Surfactant-free Colloidal Crystal of ZnO Quantum Dots

2009 ◽  
Vol 1207 ◽  
Author(s):  
Xi Zhang ◽  
Dazhi Sun ◽  
Hung-Jue Sue
Keyword(s):  
Electron Microscopy ◽  
Quantum Dots ◽  
Colloidal Crystal ◽  
Uv Light ◽  
X Ray ◽  
Transmission Electron ◽  
Close Packed Structure ◽  
Packed Structure ◽  
Zno Quantum Dots ◽  
Zno Qds

AbstractMonodisperse ZnO quantum dots (QDs) with a particle size of about 5 nm have been synthesized. Isopropanol together with hexane were utilized to precipitate ZnO nanoparticles to form condensed phases, ranging from white flocculation, to gel-like fluid, and to transparent solid. The morphology and structure in the transparent ZnO solid was characterized by UV-vis, X-ray diffraction, small-angle X-ray scattering, transmission electron microscopy, and scanning electron microscopy. The mechanisms for the formation of transparent ZnO QDs close-packed structure were monitored via UV-vis spectra, and found likely to be a colloidal crystal. The colloidal crystal is transparent and absorbs UV light efficiently. Possible conditions for the formation of the ZnO QDs colloidal crystal are discussed.

scholarly journals Hydrothermal synthesis of ZnO quantum dot/KNb3O8 nanosheet photocatalysts for reducing carbon dioxide to methanol

2017 ◽  
Vol 8 ◽  
pp. 2264-2270 ◽  
Author(s):  
Xiao Shao ◽  
Weiyue Xin ◽  
Xiaohong Yin
Keyword(s):  
Electron Microscopy ◽  
Quantum Dots ◽  
Uv Light ◽  
Formation Rate ◽  
X Ray Diffraction ◽  
Methanol Production ◽  
X Ray ◽  
Transmission Electron ◽  
Methanol Formation ◽  
Zno Quantum Dots

ZnO quantum dots and KNb3O8 nanosheets were synthesized by a two-step hydrothermal method for the photocatalytic reduction of CO2 to methanol where isopropanol is simultaneously oxidized to acetone . The as-prepared photocatalysts were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and UV–vis absorption spectroscopy (UV–vis). The photocatalytic activity of the materials was evaluated by formation rate of methanol under UV light irradiation at ambient temperature and pressure. The methanol formation rate of pure KNb3O8 nanosheets was found to be 1257.21 μmol/g/h, and after deposition of 2 wt % ZnO quantum dots on the surface of KNb3O8 nanosheets, the methanol production rate was found to increase to 1539.77 μmol/g/h. Thus, the ZnO quantum dots obviously prompted separation of charge carriers, which was explained by a proposed mechanism for this photocatalytic reaction.

Optical properties and energy transfer processes in Tb3+-doped ZnSe quantum dots

2021 ◽  
Author(s):  
Nguyen Ca ◽  
N. D Vinh ◽  
Phan Van Do ◽  
N. T. Hien ◽  
Xuan Hoa Vu ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Quantum Dots ◽  
Chemical Method ◽  
X Ray Diffraction ◽  
Wet Chemical Method ◽  
X Ray ◽  
Transfer Processes ◽  
Transmission Electron ◽  
Wet Chemical

Tb3+-doped ZnSe quantum dots (QDs) with Tb content in the range of 0.5 - 7% were successfully synthesized by a wet chemical method. X-ray diffraction (XRD) and transmission electron microscopy...

Microstructure characteristics of non-monodisperse quantum dots: on the potential of transmission electron microscopy combined with X-ray diffraction

CrystEngComm ◽  
2020 ◽  
Vol 22 (21) ◽  
pp. 3644-3655
Author(s):  
Stefan Neumann ◽  
Christina Menter ◽  
Ahmed Salaheldin Mahmoud ◽  
Doris Segets ◽  
David Rafaja
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Quantum Dots ◽  
Cdse Quantum Dots ◽  
X Ray Diffraction ◽  
X Ray ◽  
Microstructure Characteristics ◽  
Scale Bridging ◽  
Transmission Electron ◽  
Hot Injection

Capability of TEM and XRD to reveal scale-bridging information about the microstructure of non-monodisperse quantum dots is illustrated on the CdSe quantum dots synthesized using an automated hot-injection method.

scholarly journals Formation of ZnO/Zn0.5Cd0.5Se Alloy Quantum Dots in the Presence of High Oleylamine Contents

Nanomaterials ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 999
Author(s):  
Yi-An Chen ◽  
Kuo-Hsien Chou ◽  
Yi-Yang Kuo ◽  
Cheng-Ye Wu ◽  
Po-Wen Hsiao ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Quantum Dots ◽  
Particle Size ◽  
X Ray Diffraction ◽  
One Pot ◽  
X Ray ◽  
Transmission Electron ◽  
Average Size ◽  
Alloy Quantum Dots ◽  
First Time

To the best of our knowledge, this report presents, for the first time, the schematic of the possible chemical reaction for a one-pot synthesis of Zn0.5Cd0.5Se alloy quantum dots (QDs) in the presence of low/high oleylamine (OLA) contents. For high OLA contents, high-resolution transmission electron microscopy (HRTEM) results showed that the average size of Zn0.5Cd0.5Se increases significantly from 4 to 9 nm with an increasing OLA content from 4 to 10 mL. First, [Zn(OAc)2]–OLA complex can be formed by a reaction between Zn(OAc)2 and OLA. Then, Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) data confirmed that ZnO is formed by thermal decomposition of the [Zn(OAc)2]–OLA complex. The results indicated that ZnO grew on the Zn0.5Cd0.5Se surface, thus increasing the particle size. For low OLA contents, HRTEM images were used to estimate the average sizes of the Zn0.5Cd0.5Se alloy QDs, which were approximately 8, 6, and 4 nm with OLA loadings of 0, 2, and 4 mL, respectively. We found that Zn(OAc)2 and OLA could form a [Zn(OAc)2]–OLA complex, which inhibited the growth of the Zn0.5Cd0.5Se alloy QDs, due to the decreasing reaction between Zn(oleic acid)2 and Se2−, which led to a decrease in particle size.

Synthesis and Characterization of SiO2@Y2MoO6:Eu3+ Core–Shell Structured Spherical Phosphors by Sol–Gel Process

2016 ◽  
Vol 16 (4) ◽  
pp. 3914-3920 ◽  
Author(s):  
G. Z Li ◽  
F. H Liu ◽  
Z. S Chu ◽  
D. M Wu ◽  
L. B Yang ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Annealing Temperature ◽  
Uv Light ◽  
Sol Gel ◽  
Spherical Shape ◽  
Core Shell ◽  
X Ray ◽  
Transmission Electron ◽  
Sol Gel Process ◽  
Average Size

SiO2@Y2MoO6:Eu3+ core–shell phosphors were prepared by the sol–gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra as well as kinetic decays were used to characterize the resulting SiO2@Y2MoO6:Eu3+ core–shell phosphors. The XRD results demonstrated that the Y2MoO6:Eu3+ layers on the SiO2 spheres crystallized after being annealed at 700 °C and the crystallinity increased with raising the annealing temperature. The obtained core–shell phosphors have spherical shape with narrow size distribution (average size ca. 640 nm), non-agglomeration, and smooth surface. The thickness of the Y2MoO6:Eu3+ shells on the SiO2 cores could be easily tailored by varying the number of deposition cycles (70 nm for four deposition cycles). The Eu3+ shows a strong PL emission (dominated by 5D0–7F2 red emission at 614 nm) under the excitation of 347 nm UV light. The PL intensity of Eu3+ increases with increasing the annealing temperature and the number of coating cycles.

Studies on Optical Properties of CdS/ZnO Quantum Dots Prepared by Sol-Gel Method

2011 ◽  
Vol 364 ◽  
pp. 129-133 ◽  
Author(s):  
Liyana Mohd Lawi Ruhana ◽  
Taqiyuddin Mawardi Ayob Muhammad ◽  
Radiman Shahidan ◽  
Irman Abdul Rahman ◽  
Bohari M. Yamin
Keyword(s):  
Quantum Dots ◽  
Sol Gel ◽  
Emission Spectra ◽  
Blue Shift ◽  
Mixture Ratio ◽  
Gel Method ◽  
Sol Gel Method ◽  
Transmission Electron ◽  
Zno Quantum Dots ◽  
Zno Qds

CdS/ZnO quantum dots (QDs) were prepared at a temperature of 293 K by the sol-gel method with Triethanolamine (TEA) as a capping agent. The effect of CdS/ZnO mixture ratio of 1:9, 1:1 and 9:1 on the optical absorption and fluorescence spectra were investigated by UV-Vis and Fluorescence spectroscopy. By increasing ZnO composition, a blue-shift of absorption edge and emission spectra were observed. The band gap for 1:9, 1:1 and 9:1 were found to be 4.13, 3.93 and 3.11 eV, respectively. The morphology of the CdS/ZnO QDs for each mixing ratio was obtained by transmission electron microscope (TEM). The size of the QDs was found to be in the range of 5-10 nm with some agglomerated particles.

Solvothermal Synthesis of Novel 3D Peony-Like TiO2 Microstructures and its Enhanced Photocatalytic Activity

NANO ◽  
2018 ◽  
Vol 13 (05) ◽  
pp. 1850056 ◽  
Author(s):  
Yugan He ◽  
Qi Yan ◽  
Xiaoyu Chang ◽  
Meiying Zhu ◽  
Weiwei Wang ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Reaction Time ◽  
Uv Light ◽  
X Ray Diffraction ◽  
Reaction Parameters ◽  
X Ray ◽  
Uv Light Irradiation ◽  
Transmission Electron ◽  
Irradiation Power ◽  
Degussa P25

A TiO2 photocatalyst with peony-like microstructures and a large percentage of exposed {001} facets was synthesized using a facile solvethermal method. The peony-like TiO2 was obtained using HF as a capping agent, TiCl4 as the precursor and ethanol as the solvothermal agent. The parameters which influence the mophology and formation mechanism of the products including the HF concentration, the reaction time and temperature and the solvothermal solvent, were investigated. The samples were characterized using field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction and N2 adsorption and desorption analysis. As the reaction time or reaction temperature increased, the morphology TiO2 changed from hexagonally assembled microspheres to peony-like microflowers which were composed of stacks of ultrathin nanosheets. The other reaction parameters also play a crucial role in the formation of the TiO2 microstuctures. Photocatalytic experiments showed that the synthesized TiO2 outperformed Degussa P25 in the photodegradation of methelene blue under a very weak UV light irradiation (power: 8[Formula: see text]W, light intensity: 0.4[Formula: see text]mW[Formula: see text]cm[Formula: see text]).

Luminescence Properties of Sm3+/Eu3+ Co-Doped ZnO Quantum Dots

2016 ◽  
Vol 16 (4) ◽  
pp. 3597-3601
Author(s):  
Fengyi Liu ◽  
Hong Li ◽  
Yajing Hu ◽  
Na Jin ◽  
Yun Mou ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Sol Gel ◽  
Spherical Shape ◽  
Hexagonal Wurtzite Structure ◽  
Luminescence Properties ◽  
Transmission Electron ◽  
Doped Zno ◽  
Zno Quantum Dots ◽  
Zno Qds ◽  
Co Doped

In order to improve luminescence properties of semiconductor ZnO quantum dots (QDs), Sm3+/Eu3+ co-doped ZnO QDs have been controllably synthesized by sol–gel method in this paper. ZnO QDs have a spherical shape with mean diameter at about 5–6 nm, which was characterized by high-resolution transmission electron microscopy (HRTEM). ZnO QDs have hexagonal wurtzite structure with parts of Sm3+ and Eu3+ incorporated into the lattice, which was demonstrated by X-ray Diffraction (XRD). Luminescence properties at room temperature (RT) of different amount of Sm3+ and 2 mol% Eu3+ doped ZnO QDs were examined in-depth by optical spectra. In contrast to the Pr3+/Eu3+ co-doped fluorescent performance researched in our previous study, the photoluminescence (PL) spectra indicates the unique luminescence properties of Sm3+/Eu3+ co-doped ZnO QDs. In addition, fluorescence lifetimes were obtained to illustrate the luminous mechanism.

scholarly journals Synthesis, Characterization, and Photocatalytic Performance of Mesoporous α-Mn2O3 Microspheres Prepared via a Precipitation Route

2016 ◽  
Vol 2016 ◽  
pp. 1-7 ◽  
Author(s):  
Manoj Pudukudy ◽  
Zahira Yaakob
Keyword(s):  
Electron Microscopy ◽  
Uv Light ◽  
Thermal Transformation ◽  
Xrd Analysis ◽  
Structural Deformation ◽  
Blue Dye ◽  
X Ray Diffraction ◽  
Electron Microscopic ◽  
X Ray ◽  
Transmission Electron

α-Mn2O3 microspheres with high phase purity, crystallinity, and surface area were synthesized by the thermal decomposition of precipitated MnCO3 microspheres without the use of any structure directing agents and tedious reaction conditions. The prepared Mn2O3 microspheres were characterized by Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) and photoluminescence (PL) studies. The complete thermal transformation of MnCO3 to Mn2O3 was clearly shown by the FTIR and XRD analysis. The electron microscopic images clearly confirmed the microsphere-like morphology of the products with some structural deformation for the calcined Mn2O3 sample. The mesoporous texture generated from the interaggregation of subnanoparticles in the microstructures is visibly evident from the TEM and BET studies. Moreover, the Mn2O3 microstructures showed a moderate photocatalytic activity for the degradation of methylene blue dye pollutant under UV light irradiation, using air as the potential oxidizing agent.

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