Spherical Grains Research Articles

Spherical Lignin-Derived Activated Carbons for the Adsorption of Phenol from Aqueous Media.

In this work, a synthesis and activation path, which enabled the preparation of spherical activated carbon from a lignin precursor, characterized by high adsorption capacity in the removal of phenolic compounds from water, was successfully developed. Two industrial by-products, i.e., Kraft lignin and sodium lignosulfonate, were used to form spherical nanometric lignin grains using pH and solvent shift methods. The obtained materials became precursors to form porous activated carbons via chemical activation (using K2CO3 or ZnCl2 as activating agents) and carbonization (in the temperature range of 600-900 °C). The thermal stabilization step at 250 °C was necessary to ensure the sphericity of the grains during high-temperature heat treatment. The study investigated the influence of the type of chemical activator used, its quantity, and the method of introduction into the lignin precursor, along with the carbonization temperature, on various characteristics including morphology (examined by scanning electron microscopy), the degree of graphitization (evaluated by powder X-ray diffraction), the porosity (assessed using low-temperature N2 adsorption), and the surface composition (analyzed with X-ray photoelectron spectroscopy) of the produced carbons. Finally, the carbon materials were tested as adsorbents for removing phenol from an aqueous solution. A conspicuous impact of microporosity and a degree of graphitization on the performance of the investigated adsorbents was found.

Learning subsurface scattering solutions of tightly-packed granular media using optimal transport

Many materials, such as sand, rice, wheat, or other kinds of seeds, consist of numerous individual grains that determine the visual appearance of these materials. When generating images of these mixtures, the primary challenge is to simulate the interaction of light with each individual grain. While subsurface scattering effects are crucial for producing realistic images, the computation of light transport using standard path tracing methods for each grain can be prohibitively expensive. Although there have been several methods developed to address this issue, they all assume that bounding spheres of individual grains do not intersect. This restriction limits the application of these methods to almost spherical grains. Nonetheless, various grains, such as seeds and rice, are non-spherical, making this assumption lead to impractical stackings in situations involving coarse-grained materials. We address this issue by presenting a subsurface scattering model that utilizes a neural network and is trained using an optimal transport framework. Our model surpasses path tracing approaches conclusively, allowing for efficient rendering of granular mixtures that were previously unfeasible. Additionally, this method can be utilized in large-scale procedural generated scenes based on sphere packings and obtains similar results as previous methods in these cases.

Metastable microstructure evolution and grain refinement in a Low-Ta containing γ-TiAl alloy through heat treatment

The paper comprehensively describes the evolution of metastable microstructures in a cast low-Ta-containing γ-TiAl alloy during cooling-tempering-lamellarization heat treatments. The behavior and mechanism of microstructure refinement are discussed. The rapid cooling generates metastable microstructures, including Widmanstätten, feathery, and massive structures, with many γ variants in small sizes and different orientations. It significantly refines the coarsened colonies and randomizes the texture. The tempering can effectively stabilize the metastable microstructures. During tempering, the γ→α phase transformation is more active at higher temperatures while coarsening and recrystallization dominate at lower temperatures. After tempering, a refined microstructure with spherical grains and convoluted structures forms. Subsequent lamellarization treatment optimizes the microstructure and obtains a fine-grained nearly-lamellar microstructure with small colonies (∼70 μm) and dispersed fine γ grains (∼10 vol%), which yielded a 1.0 % elongation with a 487 MPa yield strength (0.2%) and a 589 MPa ultimate tensile strength at room temperature. Finally, the unique promotion effects and mechanism of a small amount of Ta addition on the nucleation, growth, evolution, and stabilization of metastable microstructures are concluded and discussed, which is crucial for the refinement of cast γ-TiAl alloy by heat treatment alone.

Study of dielectric and electrical properties of novel lead-free double perovskite oxide

The current work focuses on the synthesis of lead free novel double perovskite oxide and detailed investigation of its dielectric and electrical characteristics. Single phase lead free double perovskite Pr2FeCrO6 (PFCO) is prepared by co-precipitation technique. Structural studies reveal orthorhombic structure with Pbnm space group. Scanning electron microscopic study shows mixed type of grains; spherical and rectangular grains forming layered structures with few pores. Bonding features and local structure are analyzed via FTIR and Raman spectroscopy. Optical absorption study show narrow energy band gap of 2.14 eV. Room temperature dielectric studies show colossal dielectric constant (∼104) with low loss. The dielectric relaxation dynamics are studied in the temperature range; 25° to 200 °C. The detailed investigation of electrical properties and conduction mechanism in PFCO is carried out via impedance spectroscopy.

Flow rate in 2D silo discharge of binary granular mixtures: the role of ordering in monosized systems

A long-standing debate regarding the dynamics of silo discharge revolves around the use of mono-dispersed circular or spherical grains in simplified two-dimensional models. It is well-known that granular systems composed of particles of the same size can generate crystal or quasi-crystal domains with specific structural and dynamic behaviors. Can this ordering affect the flow rate to an extent that monosized systems cannot be good models for realistic materials? In this work, we present simulations of the discharge of two-dimensional silos filled with binary mixtures of circular grains that conserve the same mean particle size. We address the question of how ordering affects the mass flow rate, in particular considering the limit of mono-sized systems. We find that the typical hexagonal order observed does not affect the flow rate significantly. However, the flow rate does exhibit a weak, nonmonotonic dependence on packing bidispersity that correlates with changes in the outpouring speed of grains in the vicinity of the orifice.

Structural, magnetic and dielectric properties of green synthesized Ag doped NiFe2O4 spinel ferrite

Ag-doped nano NiFe2O4 spinel ferrites were successfully synthesized using an environmentally friendly sol-gel technique. Comprehensive characterization of the obtained samples was carried out, employing techniques such as X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. The results from XRD and FTIR analyses unequivocally confirmed that the synthesized samples were of high purity and in a well-defined phase. Furthermore, examination of the samples through Field Emission Scanning Electron Microscopy (FESEM) revealed the formation of spherical grains, with an average grain size of 50 nm for pure NiFe2O4 nanoparticles and an increased size of 72 nm for the Ag-doped NiFe2O4 nanoparticles. Moreover, the investigation delved into the electrical conductivity and optical properties of these nanoferrites. It was noteworthy that the electrical conductivity demonstrated a significant enhancement in the case of Ag-doped NiFe2O4, further indicating the potential for improved performance. Magnetic analysis revealed a coercivity value (Hc) of 2.27 A/m for NiFe2O4, while the Ag-doped NiFe2O4 nanoparticles exhibited long-range ferromagnetic ordering. Additionally, optical absorption experiments disclosed an energy band gap of 1.75 eV for NiFe2O4, whereas the Ag-doped NiFe2O4 showcased a reduced energy band gap of 1.256 eV. These findings collectively contribute to a better understanding of the properties and potential applications of these materials in various technological domains.

Effect of Mg doping at Fe/Cr site on magnetic and optical properties of Gd2FeCrO6 double perovskite

The influence of Mg doping on structural, magnetic and optical characteristics of Gd2FeCrO6, Gd2Fe0.75Mg0.25CrO6 and Gd2FeCr0.75Mg0.25O6 double perovskites has been systematically investigated. The monoclinic crystal structure with the P21/n space group is confirmed by powder X-ray diffraction data. From the scanning electron microscopy graphs, we noticed few nearly spherical and dumbbell-shaped grains for all compounds with an average grain size of about 76 - 85 nm. The magnetic studies demonstrated the presence of a weak ferromagnetic transition with antiferromagnetic background at low temperatures for all the samples. A decrement in the transition temperature of Gd2FeCrO6 (TC = 8.14 K) is observed on Mg doping, which is due to the smaller ionic radii of Mg at the Fe/Cr site in Gd2Fe0.75Mg0.25CrO6 and Gd2FeCr0.75Mg0.25O6 double perovskites. By analyzing the UV–visible spectroscopic absorption data, direct band gaps around 3 eV are concluded for pure and Mg doped Gd2FeCrO6 double perovskites, validating their application in wastewater photocatalysis.

Structural investigation, magnetic and DC electrical resistivity properties of Co0.5-xNixZn0.5Fe2O4 nano ferrites

The Ni2+ substituted Cobalt-Zinc nano ferrites, designated as Co0.5-xNixZn0.5Fe2O4 with x values ranging from 0.0 to 0.5, were synthesized using the sol–gel auto-combustion method. Various characterization techniques, including x-ray diffraction (XRD), field-effect scanning electron microscopy (FESEM), Fourier Transform Infrared (FTIR) spectroscopy, vibrating sample magnetometer (VSM), and DC electrical resistivity measurements, were employed to analyze the prepared samples. XRD analysis revealed a cubic spinel structure with a lattice constant ranging from 8.384 to 8.412 Å. FESEM examination indicated non-uniform-shaped spherical grains in the nanometer range for the synthesized samples. The FTIR spectra of the spinel ferrites revealed two distinctive bands, ν2 (580–592 cm−1) and ν1 (390–412 cm−1), which are the characteristics of spinel-structured ferrite nanomaterials. With progressive substitution (x varying from 0.0 to 0.5), the saturation magnetization (Ms) values exhibited a gradual decrease, starting from Ms = 60.97 emu/g (at x = 0.0) and reaching Ms = 38.79 emu/g (at x = 0.5). A discernible pattern was observed in coercivity (Hc), which rose from Hc = 115 Oe (at x = 0.0) to Hc = 920 Oe (at x = 0.5), with peak values determined through VSM analysis. Similar to semiconductors, the electrical resistivity experienced a decline with increasing temperature, indicative of a negative temperature coefficient.

Effects of gamma irradiation on the properties of Ce2S3 thin films

Cerium sulphide (Ce2S3) thin films were prepared via successive ionic layer adsorption and reaction (SILAR) scheme. The optical, structural, and electrical investigations of both virgin and gamma-exposure samples were conducted, focussing on the gamma irradiation dose. The objective was to examine the impact of gamma irradiation on the characteristics of the Ce2S3 thin films. An X-ray diffraction (XRD) study of the samples established the orthorhombic phase of the Ce2S3 thin films and revealed that the crystallinity was improved with the gamma dose. The Field emission scanning electron microscope (FESEM) images of the virgin thin film detected a smooth surface with spherical grains with distinct grain boundaries. In contrast, after the gamma exposure, the thin film surface revealed a cluster of small particles. Energy dispersive X-ray (EDX) study inveterate the stoichiometry of the prepared Ce2S3 thin films. The gamma exposure dose caused a deviation in the bandgap, which was related to the quantum confinement effect. Photoluminescence (PL) spectra proved that the emission intensity of the Ce2S3 thin films decreased with increasing gamma dosage, and this phenomenon was attributed to the additional crystallites and a smaller number of structural defects. This simple approach to amend the characteristics of Ce2S3 thin films by gamma exposure could become an attractive option to explore this material for dosimetry and radiation sensing.

Two-Phase Flow Through the PTL of PEM Water Electrolyzer: MRI Experiments and Numerical Modeling Using Phase-Field Theory

In 2021, estimation shows that the worldwide annual hydrogen production is around 94 Mt. Exploitation of native hydrogen being not mature, it is obtained by its separation from other elements by different methods such as steam methane reforming, and electrolysis of water. The latter supplied by a renewable power source will take part in the development of a green hydrogen economy [1]. In this context, Proton Exchange Membrane (PEM) Electrolyzer is a promising technology due to its flexibility and very quick adaptation to load variations. However, its current development still confronts some limitations at a large industrial scale. For instance, efficiency and durability are directly impacted by the mass transport and electrical transfer within the porous materials at the anode side. Limitation of the water supply to the catalyst layer happens once there is a poor oxygen evacuation which decreases the performance of the device by inducing high overpotential. Furthermore, the PTL has an important role as an electrical conductor for charge transfer from the catalyst layer [1]. The efficiency of all the transport phenomena through the PTL and porous electrode assembly depends on their transport properties which are related to their microstructure and operating conditions. For instance, PTL with a large pore size allows good water and gas transport, while produced electrons choose a long-distance path generating an electrical resistance higher than that in the case of PTL with a small pore size [1]. So, controlled and optimum porosity and pore size could contribute to efficient water, gas, and electron transport. To define the best porous layers morphologies, a deep and accurate understanding of the phenomena is developed in this work by combining modeling and experiments.The magnetic resonance imaging (MRI) technique was used to quantify the water content within the porous layer during the two-phase flow. Instead of the real PTL made of titanium which is paramagnetic and cannot be used in the MRI, borosilicate filters with thickness, porosity, and pore size similar to the PTL were used. After positioning the sample in the 600 MHz vertical imager (Figure 1-A), a constant water flow rate is introduced while the gas flow rate is varied. The saturation profiles measured through the porous material depend on the gas flow rate and a semi-dryness of the sample occurs (Figure 1-B) with a residual quantity trapped between pores (minimum stable water content). The water flow rate variation in the channel does not affect saturation, but a higher gas flow rate is needed to reach a minimum stable water content for higher water flow rate.The gas pressure drop through the porous medium was measured and bubble formation in the channel was also analyzed. The results show that the pressure drops and types of flow (slug, annular, and bubble flow) depend on orientation of the water channel (horizontally and vertically) and flow direction (up or downward), and on the water and gas flow rates.To reach a better understanding of the dynamic characteristics of water and oxygen transport over the PTL, the phase-field model based on the Cahn-Hilliard theory was used to simulate the two-phase flow through a porous medium [2]. In this model, the modified Navier-Stokes equations for two phases are coupled with a phase-field equation for describing the diffuse interface. Numerical simulations performed in the COMSOL® multiphysics software were carried on 2D geometries composed of spherical solid grains of different sizes, having properties similar to the PTL used in the MRI experiments. Gas is injected on one side of the sample and flows through the porous medium initially saturated and evacuated on another side in contact with the water channel (Figure 1-C). Gas flow in the porous medium and bubble formation in the water channel are studied while varying the gas and water flow rates. The simulation results give information about the gas pathways within the porous medium and the saturation profiles over time, depending on the gas/water flow rates, which will be compared with experimental results.[1] J. Parra-Restrepo, “Caractérisation des hétérogénéités de fonctionnement et de dégradation au sein d’un électrolyseur à membrane échangeuse de protons (PEM),” Université de Lorraine, 2020.[2] J. W. Cahn and J. E. Hilliard, “Free Energy of a Nonuniform System. I. Interfacial Free Energy,” The Journal of Chemical Physics, vol. 28, no. 2, pp. 258–267, Feb. 1958. Figure 1

Crystallographic, Electric and Optical Analysis of Cs1+ Doped H3PW12O40 Nanocrystalline Thin Films Deposited by Microwave Assisted Chemical Bath Deposition Method

AbstractThe polyoxometalates like phosphotungstic acid (PTA) (H3PW12O40) and Cesium (Cs+) doped phosphotungstic acid (Cs‐PTA) (Cs3‐PW12O40) nanocrystalline thin films were effectively deposited by microwave assisted chemical bath deposition (MA‐CBD) technique. The structural characterization of microwave aided H3PW12O40 and Cs3‐PW12O40 thin films were done by Thermo gravimetric (TG) and Differential thermal analysis (DTA) techniques, X‐ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and Energy dispersive X‐ray analysis (EDAX). The TGDTA analysis revealed that the complete decomposition process of Cs‐PTA compound is carried out at 600 °C and which is comparatively lower than that of other chemical method. The X‐ray diffractogram confirms the polycrystalline nature of the synthesized H3PW12O40 and Cs3‐PW12O40 thin films having spinel cubic crystal structure. The lattice parameter of H3PW12O40 and Cs3‐PW12O40 compound found to be in the range of 11.34 Å to 11.46 Å. The main absorption peaks observed nearly 800, 1000 and 1100 cm−1 confirms the formation of H3PW12O40 and Cs3‐PW12O40 materials. The porous structure of nanocrystalline spherical grains morphology of H3PW12O40 and Cs3‐PW12O40 films were confirmed from SEM analysis. An appropriate peaks of metal ions like P, W, O and Cs observed in EDAX spectra shows the stoichiometric formation of H3PW12O40 and Cs3‐PW12O40 thin films.

Experimental Phase Function and Degree of Linear Polarization of Light Scattered by Hydrogenated Amorphous Carbon Circumstellar Dust Analogs

Astronomical observations of the polarized intensity of scattered visible light have revealed the presence of dust envelopes around different types of evolved stars. These observations have helped determine the diameter and width of dust shells around stars with unprecedented accuracy. Simple geometric particle models are used in order to retrieve dust properties from these observations. In this work, we have synthesized and characterized a particulate sample of hydrogenated amorphous carbon (HAC), which is considered to be a realistic carbonaceous interstellar dust analog based on infrared absorption spectroscopy, and we have measured its phase function and degree of linear polarization curves at 514 nm using the CODULAB apparatus at IAA-CSIC. The experimental light-scattering data has been examined in order to explore possible improvements in the interpretation of astronomical observations of circumstellar dust from the point of view of the retrieval of dust properties, including size and porosity. Our results suggest that circumstellar dust observations of linearly polarized scattered light, which are commonly attributed to a population of spherical grains with a radius of ∼0.1 μm, are consistent with larger porous aggregates composed of nanometer-sized grains. In addition, an internal 50wt% mixture of HAC and ultrafine forsterite powder has been generated to study the effect of the mixing of these two components on the light-scattering behavior of dust in cometary environments and protoplanetary disks. In this case, the HAC component, which is not very absorbent, has a very small effect, and the mixture scatters light similarly to the forsterite sample.

Submicroscopic iron-rich grains throughout impact glasses in Chang'E-5 regolith

In lunar regolith returned by Chang'E-5, Apollo and Luna missions, submicron-sized iron-rich grains that are dominated by reduced iron and with sizes of about 10 s to 100 s nanometers are widespread on surfaces of impact glasses, such as glass spherules and glass that welds agglutinates. With flat or mound-like tops, such submicroscopic iron-rich grains typically occur in chains, nets and/or mists, and they were interpreted to be surface adherents that are mainly composed of native iron. Processes such as cooling of iron melt veneer, condensation of iron vapor, and in situ thermal reduction of regolith particles have been separately invoked to explain their origin. Meanwhile, some iron-rich grains have lower hemispheres being embedded in their host glasses, and spherical iron-rich grains with similar sizes, compositions and spatial distributions are also widespread in interiors of their host glasses. It is possible that both the surface and interior iron-rich grains were formed simultaneously during cooling of the host impact melt. However, the precise composition and crystallography of the surface and interior iron-rich grains have not been adequately constrained. In this study, we prepared focused ion beam (FIB) sections for chains of iron-rich mounds that occur on surfaces of impact glasses in the Chang'E-5 lunar regolith. Several FIB sections also exposed interior iron-rich grains that exhibit similar sizes and regular distribution patterns. High-resolution elemental mapping shows that both the surface and interior iron-rich grains are mainly composed of iron and sulfur, and crystallographic inspections reveal that the grains are similarly composed of α-Fe and troilite with varying volume proportions. As the glass spherules and agglutinate glasses are mainly melt products of local regolith materials, both the surface and interior iron-rich grains are most consistent with being formed due to liquid immiscibility between FeS and silicate melt. Troilite preferentially occurs along margins of the iron-rich grains due to heterogeneous distribution of S in the iron-rich melt and the relatively greater compatibility between troilite and silicate melt. The varying morphology of the surface iron-rich grains (e.g., flat tops, mounds) is likely caused by different surface tensions of FeS melt droplets and different wettability between the solidifying Fe-dominating melt and FeS melt with silicate melt. This interpretation predicts that iron-rich grains formed during cooling of impact melt may be dispersed in melt strips and even detached from the melt body during ejecta motion, and they could be subsequently adhered to surfaces of other lunar regolith particles. For reflectance spectra of lunar regolith at visible to near-infrared wavelength, the long-noticed darkening effect caused by submicron-sized iron may be caused by such two-phase iron-rich grains (i.e., α-Fe plus troilite).

Self-consistent calculations of the electric charge, ion drag force, and the drift velocity of spherical grains using Langevin dynamics and comparisons against canonical experiments

We present trajectory simulation-based modeling to capture the interactions between ions and charged grains in dusty or complex plasmas. Our study is motivated by the need for a self-consistent and experimentally validated approach for accurately calculating the ion drag force and grain charge that determine grain collective behavior in plasmas. We implement Langevin dynamics in a computationally efficient predictor–corrector approach to capture multiscale ion and grain dynamics. Predictions of grain velocity, grain charge, and ion drag force are compared with prior measurements to assess our approach. The comparisons reveal excellent agreement to within ±20% between predicted and measured grain velocities [Yaroshenko et al., Phys. Plasmas 12, 093503 (2005) and Khrapak et al., Europhys. Lett. 97, 35001 (2012)] for 0.64, 1.25 μm grains at ∼20−500 Pa. Comparisons with the measured grain charge [Khrapak et al., Phys. Rev. E 72, 016406 (2005)] under similar conditions reveal agreement to within ∼20% as well. Measurements of the ion drag force [Hirt et al., Phys. Plasmas 11, 5690 (2004); IEEE Trans. Plasma Sci. 32, 582 (2004)] are used to assess the viability of the presented approach to calculate the ion drag force experienced by grains exposed to ion beams of well-defined energy. Excellent agreement between calculations and measurements is obtained for beam energies >10 eV, and the overprediction below 10 eV is attributed to the neglect of charge exchange collisions in our modeling. Along with critical assessments of our approach, suggestions for future experimental design to probe charging of and momentum transfer onto grains that capture the effect of space charge concentration and external fields are outlined.

Effect of granular shape on radial segregation in a two-dimensional drum

Granular segregation is widely observed in nature and industry. Most research has focused on segregation caused by differences in the size and density of spherical grains. However, due to the fact that grains typically have different shapes, the focus is shifting towards shape segregation. In this study, experiments are conducted by mixing cubic and spherical grains. The results indicate that spherical grains gather at the center and cubic grains are distributed around them, and the degree of segregation is low. Through experiments, a structured analysis of local regions is conducted to explain the inability to form stable segregation patterns with obviously different geometric shapes. Further, through simulations, the reasons for the central and peripheral distributions are explained by comparing velocities and the number of collisions of the grains in the flow layer.

Effect of laser fluence on the optoelectronic properties of nanostructured GaN/porous silicon prepared by pulsed laser deposition

In this study, the fabrication of nanostructured GaN/porous Si by pulsed laser deposition (PLD) was demonstrated. The porous silicon was prepared using laser-assisted electrochemical etching (LAECE). The structural, optical, and electrical properties of GaN films were investigated as a function of laser fluence. XRD studies revealed that the GaN films deposited on porous silicon were nanocrystalline, exhibiting a hexagonal wurtzite structure along the (100) plane. Spectroscopic property results revealed that the photoluminescence PL emission peaks of the gallium nitride over porous silicon (GaN/PSi) sample prepared at 795 mJ/mm2 were centered at 260 nm and 624 nm. According to topographical and morphological analyses, the deposited film consisted of spherical grains with an average diameter of 178.8 nm and a surface roughness of 50.61 nm. The surface of the prepared films exhibited a cauliflower-like morphology. The main figures of merit of the nanostructured GaN/P-Si photodetectors were studied in the spectral range of 350–850 nm. The responsivity, detectivity, and external quantum efficiency of the photodetector at 575 nm under − 3 V were 19.86 A/W, 8.9 × 1012 Jones, and 50.89%, respectively. Furthermore, the photodetector prepared at a laser fluence of 795 mJ/mm2 demonstrates a switching characteristic, where the rise time and fall time are measured to be 363 and 711 μs, respectively.

Development of a handheld integrating sphere snow grain sizer (HISSGraS)

Abstract We developed a Handheld Integrating Sphere Snow Grain Sizer (HISSGraS) for field use to measure the specific surface area (SSA) of snow. In addition to snow samples, HISSGraS can directly measure snow surfaces and snow pit walls. The basic measurement principle is the same as that of the IceCube SSA instrument. The retrieval algorithm for SSA from reflectance employs two conversion equations formulated using spherical and nonspherical grain shape models. We observed SSAs using HISSGraS, IceCube and the gas adsorption method in a snowfield in Hokkaido, Japan. Intercomparison of the results confirmed that with HISSGraS direct measurement, SSA profile observations can be completed in just ~1/10 the time required for measurement of snow samples. Our results also suggest that HISSGraS and IceCube have similar accuracy when the same snow samples are measured using the same grain shape model. However, SSAs of near-surface snow layers measured using the three techniques exhibited some biases, possibly due to rapid snow metamorphism or melting during measurement and some technical issues with optical techniques. When excluding SSA data for the surface layer, which metamorphosed remarkably during measurement, IceCube- and HISSGraS-derived SSAs correlated strongly with those obtained by gas adsorption and HISSGraS accuracy is 21–34%.

Green Synthesis of ZnO/SnO2 Hybrid Nanocomposite for Degradation of Cationic and Anionic Dyes under Sunlight Radiation

The aim of this work was to biosynthesize SnO2-decorated ZnO (ZT) nanocomposites (NCs) of different Sn content (10, 20, and 30 mol%), namely, ZT10, ZT20, and ZT30, using Olea europaea leaf aqueous extract-based phytocompounds as nanoparticle facilitating agents for application as effective photocatalyst in the removal of dyes from polluted water. The obtained ZT NCs were characterized using various techniques, including FTIR, XRD, TGA, TEM, EDS, UV–Vis, PL, and BET surface area. X-ray diffraction patterns show that rutile SnO2 and hexagonal ZnO coexist in the composites, and their crystallite size (D) is affected by the SnO2 ratio; the obtained D-values were 17.24, 19.07, 13.99, 6.45, and 12.30 nm for ZnO, SnO2, ZT10, ZT20, and ZT30, respectively. The direct band gaps of the ZT heterostructure increase with increasing SnO2 ratio (band gap = 3.10, 3.45, 3.14, 3.17, and 3.21 eV, respectively). TEM spectroscopy revealed nanorod and spherical grain morphologies of the composites, while EDS confirmed the elemental composition, the element ratio, and the composite’s purity. All catalysts exhibit type III isotherm with macropore structure. The photocatalytic efficiency against cationic (methylene blue (MB), rhodamine B (RB)), and anionic (methyl orange (MO)) dyes, under sunlight, was optimal with ZT20. The results revealed almost complete degradation at 55, 65, and 55 min, respectively. Hence, it is evident that incorporating SnO2 improves the photocatalyst’s performance, with an apparent optimal enhancement at 20 mol% Sn decorating ZT NCs. More interestingly, the catalyst stability and activity remained unaffected even after four activating cycles.

Mg1-xNixGayFe2-yO4 nano catalysts for green hydrogen generation with highly efficient photo/electro catalytic water splitting applications

The production of nanomaterials for renewable energy as fossil fuel substitutes is anticipated as a viable solution to the pressing issues of environmental pollution and energy scarcity. We fixated on the development of Mg1-xNixGayFe2-yO4 (x = y = 0.0–0.03; steps: 0.01) nanocatalysts by sol-gel auto-combustion route (SGAC) for the hydrogen generation through overall photo and electrocatalytic water splitting. The spinel cubic phase with Fd3m space geometry was established from XRD results. FESEM images shows cubic and spherical formed grains with definite grain boundaries and grain size of 164 and 184 nm for the MgFe2O4 and Mg0.98Ni0.02Ga0.02Fe1.98O4 nanomaterials. Soft magnetic behavior with superior saturation magnetization (Ms) and moderate coercivity (Hc) of 2.72–29.24 emu/g and 51.23–257.86 Oe was obtained for all of the developed nanocatalysts. According to the research findings, Mg0.98Ni0.02Ga0.02Fe1.98O4 nanocatalyst shows the highest photocatalytic activity of 11.38 mmol gcat−1. The as-synthesised photocatalysts' repeatability and stability were evaluated throughout repeated runs of a 4-h reaction period conducted under identical circumstances. On the other hand, the electrocatalytic studies were carried via 3-electrode arrangement (i.e., working, counter and reference) in 0.5 M H2SO4 and 0.1 M KOH electrolytes for hydrogen evolution reactions (HER) and oxygen evolution reactions (OER). The overpotential for the MgFe2O4, Mg0.99Ni0.01Ga0.01Fe1.99O4, Mg0.98Ni0.02Ga0.02Fe1.98O4, and Mg0.97Ni0.03Ga0.03Fe1.97O4 electrocatalysts at 10 mA/cm2 were −0.866, −0.82, −1.02 and −0.92 V. Consequently, owing to these photocatalytic and electrocatalytic water splitting traits, the prepared nanocatalysts are highly efficient for hydrogen generation. However, MgFe2O4, and Mg0.99Ni0.01Ga0.01Fe1.99O4 nanomaterials show high zone of inhibition (ZOI) against Bacillus subtilis and Pseudomonas aeruginosa and therefore, making it valuable also for biological usages.

Electrical conductivity characterization of Bi4V2O11 doped with sulfur prepared by hydrothermal process

Bi4V2−xSxO11+δ (BiSVOx) compounds (0.0 ≤ x ≤ 0.5), prepared by the hydrothermal method, were characterized by various techniques, such as X-ray diffraction (XRD), Raman spectroscopy, IR spectroscopy, thermo-gravimetric analysis (DTA/TGA), and scanning electron microscopy (SEM). It is confirmed that this synthesis method has an important impact, especially on the crystallinity and morphology of these materials. The BiSVOx phases obtained crystallize in the tetragonal γ-Bi4V2O11 structure type. Spherical grains made of nanoparticles characterize the morphology of the powders resulting from the synthesis. The stability of the BiSVOx samples has been studied by DTA/TGA analysis performed up to 1000 °C. Electrochemical impedance spectroscopy was used to measure the electrical conductivity of these compounds. Contrary to what is generally observed in BiMeVOx, The conductivity increases with the substitution rate. The highest conductivity values were obtained in the case of the sample with composition x = 0.4.