Facile Colloidal Route Research Articles

Controlled Synthesis of Ag2 Te@Ag2 S Core-Shell Quantum Dots with Enhanced and Tunable Fluorescence in the Second Near-Infrared Window.

Fluorescence in the second near-infrared window (NIR-II, 900-1700 nm) has drawn great interest for bioimaging, owing to its high tissue penetration depth and high spatiotemporal resolution. NIR-II fluorophores with high photoluminescence quantum yield (PLQY) and stability along with high biocompatibility are urgently pursued. In this work, a Ag-rich Ag2 Te quantum dots (QDs) surface with sulfur source is successfully engineered to prepare a larger bandgap of Ag2 S shell to passivate the Ag2 Te core via a facile colloidal route, which greatly enhances the PLQY of Ag2 Te QDs and significantly improves the stability of Ag2 Te QDs. This strategy works well with different sized core Ag2 Te QDs so that the NIR-II PL can be tuned in a wide range. In vivo imaging using the as-prepared Ag2 Te@Ag2 S QDs presents much higher spatial resolution images of organs and vascular structures as compared with the same dose of Ag2 Te nanoprobes administrated, suggesting the success of the core-shell synthetic strategy and the potential biomedical applications of core-shell NIR-II nanoprobes.

Enhanced Electrocatalytic Activity of Ethanol Oxidation Reaction on Palladium-Silver Nanoparticles via Removable Surface Ligands.

This work developed a facile colloidal route to synthesize BH4--capped PdxAgy nanoparticles (NPs) in water using the reducing ionic liquids of [Cnmim]BH4, and the resulting NPs were prone to form the nanocomposites with [amim]+-modified reduced graphene (RG). The removal of the metal-free inorganic ions of BH4- can create the profoundly exposed interfaces on the PdxAgy NPs during the electrooxidation, and favor the ethanol oxidation reaction (EOR) in lowering energy barrier. The counterions of [Cnmim]+ can gather ethanol, OH- ions, and the reaction intermediates on catalysts, and synergistically interact with RG to facilitate the charge transfer in nanocomposites. The interface-modified RG nanosheets can effectively segregate the PdxAgy NPs from aggregation during the EOR. Along with the small size of 4.7 nm, the high alloying degree of 60.2%, the large electrochemical active surface area of 64.1 m2 g-1, and the great peak current density of 1501 mA cm-2 mg-1, Pd1Ag2@[C2mim]BH4-amimRG nanocomposite exhibits the low oxidation potentials, strong poison resistance, and stable catalytic activity for EOR in alkaline media, and hence can be employed as a promising anodic catalyst in ethanol fuel cells.

Semiconductor-metal core-shell nanostructures by colloidal heterocoagulation in aqueous medium

In contrast to complex syntheses for the preparation of colloidal nanocomposites in a core-shell structure proposed in the literature, we present herein a facile colloidal route based on a heterocoagulation process promoted by the electrostatic interaction among ceramic NiO nanoplatelets and metallic Ni nanoparticles (NPs). Before the heterocoagulation process, NiO and Ni were synthetized separately in presence of ultrasound, by chemical precipitation and chemical reduction of the same nickel precursor, respectively. After that, NiO-Ni core-shell nanostructures were prepared forcing the electrostatic interaction among surfaces in aqueous medium. The surface charge balances of both types of particles were tuned effectively by adjusting the pH in a free-additives suspension. For the surface modification of NiO by Ni, the ceramic suspensions maintain a positive zeta potential at pH 9, while the surface of metallic particles is negatively charged. Then the uniform coating of NiO platelets, by the electrostatically induced coagulation with Ni NPs, was favors. The degree of coverage and the formation of NiO-Ni core-shell nanostructures were followed referring the evolution of zeta potential with the geometric calculation in terms of size and morphology of both nanoparticles, and then corroborated by field emission scanning electron microscopy (FESEM).

High Quality MoSe2 Nanospheres with Superior Electrochemical Properties for Sodium Batteries

Highly ordered MoSe2 nanospheres are successfully fabricated via a facile colloidal route. The unique as-obtained MoSe2 nanospheres render the high-rate transporation of sodium ion due to small size and high specific surface area. As the anode, MoSe2 nanospheres yield the initial discharge/charge capacities of 520/430 mAh g−1 for potentials ranging from 0.1 to 3 V at a current rate of 0.1 C with an 80% capacity retention over 200 cycles. In addition, MoSe2 nanospheres also demonstrate excellent electrochemical performance at high current densities. Using first-principles simulation, the activation barriers for sodium ion transportation on the surface as well as interlayer of the MoSe2 are 0.344/1.31 eV respectively, suggesting that high specific surface area MoSe2 nanospheres can serve as an attractive anode material for Na ion batteries.

Well-defined BiOCl colloidal ultrathin nanosheets: synthesis, characterization, and application in photocatalytic aerobic oxidation of secondary amines.

We demonstrate the first colloidal synthesis of single-crystalline BiOCl ultrathin nanosheets (UTNSs) that feature a well-defined square morphology. Unlike BiOCl nanomaterials prepared by hydrothermal routes, our colloidal BiOCl UTNSs exhibit hydrophobic surface properties and high activity and selectivity toward the photocatalytic aerobic oxidation of secondary amines to corresponding imines at room temperature. Hence, the application of BiOCl nanomaterials has been successfully extended from the widely studied photodecomposition of pollutants in aqueous solution to the synthesis of fine chemicals in organic solvent using a green approach.

MoSe2 porous microspheres comprising monolayer flakes with high electrocatalytic activity

A facile colloidal route to synthesize MoSe2 porous microspheres with diameters of 400–600 nm made up of MoSe2 monolayer flakes (∼0.7 nm in thickness) is reported. The solvents trioctylamine (TOA) and oleylamine (OAM) are found to play important roles in the formation of MoSe2 microspheres, whereby TOA determines the three-dimensional (3D) microspherical morphology and OAM directs the formation of MoSe2 monolayer flakes. The robust 3D MoSe2 microspheres exhibit remarkable activity and durability for the electrocatalytic hydrogen evolution reaction (HER) in acid, maintaining a small onset overpotential of ∼77 mV and keeping a small overpotential of 100 mV for a current density of 5 mA/cm2 after 1,000 cycles. In addition, similar 3D WSe2 microspheres can also be prepared by using this method. We expect this facile colloidal route could further be expanded to synthesize other porous structures which will find applications in fields such as in energy storage, catalysis, and sensing.

Water-soluble quantum dot/carboxylic-poly (vinyl alcohol) conjugates: Insights into the roles of nanointerfaces and defects toward enhancing photoluminescence behavior

The synthesis of quantum dots (QDs) using wet chemistry with photoluminescent (PL) properties suitable to be used as biomarkers is a challenge yet to be overcome. Thus, this study demonstrates that the optical properties of aqueous colloidal semiconductor QDs can be engineered by altering the stoichiometric ratio of reagents achieving PL behavior comparable to systems using core–shell heterostructures. Here, it is reported the “bottom-up” approach for preparing quantum dot-polymer conjugates. A straightforward one-pot synthesis of CdSe nanocrystals was conducted using carboxylic functionalized poly (vinyl alcohol) as capping ligand by methods of aqueous colloidal chemistry at room temperature. Different molar ratios of reagents (Cd2+:Se2−) were prepared for investigating the effect on the kinetics of nucleation and growth of colloidal quantum dots (CQD) and their respective influence on the density of defects. These systems were characterized by UV–vis Spectroscopy, Photoluminescence Spectroscopy, and Transmission Electron Microscopy. Small QDs were produced with average particle size of 2.9 nm. The results have showed the influence of the ratio of the reagents on the photoluminescent behavior of the CQDs. Thus, a relatively facile colloidal route was developed for synthesizing water-soluble quantum dots-polymer conjugates that may potentially offer countless choices in nanotechnology for biomedical applications.

Colloidal Synthesis of Cuprite (Cu2O) Octahedral Nanocrystals and Their Electrochemical Lithiation

We report a facile colloidal route to prepare octahedral-shaped cuprite (Cu2O) nanocrystals (NCs) of ∼40 nm in size that exploits a new reduction pathway, i.e., the controlled reduction of a cupric ion by acetylacetonate directly to cuprite. Detailed structural, morphological, and chemical analyses were carried on the cuprite NCs. We also tested their electrochemical lithiation, using a combination of techniques (cyclic voltammetry, galvanostatic, and impedance spectroscopy), in view of their potential application as anodes for Li ion batteries. Along with these characterizations, the morphological, structural, and chemical analyses (via high-resolution electron microscopy, electron energy loss spectroscopy, and X-ray photoelectron spectroscopy) of the cycled Cu2O NCs (in the lithiated stage, after ∼50 cycles) demonstrate their partial conversion upon cycling. At this stage, most of the NCs had lost their octahedral shape and had evolved into multidomain particles and were eventually fragmented. Overall, the shape changes (upon cycling) did not appear to be concerted for all the NCs in the sample, suggesting that different subsets of NCs were characterized by different lithiation kinetics. We emphasize that a profound understanding of the lithiation reaction with NCs defined by a specific crystal habit is still essential to optimize nanoscale conversion reactions.