Effect of the Addition of Graphene Flakes on the Physical and Biological Properties of Composite Paints.

In this study, graphene flakes were obtained using an electrolytic method and characterized using X-ray diffraction (XRD), Raman and FTIR spectroscopy, scanning and transmission electron microscopy (SEM/TEM). Graphene-based composites with varying concentrations of 0.5%, 1% and 3% by weight were prepared with acrylic paint, enamel and varnish matrices. The mechanical properties were evaluated using micro-hardness testing, while wettability and antimicrobial activity against three pathogens (Staphylococcus aureus 33591, Pseudomonas aeruginosa 15442, Candida albicans 10231) were also examined. The results indicate that the addition of graphene flakes significantly enhances both the mechanical and antimicrobial properties of the coatings.

Optimization of the Electrochemical Method of Obtaining Graphene Nanoplatelets (GNPs).

Graphene nanoplatelets (GNPs) were prepared using the electrolytic exfoliation method on graphite foil in an ammonium sulfate solution. A series of experiments were conducted in order to optimize the production of the flakes by varying the pH of the solution, applied voltage and current, duration of electrolysis, temperature in the electrolytic system, and type and duration of the ultrasound interaction. The quality of the produced graphene nanoplatelets was analyzed using X-ray diffraction, Raman and IR spectroscopy, and TEM.

Novel composite of Zn/Ti-layered double hydroxide coupled with MXene for the efficient photocatalytic degradation of pharmaceuticals.

In the present study, a hybrid photocatalyst of Zn/Ti layered double hydroxide (LDH) coupled with MXene - Ti3C2 was synthesized for the first time and applied in photocatalytic degradation of acetaminophen and ibuprofen, two commonly present in the natural environment and prone to accumulate in the aquatic ecosystem pharmaceuticals. The effect of MXene content (0.5 wt%, 2.5 wt%, and 5 wt%) on the photocatalytic activity of LDH/MXene composite was investigated. The composite of LDH/MXene containing 2.5 wt% of MXene revealed the highest photocatalytic activity in the degradation of acetaminophen (100% within 40 min) and ibuprofen (99.7% within 60 min). Furthermore, an improvement in acetaminophen and ibuprofen mineralization was observed for the composite material. Meanwhile, the introduction of interfering ions (Na+, Ca2+, Mg2+, Cl-, SO42-) in the model seawater did not affect the removal efficiency of both pharmaceuticals. The photocatalytic experiment performed in the four subsequent cycles, as well as FTIR, TEM, and XPS analyses after the photodegradation process confirmed the excellent stability and reusability of the prepared composite material. In order to evaluate the effect of various reactive oxidizing species (ROS) on the photocatalytic process, the trapping experiment was applied. It was noticed that •O2- had the main contribution in photocatalytic degradation of acetaminophen, while •OH and h+ mainly affected the degradation of ibuprofen. Finally, based on the results of Mott Schottky analysis, bandgap calculation, and ROS trapping experiment, the possible mechanism for pharmaceuticals degradation was proposed. This research illustrates the feasibility and novelty of the treatment of pharmaceuticals by LDH/MXene composites, implying that MXene plays a significant role in the electron-hole separation and thus high photocatalytic activity.

Effect of Graphene Addition on the Thermal and Persistent Luminescence Properties of Gd2.994Ce0.006Ga3Al2O12 and Gd2.964Ce0.006Dy0.03Ga3Al2O12 Ceramics.

The gadolinium, gallium, aluminum garnet doped with cerium and co-doped with dysprosium ions were prepared using sol gel method. The SEM images show that after synthesis, the grains are below 100 nm. The powders were ultrasonically mixed with graphene nanoflakes and ceramics were prepared using the high pressure low temperature sintering technique. A series of the ceramics was prepared using different graphene content. The structure of the samples was examined using X-ray diffraction (XRD), scanning electron microscope (SEM) and Raman techniques. The spectroscopic properties were checked using conventional and persistent luminescence spectra measurements. The thermoluminescence glow curves and fading time of persistent luminescence measurements were performed to check how the graphene presence affects the electron traps number and depth. It was found that the addition of graphene improved the thermal conductivity of co-doped samples. This resulted in faster release of deeper traps and an increase in fading of persistent luminescence. The possibility of releasing energy from deep traps without additional stimulation may allow the use in different applications, the matrices and luminescent ions, which so far did not show persistent luminescence at room temperature.

Pilot-Scale Studies of WO3/S-Doped g-C3N4 Heterojunction toward Photocatalytic NOx Removal.

Due to the rising concentration of toxic nitrogen oxides (NOx) in the air, effective methods of NOx removal have been extensively studied recently. In the present study, the first developed WO3/S-doped g-C3N4 nanocomposite was synthesized using a facile method to remove NOx in air efficiently. The photocatalytic tests performed in a newly designed continuous-flow photoreactor with an LED array and online monitored NO2 and NO system allowed the investigation of photocatalyst layers at the pilot scale. The WO3/S-doped-g-C3N4 nanocomposite, as well as single components, were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller surface area analysis (BET), X-ray fluorescence spectroscopy (XRF), X-ray photoemission spectroscopy method (XPS), UV-vis diffuse reflectance spectroscopy (DR/UV-vis), and photoluminescence spectroscopy with charge carriers' lifetime measurements. All materials exhibited high efficiency in photocatalytic NO2 conversion, and 100% was reached in less than 5 min of illumination under simulated solar light. The effect of process parameters in the experimental setup together with WO3/S-doped g-C3N4 photocatalysts was studied in detail. Finally, the stability of the composite was tested in five subsequent cycles of photocatalytic degradation. The WO3/S-doped g-C3N4 was stable in time and did not undergo deactivation due to the blocking of active sites on the photocatalyst's surface.

Impact of the Synthesis Method on the Conventional and Persistent Luminescence in Gd3-xCexGa3Al2O12.

The series of Gd3-xCexGa3Al2O12 nanopowders doped with different concentrations of Ce3+ ions were prepared by Pechini (sol-gel) and combustion methods. The structure and morphology of the powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. It was found that the synthesis method has a great impact on the morphology and, consequently, spectroscopic properties of the powders. Optical properties of the powders were examined using excitation, emission, and luminescence kinetic measurements. For all powders, persistent luminescence and emission decay processes were studied. The most intense luminescence was observed for the powder with 0.5 mol % of Ce3+ synthesized using the combustion method and 1 mol % in the case of the sol-gel sample. The longest and brightest persistent luminescence was observed for the powders doped with 0.1 mol % (combustion) and 0.2 mol % of Ce3+ ions (sol-gel). The thermoluminescence measurements were done for the powders prepared using different methods to understand the impact of the synthesis conditions on the number and depths of the traps involved in persistent luminescence. On the basis of spectroscopic measurements, the mechanism of persistent luminescence was constructed and discussed.

Design of the persistent luminescence colour of a novel Gd3-xTbxGa3Al2O12 phosphor: synthesis methods, spectroscopic properties and mechanism.

The aim of this work was to check the influence of Tb3+ ion concentration and synthesis method on the persistent luminescence properties. A series of Gd3-xTbxGa3Al2O12 nanopowders were obtained by using two different synthesis methods. The crystal structure refinement was performed to check the impact of the preparation method and doping level on the crystallization process. This revealed the influence of doping level on conventional and persistent luminescence color, intensity and decay time. It was demonstrated that it is possible to tune the persistent luminescence color by changing the Tb3+ doping level. The spectroscopic measurements show that persistent luminescence appears only under UV excitation, suggesting that the 5d levels of Tb3+ play an active role in this process. Thermoluminescence measurements indicate that the depth and number of electron traps in the samples are associated with the synthesis method and dopant concentration. Based on the results, the possible mechanism of energy transfer between the traps and luminescence centers is proposed and discussed.

A Facile Synthesis and Characterization of Highly Crystalline Submicro-Sized BiFeO3.

In this study, a highly crystalline bismuth ferrite (BFO) powder was synthesized using a novel, very simple, and cost-effective synthetic approach. It was demonstrated that the optimal annealing temperature for the preparation of highly-pure BFO is 650 °C. At lower or higher temperatures, the formation of neighboring crystal phases was observed. The thermal behavior of BFO precursor gel was investigated by thermogravimetric and differential scanning calorimetry (TG-DSC) measurements. X-ray diffraction (XRD) analysis and Mössbauer spectroscopy were employed for the investigation of structural properties. Scanning electron microscopy (SEM) was used to evaluate morphological features of the synthesized materials. The obtained powders were also characterized by magnetization measurements, which showed antiferromagnetic behavior of BFO powders.

Magnetic Properties of La0.9A0.1MnO3 (A: Li, Na, K) Nanopowders and Nanoceramics.

Nanocrystalline La0.9A0.1MnO3 (where A is Li, Na, K) powders were synthesized by a combustion method. The powders used to prepare nanoceramics were fabricated via a high-temperature sintering method. The structure and morphology of all compounds were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). It was found that the size of the crystallites depended on the type of alkali ions used. The high-pressure sintering method kept the nanosized character of the grains in the ceramics, which had a significant impact on their physical properties. Magnetization studies were performed for both powder and ceramic samples in order to check the impact of the alkali ion dopants as well as the sintering pressure on the magnetization of the compounds. It was found that, by using different dopants, it was possible to strongly change the magnetic characteristics of the manganites.

Enhanced 1.5 µm emission of Er3+-doped multifunctional Bi2ZnOB2O6 microcrystals.

The efficiency of the 1.5 µm emission associated with the 4I13/2 → 4I15/2 transition of Er3+ ions of a series of Er3+ and Yb3+/Er3+-doped Bi2ZnOB2O6 microcrystalline powders was investigated. Bi2ZnOB2O6 is an excellent nonlinear optical material as well as a good host matrix for luminescent rare-earth ions. The investigated powders were synthesized by means of the modified Pechini method and their orthorhombic structure with Pba2 space group were confirmed by XRD measurements. The vibrational properties of Bi2ZnOB2O6:Yb3+/Er3+ were studied using µ-Raman spectroscopy. The low phonon energy of the Bi2ZnOB2O6 matrix allows effective phonon assisted energy transfer between rare-earth ions and/or multiphonon relaxation processes of rare-earth ions. It was revealed that the intensity of the 1.5 µm emission under 980 nm excitation increased with increasing Er3+ concentration (from 0.5 to 3.0 at%) for Bi2ZnOB2O6:Er3+, while for co-doped Bi2ZnOB2O6:Yb3+/Er3+ systems a significant increase in this emission was observed for the optimal Yb3+/Er3+ concentration (1.5/0.5 at%). Moreover, the intensity of the 1.5 µm emission decreases with increasing temperature for all investigated samples. Additionally, Bi2ZnOB2O6:Yb3+/Er3+ powders exhibit effective up-conversion luminescence in the visible range under 980 nm excitation. In the up-conversion spectra of Bi2ZnOB2O6:Yb3+/Er3+ powders, the bands corresponding to green and red emission of Er3+ ions (2H11/2 → 4I15/2/4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions, respectively), as well as the bands at about 487 nm (blue emission) associated with second harmonic generation produced by the Bi2ZnOB2O6 matrix were detected. The results indicate a potential for application of Bi2ZnOB2O6:Yb3+/Er3+ powders as effective multifunctional new-generation photonic materials.

Laser induced white lighting of graphene foam.

Laser induced white light emission was observed from porous graphene foam irradiated with a focused continuous wave beam of the infrared laser diode. It was found that the intensity of the emission increases exponentially with increasing laser power density, having a saturation level at ca. 1.5 W and being characterized by stable emission conditions. It was also observed that the white light emission is spatially confined to the focal point dimensions of the illuminating laser light. Several other features of the laser induced white light emission were also discussed. It was observed that the white light emission is highly dependent on the electric field intensity, allowing one to modulate the emission intensity. The electric field intensity ca. 0.5 V/µm was able to decrease the white light intensity by half. Origins of the laser-induced white light emission along with its characteristic features were discussed in terms of avalanche multiphoton ionization, inter-valence charge transfer and possible plasma build-up processes. It is shown that the laser-induced white light emission may be well utilized in new types of white light sources.

Mechanisms of Tenebrescence and Persistent Luminescence in Synthetic Hackmanite Na8Al6Si6O24(Cl,S)2.

Synthetic hackmanites, Na8Al6Si6O24(Cl,S)2, showing efficient purple tenebrescence and blue/white persistent luminescence were studied using different spectroscopic techniques to obtain a quantified view on the storage and release of optical energy in these materials. The persistent luminescence emitter was identified as impurity Ti(3+) originating from the precursor materials used in the synthesis, and the energy storage for persistent luminescence was postulated to take place in oxygen vacancies within the aluminosilicate framework. Tenebrescence, on the other hand, was observed to function within the Na4(Cl,S) entities located in the cavities of the aluminosilicate framework. The mechanism of persistent luminescence and tenebrescence in hackmanite is presented for the first time.

Persistent Luminescence of Tenebrescent Na8Al6Si6O24(Cl,S)2: Multifunctional Optical Markers.

Na8Al6Si6O24(Cl,S)2 materials were prepared with a solid state reaction. The products were studied using X-ray powder diffraction, reflectance measurements as well as X-ray fluorescence, conventional and persistent luminescence, nuclear magnetic resonance, and electron paramagnetic resonance spectroscopies. All materials containing sulfur showed purple tenebrescence, which persisted 2 days in a lit room at room temperature. Considerable blue persistent luminescence peaking at 460 nm and lasting for 1 h was obtained, as well. Persistent luminescence was obtained with irradiation at 365 nm, while tenebrescence required 254 nm. The materials show great promise as low-cost multifunctional optical markers.

Optically stimulated persistent luminescence of europium-doped LaAlO3 nanocrystals.

Optically stimulated persistent luminescence was investigated for europium-doped LaAlO3 nanocrystals. This system shows conventional luminescence of both the Eu(3+) line emission and the weak broad-band emission of Eu(2+) upon UV excitation. The persistent luminescence is predominantly associated with the Eu(3+) emission, and can be amplified significantly through irradiation with IR at 975 nm. The conventional luminescence from Eu(3+) is strongly enhanced when the material is excited simultaneously with both UV and IR radiation. The enhancement of persistent luminescence is accompanied by increased persistent photoconductivity. The charge transfer band of the LaAlO3:Eu(3+) nanocrystals in the UV excitation spectra significantly weakens with increasing IR excitation power, also correlating well with the enhancement of persistent luminescence. Finally, a mechanism is presented for the optically stimulated and persistent luminescence in this Eu(2+)- and Eu(3+)-doped LaAlO3 material.

The f-f emission of Pr3+ ion as an optical probe for the structural properties of YAG nanoceramics.

Transparent Pr-doped YAG nanoceramics composed of grains with an average size of about 42 nm, were fabricated with the Low Temperature High Pressure (LTHP) sintering technique using the corresponding nanopowders as the starting materials. The structure of the nanoceramics was analyzed by X-ray diffraction (XRD). The effect of the sintering conditions on the structural properties is discussed on the basis of the changes of the spectroscopic properties of Pr3+ ions. In particular, the intensities and decays of the emission transitions originating from the (3)P0 and (1)D2 levels are investigated and correlated with structural properties of the material, such as microstrains produced by the high-pressure process.