ZnWO4 scintillators for cryogenic dark matter experiments

The scintillation properties of a zinc tungstate crystal, shaped as a hexagonal prism (height 40 mm, diagonal 40 mm) were determined. An energy resolution of 10.7% for the 662 keV γ-line of ¹³⁷Cs was measured with the scintillator placed in a light collection setup similar to that used by the CRESST dark matter search. The light output and decay kinetics of ZnWO₄ were examined over the temperature range 7–300 K and confirmed to be competitive with those of CaWO₄. The radioactive contaminations of the ZnWO₄ scintillator measured in the Solotvina Underground Laboratory do not exceed 0.1–10 mBq/kg (depending on radionuclide). Our study highlights the excellent feasibility of this ZnWO₄ scintillator for a cryogenic dark matter experiment.     

Mild hydrothermal solid-phase synthesis of YVO4 nanocrystals

The tetragonal YVO₄ nanocrystals are facilely prepared via a hydrothermal solid-phase synthesis method directly utilizing bulk phase materials of V₂O₅ and Y₂O₃ as precursor. Whether additives (acid and EDTA) exist or not, the reaction can be performed in the mild temperature range from 130 to 200 °C. The products are characterized with XRD, FTIR, TEM and PL. The effect of acid and amounts of EDTA on the morphology of the product is investigated. The YVO₄ nanoparticles exhibit novel photoluminescence emission bands at 330 and 606 nm under 254 nm excitation. A growth mechanism of yttrium orthovanadate is proposed.     

Sonochemical fabrication, characterization and photocatalytic properties of Ag/ZnWO4 nanorod catalyst

A ZnWO₄ nanocrystal catalyst with rod-like structure was first synthesized by powerful ultrasonic irradiation method at room temperature. Then, Ag was introduced to ZnWO₄ nanorods by a photodeposited method. The as-synthesized Ag/ZnWO₄ catalysts have been investigated by photocatalytic reaction tests and some physicochemical characterizations like XRD, BET, IR, TEM, EDX, XPS, PL, and UV–vis DRS. The results show that the prepared samples have good crystallinity and Ag addition can improve the photocatalytic performance of ZnWO₄ in degradation of rhodamine-B (RhB) under UV light irradiation. The deposition of 1 wt% Ag over ZnWO₄ leads to about a one-time increase in the photocatalytic performance with the reference of ZnWO₄. The high performance of Ag/ZnWO₄ could be attributed to the fact that the high dispersed Ag particles could act as electron traps promoting the electron–hole separation then enhancing the photocatalytic reaction.     

Fabrication of TiO2 nanostructured films by spray deposition with high photocatalytic activity of methylene blue

TiO₂ films were successfully deposited onto hot quartz substrates by airbrush spraying using an aqueous dispersion. The films consisting of cubic or cauliflower-shaped structures expressed higher photodegradation efficiencies of methylene blue than those with prism-, flower- or fan-blade-shaped morphology due to the difference in the optical band gap energy. The photodegradation obeyed the pseudo-first-order Langmuir-Hinshelwood kinetic model with apparent rate constants ranging from 3.95 × 10^− 3 to 19.38 × 10^− 3 min^− 1 based on the film surface morphology.     

Molten salt synthesis of single-crystal Co3O4 nanorods

The synthesis of the single-crystal Co₃O₄ nanorods by molten salt approach was reported for the first time. The products were characterized by Transmission electron microscopy (TEM), X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM) and Selected-area electron diffraction (SAED). TEM results indicate that these nanorods have diameters of about 150 nm and lengths of about 2 μm. According to the analysis of the SAED and HRTEM results, we drew the conclusion that these nanorods grew along an unusual [− 1,− 1,15] direction by Ostwald ripening mechanism.     

Hydrothermal synthesis and characterization of CePO4/C core-shell nanorods

The CePO₄/C nanocomposite with core-shell nanostructure has been successfully synthesized using glucose and CePO₄ by a facile and simple hydrothermal method at 160 °C for 24 h. The new material consists of a monoclinic CePO₄ core and an amorphous-C shell. The TEM micrograph indicated that the CePO₄/C nanocomposite was core-shell nanorods. The effects of glucose concentration on the C shells and luminescent intensity of CePO₄/C nanocomposite were investigated. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). This method is simple, low-cost and does not need any surfactant.     

Characterization of nano-crystalline LiNiVO4 synthesized by hydrothermal process

LiOH·H₂O, Ni(CH₃COO)₂·4H₂O and NH₄VO₃ were used to synthesize nano-crystalline LiNiVO₄ by hydrothermal process in deionized water at 150 °C for 2 h and subsequent calcination at 300-600 °C for 6 h. By using an X-ray diffractometer (XRD), a transmission electron microscope (TEM) and a selected area electron diffraction (SAED) method, nano-crystalline LiNiVO₄ with inverse spinel structure was detected. The stretching vibration of VO₄ tetrahedrons analyzed by a Fourier transform infrared spectrometer (FTIR) was split into three bands at 661, 746 and 835 cm^− 1, and that analyzed by a Raman spectrometer was detected at 823.9 and 787.7 cm^− 1. The thermogravimetric and differential thermal analyses (TGA and DTA) show two discrete weight losses at 25-117 °C and 117-600 °C and four endothermic peaks at 84, 145, 202 and 372 °C, corresponding to the evaporation of water and the decomposition of inorganic and organic compounds.     

Surfactant/co-polymer template hydrothermal synthesis of thermally stable, mesoporous TiO2 from TiOSO4

Industrial TiOSO₄ solution was used as inorganic precursor to prepare mesoporous titania via composite template route, using cetyl-trimethylammonium bromide (CTAB) and tri-block copolymer EO₂₀PO₇₀EO₂₀ (P-123) as structure-directing agents (SDA) under high acidic conditions. Mesoporous TiO₂ with high thermal stability was obtained via controlling the hydrolysis and condensation rate of industrial TiOSO₄ solution by adjusting the pH value and post hydrothermal treating. The as-prepared materials were characterized by XRD, nitrogen adsorption-desorption, SEM and HRTEM. The powder calcined at 723 K for 2 h showed higher thermal stability, with BET specific surface area of 218.7 m²/g and an average pore diameter of 3.63 nm.     

Large-scale hydrothermal synthesis of WO3 nanowires in the presence of K2SO4

WO₃ nanowires were fabricated by a hydrothermal method in the presence of K₂SO₄. The nanowires exhibit a well crystallized one-dimensional structure with 10 nm in diameter and several microns in length. Effects of other alkali salts (KNO₃, NaNO₃ and Na₂SO₄) on the morphologies of WO₃ nanocrystals were also investigated. The important role of K₂SO₄ salt in the WO₃ nanowires synthesis has been demonstrated.     

Ligand-assisted hydrothermal synthesis of ZnWO4 rods and their photocatalytic activities

ZnWO₄ rods were prepared using a ligand-assisted hydrothermal method with ZnCl₂ and Na₂WO₄ in the presence of various amines as ligands for zinc ions. The choice of ligand was found to play an important role in the formation of ZnWO₄ rods. The aspect ratio of the ZnWO₄ rods increased with increasing ligand strength. XRD and HRTEM confirmed that the ZnWO₄ rods grow along the [1 0 0] direction. The photochemical activities of the ZnWO₄ rods for the decomposition of Rhodamine 6G were examined. The photocatalytic activity was found to depend on the aspect ratio of the ZnWO₄ rods.     

Synthesis,characterization and photocatalytic activity of ZnO-SnO2 nanocomposites

Nanocomposites of coupled ZnO-SnO₂ photocatalysts were synthesized by the coprecipitation method and were characterized by X-ray diffraction, UV–vis diffuse reflectance spectroscopy, surface area analyzer and scanning electron microscopy. Their photocatalytic activity was investigated under UV, visible and solar light and evaluated using methylene blue (MB) as a model pollutant. The performance of the coupled ZnO-SnO₂ photocatalysts was found to be related to the Zn/Sn molar ratio and to the calcination conditions. The photocatalyst with a Zn/Sn molar ratio of 1:0.05 calcined at 600 °C for 2 h showed the maximum degradation rate of MB under different lights used. Its photocatalytic activity was found to be about two times that of ZnO and about 10 times that of SnO₂ which can be explained by the heterojunction effect. Charge separation mechanism has been studied.     

Template-free synthesis of ZnWO4 powders via hydrothermal process in a wide pH range

ZnWO₄ powders with different morphologies were fabricated through a template-free hydrothermal method at 180 °C for 8 h in a wide pH range. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-visible and luminescence spectrophotometers were applied to study the effects of pH values on crystallinity, morphology, optical and luminescence properties. The XRD results showed that the WO₃ + ZnWO₄, ZnWO₄, and ZnO phases could form after hydrothermal processing at 180 °C for 8 h with the pH values of 1, 3-11, and 13, respectively. The SEM and TEM observation revealed that the morphological transformation of ZnWO₄ powders occurred with an increase in pH values as follows: star anise-, peony-, and desert rose-like microstructures and soya bean- and rod-like nanostructures. The highest luminescence intensity was found to be in sample consisting of star anise-like crystallites among all the samples due to the presence of larger particles with high crystallinity resulted from the favorable pH under the current hydrothermal conditions.     

Green hydrothermal synthesis and characterization of CdO2 nanoparticles

A green hydrothermal method has been developed for the synthesis of CdO₂ nanoparticles from Cd(OH)₂ powder and 6 vol.% H₂O₂ aqueous solution at 80-150 °C. The characterization results from X-ray diffraction, transmission electron microscopy, and thermal gravimetric and differential scanning calorimetry analysis disclosed that the resultant products were pure cubic phase CdO₂ nanoparticles with the sizes in the range of about 11-13 nm. The UV-vis absorption spectra revealed that the as-synthesized CdO₂ nanoparticles had similar optical band gaps of about 3.85 eV. The Raman spectra of the as-synthesized CdO₂ nanoparticles displayed two obvious peaks at about 348 and 830/833 cm^-1, a characteristic of pyrite-type IIB-peroxides.     

Nanosized BiVO4 with high visible-light-induced photocatalytic activity: Ultrasonic-assisted synthesis and protective effect of surfactant

Nanosized BiVO₄ with high visible-light-induced photocatalytic activity was successfully synthesized via ultrasonic-assisted method with polyethylene glycol (PEG). The BiVO₄ sample prepared under ultrasonic irradiation with 1 g PEG for 30 min was consisted of small nanoparticles with the size of ca. 60 nm. The effects of ultrasonic irradiation and surfactant were investigated. The nanosized BiVO₄ exhibited excellent visible-light-driven photocatalytic efficiency for degrading organic dye, which was increased to nearly 12 times than that of the products prepared by traditional solid-state reaction. Besides decoloring, the reduction of chemical oxygen demand (COD) concentration was also observed in the degradation of organic dye, further demonstrating the photocatalytic performance of BiVO₄. After five recycles, the catalyst did not exhibit any significant loss of photocatalytic activity, confirming the photocatalyst is essentially stable. Close investigation revealed that the crystal size, BET surface area, and appropriate band gap of the as-prepared BiVO₄ could improve the photocatalytic activities.     

Template-free synthesis of SnO2 nanostructural hollow spheres covered by nanorods

In the present work, SnO₂ nanostructural hollow spheres have been successfully synthesized in the absence of template by a simple synthetic route, and their surfaces were covered by nanorods. The synthesized nanostructural hollow spheres covered by nanorods were further characterized by XRD, SEM and TEM measurements. The diameter of SnO₂ hollow spheres and the thickness of shells are found to be ca. 150-200 and 20-30 nm, respectively. The size of the nanorod is found to be ca. 5 nm, and the length up to tens of nanometers. Based on a series of experimental results, an oxidizing-aggregating-Ostwald ripening model has been proposed for the formation of SnO₂ nanostructural hollow spheres.     

Hydrothermal synthesis and characterization of MoS2 nanorods

MoS₂ nanorods were successfully synthesized via hydrothermal method by adding sillicontungstic acid as an additive. The products were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectrum (XPS) and field-emission scanning electron microscopy (FESEM). XRD pattern result indicated that the as-prepared sample can be indexed to a mixture of hexagonal and rhombohedral phase MoS₂. XPS showed that the nanorods were only composed of Mo and S with atomic ratio of 1:2. FESEM images revealed that the MoS₂ rods had uniform sizes with mean diameters of about 20-50 nm and lengths of 400-500 nm. It was found that the addition of sillicontungstic acid played a crucial role in the formation of the rod-like MoS₂ in our experiment. The possible formation mechanism of MoS₂ nanorods is also discussed.     

Fabrication and photocatalytic activity of YMn2O5 nanoparticles

In this work, a polyacrylamide gel route is introduced to synthesize YMn₂O₅ nanoparticles. It is demonstrated that high-quality YMn₂O₅ nanoparticles with a uniform size and spherical shape can be prepared using different chelating agents. However, the average particle size of the products is found to have a dependence on the choice of the chelating agent. The sample prepared using citric acid as the chelating agent has an average particle size of ~ 45 nm, while the sample prepared by using the chelating agent EDTA has a particle size centered around 70 nm. The optical energy bandgap of the citric acid- and EDTA-resulted samples is obtained, from optical absorption measurements, to be 1.21 and 1.17 eV, respectively. The photocatalytic experiments reveal that the as-prepared YMn₂O₅ nanoparticles exhibit an interesting photocatalytic activity for oxidative decomposition of methyl red under ultraviolet and visible-light irradiation.     

Controlled hydrothermal synthesis of VO2(B) nanobelts

Large-scale VO₂(B) nanobelts have been synthesized by hydrothermal strategy via one-step method using V₂O₅ as vanadium source and C₆H₅-(CH₂)_n-NH₂ with n = 2 and 4 (2-phenylethylamine and 4-phenylbutylamine) as structure-directing templates. The composition and morphology of the nanobelts were established by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The as-obtained VO₂(B) nanobelts have a length of 3-10 μm, a wideness of 100-375 nm and a thickness of 30-66 nm.     

Highly dispersible and uniform size Cu2ZnSnS4 nanoparticles for photocatalytic application

Highly dispersible, uniform size (～7 nm) single-phase Cu₂ZnSnS₄ nanoparticles have been synthesized by hydrothermal method using non-toxic surfactant (oleic acid). High resolution transmission electron microscopy image indicates good crystallinity of the Cu₂ZnSnS₄ nanoparticles with the growth along (1 1 2) plane. X-ray photoelectron spectroscopy analyses suggested that the formation of with Cu, Zn, and Sn in +1, +2 and +4 oxidation states. The optical absorption spectrum of Cu₂ZnSnS₄ nanoparticles exhibits an absorption in the visible region and its optical band gap was found to be ～1.72 eV, which could be much more appropriate for photocatalytic application under visible light irradiation. These Cu₂ZnSnS₄ nanoparticles have been shown high photocatalytic degradation activity of methylene blue (MB) dye in the presence of visible light irradiation. The rate constant (k) value of Cu₂ZnSnS₄ nanoparticles is found to be 0.0144 min^?1. We have discussed the mechanism of dye degradation process that drives the photocatalytic degradation process. The reusability of the Cu₂ZnSnS₄ nanoparticles for the dye degradation is also demonstrated.     

Synthesis and characterization of Co3O4 hollow spheres

Co₃O₄ hollow spheres were hydrothermally prepared at 130 °C for 16 h in the presence of Poly-vinylpyrrolidone (PVP). The as-prepared products were characterized by powder X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), infrared spectrum (IR), X-ray photoelectron spectrum (XPS), and optical absorption spectrum. PVP surfactant plays important roles in the formation of Co₃O₄ hollow spheres. These Co₃O₄ hollow spheres have average diameters of ca. 350 nm, and the wall thickness around the shell is about 42 nm. The possible formation mechanism of hollow Co₃O₄ spherical structures has simply been proposed.