Theoretical and experimental analysis of droplet-to-particle formation during aerosol processing of colloidal TiO2 nanoparticles

Theoretical and experimental investigation of the particle formation during processing of colloidal nanoparticles in aerosol laminar flow reactor is presented. Simple analytical model taking into consideration all important process parameters, such as physico-chemical properties of the colloidal solution, initial droplet size, residence time and temperature, is developed in order to predict the final particle morphology. The formation of spherical, hierarchically organized, ~450 nm sized TiO2 particles has been followed at 150°C starting from colloidal TiO2 nanoparticle (~4.5 nm) solution as precursor. It has been shown that the final particle morphology is formed in the evaporation/drying stage through the self assembly processes of colloidal nanoparticles collision and aggregation. The dimensionless numbers Re, Nu, Pr and Bi, were used in modeling to briefly describe the transport properties in dispersed system and heat and mass transport phenomena. The predicted particle size and morphology is confirmed by using scanning electron microscopy (SEM/FESEM) and laser diffraction particle size analyzer (LPS). Additionally, closer morphological investigation is performed with transmission electron microscopy (TEM) and nanotomography. Correspondingly, theoretical analysis under this study presents a simple procedure to predict the final morphology and mean particle size during aerosol processing

High resolution luminescence spectroscopy and thermoluminescence of different size LaPO4:Eu3+ nanoparticles

T. G. acknowledges the ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 (1.1.1.2/16/I/001). K. S. and K. L. acknowledge the Latvian National Research Program IMIS2. The authors from Vinča Institute of Nuclear Sciences acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Project No: 45020 and 172056 ).Nanoparticles (5 nm) and nanorods (2 nm × 15 nm and 4 nm × 20 nm) of monoclinic monazite LaPO4:Eu3+ were prepared by reverse micelle and co-precipitation techniques. Effects of the particle size and surface defects on the intensity of luminescence and the emission spectrum shapes were analyzed by high resolution spectroscopy under laser (266 nm) and X-rays excitation. All synthesized LaPO4:Eu3+ samples showed similar spectral features with characteristic Eu3+ ions emission bands: 5D0→7F0 centered at 578.4 nm, magnetic-dipole transition 5D0→7F1 at 588–595 nm, electric-dipole transition 5D0→7F2 at 611.5–620.5 nm, 5D0→7F3 at (648–652 nm) and 5D0→7F4 at (684–702.5 nm), with the most dominant electric-dipole 5D0→7F2 transition. Additionally, the thermally stimulated luminescence was studied for the most dominant peak at 611.5 nm. It was shown that the Eu3+ doping creates traps in all samples. Two prominent and well resolved glow peaks at 58.7 K and 172.3 K were detected for 5 nm nanoparticles, while low-intensity glow-peaks at 212.1 K and 212.2 K were observed in the X-rays irradiated nanorods. Displayed glows could be attributed to free and bound electrons and holes or to the recombination of electrons of ionized oxygen vacancies with photogenerated holes. To obtain information about the processes and specific defect type it is necessary to carry out additional analysis for all synthesized samples. The glow curves were analyzed and trap parameters were estimated and discussed throughout the paper.ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 (1.1.1.2/16/I/001); IMIS2; Ministry of Education, Science and Technological Development of the Republic of Serbia (Project No: 45020 and 172056 ); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Particle size effects on the structure and emission of Eu3+:LaPO4 and EuPO4 phosphors

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).This paper provides the detailed study of (nano)particle's size effect on structural and luminescent properties of LaPO4:Eu3+ synthesized by four different methods: high temperature solid-state, co-precipitation, reverse micelle and colloidal. These methods delivered monoclinic monazite-phase submicron particles (> 100 nm), 4 × 20 nm nanorods and 5 nm spheres (depending on the annealing temperature), 2 × 15 nm nanorods, and ultra-small spheres (2 nm), respectively. The analysis of emission intensity dependence on Eu3+ concentration showed that quenching concentration increases with a decrease of the particle size. The critical distance for energy transfer between Eu3+ ions is found to be 18.2 Å, and the dipole-dipole interaction is the dominant mechanism responsible for the concentration quenching of emission. With the increase in Eu3+ concentration, the unit-cell parameter slightly increases to accommodate larger Eu3+ ions at sites of smaller La3+ ions. Photoluminescent emission spectra presented four characteristic bands in the red spectral region: at 592 nm (5D0→7F1), at 612 nm (5D0→7F2), at 652 nm (5D0→7F3) and at 684 nm (5D0→7F4), while in small colloidal nanoparticles additional emission bands from host defects appear at shorter wavelengths. Intensities of f-f electronic transitions change with particles size due to small changes in symmetry around europium sites, while emission bandwidths increase with the reduction of particle size due to increased structural disorder. Judd-Ofelt analysis showed that internal quantum yield of Eu3+ emission is strongly influenced by particle's morphology.Ministry of Education, Science and Technological Development of the Republic of Serbia (Projects nos. 45020 and 172056); ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 (1.1.1.2/16/I/001); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Multifunctional Eu3+- and Er3+/Yb3+-doped GdVO4 nanoparticles synthesized by reverse micelle method

Synthesis of Eu3+- and Er3+/Yb3+-doped GdVO4 nanoparticles in reverse micelles and their multifunctional luminescence properties are presented. Using cyclohexane, Triton X-100, and n-pentanol as the oil, surfactant, and co-surfactant, respectively, crystalline nanoparticles with similar to 4 nm diameter are prepared at low temperatures. The particle size assessed using transmission electron microscopy is similar to the crystallite size obtained from X-ray diffraction measurements, suggesting that each particle comprises a single crystallite. Eu3+-doped GdVO4 nanoparticles emit red light through downconversion upon UV excitation. Er3+/Yb3+-doped GdVO4 nanoparticles exhibit several functions; apart from the downconversion of UV radiation into visible green light, they act as upconvertors, transforming near-infrared excitation (980 nm) into visible green light. The ratio of green emissions from H-2(11/2)- GT I-2(15/2) and S-4(3/2)- GT I-4(15/2) transitions is temperature dependent and can be used for nanoscale temperature sensing with near-infrared excitation. The relative sensor sensitivity is 1.11%K-1, which is among the highest sensitivities recorded for upconversion-luminescence-based thermometers

Up-conversion luminescence of GdVO4:Nd3+/Er3+ and GdVO4:Nd3+/Ho3+ T phosphors under 808 nm excitation

All authors acknowledge to the COST Action CM1403: The European upconversion network - from the design of photon-upconverting nanomaterials to biomedical applications (2014–2018). The authors from the University of Belgrade acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Project Nos. 45020 and 172056 ). K. S. acknowledges the Latvian National Research Program IMIS2 (Grant No. 302/2012 ). T. G. acknowledges the ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 ( 1.1.1.2/16/I/001 ).In recent years, there exists a tendency in research of up-conversion materials to shift excitation from 980 nm to shorter wavelengths. Here, in order to produce up-conversion luminescence emission of GdVO4-based materials under 808 nm excitation, polycrystalline powders of GdVO4:Er3+/Nd3+ and GdVO4:Ho3+/Nd3+ were successfully prepared by a high-temperature solid-state reaction technique. The prepared powders were highly crystalline with a single-phase zircon-type GdVO4 structure and consisted of micrometer-sized irregular spherical particles (2–6 μm in diameter). In all studied samples, visible up-conversion luminescence was successfully achieved under 808 nm illumination. Near-infrared pumping produced emission bands in the green, yellow-orange and green regions of the visible spectrum. The bands in the green and red regions of GdVO4: Er3+/Nd3+ as well as GdVO4:Ho3+/Nd3+ were, respectively, characteristic of Er3+ and Ho3+ ions. The dominant band originating from the 4G7/2 → 4I11/2 transition in Nd3+ ions was observed around 597 nm in all samples.COST Action CM1403 (2014–2018); Ministry of Education, Science and Technological Development of the Republic of Serbia (Project Nos. 45020 and 172056 ); Latvian National Research Program IMIS2 (Grant No. 302/2012 ); ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 ( 1.1.1.2/16/I/001 ); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Radiation, thermal and optical properties of PVA films containing arylazo pyridone dyes

Films based on polyvinyl alcohol (PVA) containing different concentrations of some arylazo pyridone dyes have been introduced as plastic detectors for dosimetry. PVA was chosen due to its water solubility and the possibility to incorporate a variety of dyes. The significance of arylazo pyridone dyes resides in their simple synthesis and wide application areas. The following dyes were used in optical data storage, laser technology, dye-sensitized solar cells, non-linear optics and biological systems. The advantage of polymeric films based on arylazo pyridone dyes is a visual change of color after exposure to gamma radiation, making them easy to use. In addition, this form of dosimeters is cheap and easily portable. Films containing arylazo pyridone dyes change the color when irradiated with γ-radiation at least up to 20 kGy. The color changes were confirmed spectrophotometrically. All synthesized films were characterized by FTIR. Optical properties have been analyzed on the basis of reflection and excitation spectra. Thermal degradation processes of PVA films containing arylazo dyes were investigated with thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC).VII International Conference on Radiation in Various Fields of Research : RAD 2019 : book of abstracts; June 10-14, 2019; Herceg Novi, Montenegr

A comparative study of photocatalytically active nanocrystalline tetragonal T zyrcon- type and monoclinic scheelite-type bismuth vanadate

The authors from Vinča Institute of Nuclear Sciences acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Project no: 172056 ). The work of K. Smits was supported by Latvian National Research Program IMIS2 (Grant no. 302/2012 ).Monoclinic scheelite-type BiVO4 is currently considered as one of the most promising non-titania photocatalysts, wheras tetragonal zircon-type BiVO4 is still poorly understood. Herein, a new and simple synthetic approach was applied and nanostructured single-phase zircon-type BiVO4 was successfully prepared by a controllable ethylene-glycol colloidal route. In addition, nanostructured monoclinic scheelite-type BiVO4 powders were also fabricated through annealing of the as-prepared samples. A comparative study of the two BiVO4 polymorphs was conducted and it turned out that the novel synthetic approach had a significant impact on porosity and photocatalytic performance of zircon-structured BiVO4. All the prepared materials, as-prepared and annealed, were mesoporous, while measured values of specific surface area of some zircon-structured samples (∼34 m2/g) were ∼7 times higher than those reported thus far for this phase. Interestingly, for the first time, zircon-type BiVO4, previously considered to be a poor photocatalyst, exhibited a better overall performance in degradation of methyl orange compared to monoclinic scheelite-type BiVO4. Hence, it could be expected that the here-presented synthesis and observations will both arouse interest in scarcely studied tetragonal zircon-type BiVO4 and facilitate as well as speed up further research of its properties.Ministry of Education, Science and Technological Development of the Republic of Serbia (Project no: 172056 ); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Colloidal-chemistry based synthesis of quantized CuInS2/Se2 nanoparticles

Ternary chalcogenide nanoparticles, CuInS2 and CuInSe2, were synthesized in high- temperature boiling organic non-polar solvent. The X-ray diffraction analysis revealed that both materials have tetragonal (chalcopyrite) crystal structure. Morphology of the obtained materials was revealed by using transmission electron microscopy. Agglomerated spherical CuInS2 nanoparticles with broad size distribution in the range from 2 to 20 nm were obtained. In the case of CuInSe2, isolated particles with spherical or prismatic shape in the size range from 10 to 25 nm were obtained, as well as agglomerates consisting of much smaller particles with diameter of about 2-5 nm. The particles with the smallest diameters of both materials exhibit quantum size effect

Aerosol processing of hierarchically organized TiO2 based nano-particles

The low-temperature (T=150oC) aerosol route, representing a feasible bottom-up technique for nano materials processing in disperse system, was applied for the synthesis of spherical, non-agglomerated, hierarchically organized titanium dioxide (TiO2) nano-particles. The diverse levels of structural, morphological and functional complexity were explored simply by means of appropriate selection of different colloidal precursor solutions of either nearly spherical nano-particles[1] (a), surface modified nano-particles with dopamine (b) or nano-tubes (c). The detailed structural and morphological investigations were done by X-ray powder diffraction (XRPD), laser particle size (LPS) analysis, scanning and field emission electron microscopy (SEM/FESEM) and transmission electron microscopy (TEM). Spherical, submicronic, soft and grained TiO2 particles with the mean size from ~350 to ~450nm and with clustered inner structure, composed of primary nanocrystals (<10nm), were obtained. The optical properties and surface structure were analyzed by UV-Vis diffusive reflectance (UV-Vis DRS) and Fourier transform infrared (FTIR) spectroscopy. The obtained results offer a general route for the synthesis of self-assemblies with tunable morphology and optical properties. A significant decrease of the effective band gap values (1.7 to 1.9eV) for the processed TiO2 nanoparticles, compared to the band gap of bulk material (3.2eV), was achieved. Such hierarchical nano-structured powders, are expected to have potential application not only in the field of photovoltaic technologies[3] but also in various aspects of photo catalysis.[4]References:[1] Dugandžić I.M., Jovanović D.J., Mančić L.T., Zheng N., Ahrenkiel S.P., Milošević O.B., Šaponjić Z.V. and Nedeljković J.M., 2012 Surface modification of submicronic TiO2 particles prepared by ultrasonic spray pyrolysis for visible light absorption, J. Nanopart. Res., 14 (10) 1157 (DOI10.1007/s11051-012-1157-1)[3] Zhang Q., Myers D., Lan J., Jenekhe S.A. and Cao G., 2012 Applications of light scattering in dyesensitized solar cells, Phys. Chem. Chem. Phys., 14, 14982-14998[4] Liu B., Nakata K., Sakai M., Saito H., Ochiai T., Murakami T., Takagi K. and Fujishima A., 2012 Hierarchical TiO2 spherical nanostructures with tunable pore size, pore volume and specific surface area: facile preparation and high-photocatalytic performance Catal. Sci. Technol., 2, 1933-193

Iron salt-promoted oxidation of steroidal phenols by m -chloroperbenzoic acid: a route to possible antitumor agents

Iron salt-promoted reaction of estrone and its derivatives with meta -chloroperoxybenzoic acid was developed and epoxyquinols were further transformed. Most compounds showed in vitro antiproliferative activity. , A new oxidant, containing m -chloroperoxybenzoic acid (MCPBA) and an iron salt, was developed and used for oxidation of steroidal phenols to a quinol/epoxyquinol mixture. Reaction was optimized for estrone, by varying initiators (Fe-salts), reaction temperature, time and mode of MCPBA application. A series of five more substrates (17β-estradiol and its hydrophobized derivatives) was subjected to the optimized oxidation, providing corresponding p -quinols and 4β,5β-epoxyquinols in good to moderate yields. The obtained epoxyquinols were additionally transformed by oxidation, as well as the acid-catalyzed oxirane opening. In a preliminary study of the antiproliferative activity against human cancer cell lines, all newly synthesized compounds expressed moderate to high activity