Semi-automatic meteoroid fragmentation modeling using genetic algorithms

Meteoroids are pieces of asteroids and comets. They serve as unique probes to the physical and chemical properties of their parent bodies. We can derive some of these properties when meteoroids collide with the atmosphere of Earth and become a meteor or a bolide. Even more information can be obtained when meteoroids are mechanically strong and slow enough to drop meteorites. Through physical modeling of bright meteors, we describe their fragmentation in the atmosphere. We also derive their mechanical strength and the mass distribution of the fragments, some of which may hit the ground as meteorites. We developed a semi-automatic program for meteoroid fragmentation modeling using parallel genetic algorithms. This allowed us to determine the most probable fragmentation cascade of the meteoroid, and also to specify its initial mass and velocity. These parameters can be used in turn to derive the heliocentric orbit of the meteoroid and to place constraints on its likely age as a separate object. The program offers plausible solutions for the majority of fireballs we tested, and the quality of the solutions is comparable to that of manual solutions. The two solutions are not the same in detail, but the derived quantities, such as the fragment masses of the larger fragments and the proxy for their mechanical strength, are very similar. With this method, we would like to describe the mechanical properties and structure of both meteoroids belonging to major meteor showers and those that cause exceptional fireballs.Comment: Accepted for publication in A&A, 17 pages, 27 figure

Ultrasound exfoliation of inorganic analogues of graphene

High-intensity ultrasound exfoliation of a bulk-layered material is an attractive route for large-scale preparation of monolayers. The monolayer slices could potentially be prepared with a high yield (up to 100%) in a few minutes. Exfoliation of natural minerals (such as tungstenite and molybdenite) or bulk synthetic materials (including hexagonal boron nitride (h-BN), hexagonal boron carbon nitride (h-BCN), and graphitic carbon nitride (g-C(3)N(4))) in liquids leads to the breakdown of the 3D graphitic structure into a 2D structure; the efficiency of this process is highly dependent upon the physical effects of the ultrasound. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) were employed to verify the quality of the exfoliation. Herein, this new method of exfoliation with ultrasound assistance for application to mono- and bilayered materials in hydrophobic and hydrophilic environments is presented

Design and performance of novel self-cleaning g-C3N4/PMMA/PUR membranes

In the majority of photocatalytic applications, the photocatalyst is dispersed as a suspension of nanoparticles. The suspension provides a higher surface for the photocatalytic reaction in respect to immobilized photocatalysts. However, this implies that recovery of the particles by filtration or centrifugation is needed to collect and regenerate the photocatalyst. This complicates the regeneration process and, at the same time, leads to material loss and potential toxicity. In this work, a new nanofibrous membrane, g-C3N4/PMMA/PUR, was prepared by the fixation of exfoliated g-C3N4 to polyurethane nanofibers using thin layers of poly(methyl methacrylate) (PMMA). The optimal amount of PMMA was determined by measuring the adsorption and photocatalytic properties of g-C3N4/PMMA/PUR membranes (with a different PMMA content) in an aqueous solution of methylene blue. It was found that the prepared membranes were able to effectively adsorb and decompose methylene blue. On top of that, the membranes evinced a self-cleaning behavior, showing no coloration on their surfaces after contact with methylene blue, unlike in the case of unmodified fabric. After further treatment with H2O2, no decrease in photocatalytic activity was observed, indicating that the prepared membrane can also be easily regenerated. This study promises possibilities for the production of photocatalytic membranes and fabrics for both chemical and biological contaminant control.Web of Science124art. no. 85

Improvement of Orange II Photobleaching by Moderate Ga 3+

Highly photoactive Ga3+-doped anatase modification of titania was prepared by homogeneous hydrolysis of aqueous solutions mixture of titanium oxo-sulphate TiOSO4 and gallium(III) nitrate with urea. Incorporation of Ga3+ into the anatase lattice has a clear positive effect on the photocatalytic activity under UV and Vis light irradiation up to a certain extent of Ga. Ga3+ doping decreased the size of the crystallites, increased surface area, and affected texture of the samples. Higher amount of gallium leads to the formation of a nondiffractive phase, probably photocatalytically inactive. The titania sample with 2.18 wt.% Ge3+ had the highest activity during the photocatalysed degradation in the UV and visible light regions; the total bleaching of dye Orange II was achieved within 29 minutes. Ga concentration larger than 5% (up to 15%) significantly inhibited the growth of the anatase crystal domains which formed the nondiffractive phase content and led to remarkable worsening of the photobleaching efficiency

Recovery of Cerium Dioxide from Spent Glass-Polishing Slurry and Its Utilization as a Reactive Sorbent for Fast Degradation of Toxic Organophosphates

The recovery of cerium (and possibly other rare earth elements) from the spent glass-polishing slurries is rather difficult because of a high resistance of polishing-grade cerium oxide toward common digestion agents. It was shown that cerium may be extracted from the spent polishing slurries by leaching with strong mineral acids in the presence of reducing agents; the solution may be used directly for the preparation of a ceria-based reactive sorbent. A mixture of concentrated nitric acid and hydrogen peroxide was effective in the digestion of partially dewatered glass-polishing slurry. After the removal of undissolved particles, cerous carbonate was precipitated by gaseous NH3 and CO2. Cerium oxide was prepared by a thermal decomposition of the carbonate precursor in an open crucible and tested as reactive sorbent for the degradation of highly toxic organophosphate compounds. The samples annealed at the optimal temperature of approximately 400°C exhibited a good degradation efficiency toward the organophosphate pesticide fenchlorphos and the nerve agents soman and VX. The extraction/precipitation procedure recovers approximately 70% of cerium oxide from the spent polishing slurry. The presence of minor amounts of lanthanum does not disturb the degradation efficiency

Impact of Ge4+ Ion as Structural Dopant of Ti4+ in Anatase: Crystallographic Translation, Photocatalytic Behavior, and Efficiency under UV and VIS Irradiation

Nanometric particles of germanium-doped TiO2 were prepared by homogeneous hydrolysis of TiOSO4 and GeCl4 in an aqueous solution using urea as the precipitation agent. Structural evolution during heating of these starting Ge-Ti oxide powders was studied by X-ray diffraction (XRD) and high-temperature X-ray powder diffraction (HTXRD). The morphology and microstructure changes were monitored by means of scanning electron microscopy (SEM), Raman and infrared spectroscopy (IR), specific surface area (BET), and porosity determination (BJH). The photocatalytic activity of all samples was determined by decomposition of Orange II dye under irradiation at 365 nm and 400 nm. Moderate doping with concentration upto value 2.05 wt.% positively influences azo dye degradation under UV and Vis light. Further improvement cannot be achieved by higher Ge doping. Effect of the annealing (200, 400, and 700°C) on photocatalysis and other properties has been assessed

Novel synthesis of Ag@AgCl/ZnO by different radiation sources including radioactive isotope Co-60: Physicochemical and antimicrobial study

This research has revealed the promising, environmentally friendly and one-step modification of ZnO nano-particles (NPs) based on radiation-assisted method for antimicrobial applications. Commercially available ZnO NPs were modified in aqueous solution of silver nitrate in the presence of the artificial radiation by using different sources of radiation such as high-power UV/Vis LED units and radioactive isotope Co-60. New nano-composites were characterized by XRD, TEM, HRTEM, HRSTEM with 3D element mapping, DRS and PL spectrometry. The results showed that all samples were composed of Ag@AgCl NPs connected with ZnO NPs via stable heterojunction. The use of different radiation had significant influence on the prepared composites and the final antimicrobial activity against Gram-negative Escherichia coli, Pseudomonas aeruginosa, and Gram-positive Streptococcus salivarius, Staphylococcus aureus bacteria strains and yeast Candida albicans. The possible influence of irradiation on the final physiochemical and antimicrobial activity of Ag@AgCl/ZnO nanocomposites was proposed. It was found that the Ag@AgCl/ZnO irradiated by gamma- and beta(-) -radiation exhibited the highest antimicrobial activity.Web of Science529art. no. 14709

Reusable and Antibacterial Polymer-Based Nanocomposites for the Adsorption of Dyes and the Visible-Light-Driven Photocatalytic Degradation of Antibiotics

Adsorption and advanced oxidation processes, especially photocatalysis, are amongst the most common water treatment methodologies. Unfortunately, using each of these techniques independently does not fully eliminate the pollutants of diverse nature, which are present in wastewater. Here, an avenue for multifunctional materials for water treatment is opened by reporting for the first time the preparation, characterization, and study of the properties of a novel multifunctional nanocomposite with both adsorption and visible-light-driven photocatalysis abilities. These multifunctional nanocomposites, namely iron (II, III) oxide/poly(N-isopropylacrylamide-co-methacrylic acid)/silver-titanium dioxide (Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2), are prepared by combining magnetic polymeric microspheres (Fe3O4/P(NIPAM-co-MAA)) with silver-decorated titanium dioxide nanoparticles (Ag-TiO2 NPs). Cationic dyes, such as basic fuchsin (BF), can be adsorbed by the nanocomposites thanks to the carboxylic groups of Fe3O4/P(NIPAM-co-MAA) microspheres. Concomitantly, the presence of Ag-TiO2 NPs endows the system with the visible-light-driven photocatalytic degradation ability toward antibiotics such as ciprofloxacin (CIP) and norfloxacin (NFX). Furthermore, the proposed nanocomposites show antibacterial activity toward Escherichia coli (E. coli), thanks to the presence of silver nanoparticles (Ag NPs). Due to the superparamagnetic properties of iron (II, III) oxide nanoparticles (Fe3O4 NPs), the nanocomposites can be also recycled and reused, after the cleaning process, by using an external magnetic field

Enhanced visible-light photodegradation of fluoroquinolone-based antibiotics and E. coli growth inhibition using Ag-TiO2 nanoparticles

Antibiotics in wastewater represent a growing and worrying menace for environmental and human health fostering the spread of antimicrobial resistance. Titanium dioxide (TiO2) is a well-studied and well-performing photocatalyst for wastewater treatment. However, it presents drawbacks linked with the high energy needed for its activation and the fast electron-hole pair recombination. In this work, TiO2 nanoparticles were decorated with Ag nanoparticles by a facile photochemical reduction method to obtain an increased photocatalytic response under visible light. Although similar materials have been reported, we advanced this field by performing a study of the photocatalytic mechanism for Ag-TiO2 nanoparticles (Ag-TiO2 NPs) under visible light taking in consideration also the rutile phase of the TiO2 nanoparticles. Moreover, we examined the Ag-TiO2 NPs photocatalytic performance against two antibiotics from the same family. The obtained Ag-TiO2 NPs were fully characterised. The results showed that Ag NPs (average size: 23.9 +/- 18.3 nm) were homogeneously dispersed on the TiO2 surface and the photo-response of the Ag-TiO2 NPs was greatly enhanced in the visible light region when compared to TiO2 P25. Hence, the obtained Ag-TiO2 NPs showed excellent photocatalytic degradation efficiency towards the two fluoroquinolone-based antibiotics ciprofloxacin (92%) and norfloxacin (94%) after 240 min of visible light irradiation, demonstrating a possible application of these particles in wastewater treatment. In addition, it was also proved that, after five Ag-TiO2 NPs re-utilisations in consecutive ciprofloxacin photodegradation reactions, only a photocatalytic efficiency drop of 8% was observed. Scavengers experiments demonstrated that the photocatalytic mechanism of ciprofloxacin degradation in the presence of Ag-TiO2 NPs is mainly driven by holes and OH radicals, and that the rutile phase in the system plays a crucial role. Finally, Ag-TiO2 NPs showed also antibacterial activity towards Escherichia coli (E. coli) opening the avenue for a possible use of this material in hospital wastewater treatment.Web of Science1123139911398