Nanostructured CuCo2S4, a mixed metal thiospinel, is found to be a benchmark electrocatalyst for oxygen evolution reaction (OER) in this study with a low overpotential, a low Tafel slope, a high durability, and a high turnover frequency (TOF) at lower mass loadings. Nanosheets of CuCo2S4 are realized from a hydrothermal synthesis method in which the average thickness of the sheets is found to be in the range of 8–15 nm. Aggregated nanosheets form a highly open hierarchical structure. When used as an electrocatalyst, CuCo2S4 nanosheets offer an overpotential value of 310 mV at a 10 mA cm–2 current density, which remains consistent for 10000 measured cycles in a 1 M KOH electrolyte. A chronoamperometric study reveals constant oxygen evolution for 12 h at a 10 mV s–1 scan rate without any degradation of the activity. Furthermore, the calculated mass activity of the CuCo2S4 electrocatalyst is found to be 14.29 A/g and to afford a TOF value of 0.1431 s–1 at 310 mV at a mass loading of 0.7 mg cm–2. For comparison, nanostructures of Co3S4 and Cu0.5Co2.5S4 have been synthesized using a similar method followed for CuCo2S4. When compared to the OER activities among these three thiospinels and standard IrO2, CuCo2S4 nanosheets offered the highest OER activities at the same mass loading (0.7 mg/cm2). Extensive X-ray photoelectron spectroscopy and electron paramagnetic resonance analyses for a mechanistic study reveal that introduction of Cu into the Co3S4 lattice enhances the oxygen evolution and kinetics by offering Cu2+ sites for utilitarian adsorption of OH, O, and OOH reactive species and also by offering a highly active high-spin state of octahedral Co3+ for OER catalysis.

We report a phosphine-free synthesis of p-type copper(I) selenide nanocrystals by a colloidal approach in a mixture of oleylamine and 1-octadecene. The nanocrystals had a cuboctahedral shape and cubic berzelianite phase. Films of these nonstoichiometric copper-deficient Cu(2-x)Se nanocrystals were highly conductive and showed high absorption coefficient in the near-infrared region. These nanocrystals could be used as hole-injection layers in optoelectronic devices.

The growth behavior of cadmium chalcogenides (CdE = CdS, CdSe, and CdTe) on sphalerite Cu(2-x)Se nanocrystals (size range 10-15 nm) is studied. Due to the capability of Cu(2-x)Se to undergo a fast and quantitative cation exchange reaction in the presence of excessive Cd(2+) ions, no Cu(2-x)Se/CdE heterostructures are obtained and instead branched CdSe/CdE nanocrystals are built which consist of a sphalerite CdSe core and wurtzite CdE arms. While CdTe growth yields multiarmed structures with overall tetrahedral symmetry, CdS and CdSe arm growth leads to octapod-shaped nanocrystals. These results differ significantly from literature findings about the growth of CdE on sphalerite CdSe particles, which until now had always yielded tetrapod-shaped nanocrystals.

We report the synthesis, the structural and optical characterization of CdSe/CdS/ZnS "double shell" nanorods and their exploitation in cell labeling experiments. To synthesize such nanorods, first "dot-in-a-rod" CdSe(dot)/CdS(rod) core/shell nanocrystals were prepared. Then a ZnS shell was grown epitaxially over these CdSe/CdS nanorods, which led to a fluorescence quantum yield of the final core-shell-shell nanorods that could be as high as 75%. The quantum efficiency was correlated with the aspect ratio of the nanorods and with the thickness of the ZnS shell around the starting CdSe/CdS rods, which varied from 1 to 4 monolayers (as supported by a combination of X-ray diffraction, elemental analysis with inductively coupled plasma atomic emission spectroscopy and high resolution transmission electron microscopy analysis). Pump-probe and time-resolved photoluminescence measurements confirmed the reduction of trapping at CdS surface due to the presence of the ZnS shell, which resulted in more efficient photoluminescence. These double shell nanorods have potential applications as fluorescent biological labels, as we found that they are brighter in cell imaging as compared to the starting CdSe/CdS nanorods and to the CdSe/ZnS quantum dots, therefore a lower amount of material is required to label the cells. Concerning their cytotoxicity, according to the MTT assay, the double shell nanorods were less toxic than the starting core/shell nanorods and than the CdSe/ZnS quantum dots, although the latter still exhibited a lower intracellular toxicity than both nanorod samples.

A colloidal two-step seeded-growth approach has been devised to selectively synthesize three-component magnetic/semiconductor hybrid nanocrystals (HNCs) with a matchstick-like profile and tunable geometric parameters. The newly developed heterostructures individually comprise a single metallic Co head connected to either apexes of one rod-shaped section made of a CdSe core eccentrically embedded in a CdS shell. The specific topological arrangement realized arises from the peculiar anisotropic reactivity of the noncentrosymmetric CdSe@CdS core@shell nanorods that have been used as substrates to seed heterogeneous nucleation of Co in a surfactant-free environment from an organometallic precursor. The HNCs retain appreciable fluorescent emission in spite of photoexcited charge transfer from the semiconductor to the metal domain and exhibit unusual ferromagnetic-like behavior at room temperature.

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Size dependent surface characteristics of nanoparticles lead to use of these nanomaterials in many technologically important fields, including the field of catalysis. Here Ag(1-x)Ni(x) bimetallic alloy nanoparticles have been developed having a 5-fold twinned morphology, which could be considered as an important alloy because of their excellent and unique catalytic and magnetic properties. Alloying between Ag and Ni atoms on a nanoscale has been confirmed with detailed X-ray diffraction, high resolution transmission electron microscopy, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, and magnetization measurements. Although introduced for the first time as a catalyst due to having high active surface sites, the as-synthesized nanoparticles showed one of the best multiple catalytic activity in the industrially important (electro)-catalytic reduction of 4-nitrophenol (4-NP) and 4-nitroaniline (4-NA) to corresponding amines with noticeable reduced reaction time and increased rate constant without the use of any large area support. Additionally the same catalyst showed enhanced catalytic activity in degradation of environment polluting dye molecules. The highest ever activity parameter we report here for Ag0.6Ni0.4 composition is 156 s(-1)g(-1) with an apparent rate constant of 31.1 × 10(-3) s(-1) in a 4-NP reduction reaction where the amount of catalyst used was 0.2 mg and the time taken for complete conversion of 4-NP to 4-aminophenol was 60 s. Similarly, an incredible reaction rate constant (115 s(-1)) and activity parameter (576.6 s(-1)g(-1)) were observed for the catalytic degradation of methyl orange dye where 15 s is the maximum time for complete degradation of the dye molecules. The high catalytic performance of present AgNi alloy NPs over the other catalysts has been attributed to size, structural (twinned defect) and electronic effects. This study may lead to use of these bimetallic nanostructures with excellent recyclable catalytic efficiency in many more applications.

Cubic spinel Co3O4 nanoparticles with spherical (0D) and hexagonal platelet (2D) morphologies were synthesized using a simple solvothermal method by tuning the reaction time. XRD and HRTEM analyses revealed pure phase with growth of Co3O4 particles along [111] and [110] directions. UV-vis studies showed two clear optical absorption peaks corresponding to two optical band gaps in the range of 400-500 nm and 700-800 nm, respectively, related to the ligand to metal charge transfer events (O(2-) → Co(2+,3+)). Under the electrochemical study in two electrode assembly system (Co3O4/KOH/Co3O4) without adding any large area support or a conductive filler, the hexagonal platelet Co3O4 particles exhibited comparatively better characteristics with high specific capacitance (476 F g(-1)), energy density 42.3 Wh kg(-1) and power density 1.56 kW kg(-1) at current density of 0.5 Ag(-1), that suited for potential applications in supercapacitors. The observed better electrochemical properties of the nanoporous Co3O4 particles is attributed to the layered platelet structural arrangement of the hexagonal platelet and the presence of exceptionally high numbers of regularly ordered pores.