Green hydrothermal synthesis and photoluminescence property of ZnO2 nanoparticles

ZnO₂ nanoparticles were synthesized via a green hydrothermal method using ZnO powder and 30% H₂O₂ aqueous solution as the starting materials, and characterized by X-ray diffraction (XRD), Raman spectra, energy dispersive X-ray (EDX) spectra, field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and room temperature photoluminescence (RTPL) spectra. It was found that suitable reaction temperature (e.g., 80-140 °C) played an important role in obtaining pure cubic phase ZnO₂ nanoparticles. The RTPL spectra disclosed that the as-synthesized ZnO₂ nanoparticles exhibit one strong emission band centered at around 400 nm and one very weak emission band at around 474 nm, which may have originated from the band edge emission and the oxygen vacancy, respectively.     

Low temperature synthesis of Fe3O4 nanoparticles and its application in lithium ion batteries

Well dispersed Fe₃O₄ nanoparticles with mean size about 160 nm are synthesized by a simple chemical method at atmosphere pressure. The products are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and Raman spectrum. Electrochemical properties of the as-synthesized Fe₃O₄ nanoparticles as anode electrodes of lithium ion batteries are studied by conventional charge/discharge tests, showing initial discharge and charge capacities of 1140 mAh g⁻¹ and 1038 mAh g⁻¹ at a current density of 0.1 mA cm⁻². The charge and discharge capacities of Fe₃O₄ electrode decrease along with the increase of cycle number, arriving at minimum values near the 70th cycle. After that, the discharge and charge capacities of Fe₃O₄ electrode begin to increase along with the increase of cycle number, arriving at 791 and 799 mAh g⁻¹ after 393 cycles. The morphology and size of the electrode after charge and discharge tests are characterized by SEM, which exhibits a large number of dispersive particles with mean size about 150 nm.     

Green synthesis of ZnO2 nanoparticles from hydrozincite and hydrogen peroxide at room temperature

A green method based on the reaction between hydrozincite (Zn₅(CO₃)₂(OH)₆) powder and hydrogen peroxide (H₂O₂, 30 wt.%) in aqueous solution at room temperature was developed for the synthesis of ZnO₂ nanoparticles. Results from X-ray diffraction, transmission electron microscopy and Raman demonstrated that the resultant products were pure cubic phase ZnO₂ nanoparticles, whose sizes were in the range of 3.1-4.2 nm. Thermogravimetric analysis indicated that between 180 and 350 °C, the as-synthesized ZnO₂ nanoparticles had a weight loss of about 16.7%, consistent with the theoretical amount (16.4%) of the O₂ released from ZnO₂ decomposition (ZnO₂ = ZnO + 1/2O₂). The present method was green, simple and cost-effective, which should be suitable for large-scale production of multifunctional ZnO₂ nanoparticles.     

Solvothermal synthesis of SrMoO4:Ln (Ln = Eu, Tb, Dy) nanoparticles and its photoluminescence properties at room temperature

Rare-earth ions (Eu³⁺, Tb³⁺, Dy³⁺) doped SrMoO₄ nanoparticles were prepared by solvothermal route using oleic acid as surfactant to control the particle shape and size. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), photoluminescence spectra (PL) and the kinetic decay times were applied to characterize the obtained samples. The XRD patterns reveal that all the doped samples are assigned to the scheelite-type tetragonal structure of SrMoO₄ phase. In addition, the as-synthesized SrMoO₄:Ln (Ln = Eu³⁺, Tb³⁺, Dy³⁺) particles are high purity well crystallized and with the average size of 30-50 nm. The possible formation process of SrMoO₄:Ln (Ln = Eu³⁺, Tb³⁺, Dy³⁺) nanoparticles have been discussed as well. Upon excitation by ultraviolet radiation, the as-synthesized SrMoO₄:Ln (Ln = Eu³⁺, Tb³⁺, Dy³⁺) nanoparticles exhibit the characteristic emission lines of corresponding Eu³⁺, Tb³⁺, Dy³⁺, respectively.     

Synthesis and spectroscopic investigations of Mn3O4 nanoparticles

Trimanganese tetraoxide (Mn₃O₄) nanoparticles have been synthesized via hydrothermal process. Nevertheless, homogeneous nanoparticles of Mn₃O₄ with platelet lozange shape were obtained. The crystallite size ranged from 40 to 70 nm. The Mn₃O₄ product was investigated by X-ray diffraction, transmission electron microscopy (MET), and impedance spectroscopy. Electrical conductivity measurements showed that the as-synthesized Mn₃O₄ nanomaterial has a conductivity value which goes from 1.8 10⁻⁷ Ω⁻¹ cm⁻¹ at 298 K, to 23 10⁻⁵ Ω⁻¹ cm⁻¹ at 493 K. The temperature dependence of the conductivity between 298 and 493 K obeys to Arrhenius law with an activation energy of 0.48 eV.     

Synthesis of AgBr/ZnO nanocomposite with visible light-driven photocatalytic activity

AgBr/ZnO nanocomposite was synthesized via chemical precipitation from pure ZnO nanowires, AgNO₃, and NaBr. Inductively coupled plasma optical emission spectroscopy, X-ray diffraction, and high resolution transmission electron microscopy results confirmed the forming of AgBr/ZnO nanocomposite. High resolution transmission electron microscopy results of the as-synthesized AgBr/ZnO nanocomposite revealed that AgBr nanoparticles were attached to the surface of ZnO nanowires. UV-vis diffuse reflectance spectra of both pure ZnO and AgBr/ZnO nanocomposite displayed a band gap edge at about 350-380 nm. However, compared with pure ZnO, an additional broad tail from approximately 400 nm to 700 nm appeared in the UV-vis diffuse reflectance spectrum of AgBr/ZnO nanocomposite. The photocatalytic studies indicated that the as-synthesized AgBr/ZnO nanocomposite was a kind of promising photocatalyst in remediation of water polluted by some chemically stable azo dyes under visible light.     

Hydrothermal synthesis, characterization, photocatalytic activity and dye-sensitized solar cell performance of mesoporous anatase TiO2 nanopowders

Mesoporous anatase TiO₂ nanopowder was synthesized by hydrothermal method at 130 °C for 12 h. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), HRTEM, and Brunauer-Emmett-Teller (BET) surface area. The as-synthesized sample with narrow pore size distribution had average pore diameter about 3-4 nm. The specific BET surface area of the as-synthesized sample was about 193 m²/g. Mesoporous anatase TiO₂ nanopowders (prepared by this study) showed higher photocatalytic activity than the nanorods TiO₂, nanofibers TiO₂ mesoporous TiO₂, and commercial TiO₂ nanoparticles (P-25, JRC-01, and JRC-03). The solar energy conversion efficiency (η) of the cell using the mesoporous anatase TiO₂ was about 6.30% with the short-circuit current density (Jsc) of 13.28 mA/cm², the open-circuit voltage (Voc) of 0.702 V and the fill factor (ff) of 0.676; while η of the cell using P-25 reached 5.82% with Jsc of 12.74 mA/cm², Voc of 0.704 V and ff of 0.649.     

Hydrothermal synthesis, structure and scintillation characterization of nanocrystalline Eu-doped Gd2O3 materials and its X-ray imaging applications

Nanocrystalline Gd₂O₃:Eu scintillators were successfully synthesized using a hydrothermal method and subsequent calcination treatment in the electrical furnace as an X-ray to visible light conversion material for an indirect X-ray image sensor. In this work, various Gd₂O₃:Eu scintillators were prepared in accordance with different synthesis conditions such as doped-Eu concentration, different calcination temperatures of 600-1400 °C and calcination time of 1-10 h. The transition of morphology from nanorods to particles was observed as the calcination temperature of Gd₂O₃:Eu scintillator increased. And the phase transformation of the sample from cubic to monoclinic structure was discovered at 1300 °C calcination temperature. In addition, scintillation properties such as luminescent spectra and light intensity under 266 nm UV illumination were measured as a function of calcination condition of as-synthesized Gd₂O₃:Eu powder. The nanocrystalline Gd₂O₃:Eu scintillator with a strong red light emission at near 611 nm wavelength under photo- and X-ray excitation will be employed for its potential X-ray image sensor applications in the future.     

A new method to prepare high-surface-area N-TiO2/activated carbon

A new method, combining impregnation and vapor-hydrolysis, was developed to prepare hybrid photocatalyst: nitrogen doped TiO₂ coated activated carbon (N-TiO₂/AC). The activated carbon (AC) was impregnated into titanium tetraethoxide/urea/methanol solution, and then the impregnated AC powder was kept in water vapor at 90 °C for 3 h for hydrolysis. Then it was calcinated to fabricate N-TiO₂/AC. Transmission electron microscopy (TEM) results showed that the nitrogen doped TiO₂ (N-TiO₂) in the as-synthesized hybrid was anatase TiO₂ powder with 10-20 nm in grain size, and the bandgap was about 3.08 eV. Moreover, the hybrid photocatalyst (8 wt.% N-TiO₂) had high specific surface area that was up to 1321 m²/g. The hybrid photocatalyst is expected to have high photocatalytic performance with visible irradiation.     

Microwave direct synthesis of MgB2 superconductor

Intermetallic compound superconductor MgB₂ was synthesized from spherical magnesium powder and lower purity amorphous boron powder by microwave direct heating. Powder X-ray diffraction (XRD) analysis indicates that the phases of the synthesis sample are MgB₂ (major phase) and a small amount of MgO. Scanning electron microscope (SEM) observation shows that the MgB₂ grain size is homogeneous and the particle size is about several hundreds of nanometers. The onset superconducting transition temperature of the MgB₂ sample measured by the temperature dependence of magnetization measurement is about 37.6 K. The critical current density J_c calculated according to the Bean model are about 2.0 × 10⁵ A/cm² at 20 K in self-field and 1.0 × 10⁵ A/cm² at 20 K in 1 T applied field.     

Green hydrothermal synthesis and optical absorption properties of ZnO2 nanocrystals and ZnO nanorods

A green hydrothermal method was proposed for the controllable synthesis of ZnO₂ nanocrystals and ZnO nanorods, using the common and cost-effective 2ZnCO₃·3Zn(OH)₂ powder and 30 mass% H₂O₂ aqueous solution as the raw materials. The characterization results from X-ray diffraction, high resolution transmission electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy indicated that the products synthesized at 100-120 °C for 6 h or at 170 °C for 0 h were cubic phase ZnO₂ nanocrystals; while those synthesized at 170 °C for 3-6 h were hexagonal phase ZnO nanorods. The UV-vis absorption spectra showed that the as-synthesized ZnO₂ nanocrystals and ZnO nanorods had optical band gaps of about 4.1 and 3.3 eV, respectively.     

Solvothermal preparation and characterization of sheet-like CuInSe2 with hierarchically mesoporous structures

By using a solvothermal reaction in mixed solvent of ethylenediamine and ethylene glycol, nanoparticle-assembled sheet-like CuInSe₂ with hierarchically mesoporous structures were successfully fabricated with the absence of any template or structure-directing agent. The as-synthesized products were characterized by XRD, EDX, FESEM, TEM, HRTEM, BET nitrogen adsorption and NIR absorption spectrum. The possible formation mechanism was simply discussed. The size of mesopores is hierarchically distributed in the range of 2-30 nm and the specific surface area was estimated to be 10.15 m²/g. The value of band gap (E_g) was calculated to be 1.00 eV based on its NIR absorption spectrum.     

Interphase synthesis of Fe3O4/CdS core-shell nanoparticles

CdS and Fe₃O₄/CdS core-shell nanoparticles were synthesized by a simple interphase method. The obtained nanoparticles were characterized by TEM, XRD and spectroscopy techniques (fluorescence and UV-vis absorption). The effects of reagent concentration on the properties of obtained nanoparticles were investigated. It was shown that the UV-vis spectra of the Fe₃O₄/CdS colloidal toluene solutions have the sharp edge at 311 nm and the long tail. The broad emission bands in the photoluminescence spectra of the Fe₃O₄/CdS organosols observed at 506, 560 and 568 nm with the increasing of cadmium oleate concentration. The thickness of CdS shell was ranged from 0.2 to 1.0 nm while the average size of the magnetite core is about 9.9 nm.     

Arsenic (III,V) removal from aqueous solution by ultrafine α-Fe2O3 nanoparticles synthesized from solvent thermal method

Ultrafine iron oxide (α-Fe₂O₃) nanoparticles were synthesized by a solvent thermal process and used to remove arsenic ions from both lab-prepared and natural water samples. The α-Fe₂O₃ nanoparticles assumed a near-sphere shape with an average size of about 5 nm. They aggregated into a highly porous structure with a high specific surface area of ∼162 m²/g, while their surface was covered by high-affinity hydroxyl groups. The arsenic adsorption experiment results demonstrated that they were effective, especially at low equilibrium arsenic concentrations, in removing both As(III) and As(V) from lab-prepared and natural water samples. Near the neutral pH, the adsorption capacities of the α-Fe₂O₃ nanoparticles on As(III) and As(V) from lab-prepared samples were found to be no less than 95 mg/g and 47 mg/g, respectively. In the presence of most competing ions, these α-Fe₂O₃ nanoparticles maintained their arsenic adsorption capacity even at very high competing anion concentrations. Without the pre-oxidation and/or the pH adjustment, these α-Fe₂O₃ nanoparticles effectively removed both As(III) and As(V) from a contaminated natural lake water sample to meet the USEPA drinking water standard for arsenic.     

Synthesis of micro-sized Sb2O3 hierarchical structures by carbothermal reduction method

Micro-sized Sb₂O₃ hierarchical structures were prepared by carbothermal reduction method, using antimony doped tin oxide (ATO) nanoparticles and graphite powder as source materials. The products were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and field-emission scanning electron microscopy (FE-SEM). Furthermore, the possible growth mechanism of the as-synthesized samples was discussed. The room-temperature photoluminescence (PL) measurement exhibited one relatively strong violet emission peak at about 420 nm under the 325 nm excitation wavelength and another violet emission peak, about three times stronger in intensity than the former, at about 435 nm under the 365 nm excitation wavelength. In addition, the optimal excitation wavelength of 363 nm was obtained and the luminescence causes were speculated.     

Synthesis of high efficient nanosized Y(V,P)O4:Eu red phosphors by a new technique

A new synthesis technique (liquid-phase precursor method) has been employed to synthesize nanosized Y(V,P)O₄:Eu³⁺ red phosphor particles of size 10-35 nm. X-ray diffraction analysis confirmed the synthesis of single phase Y(V,P)O₄:Eu³⁺ nanoparticles with tetragonal structure. The surface treatment with the KOH ionic solution at room temperature enhanced the grain growth (40-70 nm) of the nanoparticles. The possible grain growth mechanism is explained on the basis of formation of more OH⁻ groups in the solid solution after KOH introduction. The photoluminescence spectra obtained from the nanophosphors showed strong red luminescence due to ⁵D₀ → ⁷F_2,4 forced electric dipole transition. The luminescence intensity of the KOH-treated nanophosphors is comparable (about 70%) with the commercial sample.     

Low temperature facile synthesis of anatase TiO2 coated multiwalled carbon nanotube nanocomposites

Anatase TiO₂ coated multiwalled carbon nanotube (MWNT) nanocomposites were prepared by combining the sol-gel method with a self assembly technique at a low temperature. XRD, TEM, FTIR and XPS spectra were applied to characterize the crystal phase, microstructure, and other physicochemical properties of the sample. The results showed that MWNTs were covered with a 12-20 nm thickness layer of anatase TiO₂ or surrounded by a 30 -290 nm thickness coating of anatase TiO₂. The layer or coating is constructed of TiO₂ nanoparticles about 5.8 nm. Furthermore, as-prepared composite was rich in surface hydroxyl groups.     

Hydrothermal synthesis and magnetic property of Cu3(OH)2V2O7·nH2O

Copper vanadium oxide hydroxide hydrate (Cu₃(OH)₂V₂O₇·nH₂O) nanoparticles with mean size of about 100 nm were successfully synthesized by a simple hydrothermal method. The structure and morphology of the as-synthesized products were characterized by X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Raman spectra, and Fourier transform infrared spectra (FTIR). The composition and purity of the as-synthesized Cu₃(OH)₂V₂O₇·nH₂O nanoparticles were characterized by Energy disperse spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The magnetic property of the as-synthesized Cu₃(OH)₂V₂O₇·nH₂O nanoparticles was characterized by vibrant sample magnetometer. Magnetic hysteresis curve indicate that the as-synthesized nanoparticles are of weak ferromagnetic property at room temperature.     

Preparation and upconversion property of TeO2:Er/Yb nanoparticles

Different crystal structure of TeO₂ nanoparticles were used as the host materials to prepare the Er³⁺/Yb³⁺ ions co-doped upconversion luminescent materials. The TeO₂ nanoparticles mainly kept the original morphology and phase after having been co-doped the Er³⁺/Yb³⁺ ions. All the as-prepared TeO₂:Er³⁺/Yb³⁺ nanoparticles showed the green emissions (525 nm, 545 nm) and red emission (667 nm) under 980 nm excitation. The green emissions at 525 nm, 545 nm and red emission at 667 nm were attributed to the ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of the Er³⁺ ions, respectively. For the α-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles, three-photon process involved in the green (²H_11/2 → ⁴I_15/2) emission, while two-photon process involved in the green (⁴S_3/2→⁴I_15/2) and red (⁴F_9/2 → ⁴I_15/2) emissions. For the β-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles, two-photon process involved in the green (²H_11/2 → ⁴I_15/2), green (⁴S_3/2 → ⁴I_15/2) and red (⁴F_9/2 → ⁴I_15/2) emissions. It suggested that the crystal structure of TeO₂ nanoparticles had an effect on transition processes of the Er³⁺/Yb³⁺ ions. The emission intensities of the α-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles and β-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles were much stronger than those of the (α + β)-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles.     

The microwave-assisted synthesis and characterization of Zn1 − xCoxO nanopowders

In this paper, we present a simple microwave-assisted synthesis of Zn_1 − xCo_xO nanopowders. With the advantages of the microwave-assisted method, we have successfully synthesized good crystalline quality and good surface morphology Zn_1 − xCo_xO nanopowders. The nanopowders are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-VIS absorption, and micro-Raman spectroscopy. We found, in the synthesis process, the surfactant Triethanolamine (TEA) plays an important role on the morphology of Zn_1 − xCo_xO nanoparticles. The XRD study shows that for Co doping up to 5%, Co²⁺ ions are successfully incorporated into the ZnO host matrix. The absorption spectra of Zn_1 − xCo_xO (x = 1-5%) nanopowders show several peaks at 660, 611 and 565 nm, indicating the presence of Co²⁺ ions in the tetrahedral sites. The Raman study shows that the linewidth of E₂^low mode increases with Co concentration, which further indicates the incorporation of Co²⁺ ions into the ZnO host matrix.