Search results for "PRECIPITATION"
showing 10 items of 826 documents
F-centre luminescence in nanocrystalline CeO2
2013
Nanocrystalline CeO2 powders were synthesized by two cost-effective methods: the self-propagating room temperature (SPRT) method and the precipitation method. Differently prepared samples exhibited different temperature-dependent photoluminescence (PL) in the ultraviolet and visible regions. The PL signals originated from different kinds of oxygen-deficient defect centres with or without trapped electrons (F0, F+ or F++ centres). The temperature-dependent PL spectra were measured using different excitation lines, below (457, 488 and 514?nm) or comparable (325?nm) to the ceria optical band gap energy, in order to investigate the positions of intragap localized defect states. Evidence for the…
Particle size effects on the structure and emission of Eu3+: LaPO4 and EuPO4 phosphors
2018
The authors acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Projects nos. 45020 and 172056). T.G acknowledges to the ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 (1.1.1.2/16/I/001).
Effect of Ce3+ concentration on persistent luminescence of YAGG:Ce3+,Cr3+,Nd3+ nanophosphors obtained by the co-precipitation method
2020
Abstract Synthesis of Y3Al2Ga3O12 garnet (YAGG) nanophosphors co-doped with Ce3+, Cr3+, and Nd3+ ions by co-precipitation is reported. The effect of Ce3+ concentration on the structure of garnet and on optical properties including persistent luminescence was investigated. The X-ray diffraction measurements showed that single garnet phase was obtained. The contraction of the crystallites size was observed with increasing the cerium concentration. The combined emission of three used co-dopants together allows to extend persistent luminescence spectral range. The photoluminescence, excitation and persistent luminescence spectra were collected and the optimal Ce3+ concentration for the highest …
Surfactant-Free Emulsion Polymerization of Various Methacrylates: Towards Monodisperse Colloids for Polymer Opals
2004
A systematic investigation of the surfactant-free emulsion polymerization (SFEP) on three different methacrylates (MMA, tert-butyl methacrylate and 2,2,2-trifluoro ethyl methacrylate) is described to obtain monodisperse colloids for the preparation of artificial polymer opals. The experimental results are in agreement with a model, in which seed particles are formed very early during the polymerization process. The particles are formed very early during the polymerization process. The particles grow afterwards into the colloids until all monomer is consumed. This gives rise to a linear relationship between the volume of the colloids and the ratio of monomer to water in the reaction batch. T…
PAA-PAMPS Copolymers as an Efficient Tool to Control CaCO3 Scale Formation
2013
Scale formation, the deposition of certain minerals such as CaCO3, MgCO3, and CaSO4 center dot 2H(2)O in industrial facilities and household devices, leads to reduced efficiency or severe damage. Therefore, incrustation is a major problem in everyday life. In recent years, double hydrophilic block copolymers (DHBCs) have been the focus of interest in academia with regard to their antiscaling potential. In this work, we synthesized well-defined blocklike PAA-PAMPS copolymers consisting of acrylic acid (AA) and 2-acrylamido-2-methyl-propane sulfonate (AMPS) units in a one-step reaction by RAFT polymerization. The derived copolymers had dispersities of 1.3 and below. The copolymers have then b…
Influence of Temperature on Calcium Hydroxyapatite Nanopowders
2012
The aim of this work is to investigate the effects of thermal treatment, in the range of temperature between 80°C - 900°C, on crystallinity, morphology and particles size of calcium hydroxylapatite nanopowders (HAp). A complete study was carried out applying 31P Magic Angle Spinning NMR, X-ray diffraction, nitrogen porosimetry and Transmis- sion Electron Microscopy techniques. HAp specimens were prepared by chemical precipitation in an aqueous solution of calcium nitrate and ammonium hydrogen phosphate. The thermal treatment performed, showed the formation of crystals whose appearance has three main morphologies and different particles size. HAp treated up to 500°C showed a set of needle-li…
Preparation of Catalysts and Photocatalysts Used for Similar Processes
2019
Abstract This chapter reports the main techniques used to synthesize powders and films of heterogeneous catalysts and photocatalysts, often used for similar processes. Traditional preparation processes of bulky (photo)catalysts including precipitation, sol–gel technique, hydrothermal or solvothermal method, solid-state reactions, and flame syntheses were briefly described. The sonochemical method and microwave irradiation technique were also considered. The syntheses of supported catalysts by different techniques, including deposition–precipitation, impregnation, and wet coating technologies were also described. Moreover, a survey is reported of methods to deposit thin films of catalysts on…
Graphene as a carbon source effects the nanometallurgy of nickel in Ni,Mn layered double hydroxide-graphene oxide composites.
2012
[EN] Thermal treatment of the hybrid material formed by the spontaneous precipitation of graphene oxide and Ni,Mn layered double hydroxide leads to the segregation of nickel metal nanoparticles (Ni NPs) and the decomposition of graphene to CO2. Increasing the temperature increases the Ni NP size and results in the complete disappearance of graphene.
Calcium Sulfate Nanoparticles with Unusual Dispersibility in Organic Solvents for Transparent Film Processing
2018
Calcium sulfate is one of the most important construction materials. Today it is employed as high-performance compound in medical applications and cement mixtures. We report a synthesis for calcium sulfate nanoparticles with outstanding dispersibility properties in organic solvents without further functionalization. The nanoparticles (amorphous with small γ-anhydrite crystallites, 5–50 nm particle size) form long-term stable dispersions in acetone without any sign of precipitation. 1H NMR spectroscopic techniques and Fourier-transform infrared spectroscopy (FTIR) reveal absorbed 2-propanol on the particle surfaces that induce the unusual dispersibility. Adding water to the nanoparticle disp…
Chromium oxide nanoparticles with controlled size prepared from hydrothermal chromium oxyhydroxide precursors
2017
Abstract This work reports the preparation of morphologically well-defined chromium oxide nanoparticles with controlled sizes of 20–30 nm. The synthetic procedure encompass two stages, the first one refers to the preparation of chromium oxyhydroxide nanoparticles by a hydrothermal approach of previously precipitated xerogels, followed by a thermal transformation of CrOOH nanoparticles to Cr2O3. The series of chromium oxyhydroxide particles sized over the range 15–50 nm were prepared through the control of the pH of precipitation of the xerogels and the water/xerogel ratio of the hydrothermal aging. Results showed the formation of non-aggregated oxyhydroxide nanoparticles with two different …