Synthesis Of Colloidal Nanocrystals Research Articles

Colloidal nanocrystals of lithiated group 14 elements.

The synthesis of colloidal nanocrystals (NCs) of lithiated group 14 elements (Z=Si, Ge, and Sn) is reported, which are Li4.4 Si, Li3.75 Si, Li4.4 Ge, and Li4.4 Sn. Lix Z compounds are highly reactive and cannot be synthesized by existing methods. The success relied on separating the surface protection from the crystal formation and using a unique passivating ligand. Bare Lix Z crystals were first produced by milling elemental Li and Z in an argon-filled jar. Then, under the assistance of additional milling, hexyllithium was added to passivate the freshly generated Lix Z NCs. This ball-milling-assisted surface protection method may be generalized to similar systems, such as Nax Z and Kx Z. Moreover, Li4.4 Si and Li4.4 Ge NCs were conformally encapsulated in carbon fibers, providing great opportunities for studying the potential of using Lix Z to mitigate the volume-fluctuation-induced poor cyclability problem confronted by Z anodes in lithium-ion batteries.

Continuous Microwave-Assisted Gas–Liquid Segmented Flow Reactor for Controlled Nucleation and Growth of Nanocrystals

Hot-injection techniques are currently the state-of-the-art method for the synthesis of high-quality colloidal nanocrystals (NCs) but have typically been limited to small batch reactors. The nature of this method leads to local fluctuations in temperature and concentration where inhomogeneity due to mixing makes precise control of reaction conditions very challenging at a large scale. Therefore, development of methods to produce high-quality colloidal NCs with high-throughput is necessary for many technological applications. Herein, we report a high-quality and high-throughput NC synthesis method via a continuous microwave-assisted flow reactor where separation of nucleation and growth is demonstrated. A significant issue of microwave heating in a single-phase continuous flow microwave reactor is the deposition of in situ generated NCs on the inner wall of the reactor in the microwave zone. This deposited material leads to significantly enhanced microwave absorption and rapid heating and can result in sparking in the reactor. A gas–liquid segmented flow is used to avoid this problem and also results in improved residence time distributions. The use of this system allows for finely tuned parameters to achieve a high level of control over the reaction by separating the nucleation and growth stages.

Facile synthesis of colloidal InAs nanocrystals using triphenylarsine as an arsenic source

Colloidal InAs nanocrystals (NCs) were synthesized by heating an organometallic solution, containing triphenylarsine as the arsenic source. Because the triphenylarsine is quite stable in ambient conditions at room temperature, the reaction is easy to handle compared with conventional synthesis using tris(trimethylsilyl)arsine. The average size of InAs NCs obtained was varied in the range from 12nm to 20nm according to the reaction time, and their optical gap was larger than that of the bulk InAs because of quantum size effect. The reaction mechanism of InAs NCs formation was discussed based on the infrared absorption spectra of reaction solutions, and formation of a reaction intermediate was suggested during the long induction period, ≈80min, of InAs NCs formation.

Synthesis of colloidal metal nanocrystals in droplet reactors: the pros and cons of interfacial adsorption.

Droplet reactors have received considerable attention in recent years as an alternative route to the synthesis and potentially high-volume production of colloidal metal nanocrystals. Interfacial adsorption will immediately become an important issue to address when one seeks to translate a nanocrystal synthesis from batch reactors to droplet reactors due to the involvement of higher surface-to-volume ratios for the droplets and the fact that nanocrystals tend to be concentrated at the water-oil interface. Here we report a systematic study to compare the pros and cons of interfacial adsorption of metal nanocrystals during their synthesis in droplet reactors. On the one hand, interfacial adsorption can be used to generate nanocrystals with asymmetric shapes or structures, including one-sixth-truncated Ag octahedra and Au-Ag nanocups. On the other hand, interfacial adsorption has to be mitigated to obtain nanocrystals with uniform sizes and controlled shapes. We confirmed that Triton X-100, a nonionic surfactant, could effectively alleviate interfacial adsorption while imposing no impact on the capping agent typically needed for a shape-controlled synthesis. With the introduction of a proper surfactant, droplet reactors offer an attractive platform for the continuous production of colloidal metal nanocrystals.

Microwave synthesis of colloidal stable AlPO-5 nanocrystals with high water adsorption capacity and unique morphology

Colloidal stable nanosized AlPO-5 crystals (ca. 300nm) were synthesized via microwave-assisted hydrothermal method using a new template 1-ethyl-2,3-dimethylimidazolium hydroxide, [edmim]OH. The results revealed that [edmim]OH has a templating effect on the AlPO-5 nanocrystals. With microwave energy, colloidal AlPO-5 nanocrystals of high crystallinity and porosity were produced. Additionally, an interesting morphology of AlPO-5 nanocrystals was exhibited due to the microwave energy and unique properties of [edmim]+. The microwave-prepared AlPO-5 nanocrystals were also found to have a higher water adsorption capacity than those prepared from hydrothermal method.

Synthesis of unstable colloidal inorganic nanocrystals through the introduction of a protecting ligand.

We demonstrate a facile and general strategy based on ligand protection for the synthesis of unstable colloidal nanocrystals by using the synthesis of pure p-type NiO nanocrystals as an example. We find that the introduction of lithium stearate, which is stable in the reaction system and capable of binding to the surface of NiO oxide nanocrystals, can effectively suppress the reactivity of NiO nanocrystals and thus prevent their in situ reduction into Ni. The resulting p-type NiO nanocrystals, a highly demanded hole-transporting and electron-blocking material, are applied to the fabrication of organic solar cells and polymer light-emitting diodes, demonstrating their great potential as an interfacial layer for low-cost and large-area, solution-processed optoelectronic devices.

Green Synthesis of CdSe Colloidal Nanocrystals with Strong Green Emission by the Sol–Gel Method

In this paper, high-quality CdSe colloidal nanocrystals were synthesized by an improved Sol–Gel green technique. These colloidal nanocrystals were characterized by different techniques: Transmission Electron Microscopy (TEM) showed that the diameter of colloidal nanocrystals is about 3 nm; X-ray diffraction (XRD) demonstrated that CdSe colloidal nanocrystals formed in cubic phase; Fourier Transform Infrared spectroscopy (FT-IR) was employed to study the chemical compounds of as-prepared sol; UV–visible absorption spectroscopy was used to evaluate optical properties of prepared CdSe colloidal nanocrystals, which indicated that the absorption peak is around 500 nm; Photoluminescence (PL) spectroscopy demonstrated that quantum yields for colloidal nanocrystals are 50.2% with 440 nm excitation wavelengths. Experimental observation has shown that highly stable CdSe colloidal nanocrystals with a strong green emission were synthesized. The mentioned optical properties have not been reported before.

Colloidal synthesis of chalcostibite copper antimony sulfide nanocrystals

We report the colloidal synthesis of monodisperse phase pure chalcostibite CuSbS2 nanocrystals in high boiling point solvent. The use of dodecanethiol as ligands had an advantage over oleylamine on avoiding the hydrolysis of Sb precursor. The effect of reaction temperature and Cu/Sb feed molar ratio on the synthesis of copper antimony sulfide nanocrystals in dodecanethiol system was investigated. As a result of the reactivity difference between Cu and Sb precursors, the formation of CuSbS2 nanocrystals involves the preferential nucleation of Cu-rich nanocrystals and their subsequent reaction with remaining Sb precursors. The band gap of the resulting CuSbS2 nanocrystals was measured to be ~1.59eV.

The Effects of the Size and the Doping Concentration on the Power Factor of n-type Lead Telluride Nanocrystals for Thermoelectric Energy Conversion

For the first time, we demonstrate a successful synthesis of colloidal n-type lead telluride nanocrystals doped with iodine. By tuning the reaction time and iodine concentration in the precursor solution, nanocrystals with different sizes and doping concentrations are synthesized. The Seebeck coefficient and electrical conductivity of the nanocrystals are measured on nanocrystal thin films fabricated by dip-coating glass substrates in the nanocrystals solution. Investigations on the influence of size and doping concentration on the electrical properties have been performed. The results show that the size of the nanocrystals significantly influences the electrical conductivity but not the Seebeck coefficient of nanocrystal films, while higher doping concentration leads to lower Seebeck coefficient but higher electrical conductivity in the nanocrystal films. Proof-of-concept thin-film thermoelectric modules are also fabricated using both p-type and n-type PbTe nanocrystals for the conversion of thermal energy into electrical energy.

Couples of colloidal semiconductor nanorods formed by self-limited assembly

Colloidal nanocrystal synthesis provides a powerful approach for creating unique nanostructures of relevance for applications. Here, we report that wurtzite ZnSe nanorod couples connected by twinning structures can be synthesized by means of a self-limited assembly process. Unlike for individual nanorods, the band-edge states calculated for the nanorod couples are predominantly confined to the short edges of the structure and this leads to low photoluminescence polarization anisotropy, as confirmed by single-particle fluorescence. Through a cation-exchange approach, the composition of nanorod couples can be readily expanded to additional materials, such as CdSe and PbSe. We anticipate that this family of nanorod-couple structures with distinct compositions and controlled properties will constitute an ideal system for the investigation of electronic coupling effects between individual nanorod components on the nanoscale, with relevance to applications in optics, photocatalysis and optoelectronic devices.

Scaling up the Production of Colloidal Nanocrystals: Should We Increase or Decrease the Reaction Volume?

Recent progress in facet-controlled syntheses has started to produce nanocrystals with great promise as the next-generation catalysts for a variety of applications. To move from academic studies to industrial applications, however, one has to address the issue of scaling up a synthesis that has been commonly conducted in a batch format. There are two opposite approaches to scaling up the production of colloidal nanocrystals: increasing and decreasing the reaction volume. Contrary to conventional wisdom, continuous flow synthesis based on droplets is expected to provide a more practical platform for scaling up the synthesis. Here we highlight recent progress in using droplet reactors for the synthesis of colloidal noble-metal nanocrystals with controlled sizes and shapes, with an aim towards high-volume production.

Controllable synthesis of colloidal CuInS2 nanocrystals with tunable structures and its nonlinear optical properties

Monodisperse CuInS2 nanocrystals (CIS NCs) with wurtzite (hexagonal) and chalcopyrite (tetragonal) structures have been obtained via a facile route of thermal decomposition of metal–thiolate. The morphologies of the nanocrystals were tuned from pyramid-shaped to nanospheres by varying the concentrations of oleylamine (OLA). The band gaps of the nanocrystals ranged from 2.73eV to 2.65eV when reaction time changed. Furthermore, the third-order optical nonlinearities of WZ–CIS NCs in n-Hexane were studied by Z-scan at a wavelength of 770nm. By increasing the concentration of OLA, the value of the third-order nonlinear-index coefficient γ, the nonlinear absorption coefficient β and nonlinear susceptibility χ(3) became larger.

Mechanistic Insights into the Role of Alkylamine in the Synthesis of CdSe Nanocrystals

This paper reports a detailed mechanistic study of the effect of alkylamine on the synthesis of CdSe nanocrystals. Alkylamines are one of the most important additives for the synthesis of colloidal semiconductor nanocrystals. However, their effect on the monomer production as well as nanocrystal nucleation and growth are not well understood, as indicted by inconsistent and contradictory conclusions in the literature. We found that alkylamines slow down the reaction between cadmium oleate and trialkyl phosphine selenide by binding to cadmium and preventing the activation of trialkyl phosphine selenide. A linear correlation was observed between the observed reaction rate constant and the (31)P NMR chemical shift or (1)J(P-Se) of phosphine selenide. In the presence of alkylamine, an alkylaminophosphonium intermediate was observed. Mechanistic study suggests that the cleavage of P═Se bond is through nucleophilic attack by carboxylate instead of alkylamine. Interestingly, although alkylamines decrease the rate of monomer production, it increases the rate of CdSe nanocrystal growth. Although seemingly contradictory, this is due to a drastic decrease in the nanocrystal nucleation events in the presence of alkylamines. As a result, each nucleus is fed with more monomers and grows faster in the presence of alkylamine than in its absence.

ChemInform Abstract: Precision Synthesis of Colloidal Inorganic Nanocrystals Using Metal and Metalloid Amides

AbstractReview: 129 refs.

Synthesis of boron and phosphorus codoped all-inorganic colloidal silicon nanocrystals from hydrogen silsesquioxane.

We present a new route for mass-production of B and P codoped all-inorganic colloidal Si nanocrystals (NCs) from hydrogen silsesquioxane (HSQ). Codoped Si NCs are grown in glass matrices by annealing mixture solutions of HSQ and dopant acids, and then extracted from the matrices by hydrofluoric acid etching. The free-standing NCs are dispersible in methanol without any surface functionalization processes. The structural analyses suggest the formation of heavily B and P doped hydrophilic shells on the surface of Si NCs. The NCs show efficient size-tunable photoluminescence in the near infrared to visible region.

Colloidal semiconductor nanocrystals: controlled synthesis and surface chemistry in organic media

State-of-the-art development of the controlled synthesis of colloidal semiconductor nanocrystals has been discussed in this review article.

Synthesis of bright CdSe nanocrystals by optimization of low-temperature reaction parameters

The reaction parameters of low-temperature synthesis of colloidal nanocrystals were investigated. It was found the structural and optical properties of CdSe nanocrystal quantum dots synthesized at 130 °C are particularly sensitive to alkyl-chain lengths of ligands, the cadmium source, and ligand to precursor ratios. Under optimized synthesis conditions CdSe quantum dots with narrow ensemble size distribution and excellent photoluminescence quantum efficiencies of up to 40 percent were obtained.

CdTe-CdSe nanocrystals capped with dimethylaminoethanethiol as ultrasensitive fluorescent probes for chromium(VI)

We report on the synthesis of water-soluble luminescent colloidal CdTe nanocrystals capped with various stabilizers (mercaptopropanol, thioglycolic acid, mercaptosuccinic acid, mercaptopropionic acid, L-cysteine, reduced L-glutathione, mercaptoethanol and dimethylaminoethanethiol), and their use as fluorescent probes for chromium(VI) ions. The results show that Cr(VI) ions can be ultrasensitively detected with CdTe NCs capped with dimethylaminoethanethiol (DMAET), with high selectivity over Cr(III) and other ions. Synchronous fluorescence spectroscopy was applied to quantify trace levels of Cr(VI) ions with this probe in the 3.0 nM to 0.2 μM concentration range, with a detection limit as low as 0.57 nM. The interaction between the nanocrystals and Cr(VI) ions was investigated in a study on the zeta potentials, UV-Vis absorption spectroscopy and time-resolved luminescence spectroscopy. Electron transfer process occurred and the decay times of the probe remain constant (about 14 ns). This simple and ultrasensitive analytical method was successfully applied to the direct determination of Cr(VI) in spiked samples of environmental waters.

Solution-Phase Synthesis and Magnetic Properties of Single-Crystal Iron Germanide Nanostructures

Iron–germanium (Fe–Ge) is a complex alloy system that includes several structurally and compositionally diverse phases that exhibit a range of interesting magnetic properties that can change significantly when reduced to nanoscale dimensions. Fe–Ge nanostructures have been synthesized using chemical and physical deposition methods but have not previously been accessible as solution-synthesized colloidal materials. Here, we show that colloidal Fe–Ge nanostructures can be synthesized via the hot injection of an oleylamine solution of Fe(CO)5 into a solution containing GeI4, oleylamine, oleic acid, and hexamethyldisilazane. This approach effectively merges recent advances in the synthesis of colloidal Ge nanocrystals with methods routinely used to synthesize metal and alloy nanoparticles. At 260 °C, spherical nanocrystals of Ni2In-type Fe3Ge2 form. Heating the solution at 300 °C transforms the spherical Fe3Ge2 nanocrystals into CoGe-type FeGe nanowires. The Fe3Ge2 nanocrystals are ferromagnetic with T c ≈ 26...

Layered Phosphonates in Colloidal Synthesis of Anisotropic ZnO Nanocrystals

We describe the role of phosphonic acids in the synthesis of anisotropic colloidal ZnO nanocrystals (nanorods) and, specifically, the discovery of an insoluble layered Zn–phosphonate intermediate. This compound is formed by the reaction of the molecular Zn precursor Zn(OAc)2 with phosphonic acids, and it acts as a heterogeneous Zn source during nanocrystal formation. Layered metal phosphonates have been studied extensively but have not been described in the context of nanocrystal synthesis. Layered Zn–octadecylphosphonate can be used as a sole precursor to obtain isotropic, soluble ZnO nanocrystals. However, for anisotropic rod-like shapes both the heterogeneous and the homogeneous (Zn(OAc)2) sources of Zn are necessary. The existence of a heterogeneous metal source described here is in contrast to the mechanisms of particle nucleation and growth from homogeneous molecular precursors often used to describe nanocrystal formation. Since many metals form layered phosphonates, our findings have implications f...