Measurements of size distribution of titanium dioxide fine particles in a highly concentrated non-aqueous suspension by using particle self-assembly under an electric field

This paper describes the measurement of size distribution of TiO₂ fine particles in a highly concentrated non-aqueous suspension by using self-assembly of particles under an electric field. Interactive force apparatus (IFA) was used to conduct the measurement. IFA first assembled pearl chains of particles between two electrodes, and then applied the compressive force to change the pearl chain structure by shortening the distance between electrodes. The repulsive force generated when the chain curved while the attractive force created when the chain was broken. The cycle of repulsive and attractive forces corresponds to the size of particles. The results obtained with IFA were compared with results obtained from size measurement by analyzing SEM photographs. IFA indicated the comparable results with the one obtained using SEM. The particle size distribution measured by IFA decreased as a result of increasing the supply voltages. Changes in correlation between size distribution measured by SEM and IFA at different supply voltages were observed in different size ranges. At smaller than 300 nm, result at 0.24 V fit well with the SEM result while at >600 nm gives better agreement with the results at 0.48 V. The difference is mainly due to the increase in number of particles in fine size fraction with increasing supply voltages. Decrease in size indicated that the breakage of aggregate particles and/or disintegration of doublet particles occurred due to the electrical fragmentation. The fragmentation was explained by monitoring the mean diameters and their deviation obtained from IFA measurements at different supply voltages.     

Photoluminescent properties of nanostructured Y2O3:Eu3+ powders obtained through aerosol synthesis

Red emitting Y₂O₃:Eu³⁺ (5 and 10 at.%) submicronic particles were synthesized through ultrasonic spray pyrolysis method from the pure nitrate solutions at 900 °C. The employed synthesis conditions (gradual increase of temperature within triple zone reactor and extended residence time) assured formation of spherical, dense, non-agglomerated particles that are nanostructured (crystallite size ∼20 nm). The as-prepared powders were additionally thermally treated at temperatures up to 1200 °C. A bcc Ia-3 cubic phase presence and exceptional powder morphological features were maintained with heating and are followed with particle structural changes (crystallite growth up to 130 nm). Emission spectra were studied after excitation with 393 nm wavelength and together with the decay lifetimes for Eu³⁺ ion ⁵D₀ and ⁵D₁ levels revealed the effect of powder nanocrystalline nature on its luminescent properties. The emission spectra showed typical Eu^{3+ 5}D₀ → ⁷F_i (i = 0, 1, 2, 3, 4) transitions with dominant red emission at 611 nm, while the lifetime measurements revealed the quenching effect with the rise of dopant concentration and its more consistent distribution into host lattice due to the thermal treatment.     

Synthesis of MSnO3 (M = Ba,Sr) nanoparticles by reverse micelle method and particle size distribution analysis by whole powder pattern modeling

Light-to-electricity conversion efficiency in dye-sensitized solar cells critically depends not only on the dye molecule, semiconducting material and redox shuttle selection but also on the particle size and particle size distribution of the semiconducting photoanode. In this study, nanocrystalline BaSnO₃ and SrSnO₃ particles have been synthesized using the microemulsion method. Particle size distribution was studied by whole powder pattern modeling which confirmed narrow particle size distribution with an average size of 18.4 ± 8.3 nm for SrSnO₃ and 15.8 ± 4.2 nm for BaSnO₃. These values are in close agreement with results of transmission electron microscopy. The prepared materials have optimal microstructure for successive investigation in dye-sensitized solar cells.     

Three-dimensionally ordered macroporous Ti1−xTaxO2+x/2 (x = 0.025, 0.05, and 0.075) nanoparticles: Preparation and enhanced photocatalytic activity

Anatase phase, three-dimensionally ordered macroporous (3 DOM) Ti_1−xTa_xO_{2 + x / 2} (x = 0.025, 0.05, and 0.075) nanoparticles with macropore diameter 290 to 310 nm, wall thickness 50 to 80 nm, and particle size 10 to 12 nm were prepared by combination of the sol–gel chemistry and polystyrene (PS) templating procedure. The products exhibited relatively narrower band gaps and larger BET surface areas than those of the starting solitary 3 DOM metal oxides, and their photocatalytic activities for the degradation of an aqueous 4-nitrophenol remarkably enhanced compared with 3 DOM anatase TiO₂, Ta₂O₅, and Degussa P-25.     

Structural and magnetic properties of pristine and Fe-doped NiO nanoparticles synthesized by the co-precipitation method

Ni_1?xFe_xO (x = 0 and 0.03) nanoparticles are synthesized by a chemical route. XRD and TEM measurements confirm phase purity and crystallinity of the nanoparticles. Fe substitution in NiO reduces considerably the average particle size of the nanoparticles. The pristine NiO sample with size 14 nm and Fe-substituted sample having size 7 nm show room temperature ferromagnetism. The pristine NiO having 31 nm size and Fe-substituted sample with size 25 nm are found to be antiferromagnetic. The M–H and M–T behavior of the pristine and Fe-doped samples are explained with a core–shell model with an antiferromagnetic core and a ferromagnetic shell. The disordered spins at the shell give rise to a spin-glass like frozen state below 10 K. The obtained room temperature ferromagnetism in the pristine and Fe-doped NiO has been attributed to particle size effect.     

A Novel near white light emitting nanocrystalline Zn2P2O7:Sm3+ derived using citrate precursor route: Photoluminescence spectroscopy

Nanocrystalline Zn₂P₂O₇:Sm³⁺ was synthesized using citrate precursor route. Rietveld refined XRD shown the formation of pure phase at 900 °C. Based on scanning electron microscopy, size distribution of the pyrophosphate particle was found to be in the range of 50–100 nm. Upon near UV light excitation (403 nm), Zn₂P₂O₇:Sm³⁺exhibits host emission at 450 nm along with characteristic emission lines of Sm³⁺. Based on PL decay measurement, it was inferred that two different types of Sm³⁺ ions were present in the zinc pyrophosphate. The first type was a short lived species (∼τ = 100 μs) present at less symmetric ‘5-coordinated Zn’ sites, while the second was a long lived species (∼τ = 1.9 ms) present at symmetric ‘6-coordinated Zn’ sites. The color coordinates of the system were evaluated using CIE index diagram to be 0.36 and 0.37, which suggest that the prepared material is a potential near white light emitting phosphor.     

Photoluminescence properties of Y3Al5O12:Eu nanocrystallites prepared by co-precipitation method using a mixed precipitator of NH4HCO3 and NH3·H2O

Europium-doped yttrium aluminum garnet (Y₃Al₅O₁₂:Eu, YAG:Eu) nanocrystallites were prepared by calcining the precursors obtained via a co-precipitation method using a mixed solution of NH₄HCO₃ and NH₃·H₂O as the precipitator. The results of XRD, FTIR and thermal analysis showed that phase-pure YAG:Eu without any other phases was obtained at 900 °C. TEM results indicated that the particle sizes are 50–100 nm. YAG:Eu nanocrystallites showed four emission bands ascribed to ⁵D₀ → ⁷F₁ transition (592 and 597 nm) and ⁵D₀ → ⁷F₂ transition (611 and 633 nm) of Eu³⁺, respectively. The intensity of the magnetic dipole transition (⁵D₀ → ⁷F₁) is stronger than that of the electric dipole transition (⁵D₀ → ⁷F₂). The influence of the precipitators with different molar ratios of NH₄HCO₃ to NH₃·H₂O on the thermal properties of the as-prepared precursors and luminescent properties of the resulting YAG:Eu nanocrystallites was also investigated.     

Nanoparticles synthesis of tungsten disulfide via AOT-based microemulsions

The tungsten disulfide (WS₂) nanoparticles (most probably inorganic fullerene (IF)) with a narrow size distribution were synthesized by a reverse micelle technique for the first time. The particle size was controlled by varying water-to-surfactant molar ratio (W₀), aging time and reagent concentration. The synthesized WS₂ nanoparticles were characterized by zetasizer, UV–visible spectrophotometers and transmission electron microscopy (TEM). The WS₂ nanoparticles with particle diameter size of 7–12 nm were obtained via 24 h aging time. The particle size was controlled by changing the aging time and molar ratio of water/surfactant. Doubling W₀ increased the amount and particle size of WS₂ by 22 and 26%, respectively. The effect of aging time in the range of 6–24 h was investigated and the complete disappearance of yellowish color at 24 h resulted in an optically clear solution, which was the indication of WS₂ formation with 100% conversion of reactant ((NH₄)₂WS₄) in the batch reactor.     

Nanosized pure and Cr doped Al2−xScx(WO4)3 solid solutions

Nanosized solid solutions of the formula Al_2?x?ySc_xCr_y(WO₄)₃, where x varies from 0 to 2 and y from 0.02 to 0.1 are synthesized for the first time by the co-precipitation method. X-ray powder diffraction, DTA/TG and TEM analyses demonstrate that the powders are pure solid solution compounds with orthorhombic structure, space group Pnca. Particle sizes between 10 and 70 nm are obtained after thermal treatment of the precipitates at 550 °C for 1 h for all compositions except in the case of Sc_1.9Cr_0.1(WO₄)₃. For the last one mean particle size of 64 nm was obtained after thermal treatment at 500 °C. The influence of the concentrations of Sc and Cr as well as of the temperature and duration of the thermal treatment on the particle size and size distribution are established and discussed.     

Influence of processing method on the properties of hydroxyapatite nanoparticles in the presence of different citrate ion concentrations

The objective of this study was to investigate the effect of processing methods on the formation of ultra fine hydroxyapatite (HAp) nanoparticles in the presence of citrate ions and analyze their various physical properties. The addition of the citrate ions was found to reduce the size and prevent the agglomeration of HAp particles dramatically in the high gravity (HG) method compared to precipitation method. In precipitation method, the particle size reduced from 300 ± 70 nm to 90 ± 20 nm with the addition of citrate ions. In high gravity method, the particle size decreased more significantly from 80 ± 10 nm to 13 ± 5 nm with the addition of citrate ions. Furthermore, more uniform size distribution of nanoparticles was achieved in high gravity method. X-ray diffraction of nanoparticles prepared in both method exhibited slight shift of peaks to the higher angle with the addition of citric acid, indicating the incorporation of carbonate (CO₃) content in the HAp nanoparticles irrespective of the particle size. The mechanical properties of HWMPE matrix composite reinforced with nanoparticles was examined and this nanocomposite with nanoparticles prepared in high gravity method with the addition of citrate ions showed increased mechanical strength due to the considerable reduction in the particle size and higher uniformity of the particles. In vitro cellular analyses of the nanoparticle prepared in high gravity with the addition of citrate ions also displayed the most pronounced spreading of cell growth.     

Synthesis and luminescence properties of red long-lasting phosphor Y2O2S:Eu3+, Mg2+, Ti4+ nanoparticles

We report an effective method to synthesize Y₂O₂S:Eu³⁺, Mg²⁺, Ti⁴⁺ nanoparticles. Tube-like Y(OH)₃ were firstly synthesized by hydrothermal method to serve as the precursor. Nanocrystalline long-lasting phosphor Y₂O₂S:Eu³⁺, Mg²⁺, Ti⁴⁺ was obtained by calcinating the precursor with co-activators and S powder. XRD investigation shows a pure phase of Y₂O₂S, indicating no other impurity phase appeared. SEM and TEM observation reveals that the precursor synthesized via a hydrothermal routine has tube-like structure and the final phosphor reveals a hexagonal shape. The fine nanoparticles which have the particle size ranging from 30 to 50 nm show uniform size and well-dispersed distribution. From the spectrum, the main emission peaks are ascribed to Eu³⁺ ions transition from ⁵D_J (J = 0, 1, 2) to ⁷F_J (J = 0, 1, 2, 3, 4). After irradiation by 325 nm for 10 min, the Y₂O₂S:Eu³⁺, Mg²⁺, Ti⁴⁺ long-lasting phosphor shows very bright red afterglow and the longest could last for more than 1 h even after the irradiation source had been removed. It is considered that the long-lasting phosphorescence is due to the contribution from the electron traps with suitable trap depth.     

Study of optical properties of GeO2 nanocrystals as synthesized by hydrothermal technique

The GeO₂ nanocrystals (α-quartz type structure) with β-phase are synthesized at relatively lower temperature by hydrothermal route using autoclave. All samples are characterized by XRD, FESEM, EDS, TEM, photoluminescence (PL) and UV–vis absorption spectroscopy techniques. Synthesized nanocrystals have uniform shape and uniform size distribution for a particular synthesis condition, which is about 30–300 nm depending on synthesis conditions. The XRD results indicate that grown GeO₂ crystals only shows peak related to α-quartz structure with lattice parameters a = 4.985 Å and c = 5.648 Å. UV–vis absorption spectroscopy measurements reveal the bandgap energies corresponding to the GeO₂ α-quartz structure. Synthesized nanocrystals are capable to emit strong blue light around 425–435 nm under excitation of 300 nm and 325 nm and consequently the as synthesized material can be used in integrated optical devices.     

Agglomeration of urinary nanocrystallites: Key factor to formation of urinary stones

With transmission electron microscopy (TEM) and nanoparticle size analyzer, comparative studies were conducted on the property variation of nanocrystallites in the urine of 5 lithogenic patients and 5 healthy subjects following the placement time (t₁). These properties include average particle size (d?), size distribution, intensity–autocorrelation function, Zeta potential (ζ) and aggregation state. With the prolongation of t₁ from 0 h to 4 h, d? value of the nanocrystallites in urine of lithogenic patients increased from 742 nm to 1667 nm, the autocorrelation time increased from 7.68 ms to 1050 ms and ζ decreased from ?1.52 mV to ?4.44 mV, respectively; the autocorrelation curves were of fluctuating and unsmooth, and TEM showed that most of the patient's urinary nanocrystallites were in aggregation state and three types of agglomeration were observed. However, for nanocrystallites in urine of healthy subjects, there was little variation in the above properties within 4 h. The autocorrelation curves were of regular and smooth, and TEM showed that healthy urinary nanocrystallites were well-dispersed. The above results show that the nanocrystallites in urine of healthy subjects can keep stability, whereas those of lithogenic patients are easier to agglomerate gradually; and the agglomeration of urinary nanocrystallites is the key factor to stone formation.     

Facile synthesis,characterization and photocatalytic activity of niobium carbide

Niobium carbide (NbC) powders were prepared via a novel route at 550 °C and 8 h, using metallic magnesium powders, niobium pentoxide (Nb₂O₅), and potassium acetate (CH₃COOK) as starting materials. The structure and morphology of the product were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that as-prepared product was crystallized in pure cubic NbC phase and the size of the sample was estimated to be around 120 nm. The Rietveld refinement of the XRD data gives the cell constant a = 4.4718 Å. According to the Scherrer formula, the real grain size was about 70 nm. The BET surface area of the sample was ca.29.3 m²/g. The grain size distribution of the sample was about 467 nm, which was characterized by N4 PLUS submicron Particle Size Analyzer. The cubic NbC powders exhibited photocatalytic activity in degradation of Rhodamine-B (RhB) under 300 W mercury lamp light irradiation.     

Low temperature synthesis,crystal structure and thermal stability studies of nanocrystalline VN particles

The simultaneous thermal decomposition and nitridation of [VO(NH₂O)₂Gly]·H₂O complex in NH₃ atmosphere at 723–973 K gives the nanocrystalline vanadium nitride (VN) having crystallite size of 8–32 nm. It shows cubic NaCl structure with lattice parameter of a = 4.137 nm. XRD pattern Rietveld analysis program for crystal structure of VN shows the space group-Fm3m. The particle sizes measured by BET and SEM techniques are in the range of 26–100 nm. The particles are spherical and distributed homogeneously and found larger than XRD crystallite size because of agglomeration of crystallites. The fundamental IR absorption of VN material is found at 995 cm⁻¹ which gives the force constant of 634.3 Nm⁻¹. The electrical resistivity and magnetic studies show the superconducting to normal transition (T_c) at 9.2 K. Thermal decomposition of VN is carried out in O₂ atmosphere which goes through the formation of an oxynitride (V–N_p–O_q) intermediate phase up to 913 K. Finally, nanocrystalline V₂O₅ is formed at 973 K. The V₂O₅ has orthorhombic structure with lattice parameters of a = 11.537, b = 3.568 and c = 4.380 Å and the XRD crystallite size of 10 nm.     

Fluorescence properties and relaxation processes of Tb3+ ions in ZnCl2-based glasses

60ZnCl₂–20KCl–20BaCl₂–xTbCl₃ glasses (x = 0.10, 0.25, 0.50, 0.75, 1.00, and 1.25) were prepared by melt-quenching method, and Tb³⁺ fluorescence properties were investigated under 355 nm excitation. Regardless of x values, the electrons that were relaxed from the ⁵D₃ to ⁵D₄ level of Tb³⁺ ions by the multiphonon relaxation, were repressed to 28% of all the excited electrons because the ZnCl₂-based glass had much lower phonon energy than oxide glasses. For 0 < x ≤ 0.34, the cross relaxation, (⁵D₃ → ⁵D₄) → (⁷F₀ ← ⁷F₆), was repressed, and consequently 72% and 28% of all the excited electrons were radiatively relaxed by the ⁵D₃ → ⁷F_J (J = 6, 5, 4, 3, and 2) and ⁵D₄ → ⁷F_J (J = 6, 5, 4, and 3) transitions, respectively. The lifetimes of the ⁵D₃ and ⁵D₄ initial levels were obtained to be 1.1 and 2.1 ms, respectively.     

Synthesis and sintering of tin-doped indium oxide nanoparticles with uniform size

The urea-based hydrothermal (UBH) method can synthesize indium tin oxide (ITO) nanopowders with good monodispersity and size uniformity. However, the resulting formation of high pressure CO₂ gas by the hydrolysis of urea during the hydrothermal process is unsafe. The pressure generated by the UBH method can be lowered by connecting the hydrothermal reactor to a vessel containing sodium hydroxide solution to quickly absorb CO₂ gas. ITO nanoparticles with particle sizes of 90 ± 3 nm and 40 ± 3 nm can be produced. The size of the as-prepared nanoparticles is readily controlled by adjusting the precursor concentration. Using properly mixed nanoparticles with a volume ratio of V_40 nm:V_90 nm = 30:70 as the raw materials, ITO can be sintered to a high and consistent density of 99.3–99.5% of the theoretical density.     

Formation and spectral probing of transparent oxyfluoride glass-ceramics containing (Eu2+, Eu3+:BaGdF5) nano-crystals

In the present study, we report the formation of transparent glass-ceramics containing BaGdF₅ nanocrystals under optimum ceramization of SiO₂–BaF₂–K₂O–Sb₂O₃–GdF₃–Eu₂O₃ based oxyfluoride glass and the energy transfer mechanisms in Eu²⁺ → Eu³⁺ and Gd³⁺ → Eu³⁺ has been interpreted through luminescence study. The modification of local environment surrounding dopant ion in glass and glass ceramics has been studied using Eu³⁺ ion as spectral probe. The optimum ceramization temperature was determined from the differential scanning calorimetry (DSC) thermogram which revealed that the glass transition temperature (T_g), the crystallization onset temperature (T_x), and crystallization peak temperature (T_p) are 563 °C, 607 °C and 641 °C, respectively. X-ray diffraction pattern of the glass-ceramics sample displayed the presence of cubic BaGdF₅ phase (JCPDS code: 24-0098). Transmission electron microscopy image of the glass-ceramics samples revealed homogeneous distribution of spherical fluoride nanocrystals ranging 5–15 nm in size. The emission transitions from the higher excited sates (⁵D_J, J = 1, 2, and 3) as well as lowered asymmetry ratio of the ⁵D₀ → ⁷F₂ transition (forced electric dipole transition) to that of the ⁵D₀ → ⁷F₁ transition (magnetic dipole) of Eu³⁺ in the glass-ceramics when compared to glass sample demonstrated the incorporation of dopant Eu³⁺ ions into the cubic BaGdF₅ nanocrystals with higher local symmetry with enhanced ionic nature. The presence of absorption bands of Eu²⁺ ions and Gd³⁺ ions present in the glass matrix or fluoride nanocrystals in the excitation spectra of Eu³⁺ by monitoring emission at 614 nm indicated energy transfer from (Eu²⁺ → Eu³⁺) and (Gd³⁺ → Eu³⁺) in both glass and glass-ceramics samples.     

Encapsulation of a pressure sensitive adhesive by spray-cooling: Optimum formulation and processing conditions

An industrial pressure sensitive adhesive (PSA) was encapsulated by spray-cooling using hydrogenated palm oil. A screening design methodology was used to evaluate the impact of some formulation and process variables on the particle properties. Six operating factors were retained and the results considered were the production yield, the particle volume-surface average diameter D₃₂, the residual humidity, the ratio of the fusion enthalpies of the polymorphs α and β′/β and the normalized peeling force. The statistical analysis of the results showed a negligible impact of the parameters related to the process. The heating temperature, the PSA and surfactant ratios were the most significant factors. It was possible to produce spherical particles with a mean size of 17.7 μm and a normalized peeling force of 0.218 N m²/g. The production yield was 70%. A duplicate test confirmed the results. Mechanical tests on unitary particles showed an increase of the rupture and adhesion forces with particle size.     

Synthesis of TbMnO3 nanoparticles via a polyacrylamide gel route

We report here the synthesis of TbMnO₃ nanoparticles via an acrylamide gel route. XRD, TG analysis, DSC analysis, and FTIR spectroscopy are combinatively used to investigate the thermal decomposition process of precursor xerogels and the formation of TbMnO₃ phase. It is demonstrated that high-phase-purity TbMnO₃ nanoparticles can be prepared by using different chelating agents at a sintering temperature of 800 °C. SEM observation and XRD analysis reveal that the particle size and morphology of the products have a dependence on the chelating agent. The particles prepared using citric acid as the chelating agent appear to be regularly spherical in shape and highly uniform in size with a diameter of ～67 nm, while the sample prepared by using the chelating agent EDTA mainly consists of sphere-, ellipsoid-, and rod-like particles and exhibits a relatively broad particle size distribution with an average particle size centered around 115 nm. The use of a combination of citric acid and EDTA generally results in sphere- and ellipsoid-like particles with an average particle size between those of the samples prepared separately by using the two chelating agents.