnetic stirrer</td><td>IKA RCT&amp;nbsp;</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 ...

synthesis-ligand-free-cds-nanoparticles-within-sulfur-copolymer

Research

JoVE Journal

Chemistry

9.5K Views.  University of Washington. 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.

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

Seeded Synthesis of CdSe/CdS Rod and Tetrapod Nanocrystals

We demonstrate a method for the synthesis of multicomponent nanostructures consisting of CdS and CdSe with rod and tetrapod morphologies. A seeded synthesis strategy is used in which spherical seeds of CdSe are prepared first using a hot-injection technique. By controlling the crystal structure of the seed to be either wurtzite or zinc-blende, the subsequent hot-injection growth of CdS off of the seed results in either a rod-shaped or tetrapod-shaped nanocrystal, respectively. The phase and morphology of the synthesized nanocrystals are confirmed using X-ray diffraction and transmission electron microscopy, demonstrating that the nanocrystals are phase-pure and have a consistent morphology. The extinction coefficient and quantum yield of the synthesized nanocrystals are calculated using UV-Vis absorption spectroscopy and photoluminescence spectroscopy. The rods and tetrapods exhibit extinction coefficients and quantum yields that are higher than that of the bare seeds. This synthesis demonstrates the precise arrangement of materials that can be achieved at the nanoscale by using a seeded synthetic approach.

A protocol for the seeded synthesis of rod-shaped and tetrapod-shaped multicomponent nanostructures consisting of CdS and CdSe is presented.

We demonstrate a method for the synthesis of multicomponent nanostructures consisting of CdS and CdSe with rod and tetrapod morphologies. A seeded ...

A Technique to Functionalize and Self-assemble Macroscopic Nanoparticle-ligand Monolayer Films onto Template-free Substrates

This protocol describes a self-assembly technique to create macroscopic monolayer films composed of ligand-coated nanoparticles1,2. The simple, robust and scalable technique efficiently functionalizes metallic nanoparticles with thiol-ligands in a miscible water/organic solvent mixture allowing for rapid grafting of thiol groups onto the gold nanoparticle surface. The hydrophobic ligands on the nanoparticles then quickly phase separate the nanoparticles from the aqueous based suspension and confine them to the air-fluid interface. This drives the ligand-capped nanoparticles to form monolayer domains at the air-fluid interface.&#160; The use of water-miscible organic solvents is important as it enables the transport of the nanoparticles from the interface onto template-free substrates.&#160; The flow is mediated by a surface tension gradient3,4 and creates macroscopic, high-density, monolayer nanoparticle-ligand films.&#160; This self-assembly technique may be generalized to include the use of particles of different compositions, size, and shape and may lead to an efficient assembly method to produce low-cost, macroscopic, high-density, monolayer nanoparticle films for wide-spread applications.

A simple, robust and scalable technique to functionalize and self-assemble macroscopic nanoparticle-ligand monolayer films onto template-free substrates is described in this protocol.

This protocol describes a self-assembly technique to create macroscopic monolayer films composed of ligand-coated nanoparticles1,2. The simple, robust and ...

Using Polystyrene-block-poly(acrylic acid)-coated Metal Nanoparticles as Monomers for Their Homo- and Co-polymerization

We present a template-free method for &#8220;polymerizing&#8221; nanoparticles into long chains without side branches. A variety of nanoparticles are encapsulated in polystyrene-block-poly(acrylic acid) (PSPAA) shells and then used as monomers for their self-assembly. Spherical PSPAA micelles upon acid treatment are known to assemble into cylindrical micelles. Exploiting this tendency, the core-shell nanoparticles are induced to aggregate, coalesce, and then transform into long chains. When more than one type of nanoparticles are used, random and block &#8220;copolymers&#8221; of nanoparticles can be obtained. Detailed procedures are reported for the PSPAA encapsulation of nanoparticles, homo- and co-polymerization of the core-shell nanoparticles, separation and purification of the resulting nanoparticle chains. Transformations of single-line chains into double- and triple-line chains are also presented. The synergy between the polymer shell and the embedded nanoparticles leads to an unusual chain-growth polymerization mode, giving long nanoparticle chains that are distinct from the products of the traditional step-growth aggregation process.

Using Polystyrene-block-polyacrylic acid-coated Metal Nanoparticles as Monomers for Their Homo- and Co-polymerization

We report protocols for &#8220;polymerizing&#8221; various types of polymer-encapsulated metal nanoparticles into long chains of &#8220;homo-&#8220; and &#8220;co-polymers&#8221;.

We present a template-free method for &#8220;polymerizing&#8221; nanoparticles into long chains without side branches. A variety of nanoparticles are ...

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 ...

Synthesis and Characterization of Placental Chondroitin Sulfate A (plCSA)-Targeting Lipid-Polymer Nanoparticles

An effective cancer therapeutic method reduces and eliminates tumors with minimal systemic toxicity. Actively targeting nanoparticles offer a promising approach to cancer therapy. The glycosaminoglycan placental chondroitin sulfate A (plCSA) is expressed on a wide range of cancer cells and placental trophoblasts, and malarial protein VAR2CSA can specifically bind to plCSA. A reported placental chondroitin sulfate A binding peptide (plCSA-BP), derived from malarial protein VAR2CSA, can also specifically bind to plCSA on cancer cells and placental trophoblasts. Hence, plCSA-BP-conjugated nanoparticles could be used as a tool for targeted drug delivery to human cancers and placental trophoblasts. In this protocol, we describe a method to synthesize plCSA-BP-conjugated lipid-polymer nanoparticles loaded with doxorubicin (plCSA-DNPs); the method consists of a single sonication step and bioconjugate techniques. In addition, several methods for characterizing plCSA-DNPs, including determining their physicochemical properties and cellular uptake by placental choriocarcinoma (JEG3) cells, are described.

Synthesis and Characterization of Placental Chondroitin Sulfate A plCSA-Targeting Lipid-Polymer Nanoparticles

Here, we present a protocol for the synthesis of placental chondroitin sulfate A binding peptide (plCSA-BP)-conjugated lipid-polymer nanoparticles via single-step sonication and bioconjugate techniques. These particles constitute a novel tool for the targeted delivery of therapeutics to most human tumors and placental trophoblasts to treat cancers and placental disorders.

An effective cancer therapeutic method reduces and eliminates tumors with minimal systemic toxicity. Actively targeting nanoparticles offer a promising ...

Cancer Research

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 ...

Facet-to-facet Linking of Shape-anisotropic Colloidal Cadmium Chalcogenide Nanostructures

Here, we describe a protocol that allows for shape-anisotropic cadmium chalcogenide nanocrystals (NCs), such as nanorods (NRs) and tetrapods (TPs), to be covalently and site-specifically linked via their end facets, resulting in polymer-like linear or branched chains. The linking procedure begins with a cation-exchange process in which the end facets of the cadmium chalcogenide NCs are first converted to silver chalcogenide. This is followed by the selective removal of ligands at their surface. This results in cadmium chalcogenide NCs with highly reactive silver chalcogenide end facets that spontaneously fuse upon contact with each other, thereby establishing an interparticle facet-to-facet attachment. Through the judicious choice of precursor concentrations, an extensive network of linked NCs can be produced. Structural characterization of the linked NCs is carried out via low- and high-resolution transmission electron microscopy (TEM), as well as energy-dispersive X-ray spectroscopy, which confirm the presence of silver chalcogenide domains between chains of cadmium chalcogenide NCs.

A protocol detailing how shape-anisotropic colloidal cadmium chalcogenide nanocrystals can be covalently linked via their end facets is presented here.

Here, we describe a protocol that allows for shape-anisotropic cadmium chalcogenide nanocrystals (NCs), such as nanorods (NRs) and tetrapods (TPs), to be ...

Ligand-Mediated Nucleation and Growth of Palladium Metal Nanoparticles

The size, size distribution and stability of colloidal nanoparticles are greatly affected by the presence of capping ligands. Despite the key contribution of capping ligands during the synthesis reaction, their role in regulating the nucleation and growth rates of colloidal nanoparticles is not well understood. In this work, we demonstrate a mechanistic investigation of the role of trioctylphosphine (TOP) in Pd nanoparticles in different solvents (toluene and pyridine) using in situ SAXS and ligand-based kinetic modeling. Our results under different synthetic conditions reveal the overlap of nucleation and growth of Pd nanoparticles during the reaction, which contradicts the LaMer-type nucleation and growth model. The model accounts for the kinetics of Pd-TOP binding for both, the precursor and the particle surface, which is essential to capture the size evolution as well as the concentration of particles in situ. In addition, we illustrate the predictive power of our ligand-based model through designing the synthetic conditions to obtain nanoparticles with desired sizes. The proposed methodology can be applied to other synthesis systems and therefore serves as an effective strategy for predictive synthesis of colloidal nanoparticles.

The main goal of this work is to elucidate the role of capping agents in regulating the size of palladium nanoparticles by combining in situ small angle x-ray scattering (SAXS) and ligand-based kinetic modeling.

The size, size distribution and stability of colloidal nanoparticles are greatly affected by the presence of capping ligands. Despite the key contribution ...

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.

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 ...

Synthesis and Characterization of Amphiphilic Gold Nanoparticles

Gold nanoparticles covered with a mixture of 1-octanethiol (OT) and 11-mercapto-1-undecane sulfonic acid (MUS) have been extensively studied because of their interactions with cell membranes, lipid bilayers, and viruses. The hydrophilic ligands make these particles colloidally stable in aqueous solutions and the combination with hydrophobic ligands creates an amphiphilic particle that can be loaded with hydrophobic drugs, fuse with the lipid membranes, and resist nonspecific protein adsorption. Many of these properties depend on nanoparticle size and the composition of the ligand shell. It is, therefore, crucial to have a reproducible synthetic method and reliable characterization techniques that allow the determination of nanoparticle properties and the ligand shell composition. Here, a one-phase chemical reduction, followed by a thorough purification to synthesize these nanoparticles with diameters below 5 nm, is presented. The ratio between the two ligands on the surface of the nanoparticle can be tuned through their stoichiometric ratio used during synthesis. We demonstrate how various routine techniques, such as transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), and ultraviolet-visible (UV-Vis) spectrometry, are combined to comprehensively characterize the physicochemical parameters of the nanoparticles.

Amphiphilic gold nanoparticles can be used in many biological applications. A protocol to synthesize gold nanoparticles coated by a binary mixture of ligands and a detailed characterization of these particles is presented.

Gold nanoparticles covered with a mixture of 1-octanethiol (OT) and 11-mercapto-1-undecane sulfonic acid (MUS) have been extensively studied because of ...