Field Emission Gun Research Articles

Nano- and Micrometer-Sized PGM in Ni-Cu-Fe Sulfides from an Olivine Megacryst in the Udachnaya Pipe, Yakutia, Russia

ABSTRACT This paper focuses on a nanoscale study of nano- and micrometer-size Os-rich mineral particles hosted in a Ni-Fe-Cu sulfide globule found in an olivine megacryst from the Udachnaya pipe (Yakutia, Russia). These platinum-group element mineral particles and their host sulfide matrices were investigated using a combination of techniques, including field emission gun electron probe microanalyzer, field emission scanning electron microscopy, and focused ion beam and high-resolution transmission electron microscopy. The sulfide globule is of mantle origin, as it is hosted in primitive olivine (Fo90–93), very likely derived from the crystallization of Ni-Fe-Cu sulfide melt droplets segregated by liquid immiscibility from a basaltic melt in a volume of depleted subcontinental lithospheric mantle. Microscopic observations by means of field emission scanning electron microscopy and single-spot analysis and mapping by field emission gun electron probe microanalyzer reveal that the sulfide globule comprises a core of pyrrhotite with flame-like exsolutions (usually <10 μm thickness) of pentlandite, which is irregularly surrounded by a rim of granular pentlandite and chalcopyrite. Elemental mapping by energy dispersive spectroscopy (acquired using the high-resolution transmission electron microscopy) of the pyrrhotite (+ pentlandite) core reveals that pentlandite exsolution in pyrrhotite is still observable at the nanoscale as fringes of 100 to 500 nm thicknesses. The sulfide matrices of pyrrhotite, pentlandite, and chalcopyrite contain abundant nano- and micrometer-size platinum group element mineral particles. A careful inspection of eight of these platinum group element particles under focused ion beam and high-resolution transmission electron microscopy showed that they are crystalline erlichmanite (OsS2) with well-developed crystal faces that are distinctively oriented relative to their sulfide host matrices. We propose that the core of the Ni-Fe-Cu sulfide globule studied here was derived from a precursor monosulfide solid solution originally crystallized from a sulfide melt at >1100 °C, which later decomposed into pyrrhotite and the pentlandite flame-like exsolutions upon cooling at <600 °C. Once solidified, the solid monosulfide solid solution reacted with non-equilibrium Cu-and Ni-rich sulfide melt(s), giving rise to the granular pentlandite in equilibrium with chalcopyrite now forming the rim of the sulfide globule. Meanwhile, nano- to micron-sized crystals of erlichmanite crystallized directly from or slightly before monosulfide solid solution from the sulfide melt. Thus, Os, and to a lesser extent Ir and Ru, were physically partitioned by preferential uptake via early formation of nanoparticles at high temperature instead of low-temperature exsolution from solid Ni-Fe-Cu sulfides. The new data provided in this paper highlight the necessity of studying platinum group element mineral particles in Ni-Fe-Cu sulfides using analytical techniques that can image nanoscale textural features in order to better understand the mechanisms of platinum group element fractionation in magmatic systems. These processes may play a crucial role in controlling the background geochemical budgets for siderophile and chalcophile elements in a wide range of mantle-derived magmas.

The Role of Selenium on the Formation of Spheroidal Graphite in Cast Iron

Sulfur, an element that belongs to group 16 (chalcogens) of the periodic table, is an excellent promoter of nucleation substrates for graphite in cast iron. In ductile iron, sulfur favors a higher nodule count, which inhibits the risk of carbides and of microporosity. It is reasonable to expect that other elements from group 16, such as selenium or tellurium, play similar roles in the nucleation of graphite. The objective of this paper was to investigate the effect of selenium on the process of graphite formation. Thermal analysis cups were poured to evaluate the nodule count and size distribution. Some of the cups were not inoculated, while others were inoculated with a Ce-bearing inoculant, or with the Ce inoculant and additions of Se. Cross-shaped castings were also poured to quantify the microporosity regions by tomography. It appears that selenium additions modify the number and size of graphite particles, as well as the volume of microshrinkage. Direct correlations between these three parameters were found. Advanced Extensive Field Emission Gun Scanning Electron Microscope (FEG-SEM) techniques were used to identify the nature of the main nucleation compounds. Selenides, combined with Mg and rare earths, were observed to serve as nuclei for graphite. Their presence was justified by thermodynamics calculations.

Hydrothermal aging affects the three-dimensional fit and fatigue lifetime of zirconia abutments

ObjectiveEvaluate the effect of aging using two different methods on the three-dimensional fit of zirconia abutments at the implant-abutment connection and estimate the probability of survival of anterior crowns supported by straight and 17-degree angled abutments. Materials and methodsTwo different zirconia abutment designs, straight and 17-degree angled abutments (n = 63/group), were evaluated in the current study. The abutments were randomly allocated into three experimental groups according to laboratory aging condition (134°C, 2.2 bar, 20 h): (i) control, (ii) autoclave aging, and (iii) hydrothermal reactor aging. Crystalline content was determined by X-Ray diffraction (XRD) and Raman spectroscopy, and microstructure was analyzed using field-emission gun scanning electron microscope (FEG-SEM). Implant-abutment volume misfit was determined in the straight abutments by micro-computed tomography using the silicone replica technique. For fatigue testing, abutments were torqued to the implants and connected to standardized maxillary incisor zirconia crowns. The assemblies were subjected to step-stress accelerated life testing (SSALT) in water until fracture or suspension. The use level probability Weibull curves and probability of survival for a mission of 50,000 cycles at 50, 100, 150 and 200 N were calculated and plotted. Fractured samples were analyzed using a stereomicroscope and scanning electron microscope. ResultsThe crystalline spectra depicted a zirconia system primarily composed of the tetragonal phase. Laboratory aging yielded a 20%- and 37%-increase in the monoclinic content for abutments aged in autoclave and hydrothermal reactor relative to control, respectively. A fully crystalline matrix with a regular grain size was observed in the FEG-SEM for control abutments, with a considerable presence of intergranular defects. While autoclave aging triggered no significant alteration to the microstructure, defect population was reduced after hydrothermal reactor aging. Control abutments presented a significantly higher volume misfit (2.128 ± 0.54 mm3) relative to aged abutments using autoclave (1.244 ± 0.48 mm3) or hydrothermal reactor (1.441 ± 0.41 mm3). The beta (β) values indicated that failures were predominantly controlled by material strength rather than fatigue damage accumulation for all groups, except for straight control abutments. Irrespective of aging, the probability of survival of straight and angled zirconia abutments was up to 95% (95–100%) at 50 and 100 N. A 50N-increase in the load resulted in wider range of survival estimate, with straight autoclave abutments percentage significantly lower probability of survival (77%) than angled hydrothermal reactor abutments (99%). At 200N, angled hydrothermal reactor (97%) or autoclave (82%) aged abutments demonstrated the highest probability of survival, angled control (71%) and straight hydrothermal reactor (69%) abutments intermediate values, and straight autoclave (23%) and control (7%) abutments the lowest estimate. The failure mode predominantly involved abutment and/or abutment screw fracture for both straight and angled abutments. ConclusionsHydrothermal aging significantly influenced volume misfit, as well as the probability of survival of zirconia abutments at higher loads for both angled and straight abutments.

Deposition of Ni thin films on alumina foams by magnetron sputtering for application as heterogeneous catalysts

The development of new methods to produce heterogeneous catalysts for energy conversion is still a great challenge. Non-thermal plasmas are increasingly investigated as a possible supplementary step for heterogeneous metal catalysts, where the magnetron sputtering technique emerges as an alternative solution. In this paper, Ni thin films were deposited on alumina foams by magnetron sputtering as a function of the deposition time. Samples were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy with field emission gun, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Results indicate that deposition of Ni does not affect the structure and morphology of the foams. The substrate surface was covered by a homogeneous layer smoother than those obtained by traditional methods, such as, washcoating, also avoiding pore blocking, a common effect observed in synthesis by chemical methods. Films present a combination of metallic and oxide structures, respectively, in crystalline and amorphous phases. In addition, chemical investigations show electrons from Ni atoms near to the Fermi level, indicating the catalytic activity of the surfaces.

Solving the iron quantification problem in low-kV EPMA: An essential step toward improved analytical spatial resolution in electron probe microanalysis—Fe-sulfides

Abstract The use of the field emission gun in scanning electron microscopy permits the imaging of submicrometer-size features. However, achieving sub-micrometer analytical spatial resolution in electron probe microanalysis (EPMA) requires both reducing the electron beam size and reducing the accelerating voltage to achieve the desired sub-micrometer interaction volume. The resulting quantification of the first-row transition metals at low accelerating voltage, i.e., below 7–8 kV, is problematic as the main characteristic X-ray lines (Kα) cannot be excited at these conditions. Furthermore, the use of the Lα and Lβ soft X-ray lines for quantification is complicated by bonding and self-absorption effects resulting in not-yet-determined mass absorption coefficients and hence in the failure of the traditional matrix correction procedure. We propose two methods to circumvent these low-kilovolt (low-kV) analysis limitations: using the non-traditional FeLℓ line and using universal calibration curves for the more traditional FeLα and Lβ lines. These methods were successfully applied to Fe-sulfide minerals showing accurate quantification results by EPMA at reduced kV, necessary for accurate quantification of sub-micrometer sulfide grains.

Biomass-Derived Activated Carbon-Supported Copper Catalyst: An Efficient Heterogeneous Magnetic Catalyst for Base-Free Chan-Lam Coupling and Oxidations.

Development of heterogeneous catalysts from biomass-derived activated carbon is a challenging task. Biomass-derived activated carbon possesses a large specific surface area, highly porous structure, and good thermal/chemical stability. Magnetic copper catalysts based on biomass-derived activated carbon exhibited good catalytic activity in base-free Chan–Lam coupling and oxidations. Herein, biomass-derived activated carbon was prepared by the carbonization of neem dead leaves (abundant waste biomass) followed by chemical activation with KOH. Such a porous carbon material was used as a low cost and highly efficient support material for the preparation of inexpensive and environmentally benign magnetic catalysts [Cu@KF-C/MFe2O4, M = Co, Cu, Ni, and Zn]. In addition, KF modification was done to impart basic character to the catalyst that can perform C–N coupling under base-free conditions. Initially, Brunauer–Emmett–Teller (BET) analysis of the synthesized catalysts was carried out, which indicated that Cu@KF-C/CoFe2O4 possess more surface area as well as pore volume, and so accounting for the highest activity among the other synthesized catalysts. Further, X-ray photoelectron spectroscopy (XPS) analysis was performed, which inferred that Cu@KF-C/CoFe2O4 contains most of the copper in reduced form, i.e., Cu(0), which is the active species responsible for better catalytic activity toward Chan–Lam coupling reactions as well as oxidation of alcohols and hydrocarbons. The physiochemical properties of the most active catalyst, Cu@KF-C/CoFe2O4, was examined by BET, XPS, Fourier transform infrared Spectroscopy (FTIR), thermogravimetric analysis (TGA), field emission gun scanning electron microscopy (FEG-SEM), high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray (EDX) mapping, energy dispersive X-ray (EDX), inductively coupled plasma atomic emission spectroscopy (ICP-AES), powder X-ray diffraction (XRD), and vibrating sample magnetometry (VSM). Moreover, Cu@KF-C/CoFe2O4 shows excellent stability as well as reusability and could be easily separated with the help of an external magnet.

EVALUATION OF CALCIUM CARBONATE CONTENT IN EGGSHELLS OF AVIAN, TURTLE, SNAIL, AND OSTRICH USING CHEMICAL ANALYSIS AND SCANNING ELECTRON MICROSCOPY

In the present study, different eggs were collected and analyzed from five various animal species: European pond turtle (Emys orbicularis (Linnaeus, 1758)), giant African land snail (Achatina fulica (Bowdich, 1822)), common ostrich (Struthio camelus (Linnaeus, 1758)), white, light-brown, and dark-brown laying hen (Gallus gallus domesticus (Linnaeus, 1758) and European quail (Coturnix coturnix (Linnaeus, 1758). The typical mineral shell mainly composed of the calcite polymorph of CaCO3 but the eggshell consists of membranes, that composed mainly of proteins. The shell quality also could be assigned by several external and internal factors such as oviposition time, animal genotype and age, housing system (for poultry), and mineral nutrition complex. The CaCO3 content was determined by the standard titration method, coz the titration could provide a reliable method for evaluation of CaCO3 content in different types of eggshells. The structural surface characterization of eggshells was performed by scanning electron microscopy (SEM) with a field emission gun. In terms of chemical composition, ostrich eggshells generally did not differ much from those of laying hen, turtles, giant snails, or quail eggs, but the concentration of calcium carbonate was the highest. The average calcium carbonate content of various eggshells is between 84 and 98%. The thickness of the eggshell ranges from 0.08 to 1.89 mm, and it is not the same over the entire surface of the egg. At the sharp end of the egg, the shell is slightly thicker than at the blunt end. The purpose of this study was to study the quantitative content of calcium carbonate in various eggshells of different animals to draw further conclusions in which animals the eggshell contains the maximum amount of biological calcium carbonate.

Silver nanoparticles stabilized by ramnolipids: Effect of pH

Rhamnolipids are glycolipid biosurfactants that have remarkable physicochemical characteristics, such as the capacity for self-assembly, which makes these biomolecules a promising option for application in nanobiotechnology. Rhamnolipids produced from a low-cost carbon source (glycerol) were used to stabilize silver nanoparticles. Silver nanoparticles (AgNPs) have been the subject of studies due to their physical chemical as well as biological properties, which corroborate their catalytic and antimicrobial activity. We compared nanoparticles obtained with three different pH values during synthesis (5, 7 and 9) in the presence of rhamnolipids. Dynamic light scattering showed that larger particles were formed at pH 5 (78–190 nm) compared to pH 7 (6.5–43 nm) and 9 (5.6–28.1 nm). Moreover, nanoparticle stability (analyzed based on the zeta potential) was enhanced with the increase in pH from 5 to 9 (−29.86 ± 1.04, −37.83 ± 0.90 and −40.33 ± 0.57 mV, respectively). Field emission gun scanning electron microscopy confirmed the round morphology of the silver nanoparticles. The LSPR spectra of AgNP for the pHs studied are conserved. In conclusion, different pH values in the presence of rhamnolipids used in the synthesis of silver nanoparticles directly affect nanoparticle size and stability.

Field-emission electron gun for a MEMS electron microscope

This article presents a field-emission electron gun intended for use in a MEMS (microelectromechanical system) electron microscope. Its fabrication process follows the technology of a miniature device under development built from silicon electrodes and glass spacers. The electron gun contains a silicon cathode with a single very sharp protrusion and a bundle of disordered CNTs deposited on its end (called a sharp silicon/CNT cathode). It was tested in diode and triode configurations. For the diode configuration, a low threshold voltage <1000 V and a high emission current that reached 90 µA were obtained. After 30 min of operation at 900 V, the emission current decreased to 1.6 µA and was stable for at least 40 min, with RMS fluctuation in the anode current lower than 10%. The electron beam spot of the source was observed on the phosphor screen. In the diode configuration, the spot size was the same as the emission area (~10 µm), which is a satisfactory result. In the triode configuration, an extraction electrode (gate) control function was reported. The gate limited the emission current and elongated the lifetime of the gun when the current limit was set. Moreover, the electron beam current fluctuations at the anode could be reduced to ~1% by using a feedback loop circuit that controls the gate voltage, regulating the anode current. The developed sharp silicon/CNT cathodes were used to test the MEMS electron source demonstrator, a key component of the MEMS electron microscope, operating under atmospheric pressure conditions. Cathodoluminescence of the phosphor layer (ZnS:Ag) deposited on the thin silicon nitride membrane (anode) was observed.

CHARACTERIZATION OF CHROMIUM NITRIDE PRECIPITATION IN THE HEAT AFFECTED ZONE OF THE SUPERDUPLEX STAINLESS STEEL UNS S32750: AN EXPERIMENTAL AND NUMERICAL ANALYSIS

It is well known that pitting corrosion resistance of duplex and superduplex stainless steels strongly depends on &#x0D; microstructural characteristics such as ferrite/austenite proportion, presence of intermetallic phases and elemental partitioning between the austenite and ferrite phases. In particular, during the welding operation, very fine chromium nitrides may precipitate &#x0D; within ferrite grains of the heat affected zone drastically reducing the corrosion resistance of welded joints of duplex and super duplex stainless steels. However, due to their small size and low distribution, analyzing the chemical composition and crystallography of chromium nitrides is quite difficult and only a restricted number of advanced techniques of investigation may discriminate their signal from the surrounding matrix. This work is aimed at supporting the microstructural characterization of a welded joint of a superduplex stainless steel by means of a field-emission gun scanning electron microscope. Sub-micron chromium nitride precipitates, identified within the ferritic grains of the heat affected zone, are recognized to be the main reason for the reduced pitting corrosion resistance of the analyzed welded joints. The results are supported by a multi-pass welding process numerical simulation aimed at estimating the cooling rates promoting chromium nitride precipitation in the heat affected zone.

Biochar Derived from Treated Lotus Stem and Adsorption of Phthalic Acid Esters

Phthalic acid ester (PAE), a plasticizer, is increasingly being detected in different environments. These compounds can gravely affect the human endocrine system. The present study aims to prepare adsorbents that can effectively adsorb PAE pollutants. To fabricate a better carbon structure than conventional biochar, the sodium hydroxide solution was used as a hydrolyzing agent to pretreat the biomass in order to weaken the bonds in lignin, cellulose, and hemicellulose. As a result, biochar with a special porous carbon structure is obtained. To study the characteristics of the biochar and its adsorption properties, dimethyl phthalate (DMP)—a PAE—was selected as the adsorbate. The morphology and structural composition of the biochar were examined via an environment scanning electron microscope with a field emission gun (SEM), surface area analyzer (BET), Fourier transform infrared spectrometer (FTIR), thermal gravimetry (TG/DTG), X-ray diffractometry (XRD), and Raman spectroscopy. The BET data of the biochar increased by 125.3 times than that of the original biochar. The layer spacing and the surface functional groups of the pretreated biochar also increased. After performing the micro-morphological regulation of biomass using sodium hydroxide, the adsorption performance of biochar with regard to PAE effectively improved and an adsorption capacity of 125 mg/g was observed for DMP. The adsorption kinetics and thermodynamic experiments showed that DMP adsorption by biochar follows the Langmuir and pseudo-second-order models.

Biogenic ZnO Nanoparticles Synthesized Using a Novel Plant Extract: Application to Enhance Physiological and Biochemical Traits in Maize.

The need to increase crop productivity and resistance directs interest in nanotechnology. Indeed, biogenic metal oxide nanoparticles can promote beneficial effects in plants, while their synthesis avoids the environmental impacts of conventional synthetic procedures. In this context, this research aimed to synthesize biogenic zinc oxide nanoparticles (ZnO-NPs) using, for the first time, an extract of a wild and spontaneous aquatic species, Lemna minor (duckweed). The effectiveness of this biogenic synthesis was evidenced for comparison with non-biogenic ZnO-NPs (obtained without using the plant extract), which have been synthesized in this research. XRD (X-ray diffraction), FE-SEM (field emission gun electron scanning microscopy), EDX (energy dispersive x-ray spectroscopy), TEM (transmission electron microscope) and UV-vis (ultraviolet-visible spectrophotometry) showed the biogenic approach effectiveness. The duckweed extract was subjected to UHPLC-ESI/QTOF-MS (ultra high-pressure liquid chromatography quadrupole time of flight mass spectrometry) phenolic profiling. This untargeted characterization highlighted a high and chemically diverse content in the duckweed extract of compounds potentially implicated in nanoparticulation. From an application standpoint, the effect of biogenic nanoparticles was investigated on some traits of maize subjected to seed priming with a wide range of biogenic ZnO-NPs concentrations. Inductive effects on the shoot and root biomass development were ascertained concerning the applied dosage. Furthermore, the biogenic ZnO-NPs stimulated the content of chlorophylls, carotenoids, and anthocyanin. Finally, the study of malondialdehyde content (MDA) as a marker of the oxidative status further highlighted the beneficial and positive action of the biogenic ZnO-NPs on maize.

A molecularly imprinted polymer on reduced graphene oxide-gold nanoparticles modified screen-printed electrode for selective determination of ferulic acid in orange peels

This work reports the development of a molecularly imprinted polymer used for the sensitive and selective electrochemical detection of ferulic acid. The device was prepared by the electropolymerization of molecularly imprinted poly(phenol) film on screen-printed electrode modified with reduced graphene oxide and gold nanoparticles. The modified electrode was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy with field emission gun, energy dispersive X-ray spectroscopy, RAMAN spectroscopy and atomic force microscopy. Under optimized conditions, the proposed electrode presented a linear working range of 10 nM to 1 µM and a detection limit of 3.1 nM (n = 3). The sensor displayed good repeatability and stability over time, as well as excellent selectivity when applied for the detection of ferulic acid molecule. The method proposed here was successfully applied for ferulic acid detection in orange peels. The analyses were validated by recovery assays, where recovery values between 99 and 103% were obtained. The results of the study show that this electroanalytical methodology has good accuracy when employed for the detection of ferulic acid.

Extending Cryo-EM to Nonaqueous Liquid Systems.

ConspectusCryogenic-temperature transmission electron microscopy (cryo-TEM) of aqueous systems has become a widely used methodology, especially in the study of biological systems and synthetic aqueous systems, such as amphiphile and polymer solutions. Cryogenic-temperature scanning electron microscopy (cryo-SEM), while not as widely used as cryo-TEM, is also found in many laboratories of basic and applied research. The application of these methodologies, referred to collectively as cryogenic-temperature electron microscopy (cryo-EM) for direct nanostructural studies of nonaqueous liquid systems is much more limited, although such systems are important in basic research and are found in a very large spectrum of commercial applications. The study of nonaqueous liquid systems by cryo-EM poses many technical challenges. Specimen preparation under controlled conditions of air saturation around the specimen cannot be performed by the currently available commercial system, and the most effective cryogen, freezing ethane, cannot be used for most such liquid systems. Imaging is often complicated by low micrograph contrast and high sensitivity of the specimens to the electron beam.At the beginning of this Account, we describe the basic principles of cryo-EM, emphasizing factors that are essential for successful direct imaging by cryo-TEM and cryo-SEM. We discuss the peculiarities of nonaqueous liquid nanostructured systems when studied with these methodologies and how the technical difficulties in imaging nonaqueous systems, from oil-based to strong acid-based liquids, have been overcome, and the applicability of cryo-TEM and cryo-SEM has been expanded in recent years. Modern cryo-EM has been advanced by a number of instrumental developments, which we describe. In the TEM, these include improved electron field emission guns (FEGs) and microscope optics, the Volta phase plate to enhance image contrast by converting phase differences to amplitude differences without the loss of resolution by an objective lens strong underfocus, and highly sensitive image cameras that allow the recording of TEM images with minimal electron exposure. In the SEM, we take advantage of improved FEGs that allow imaging at a low (around 1 kV) electron acceleration voltage that is essential for high-resolution imaging and for avoiding specimen charging of uncoated nonconductive specimens, better optics, and a variety of sensitive detectors that have considerably improved resolution and, under the proper conditions, give excellent contrast even between elements quite close on the periodic table of the elements, such as the most important oxygen and carbon atoms.Finally we present and analyze several examples from our recent studies, which illustrate the issues presented above, including the remarkable progress made in recent years in this field and the strength and applicability of cryo-EM methodologies.

A comprehensive investigation of waste expanded polystyrene recycling by dissolution technique combined with nanoprecipitation

In this work, an environmentally friendly and value-added technique was employed to obtain polystyrene (PS) nanoparticles from expanded polystyrene (EPS) waste. The waste was dissolved in ethyl acetate and nanoprecipitated in ethyl alcohol, which are green and renewable solvents. The EPS concentration, stirring speed and solvent/non-solvent ratio (S/N) were evaluated in obtaining nanoparticles. The precipitated nanomaterial was characterized by Dynamic Light Scattering (DLS), Field Emission Gun Scanning Electron Microscopy (FEG-SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Thermogravimetric Analysis (TG), Differential Scanning Calorimetry (DSC) and Gel Permeation Chromatography (GPC). It was verified that the smaller nanoparticles were obtained with lower PS concentration (1 wt.%), greater stirring speed (2500 RPM), and higher S/N ratio (1:30). The observed morphology was spherical and no change in the chemical structure of the sample was verified, the glass transition temperature (Tg) was similar (101 °C) and there was no change in the crystalline structure of the sample. Regarding the efficiency and sustainability of the process, all used solvents can be easily recovered by distillation process.

Metformin hydrochloride sustained release biopolymeric system composed by PLLA‐CMC microparticles

AbstractMetformin hydrochloride (MetHCl) is a drug extensively used to treat diabetes mellitus Type 2. However, its high hydrophilicity drastically reduces its metabolic absorption. Consequently, high drug concentrations should be taken by patients to achieve the desired therapeutical efficiency, causing several side effects. The present study proposes the development of a MetHCl sustained release biopolymeric system composed of poly(l‐lactic acid) (PLLA) and carboxymethyl cellulose (CMC) as a strategy to minimize the problems aforementioned. The PLLA‐CMC microparticles were produced by the double emulsion‐solvent evaporation technique using two distinct emulsifiers in the first emulsion (Span 80 and Tween 80). The microparticles were characterized by ultraviolet–visible spectrophotometry, scanning electron microscopy with field emission gun, thermogravimetric analyses, and differential scanning calorimetry (DSC). Additionally, in vitro drug release assays were performed. The results demonstrated that the emulsion stability and encapsulation efficiency increased in a dependent fashion way with the CMC concentration. DSC findings showed that the choice of the emulsifier of the first emulsion influences the polymer particle's crystallinity and, consequently, the releasing behavior of the drug. The in vitro studies revealed that the encapsulation of MetHCl in PLLA‐CMC microparticles is a promising sustained release system compatible with a zero‐order kinetic mechanism.

Acid–base sensor based on sol–gel encapsulation of bromothymol blue in silica: application for milk spoilage detection

In this work, silica capsules containing bromothymol blue (BTB) were synthesized by a modified Stober sol–gel method. These silica capsules were dispersed into a high-density polyethylene (HDPE)/ethylene-vinyl acetate (EVA) polymeric matrix and then applied in milk spoilage detection tests. The effect of the KOH/BTB molar ratio used in the sol–gel synthesis on the structural, textural, and morphological characteristics of the resulting silica capsules was also investigated. Field emission gun scanning electron microscopy images of the silica capsules showed particles with spherical morphology and size ranging from 0.1 to 1 µm. All silica capsules presented a very low porosity and an encapsulated BTB content in the range of 12–37 µmol g−1. The increase of the KOH/BTB molar ratio resulted in an increase in the relative amount of six-fold siloxane rings and a decrease in the BET surface area of the silica capsules. Spoilage kinetics of milk at room and fridge temperature were much different, as evidenced by pH milk measurements. The milk storage temperature and the KOH content in the silica capsules affected the intensity and rate of blends color change. Blends (HDPE/EVA/silica capsules) with lower KOH content in the capsules showed faster kinetics and higher intensities of color change during the milk spoilage at both tested temperatures. These results showed the potential of the HDPE/EVA/silica capsules as a base material to a sensor packaging, which allows the verification of the milk quality by the end-users.

Effect of Ag decoration on the photodetection of catalyst-free synthesized vertically oriented SiOx NW arrays

This study reports a catalyst-free synthesis of silver (Ag) nanoparticles (NPs) decorated SiOx nanowire (NW) arrays on silicon (Si) substrates by employing the GLAD technique. A huge enhancement in optical absorption was seen all over the visible spectrum as compared to bare SiOx NW arrays. Photoluminescence measurement showed many defect-related emissions in the UV-vis region. The successful growth of vertically oriented Ag decorated SiOx NWs on Si substrate was manifested through the field emission gun scanning electron microscopy (FEGSEM) with energy dispersive X-ray spectroscopy (EDS) analysis. The transmission electron microscope analysis revealed the crystalline and amorphous nature of Ag NPs and SiOx NWs respectively. Through Tauc plot, a low bandgap of 1.9 eV was obtained after decorating the bare SiOx NWs with Ag NPs. The device successfully exhibited properties of Schottky diode through its rectifying behaviour. Most interestingly, very low turn-on voltages of 1.4 V and 1.8 V were obtained for Ag decorated SiOx NWs corresponding to the white light and dark conditions as compared to bare SiOx NWs whose turn–on voltages were 1.8 V and 2.8 V respectively. The Ag decorated SiOx NW detector gave a low ideality factor of only 10.27 as compared to 20.99 for bare SiOx NW detector. At −5 V, the device showed a responsivity of 1.54 A/W, detectivity of 2.12 × 1010 Jones and EQE of 5.17 × 102 %. Moreover, seven-fold enhancement of photocurrent to dark current contrast ratio was obtained for the Ag decorated SiOx NW device at -0.2 V accompanied with a fast response of 0.12 s (rise time) and 0.11 s (fall time), thus expanding its usability.

Chitosan and chitosan/PEG nanoparticles loaded with indole-3-carbinol: Characterization, computational study and potential effect on human bladder cancer cells

Indole-3-carbinol (I3C) is a plant molecule known to be active against several types of cancer, but some chemical characteristics limit its clinical applications. In order to overcome these limitations, polymeric nanoparticles can be used as carrier systems for targeted delivery of I3C. In this study, chitosan and chitosan/polyethylene glycol nanoparticles (CS NP and CS/PEG NP, respectively) were prepared to encapsulate I3C by ionic gelation method. The polymeric nanoparticles were characterized by Dynamic Scattering Light (DLS), Zeta Potential (ZP), Fourier Transform Infrared (FTIR) spetroscopy, X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and Field Emission Gun Scanning Electron Microscopy (FEG-SEM). I3C release testing was performed at an acidic media and the interactions between I3C and chitosan or PEG were evaluated by Density Functional Theory (DFT). Cytotoxicity of nanoparticles in bladder cancer T24 cell line was evaluated by the Methyl-thiazolyl-tetrazolium (MTT) colorimetric assay. The average size of the nanoparticles was observed to be in the range from 133.3 ± 3.7 nm to 180.4 ± 2.7 nm with a relatively homogeneous distribution. Samples had relatively high positive zeta potential values (between +20.3 ± 0.5 mV and + 24.3 ± 0.5 mV). Similar encapsulation efficiencies (about 80%) for both nanoparticles were obtained. Physicochemical and thermal characterizations pointed to the encapsulation of I3c. electron microscopy showed spherical particles with smooth or ragged surface characteristics, depending on the presence of PEG. The mathematical fitting of the release profile demonstrated that I3C-CS NP followed the Higuchi model whereas I3C-CS/PEG NP the Korsmeyer-Peppas model. Chemical differences between the nanoparticles as based on the I3C/CS or I3C/PEG interactions were demonstrate by computational characterization. The assessment of cell viability by the MTT test showed that the presence of both free I3C and I3C-loaded nanoparticles lead to statistically significant reduction in T24 cells viability in the concentrations from 500 to 2000 μM, when comparison to the control group after 24 h of exposure. Thus, CS and CS/PEG nanoparticles present as feasible I3C carrier systems for cancer therapy.

TiO2 nanoparticle deposition on cotton fabric through pulsed electrical current in water/TiO2 solution

The present paper investigates TiO2 nanoparticle (TiO2-NP) deposition on cotton fabric through a pulsed electrical current in a water/TiO2-NP solution. The experiments used short voltage pulses with an amplitude around 1200 V, an intermediate value between those used in electrophoretic deposition (tens of V) and plasma discharge in liquids (tens of thousands of V). A sequence of pulse trains with five pulses of 1.0 μs delivered electrical energy to the mixture. The electrodes were kept 28 mm apart. An asymmetry appeared in the current waveform when the medium contained TiO2-NPs. The pieces of cotton fabric were characterized using X-ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). The electrical discharge treatment increased the Ti concentration on the fabric surface by as much as 6% according to XPS analysis. XRD analysis confirmed the XPS results for treated samples, indicating the presence of anatase TiO2. In the FTIR analysis, a shoulder at 800 cm−1 was observed and can be associated with coordination interactions between Ti and the OH groups of glucose. The nanoparticle adhesion was verified by observing the cotton fabric surface through field emission gun scanning electron microscopy after multiple washes. Even after 20 washing cycles, there was a considerable amount of nanoparticles on the sample surface.