In the colloidal synthesis of iron sulfides, a series of dialkyl disulfides, alkyl thiols, and dialkyl disulfides (allyl, benzyl, tert-butyl, and phenyl) were employed as sulfur sources. Their reactivity was found to tune the phase between pyrite (FeS2), greigite (Fe3S4), and pyrrhotite (Fe7S8). DFT was used to show that sulfur-rich phases were favored when the C–S bond strength was low in the organosulfurs, yet temperature dependent studies and other observations indicated the reasons for phase selectivity were more nuanced; the different precursors decomposed through different reaction mechanisms, some involving the oleylamine solvent. The formation of pyrite from diallyl disulfide was carefully studied as it was the only precursor to yield FeS2. Raman spectroscopy indicated that FeS2 forms directly without an FeS intermediate, unlike most synthetic procedures to pyrite. Diallyl disulfide releases persulfide (S–S)2– due to the lower C–S bond strength relative to the S–S bond strength, as well as facile decomposition in the presence of amines through SN2′ mechanisms at elevated temperatures.

A new ligand that covalently attaches to the surface of colloidal CdSe/CdS nanorods and can simultaneously chelate a molecular metal center is described. The dithiocarbamate–bipyridine ligand system facilitates hole transfer through energetic overlap at the inorganic–organic interface and conjugation through the organic ligand to a chelated metal center. Density functional theory calculations show that the coordination of the free ligand to a CdS surface causes the formation of two hybridized molecular states that lie in the band gap of CdS. The further chelation of Fe(II) to the bipyridine moiety causes the presence of seven midgap states. Hole transfer from the CdS valence band to the midgap states is dipole allowed and occurs at a faster rate than what is experimentally known for the CdSe/CdS band-edge radiative recombination. In the case of the ligand bound with iron, a two-step process emerges that places the hole on the iron, again at rates much faster than band gap recombination. The system was experimentally assembled and characterized via UV–vis absorbance spectroscopy, fluorescence spectroscopy, time-resolved photoluminescence spectroscopy, and energy dispersive X-ray spectroscopy. Theoretically predicted red shifts in absorbance were observed experimentally, as well as the expected quench in photoluminescence and lifetimes in time-resolved photoluminescence.Keywords: CdSe/CdS nanorod; density functional theory; dithiocarbamate; Hole transfer; midgap states;

Two-dimensional (2D) nanostructures have generated significant interest in the scientific community as a result of their high surface area and remarkable optoelectronic properties. In this work, we present a simple colloidal synthesis for ultrathin nanosheets of both In2S3 and CuInS2. Contradictory phase designations exist for In2S3 at the nanoscale as a result of overlapping reflections from multiple phases in X-ray diffraction. We use high-resolution transmission electron microscopy to demonstrate definitively that hexagonal γ-In2S3 is formed. Continued heating of these nanostructures results in the formation of nanodisks twice the thickness of the original structure via folding and tearing of the intermediate sheet. Treatment of the In2S3 nanosheet with Cu+ accelerates this process of tearing of the nanosheet of In2S3 and results in the formation of one-dimensional nanoribbons of CuInS2. High-resolution transmission electron microscopy images and medium-angle X-ray scattering measurements indicate that these nanoribbons consist of face-to-face stacked nanodisks.

Petaled MoS2 electrodes grown hydrothermally from Mo foils are found to have an 800 nm, intermediate, MoSxOy layer. Similar petaled MoS2 films without this intermediate layer are grown on Au. X-ray photoelectron and Raman spectroscopies and transmission electron microscopy indicate the resulting petaled multilayer MoS2 films are frayed and exhibit single-layer, 1T-MoS2 behavior at the edges. We compare the electrocatalytic hydrogen evolution reaction activity via linear sweep voltammetry with Tafel analysis as well as the impedance properties of the electrodes. We find that petaled MoS2/Au and petaled MoS2/Mo exhibit comparable overpotential to 10 mA cm–2 at −279 vs −242 mV, respectively, and similar Tafel slopes of ∼68 mV/decade indicating a similar rate-determining step. The exchange current normalized to the geometric area of petaled MoS2/Au (0.000921 mA cm–2) is 3 times smaller than that of petaled MoS2/Mo (0.00290 mA cm–2), and is attributed to the lower petal density on the Au support. However, Au supports increase the turnover frequency per active site of petaled MoS2 to 0.48 H2 Mo–1 s–1 from 0.25 H2 Mo–1 s–1 on Mo supports. Both petaled MoS2 films have nearly ohmic contacts to their supports with uncompensated resistivity Ru of <2.5 Ω·cm2.Keywords: contact; EIS; HER; metallic; MoS2; self-supported; Tafel; TOF

CuInS2 nanocrystals with the wurtzite structure show promise for applications requiring efficient energy transport due to their anisotropic crystal structure. We investigate the source of photoluminescence in the near-infrared spectral region recently observed from these nanocrystals. Spectroscopic studies of both wurtzite CuInS2 itself and samples alloyed with Cd or Zn allow the assignment of this emission to a radiative point defect within the nanocrystal structure. Further, by varying the organic passivation layer on the material, we are able to determine that the atomic species responsible for nonradiative decay paths on the nanocrystal surface are Cu- or S-based. Density functional theory calculations of defect states within the material allow identification of the likely radiative species. Understanding both the electronic structure and optical properties of wurtzite CuInS2 nanocrystals is necessary for their efficient integration into potential biological, photovoltaic, and photocatalytic applications.

The capacity of fluorescent colloidal semiconductor nanocrystals for commercial application has led to the development of nanocrystals with nontoxic constituent elements as replacements for the currently available Cd- and Pb-containing systems. CuInS2 is a good candidate material because of its direct band gap in the near-infrared spectral region and large optical absorption coefficient. The ternary nature, flexible stoichiometry, and different crystal structures of CuInS2 lead to a range of optoelectronic properties, which have been challenging to elucidate. In this Perspective, the optoelectronic properties of CuInS2 nanocrystals are described and what is known of their origin is discussed. We begin with an overview of their synthesis, structure, and mechanism of formation. A complete discussion of the tunable luminescence properties and the radiative decay mechanism of this system is then presented. Finally, progress toward application of these “green” nanocrystals is summarized.

The ternary copper chalcogenide semiconductor nanoparticles have gained much attention as their optical properties make them ideal candidates for many applications ranging from photovoltaics to bioimaging. While their synthesis is well documented, there have been few reports on the synthesis of ternary copper chalcogenide–metal hybrid nanoparticles, which can further expand the list of potential applications through synergistic properties. To this end, Pt–CuInS2 hybrids have been synthesized by a two-step approach in high boiling organic solvents. The hybrid nanostructures were characterized employing transmission electron microscopy, X-ray diffraction, UV–Vis spectroscopy, and energy-dispersive X-ray spectroscopy mapping. We find that during hybrid nanoparticle synthesis under conditions modified from typical Pt nanoparticle reaction schemes, a near-complete shell of Pt forms on the semiconductor nanoparticles. Careful control of the reactivity of the Pt precursor, through choice of organic reducing agent and Pt coordinating ligands, was successfully used to obtain controlled and isolated domains on the semiconductor nanoparticles. This strategy was further extended for the synthesis of Pd–CuInS2 hybrids.

Nanocrystals of CuInS2 with the hexagonal wurtzite structure hold great potential for applications requiring efficient energy transport, such as photocatalysis, due to their anisotropic crystal structure. However, thus far their optical properties have proven difficult to study, as luminescence from wurtzite nanocrystals has only recently been observed. In this work, we report the colloidal synthesis of single crystalline, luminescent CuInS2 nanocrystals with both the cubic and hexagonal structures. The crystalline phase, optical properties and mechanism of formation of nanocrystals are controlled by changing the reaction temperature. Photoluminescence is observed in the visible and near-infrared spectral regions, which results from the cubic and hexagonal nanocrystals respectively. Synthetic studies combined with XRD, TEM and EDS mapping provide evidence for the mechanisms behind phase selection.

The use of thiol ligands as a sulfur source for nanocrystal synthesis has recently come en vogue, as the products are often high quality. A comparative study was performed of dodecanethiol-capped Cu2S prepared with elemental sulfur and thiol sulfur reagents. XPS and TGA-MS provide evidence for differing binding modes of the capping thiols. Under conditions where the thiol acts only as a ligand, the capping thiols are “surface-bound” and bond to surface cations in low coordination number sites. In contrast, when thiols are used as a sulfur source, “crystal-bound” thiols result that sit in high coordination sites and are the terminal S layer of the crystal. A 1H NMR study shows suppressed surface reactivity and ligand exchange with crystal-bound thiols, which could limit further application of the particles. To address the challenge and opportunity of nonlabile ligands, dodecyl-3-mercaptopropanoate, a molecule possessing both a thiol and an ester, was used as the sulfur source for the synthesis of Cu2S and CuInS2. A postsynthetic base hydrolysis cleaves the ester, leaving a carboxylate corona around the nanocrystals and rendering the particles water-soluble.Keywords: Cu2S; CuInS2; nanocrystals; surface chemistry; water solubility;

Nanocrystals of CuInS2 with the hexagonal wurtzite structure hold great potential for applications requiring efficient energy transport, such as photocatalysis, due to their anisotropic crystal structure. However, thus far their optical properties have proven difficult to study, as luminescence from wurtzite nanocrystals has only recently been observed. In this work, we report the colloidal synthesis of single crystalline, luminescent CuInS2 nanocrystals with both the cubic and hexagonal structures. The crystalline phase, optical properties and mechanism of formation of nanocrystals are controlled by changing the reaction temperature. Photoluminescence is observed in the visible and near-infrared spectral regions, which results from the cubic and hexagonal nanocrystals respectively. Synthetic studies combined with XRD, TEM and EDS mapping provide evidence for the mechanisms behind phase selection.

In this report, we present a new path to the control of quantum dot surface chemistry that can lead to a better understanding of nanoscale interfaces and the development of improved photocatalysts. Control of the synthetic methodology leads to QDs that are concomitantly ligated by crystal-bound organics at the surface anion sites and small X-type ligands on the surface cation sites.