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

Published: May 1st, 2016



1Department of Materials Science and Engineering, University of Washington, 2Molecular Engineering and Sciences Institute, University of Washington, 3Clean Energy Institute, University of Washington, 4Institut für Nanospektroskopie, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 5Department of Chemical Engineering, University of Washington, 6Department of Chemistry, 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.

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.

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 comple....

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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.......

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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 °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

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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.......

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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.


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

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