As-prepared Nanocrystals Research Articles

Colloidal Sb2S3nanocrystals: synthesis, characterization and fabrication of solid-state semiconductor sensitized solar cells

Antimony sulfide nanocrystals of various shapes and different phases are synthesized using a colloidal hot-injection method, and the as-prepared nanocrystals are used as a light harvesting material in photovoltaic devices.

Colloidal synthesis of Cu-ZnO and Cu@CuNi-ZnO hybrid nanocrystals with controlled morphologies and multifunctional properties.

Metal-semiconductor hybrid nanocrystals have received extensive attention owing to their multiple functionalities which can find wide technological applications. The utilization of low-cost non-noble metals to construct novel metal-semiconductor hybrid nanocrystals is important and meaningful for their large-scale applications. In this study, a facile solution approach is developed for the synthesis of Cu-ZnO hybrid nanocrystals with well-controlled morphologies, including nanomultipods, core-shell nanoparticles, nanopyramids and core-shell nanowires. In the synthetic strategy, Cu nanocrystals formed in situ serve as seeds for the heterogeneous nucleation and growth of ZnO, and it eventually forms various Cu-ZnO hetero-nanostructures under different reaction conditions. These hybrid nanocrystals possess well-defined and stable heterostructure junctions. The ultraviolet-visible-near infrared spectra reveal morphology-dependent surface plasmon resonance absorption of Cu and the band gap absorption of ZnO. Furthermore, we construct a novel Cu@CuNi-ZnO ternary hetero-nanostructure by incorporating the magnetic metal Ni into the pre-synthesized colloidal Cu nanocrystals. Such hybrid nanocrystals possess a magnetic Cu-Ni intermediate layer between the ZnO shell and the Cu core, and exhibit ferromagnetic/superparamagnetic properties which expand their functionalities. Finally, enhanced photocatalytic activities are observed in the as-prepared non-noble metal-ZnO hybrid nanocrystals. This study not only provides an economical way to prepare high-quality morphology-controlled Cu-ZnO hybrid nanocrystals for potential applications in the fields of photocatalysis and photovoltaic devices, but also opens up new opportunities in designing ternary non-noble metal-semiconductor hybrid nanocrystals with multifunctionalities.

Tuning the surface oxygen concentration of {111} surrounded ceria nanocrystals for enhanced photocatalytic activities.

For oxide semiconductors, the morphology, particle size and oxygen vacancies are usually considered as key influential parameters for photocatalytic degradation of organic pollutants/dyes. It is widely accepted that cation doping not only modifies their phase and microstructures but also introduces variations in oxygen vacancy concentration. Herein, we report the fabrication of sub-10 nm sized pure and indium doped CeO2 nanocrystals (NCs) via a facile, green hydrothermal method for the investigation of photocatalytic activities. X-ray diffraction and transmission electron microscopy were employed to examine the crystal phase and morphology of the as-prepared nanocrystals. Raman and X-ray photoelectron spectroscopy techniques were implemented to investigate the presence and variations in oxygen vacancy concentration in un-doped and indium doped CeO2 nanocrystals. The photocatalytic activity results revealed that 10 at% doping is the optimal indium doping level to demonstrate superior dye removal efficiency (∼40%) over un-doped and doped CeO2 NCs. Moreover, the 10% In-doped CeO2 nanocrystals expressed excellent cycling stability and superior photocatalytic performance toward other dye pollutants. Finally, on the basis of our findings, a possible photocatalytic mechanism in which indium doping can generate more surface oxygen vacancies in the ceria lattice which delay the electron-hole recombination rates, thus increasing the lifetime of electron-hole separation for enhanced photocatalytic performances was proposed.

Preparation of nanocrystalline cubic ZrO2 with different shapes via a simple precipitation approach

In this study, Triethylenetetramine (Trien) was employed not only as precipitator, but also as morphology- and size-modifier to prepare pure cubic zirconium dioxide nanocrystals. Trien with high steric hindrance effect was employed as morphology- and size-modifier. Besides Trien as novel precipitator, zirconyl nitrate was employed as zirconium source for the synthesis of pure cubic zirconium dioxide nanocrystals through a facile surfactant-free precipitation process. SEM results of this investigation reveal that grain size and shape of the zirconium dioxide powders can be modified by changing key preparation factors such as the solvent sort, precipitator concentration and reaction time. XRD, FESEM, DR–UV–vis, PL, FT-IR and EDX were used to characterize the as-produced zirconium dioxide nanocrystals. Moreover, the photocatalytic performance of as-prepared zirconium dioxide nanocrystals was evaluated by degradation of erythrosine dye as a model of water pollutant.

Hydrothermal synthesis of vanadium oxide nanorods and their electrochromic performance

Nanorod-like V2O5 was fabricated using a simple one-step hydrothermal method using NH4VO3 and oxalic acid as precursors. The morphology and structure of the as-prepared V2O5 nanocrystals were characterized by different techniques. Furthermore, based on the analyses of cyclic voltammetric curves and electrochromism test, the thin V2O5 nanorod film have been found to exhibit promising electrochromic performance, which can be attributed to their nanorod architecture. The as-prepared V2O5 nanocrystals are promising electrochromic candidate for potential application in smart window.

Synthesis, morphology, and luminescence of ZnNb2O6 nanocrystals by hydrothermal method

The effect of hydrothermal treatment conditions on the formation, morphology, crystal growth, and photoluminescence of columbite-type ZnNb2O6 nanocrystals having rose-like morphology that were directly formed from aqueous precursor solutions of ZnSO4 and NbCl5 in the presence of aqueous ammonia was investigated. The crystallization of ZnNb2O6 nanocrystals was observed at 210 °C, but the hydrothermal treatment at 240 °C for 5 h under weakly basic condition around pH=8.4 was necessary for the sufficient crystallite growth of columbite-type ZnNb2O6 phase. On the other hand, the solid product formed at 240 °C from the precursor solution at pH=9.0 was almost amorphous. The observation by means of the transmission electron microscopy, selected area diffraction, and energy dispersive X-ray spectrometry showed that the ZnNb2O6 particles with the morphology like flower or rose consisted of arrayed nanosized-sheets having crystallite size of 11 nm. The ZnNb2O6 particles grew from about 1 to 4μm accompanying crystal growth with morphological change into rose-like shape via the solution and precipitation mechanism as hydrothermal holding time at 240 °C increased from 5 to 72 h. The as-prepared ZnNb2O6 nanocrystals showed a broad-band emission in the UV-blue region centered at 420 nm (and peaked at 360 nm) under excitation at 276 nm.

Aqueous Synthesis of Tunable Highly Photoluminescent CdTe Quantum Dots Using Rongalite and Bioimaging Application

Abstract Rongalite is a cheap, strong and stable reducing agent with broad industrial applications. Herein we report novel method for the preparation of water-soluble and small-size CdTe quantum dots (QDs) using rongalite to produce Te 2− species in reaction medium for the first time. The synthesized QDs were characterized with transmission electron microscopy, spectroscopy, and confocal laser scanning microscopy. The influence of parameters such as the pH value of the precursor solution and the molar ratio of Cd 2+ to TGA and Cd 2+ to Te 2− on the quantum yields of CdTe QDs was systematically investigated. Under the optimal conditions at pH 11.6 and selecting thioglycolic acid as capping agent, the as-synthesized CdTe QDs possessed 66% quantum yield with narrow bandwidth of 24 nm. Moreover, methyl thiazolyl tetrazolium (MTT) assays were employed to evaluate the cytotoxicity of the as-prepared semiconductor nanocrystals on HeLa cell lines. Bioimaging studies showed that the as-synthesized QDs were quickly taken up by HeLa cells and did not have obvious damage to the cells within an incubation period of 24 h. The results show that Rongalite is a very promising agent for the synthesis of a variety of quantum dots and Rongalite-based QDs may find broad applications.

Hydrothermal Synthesis and Upconversion Properties of <I>α</I>-NaYF<SUB>4</SUB>:Yb<SUP>3+</SUP>, Er<SUP>3+</SUP> Nanocrystals Using Citric Acid as Chelating Ligand and NaNO<SUB>3</SUB> as Mineralizer

Yb3+ and Er3+ ions co-doped α-NaYF4:Yb3+, Er3+ nanocrystals were successfully synthesized via a facile hydrothermal method using citric acid (CA) as chelating ligand and NaNO3 as mineralizer. The influences of the CA/RE (RE = Y+Yb+ Er) molar ratio, reaction time, reaction temperature and the NaNO3/RE molar ratio on the crystal phases and shapes of as-prepared products have been well investigated. The possible formation mechanism has been discussed in detail and an aggregation growth theory has been proposed. X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), and photoluminescence (PL) spectra were used to characterize the products. Under 980 nm excitation, the emission intensities of the as-prepared nanocrystals were much stronger than that of the nanocrystals modified by ethylenediaminetetraacetic acid (EDTA). Additionally, the as-prepared products maintained spherical shape and high degree of monodispersion, which is expected to be suggestive for the preparation of other complex rare earth fluoride compounds.

Preparation and photocatalytic properties of zinc oxide nanoparticles by microwave-assisted ball milling

Hexagonal wurtzite ZnO nanoparticles with the average size of about 15nm were successfully prepared by microwave-assisted ball milling. The as-prepared ZnO nanocrystals were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–visible spectrophotometer, fluorescence measurements, and electroconductivity detections. The results showed that single-phase hexagonal wurtzite ZnO nanoparticles were obtained after 20h by microwave-assisted ball milling. The UV spectrophotometer analysis confirms that photocatalytic activity of as-synthesized ZnO nanoparticles under ultraviolet light is demonstrated via methyl orange degradations of 95%. In addition, the measurement results of the relative content of OH radicals in the aqueous solution and the relative conductivity of the solutions verify that the coupling of microwave and ball milling significantly enhanced the chemical reaction.

Fabrication of worm-like Ag2S nanocrystals under mediation of protein

A simple protein-assisted method was reported to synthesize pepsin-conjugated Ag2S nanocrystals in aqueous solution. The morphology, composition and structure of the products were characterized by transmission electron microscopy, high-resolution transmission electron microscopy, energy-dispersive spectroscopy, selected area electron diffraction and X-ray diffraction measurements. The results showed that as-prepared monoclinic Ag2S nanocrystals are worm-like nanochains in shape with sizes about 25 nm in diameter and up to hundreds of nanometres in length. The multiple coordinate bonds of pepsin molecules to the surface of Ag2S nanocrystals make as-prepared samples have good colloidal stability and biocompatibility as elucidated by Fourier transform infrared examination. Thermogravimetry–differential scanning calorimetry analysis indicated that the obtained products are inorganic–organic nanocomposites and there is strong interaction between Ag2S and pepsin. This interaction could result in the change of hydrophilic environment of pepsin and consequently intrinsic fluorescence of protein was quenched by Ag2S nanocrystals. Furthermore, the nanochains assembly of particle–particle and rod–rod oriented attachment was discussed to investigate the growth mechanism.

Synthesis and photocatalytic properties of multi-morphological AuCu3-ZnO hybrid nanocrystals

Noble metal–semiconductor hybrid nanocrystals represent an important class of materials for many potential applications, especially for photocatalysis. The utilization of transition metals to form alloys with noble metals can not only reduce the preparation costs, but may also offer tunable optical and catalytic properties for a broader range of applications. In this study, we report on the solution synthesis of AuCu3–ZnO hybrid nanocrystals with three interesting morphologies, including urchin-like, flower-like and multipod-like nanocrystals. In the synthetic strategy, Au–Cu bimetallic alloy seeds formed in situ are used to induce the heteroepitaxial growth of ZnO nanocrystals on the surface of bimetallic alloy cores; thus different types of morphologies can be achieved by controlling the reaction conditions. Through high-resolution transmission electron microscopy observations, well-defined interfaces between ZnO and AuCu3 are observed, which indicate that ZnO has a (0001) orientation and prefers to grow on AuCu3 {111} facets. The as-prepared hybrid nanocrystals demonstrate morphology- and composition-dependent surface plasmon resonance (SPR) absorption bands. In addition, much higher photocatalytic efficiency than pure ZnO nanocrystals is observed for the hybrid nanocrystals in the degradation of methylene blue. In particular, the multipod-like AuCu3–ZnO hybrid nanocrystals show the highest catalytic performance, as well as more than three times higher photocurrent density than the pure ZnO sample. The reported synthetic strategy provides a facile route to the effective combination of a plasmonic alloy with semiconductor components at the nanoscale in a controlled manner.

Size-Dependent Synthesis of Cu12Sb4S13Nanocrystals with Bandgap Tunability

Copper antimony sulfide (CAS) is an attractive material with a suitable bandgap for sunlight absorption and a high absorption coefficient in solar cells. There are few works focused on the size-controllable synthesis of CAS nanocrystals, and no work reports on the special character of bandgap tunability until now. Herein, high-quality monodispersed tetrahedrite (Cu12Sb4S13) nanocrystals are synthesized through a novel solution-based method by using thiols as ligands. The as-prepared Cu12Sb4S13 nanocrystals have a narrow size distribution and wide size range from 2 to 16 nm, while their absorption band edges are continuously tunable from 620 to 780 nm. The quantum size effects with bandgap tunability of Cu12Sb4S13 nanocrystals are observed for the first time.

High temperature recrystallization of kersterite Cu2ZnSnS4 towards enhanced photocatalytic H2 evolution

Kesterite Cu2ZnSnS4 (CZTS) with different crystallinities were obtained by high temperature recrystallization of as-prepared kesterite CZTS nanocrystals under elevated temperature. The effect of temperature on the crystallinity, crystallite size and specific surface area, thus the photocatalytic H2 evolution activity were discussed in detail. The maximum photocatalytic H2 evolution rate was achieved under an intermediate annealing temperature (450 and 550 °C), which show moderate crystallinity and specific surface area. However, the surface specific activity of CZTS, namely the amount of H2 evolution per surface area, show the highest value when the annealing temperature increased up to 750 °C. A rapid cooling process which induces the improvement of crystallinity without significant loss of specific surface area was used to further enhance the photocatalytic H2 evolution activity of CZTS.

Preparation of multi-branched Au–ZnO hybrid nanocrystals on graphene for enhanced photocatalytic performance

Hybrid nanostructures containing multiple components have received intensive interests. Herein, we report a solution method for the preparation of Au–ZnO/graphene nanocomposites in which multi-branched Au–ZnO hybrid nanocrystals with ZnO nanorods growing on octahedral Au cores are anchored on graphene. The as-prepared hybrid nanocrystal and nanocomposite samples are characterized by transmission electron microscopy, X-ray diffraction and ultraviolet visible spectroscopy. The photocatalytic activity is investigated by the degradation of Rhodamine B (RhB) under ultraviolet light irradiation. The results show that Au–ZnO/graphene nanocomposites not only have optical absorptions in both UV and visible ranges, but also exhibit much enhanced photocatalytic performance compared to pure Au–ZnO hybrid nanocrystals.

Lactoferrin-assisted synthesis of zinc ferrite nanocrystal: Its magnetic performance and photocatalytic activity

Lactoferrin (LF) was used to assist the synthesis of zinc ferrite (ZnFe2O4, ZFO) semiconductor photocatalysts in this study, and superparamagnetic ZFO nanocrystals with an average crystallite size ranging from 11.3 nm to 20.1 nm were successfully obtained via the hydrothermal method. It was found that LF was conducive to fast formation of ZFO nuclei, which resulted in remarkable crystallinity enhancement of the as-prepared ZFO nanocrystals. The saturation magnetization (Ms) of the as-prepared ZFO crystals would be greatly improved with increasing the LF content, and the Ms of the as-prepared ZFO crystals synthesized with 50 mg of LF (ZFO-50LF) could reach 19.9 emu/g, whereas the Ms of the as-prepared ZFO crystals synthesized in the absence of LF (ZFO-0LF) was only 8.8 emu/g. In addition, although the specific surface area of ZFO-0LF nanocrystals (127.2 m2/g) was larger than that of ZFO-50LF nanocrystals (101.6 m2/g), and ZFO-0LF exhibited a higher absorption of methyl orange (MO) molecules in contrast with ZFO-50LF, but ZFO-50LF possessed a larger optical absorption coefficient, smaller band gap and higher photocatalytic degradation efficiency per unit area. After being irradiated under UV light for 3 h, ZFO-50LF almost could make MO molecules completely degrade. Therefore, the LF-assisted synthesized ZFO nanocrystals have a promising application prospect to be used as a new high-efficiency recyclable photocatalyst.

Highly active and thermo-stable anatase TiO2 photocatalysts synthesized by a microwave-assisted hydrothermal method

Phase-pure anatase titanium dioxide (A-TiO2) with high thermal stability is synthesized by a microwave-assisted hydrothermal (MAH) method. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption–desorption isotherms, and photoluminescence spectra (PL) analysis. The photo-electrochemical responses are examined via linear sweep voltammetry (LSV), intensity-modulated photocurrent spectroscopy (IMPS), and intensity-modulated photovoltage spectroscopy (IMVS). The photocatalytic activity of TiO2 nanoparticles (NPs) has been confirmed through the methylene blue (MB) de-colorization under the simulated sunlight. The results show that the as-prepared TiO2 nanocrystals possess thermal stability for the anatase-to-rutile phase transformation up to 900 °C. The phase-pure A-TiO2 annealed at 800 °C exhibits a much higher de-colorization rate than the commercially available TiO2 (Degussa P25) powders. The higher photocatalytic activity of this sample is due to its enhanced crystallinity, leading to a lower rate of electron/hole pair recombination and a larger photocurrent density in comparison with all other samples and P25. The sample annealed at 900 °C shows the highest specific activity on MB de-colorization, demonstrating the importance of thermal stability and crystalline phase.

Plasmonic Metal Oxide Nanocrystals and Their Near Infrared Electrochromism

Degenerately doped metal oxide semiconductors, like ITO, exhibit plasmonic resonance at near and mid-infrared wavelengths tunable by varying their composition. Nanocrystals of many such materials have now been synthesized and applications are emerging that leverage the responsiveness of their localized surface plasmon resonance (LSPR) to electronic charging and discharging. One such application is electrochromic glass that can dynamically control heat loads in buildings as the plasmonic absorption of the nanocrystals is electrochemically modulated. I will discuss the principles of electrochromic switching in such materials and describe our efforts to integrate plasmonic nanocrystals into full electrochromic devices. Fundamental understanding of the nature of the electronic states giving rise to infrared absorption is also being pursued. For example, near-edge x-ray absorption spectroscopy is illuminating the charge state of the metal cations in as-prepared doped nanocrystals and in electrochemically-charged materials. Localization of charge upon lithium insertion gives rise to visible tinting, useful for controlling daylight intensity in smart windows. Finally, fabrication strategies compatible with flexible substrates are explored, opening the door to low cost manufacturing.

Controllable synthesis of β-NaLuF4:Yb3+, Er3+ nanocrystals and their application in polymer-based optical waveguide amplifiers

Abstract Hexagonal structured NaLuF4 (β-type) nanocrystals (NCs) with controllable particle size were prepared by thermal decomposition approach. The as-prepared NCs possessed good dispersibility in organic solvents. Under a 980 nm laser excited, these Er3+ and Yb3+ co-doped β-NaLuF4 NCs demonstrated emission around 1530 nm. These β-NaLuF4:Yb3+, Er3+ NCs were dispersed into SU-8 polymer to fabricate polymer waveguides, and the results showed that their crystal size influenced greatly on the performance of polymer waveguides. The relative optical gain of 2.413 dB, 1.653 dB and 0.481 dB at 1530 nm was achieved when the particle size was about 8 nm, 15 nm, and 23 nm, respectively. These results show that β-NaLuF4:Yb3+, Er3+ NCs with small particle size were promising materials for building Er3+-doped polymer-based optical waveguide amplifiers.

Solvothermal synthesis of octahedral NiFe2O4 nanocrystals and catalytic properties for the reduction of some aromatic nitrocompounds

In this paper, we report the successful synthesis of octahedral NiFe2O4 nanocrystals with room-temperature ferrimagnetism via a mixed solvothermal process at 170 °C for 15 h, using Fe(NO3)3 and NiCl2 as starting reactants. The phase and morphology of the as-prepared product is characterized by means of powder X-ray diffraction, energy dispersive spectrometry, selected area electron diffraction (SAED), (high resolution) transmission electron microscopy, and scanning electron microscopy. Experiments showed that the as-prepared octahedral NiFe2O4 nanocrystals owned strong catalytic activity for the reduction of some aromatic nitro-compounds such as 4-nitrophenol, 2-nitroaniline, 4-nitroaniline, and 2,4-dinitrophenol. Under the presence of 9 mg NiFe2O4 nanocrystals, the rate constants of the reductive reactions were in turn 3.16 × 10−2min−1 for 4-nitrophenol, 4.28 × 10−2min−1 for 2-nitroaniline, 6.79 × 10−2min−1 for 4-nitroaniline, and 3.26 × 10−2min−1 for 2,4-dinitrophenol. Moreover, the present catalyst could be conveniently recycled due to its magnetism. After ten cycles, its catalytic efficiency did not obviously decrease.

Investigation of PbS nanocrystals sensitized extremely thin absorber (ETA) solar cell

Colloidal PbS nanocrystals (NCs) were prepared by an environmental friendly route. The as-prepared colloidal PbS nanocrystals were characterized by powdered X-ray diffraction and high-resolution transmission electron microscopy (HR-TEM). The ground state excitonic transition energies determined from the position of the first excitonic absorption peaks (2.5nm±0.2 (J1), 2.8nm±0.15 (J2) and 3.1nm±0.3 (J3) were 1.71, 1.35 and 1.15eV respectively). These PbS nanocrystals were then used to sensitize a nanostructured ZnO–SnO2 electrode by using In2S3 as a buffer layer. The results showed that sensitization procedure of PbS NCs with electrode played a significant role in the charge separation and transport. The cell fabricated by PbS NCs in which linker molecules were exchanged on the surface of electrode showed considerably higher incident to photon conversion efficiency (IPCE) compared to pre-ligand modified PbS NCs. The findings presented here can potentially be applied for the design of low-cost ETA devices for commercial applications.