X-ray Photoelectron Research Articles

Mechanistic study of β-Ga2O3 nitridation by RF nitrogen plasma for GaN heteroepitaxy

The transformation of 2¯01β-Ga2O3 to h-GaN under exposure to RF nitrogen plasma was monitored in situ by reflection high-energy electron diffraction. Analysis of the reaction kinetics reveals that the nitridation process is initiated by the formation of an oxynitride phase and proceeds via two-dimensional nucleation and growth of wurtzite GaN grains. X-ray photoelectron spectra suggest a Ga−(NxO1−x) type configuration dominates the surface early in the nitridation process. The surface restructuring is followed by a diffusion-fed phase transformation, which propagates the wurzite GaN structure into the substrate upon reaching 70% nitrogen anion site occupation, corresponding to the oxygen solubility in h-GaN. A direct correlation is observed between the nitridated film morphology and the epitaxial film crystallinity, demonstrating control of the residual strain, lateral coherence, and mosaicity in subsequent GaN epitaxy by the nitridation conditions. This study provides mechanistic details of the nitridation reaction of 2¯01β-Ga2O3 facilitating the optimization of the nitridation process toward improving GaN-2¯01β-Ga2O3 heterojunctions.

Chemical space-informed machine learning models for rapid predictions of x-ray photoelectron spectra of organic molecules

Abstract We present machine learning models based on kernel-ridge regression for predicting X-ray photoelectron spec- tra of organic molecules originating from the ionization energies of 1s electrons in carbon (C), nitrogen (N), oxygen (O), and fluorine (F) atoms. We constructed training dataset through high-throughput calculations of core-electron binding energies (CEBEs) for 12,880 small organic molecules in the bigQM7ω dataset, employing the ∆-SCF formalism coupled with meta-GGA-DFT and a variationally converged basis set. The models are cost-effective, as they require the atomic coordinates of a molecule generated using universal force fields while estimating the target-level CEBEs corresponding to DFT-level equilibrium geometry. We explore transfer learning by utilizing the atomic environment feature vectors learned using a graph neural network framework in kernel-ridge regression. Additionally, we enhance accuracy using the ∆-machine learning framework by leveraging inexpensive baseline spectra derived from Kohn–Sham eigenvalues. Upon application to 208 com- binatorially substituted uracil molecules, larger than those in the training set, our analyses reveal that while the models may not yield quantitatively accurate predictions of CEBEs on a molecule-by-molecule basis, they do exhibit a strong linear correlation, which proves valuable for virtual high-throughput screening purposes. We present the dataset and models as the Python module, cebeconf, to facilitate further explorations.

Optical and sign-flipping nonlinear optical properties of NiO/PMMA/PANI nanocomposite films

In this study, we introduce an efficient nanocomposite system to enhance optical properties of Nickel oxide (NiO) integrated with two polymers matrix. NiO nanoparticles is prepared using chemical co-precipitation method and its nanocomposite films (NCFs) were prepared with poly methyl methacrylate (PMMA) and polyaniline (PANI) using drop-casting method on glass substrate and was optimized by changing the concentration of NiO. The prepared NCFs were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), ultraviolet (UV)-visible absorption spectroscopy, photoluminescence (PL) spectroscopy and X-ray photoelectron (XPS) spectroscopy. The open-aperture z-scan method is employed for nonlinear optical investigations, utilizing a nanosecond pulsed laser with a wavelength of 532 nm for excitation. The findings indicate that the NCFs exhibit sign-flipping nonlinear behavior, indicating a transition from saturable absorption to reverse saturable absorption. This suggests that our NCFs exhibit optical limiting properties and potential for applications in photonic devices, such as optical switches and laser protection systems.

Dihydrotetrazine-Functionalized Zirconium-Based Metal-Organic Frameworks for High-Capacity Oil Denitrogenation.

High structural stability, dual organic-inorganic nature, and tunability in chemical functionality are promising characteristics of zirconium-based metal-organic frameworks (Zr-MOFs). These properties assist Zr-MOFs in extending their applications in various fields, especially adsorptive removal of pollutants. In this work, two well-known Zr-MOFs (UiO-66(Zr) and MIL-140(Zr) with the formula Zr6O4(OH)4(BDC)6, H2BDC is benzene 1,4-dicarboxylic acid) were synthesized and decorated with a dihydrotetrazine functional group through postsynthesis linker exchange (PSLE). Two dihydrotetrazine (DHTZ)-functionalized frameworks, UiO-66(Zr)-DHTZ and MIL-140(Zr)-DHTZ, were applied for the removal of quinoline (Qui) and indole (Ind) from the model oil. The results of adsorption experiments at room temperature display that these functionalized Zr-MOFs have significantly improved removal capacities for Qui (875% for UiO-66(Zr)-DHTZ and 303% for MIL-140(Zr)-DHTZ) and Ind (722% for UiO-66(Zr)-DHTZ and 257% for MIL-140(Zr)-DHTZ). Mechanistic studies based on X-ray photoelectron (XPS) and Fourier-transform infrared (FT-IR) spectroscopies reveal that there is a specific kind of host-guest interaction between dihydrotetrazine and nitrogen-containing compounds (NCCs). UiO-66(Zr)-DHTZ adsorbs 1426 mg·g-1 Qui and 1176 mg·g-1 Ind, while MIL-140(Zr)-DHTZ adsorbs 619 mg·g-1 Qui and 511 mg·g-1 Ind. The lower adsorption capacities of MIL-140(Zr)-DHTZ compared to UiO-66(Zr)-DHTZ are related to its lower surface area (783 m2·g-1 versus 330 m2·g-1). The recyclability of the frameworks goes up to five cycles without any significant decrease in the removal capacity. These results indicate that dihydrotetrazine-functionalized Zr-MOFs are highly stable platforms with superior adsorption capacity compared to basic and neutral NCCs.

B-Doped Graphdiynes and Several of Their Corresponding Oxides: A Theoretical Study by X-ray Spectra.

Boron doping can significantly improve the electronic structure and physical and chemical properties of graphdiyne (GDY), which also expands its application prospects in photoelectricity, catalysis, and biology. The accurate configurations characterization of B-doped graphdiyne (B-GDY) has not been achieved due to insufficient experimental and theoretical research. The current work involves the simulation of the geometries of 11 typical B-GDY and B-doped graphdiyne oxides [B(O)-GDY] as well as a pristine GDY, along with their X-ray photoelectron (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra at the density functional theory (DFT) level. The boron and carbon spectra for various bonding types were theoretically imitated to assess the spectral contributions. Calculated outcomes indicate that there is a noticeable dependence of the NEXAFS spectra on the local structure. The simulated XPS spectra provide precise assignments and an extra supplement to the spectra peaks, in addition to the position and general peak forms of simulated spectral peaks matching the experimental spectra fairly well. The combination of XPS and NEXAFS spectra can give useful information for identifying typical B-GDY and B(O)-GDY molecules. This paper offers a comprehensive structure-spectrum relationship of B-GDY and its oxides as well as a further theoretical prediction and guidance for experimental synthesis, which is helpful to solve the challenging issue of identification of B-doped carbon-based materials.

Mechanisms of enhanced performance in Zr4+/Ta5+ codoped rutile-TiO2 ceramics via broadband dielectric spectroscopy.

Aliovalent dopant codoped rutile-TiO2 materials have garnered attention due to their excellent performance properties, characterized by low loss tangent (tanδ), high dielectric permittivity (ε'), and stable ε' over a broad temperature range. This performance is primarily due to the electron-pinned defect-dipoles (EPDDs) of the complex defects [Formula: see text]Ti3+-[Formula: see text]Ti3+BTi. Notably, the excellent dielectric properties in ZrxTa2.5%Ti0.975-xO2 (Zr-TTO) ceramics can be achieved using the traditional mixed oxide method without the EPDDs, due to the absence of A3+ (acceptor doping ions). Instead, the existence of localized free electrons and oxygen vacancies ([Formula: see text]) in Zr-TTO structures, due to doping ions and the sintering process, was confirmed by X-ray photoelectron and Raman spectroscopies. These ceramics exhibited ε'~ 2 × 104 and tanδ < 0.03 at 1kHz and 25°C in the 2.5-10%Zr-TTO samples. Moreover, all ceramics demonstrated a maximum ε' change (∆ε') of less than ±15% over the temperature range suitable for X7R and X8R type ceramic capacitors. Significantly, the change in ε' related to relative humility was calculated to be less than ±0.5% over the range of 50-95% RH, indicating the environmental stability of the dielectric properties, which is essential for capacitor applications. Investigations suggested that at least four mechanisms contributed to this system: the intrinsic effect of ionic polarization, Ti4+ · e- -[Formula: see text]- Ti4+ · e- and Ti4+ · e- - [Formula: see text] defects, interfacial polarization at insulating grain boundaries, and non-Ohmic contact between the surface sample and the metal electrode.

Templating Iron(III) Oxides on DNA Molecules.

Fe(III) oxides were prepared as free nanoparticles and on DNA templates via the precipitation of Fe(III) salts with NaOH in the presence/absence of DNA. Through control of the pH and temperature, FeOOH and Fe2O3 were synthesised. The formation of templated materials FeOOH/DNA and Fe2O3/DNA was confirmed using UV-Vis absorption and FTIR spectra. The direct optical gap of Fe2O3/DNA was estimated as 3.2 eV; the absorption by FeOOH/DNA and Fe2O3/DNA at longer wavelengths is weaker, but consistent with indirect gaps near 2 eV. X-ray photoelectron spectra confirmed the presence of Fe(III) and DNA in the templated samples. Analysis of the X-ray diffraction patterns of both templated and non-templated FeOOH and Fe2O3 demonstrated that the materials were the α-FeOOH and α-Fe2O3 polymorphs with crystallite diameters of the DNA-templated materials estimated as 7.6 nm and 6.8 nm. Transmission electron microscopy showed needle-like crystals of both FeOOH and Fe2O3, but the Fe2O3 contains some globular structures. In contrast, the morphology of FeOOH/DNA and Fe2O3/DNA consists of needle-like crystallites of the respective oxides organised into complex dendritic structures with a length on the 10 μm scale formed by the DNA molecules. Finally, scanned conductance microscopy provided evidence for the conductivity of the FeOOH/DNA after alignment via molecular combing on an Si/SiO2 substrate. Fe2O3/DNA did not exhibit any detectable conductivity.

Thermal and photochemical degradation of CsGeI3 and CsGeBr3: XPS and optical studies

The toxicity of complex lead halides significantly limits the commercialization and practical application of perovskite solar cells. In recent days, lead-free complex lead halides with a perovskite structure have become increasingly popular, among which germanium systems are the least studied. Here we present for the first time a systematic study of the thermal and photochemical stability of perovskite thin films of CsGeI3 and CsGeBr3. The measurements of optical absorbance and X-ray photoelectron spectra (XPS) of core levels and valence bands of Ge-based halide perovskites after light soaking and heat stress were thoroughly performed. It has been found the effect of thermal and photochemical degradation of Ge perovskites which is accompanied by reduction of I:Ge and Br:Ge ratios and appearance of tetravalent metal species fixed in XPS Ge 2p and Ge 3d spectra. The XPS O 1s measurements of irradiated and annealed Ge-based perovskites and their comparison with spectra of GeO2 have shown that formation of Ge4+-species is not due to metal oxidation but owing to defect-mediated hole-doping. While the Ge2+→Ge4+ process lowers the thermal and photochemical stability of Ge-based perovskites and limits their use in photovoltaics, the temperature induced hole doping is favorable for thermoelectric applications.

X-ray photoelectron and NEXAFS spectroscopy of thionated uracils in the gas phase.

We present a comprehensive, combined experimental and theoretical study of the core-level photoelectron and near-edge x-ray absorption fine structure (NEXAFS) spectra of 2-thiouracil, 4-thiouracil, and 2,4-dithiouracil at the oxygen 1s, nitrogen 1s, carbon 1s, and the sulfur 2s and 2p edges. X-ray photoelectron spectra were calculated using equation-of-motion coupled-cluster theory (EOM-CCSD), and NEXAFS spectra were calculated using algebraic diagrammatic construction and EOM-CCSD. For the main peaks at O and N 1s as well as the S 2s edge, we find a single photoline. The S 2p spectra show a spin-orbit splitting of 1.2eV with an asymmetric vibrational line shape. We also resolve the correlation satellites of these photolines. For the carbon 1s photoelectrons, we observe a splitting on the eV scale, which we can unanimously attribute to specific sites. In the NEXAFS spectra, we see very isolated pre-edge features at the oxygen 1s edge; the nitrogen edge, however, is very complex, in contrast to the XPS findings. The C 1s edge NEXAFS spectrum shows site-specific splitting. The sulfur 2s and 2p spectra are dominated by two strong pre-edge transitions. The S 2p spectra show again the spin-orbit splitting of 1.2eV.

Selective extraction of Lead from Chelator-Rich effluents using a Biomass-Based sorbent

The efficient removal of lead (Pb) from waste streams containing chelators presents a significant challenge due to the high stability and mobility of Pb-chelator complexes. This study investigates a novel approach utilizing a biomass-based sorbent, proline-incorporated dithiocarbamate-modified cellulose with epoxy-cross-linkage (DMC-Pro-Epo6), to extract Pb from effluents with excess chelators. DMC-Pro-Epo6 exhibited exceptional Pb(II) sorption performance under controlled and various chelator-rich conditions. The sorbent maintained high sorption efficiency even with 100-fold excess chelator concentration and competing metal ions. DMC-Pro-Epo6 also outperformed commercially-available ion-selective sorbents in terms of separation efficiency. The sorption kinetics followed a pseudo-second order model, demonstrating rapid sorption with equilibrium reached within 20 min. The maximum sorption capacities of DMC-Pro-Epo6 obtained from the Langmuir isotherm model were 1267 and 659 µmol/g in Pb(II)-containing aqueous solution and Pb(II)-containing EDTA solution, respectively. X-ray photoelectron and absorption spectroscopy analyses, along with sorption parameters, confirmed a chemisorption mechanism for Pb(II) sorption onto DMC-Pro-Epo6. Validation of the protocol using real waste samples with complex chelator and base metal ion matrices resulted in a quantitative and selective extraction of 92 to 99 % of Pb(II). This success suggests the potential for scaling up the developed process. Compared to conventional treatment methods, the proposed technique offers a more efficient and streamlined process for separating metal ions and chelators from effluents.

Structure and tunable temperature coefficient of magnetization of Mn4-xGaxC alloys prepared by induction melting method

Abstract The magnetization of most magnetic materials decreases monotonically with increasing temperature. In this work, we found that the temperature coefficient of magnetization of Mn4-x Ga x C alloys can be tuned from negative values to positive values by controlling the composition x. The antiperovskite-type Mn4-x Ga x C (0.05≤x≤0.75) alloys were prepared by using induction melting method, which is more efficient in large-scale production and obtaining full-density alloys in comparison with the traditional solid-state-reaction method. The values of the temperature coefficient of magnetization of Mn4-x Ga x C change continuously from negative to positive with decreasing x. The Mn4-x Ga x C alloys with highly thermal-stable magnetization is expected to present in the composition range of 0.15&lt;x&lt;0.25. The saturation magnetization of Mn4-x Ga x C increases with increasing x, owing to the reduced number of antiferromagnetically coupled Mn atoms at the cubic corner with the face-centered Mn atoms. Most Mn4-x Ga x C alloys with varying x display near-zero remanent magnetization and coercivity at room temperature. The Currie temperature of Mn4-x Ga x C decreases with increasing x. The x-ray photoelectron spectra of Mn 2p, Ga 2p, and C 1 s reveal distinct splitting due to the diverse chemical states of these atoms at different lattice positions and/or phases. Our work has developed a class of alloys capable of offering a desired temperature coefficient of magnetization across a broad temperature range, thereby offering a method to manipulate the thermodynamics of magnetization.

Multimodal applications of green carbon dots derived from Potentilla indica (mock strawberry): Antioxidant, antimicrobial, and quenching based quercetin sensor

This study utilized a simple hydrothermal technique to synthesize negatively charged carbon dots from Potentilla indica fruit (MSTCDs) with antioxidant and broad-spectrum antimicrobial properties, as well as a specific capacity to detect quercetin. The characterization of MSTCDs was performed using spectrophotometry (UV–vis, fluorescence, X-ray photoelectron, and Fourier-transform infrared), zeta potential, and transmission electron microscopy. The prepared MSTCDs had an average size of 8 ± 0.22 nm and zeta potential of −21 mV. The prepared MSTCDs showed negligible cytotoxicity and were found to be biocompatible with human microglial cells. MSTCDs used the static quenching and inner filter effect as their two sensing mechanisms to detect quercetin. The fluorescence intensity of the MSTCDs decreased as the dose of quercetin increased, showing a linear correlation within the dose range of 0.01–70 μM (R2 = 0.9980) and the lowest detection limit of 2 nM. The prepared MSTCDs were applied to detect quercetin in the orange and grape juice, yielding values of 3.27 and 7.04 μM, respectively. Further, the MSTCDs displayed antioxidant activity by scavenging 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl, and hydroxyl radicals, with an EC50 value of 9.3, 140.82, and 187.91 µg/mL, respectively. The antiradical activity of MSTCDs was slightly lower than the ascorbic acid except for ABTS radicals, where MSTCDs showed superior scavenging ability (EC50 = 9.3 µg/mL) compared to the control (EC50 = 33.7 µg/mL). MSTCDs exhibited dose-dependent antimicrobial activity against fungi, Gram-negative bacteria, and Gram-positive bacteria. Thus, the developed CDs showed potential as antioxidant, antimicrobial, and quenching-based quercetin sensor.

In-situ formation of spinel protective layer through extremely low K-doping for enhanced performance of Ni-rich layered cathodes

Herein, we demonstrate a novel and feasible strategy to stabilize the LiNi0.83Co0.12Mn0.05O2 (NCM) structure via the in-situ formation of a superficial spinel layer with potassium (K) doping. While K+ doped NCM is not new, the formation of the protective spinel layer gives surprising results with even a trace amount of doping, which is unique and novel, and nowhere reported. The structural transformation from layered to spinel on the surface region of NCM is achieved with a K-doping level of 0.05 mol% (NCM-0.05K) and the formed spinel layer acted as a protective pillar for stabilizing the host structure, leading to substantially improved electrochemical performance. The X-ray photoelectron spectra demonstrate a large increase in nickel (Ni2+) distribution after cycling for pristine but almost no change for the NCM-0.05K, suggesting a stable preformed spinel layer. The above results reveal that the K+ doping can strongly reduce the Ni4+ to stable Ni2+ under the spinel phase formation and improves cell performances in terms of specific capacity, capacity retention, rate capability, and Li+ diffusivity. The internal micro-cracking of host NCM is also effectively suppressed by the low amount of K doping. Excessive K-doping, in contrast, leads to a reduction in (de)lithiation rate and greater polarization.

Experiment and density functional theory researches on (Mn, Hf) co-doped Ce-based applied surface catalysts for carbon monoxide oxidation and thermal stability

Catalyst addition can improve system after treatment efficiency of pollutants purification. In this study, the performance of (Mn, Hf) co-doped Ce-based catalysts has been investigated in oxidation to mitigate CO emission of engines. A series of Ce-Mn-Hf-Ox with different metal ratios (Ce: Mn: Hf = 8:1:1,7:2:1,7:1:2,6:1:3,6:2:2 and 6:3:1) catalysts were prepared. DFT (density functional theory) calculations were carried out to investigate the mechanism of applied surface catalytic reaction. XRD (X-ray Diffraction) analysis and SEM (Scanning Electron Microscope) revealed Mn and Hf doping increased the catalysts surface area contact with the CO gas with the catalytic performance improvement. XPS (X-ray Photoelectron Spectra), H2-TPR (Temperature-Programmed Reduction) and DFT calculations manifested the Mn and Hf doping would promote the formation of oxygen vacancy to enhance the catalytic performance for CO oxidation. The thermal stability of the catalysts increased with Hf content increasement. Ce6Mn3Hf1 had the highest catalytic activity with the favorable thermal stability according to the temperature-programmed oxidation of CO experiment. T10, T50 and T90 of CO oxidation were 156, 188 and 198 °C, which lost 4.82 % mass at 500°C and 6.18 % mass at 900 °C. Ce6Mn1Hf3Ox displayed the best thermal stability according to TG with the lowest catalytic activity.

Upheaval of Negative Dielectric Permittivity and Semiconductor to Metallic Transition in a Thermally Induced Sn-Doped β-Ga2O3 (-201) Single Crystal.

Thermally induced dielectric and conductivity properties of an Sn-doped β-Ga2O3 (-201) single crystal were investigated by frequency-domain impedance spectroscopy in the frequency window from 100 Hz to 1 MHz with temperatures between 293 and 873 K. The (-201) plane-orientated single crystalline nature and the presence of an Sn dopant in β-Ga2O3 were confirmed by X-ray diffraction (XRD) and X-ray photoelectron (XPS) spectroscopy. Two different trends of impedance spectra have been discussed by the modulation of relaxation times and semiconductor to metallic transition after ∼723 K due to activation of a significant number of Sn dopants and their movements with temperature. The negative impedance values were encountered in the Nyquist plots (Z' vs Z″) after 573 K and constitute a reverse movement after 723 K with temperature. The average normalized change (ΔZ'/Δf)/Z0 of impedance exhibits a broad downward relaxation plateau near 723 K, indicating a weak electrical transition. The increases in the positive value of the dielectric constant (εr') below a percolating threshold temperature 573 K is attributed to the interfacial and dipolar polarizations, and the plasma oscillation of delocalized electrons governed by the Drude theory is responsible for the negative dielectric constant above 573 K. The 3D projections of the real dielectric constant create a sharp downward sinkhole near 723 K, indicating the existence of negative dielectric permittivity. The electrical conductivity dramatically changes its trends after 523 K and confirms a transition from hopping conduction (dielectric or semiconductor) following Jonscher's power law to metallic conduction by Drude theory. Below the percolating threshold temperature, a nonoverlapping small polaron tunneling conduction mechanism was unveiled with defect-induced activation energy of 0.21 eV. The Sn-doped β-Ga2O3 exhibits unique and tailored electromagnetic responses with temperatures that can be associated with a variety of applications in electromagnetic wave manipulations, cloaking devices, antennas, sensors, medical imaging, seismic wave propagation, etc.

Hierarchical Branched TiO2 Photo/Photoelectrocatalyst with Directed Charge Transfer for Efficient Hydrogen Production from Seawater.

The directed electron transport channel design in semiconductors, which could promote charge utilization, is attractive but rarely reported. Hierarchical branched titanium dioxide (HB-TiO2), possessing a charge cascade transfer channel, was constructed by assembling titanium-defected TiO2 nanobranches on oxygen-defected TiO2 nanobelts. The interfacial Ti/O vacancies have been detected by X-ray photoelectron and electron paramagnetic resonance spectroscopies, and the vacancies act as the "bridge" of photogenerated carrier transport. This structure maintained high photoactivity in H2 production in different mass fractions of NaCl solutions. The photocurrent density of the HB-TiO2 photoanode in natural seawater is 3.9, 2.1, and 2.6 times that of oxygen-defected TiO2 nanobelts, titanium-defected TiO2 nanobranches, and their mixture, respectively. Besides, the charge transport mechanism from the inner lattice to the TiO2 surface is proposed.

Crystal chemical investigations on TiU8S17 and U36Lu21S93I3 - ordered and disordered multinary uranium sulfides

The crystal chemistry of uranium sulfides is characterized by a large diversity in composition, crystal structures, oxidation states and physical properties. This holds also for TiU8S17 and U36Lu21S93I3, of which large single crystals up to several mm in length were grown by chemical vapor transport using iodine as a transport agent. TiU8S17 crystallizes with the monoclinic CrU8S17 structure type (C2/m, a = 13.3477(2) Å, b = 8.4927(2) Å, c = 10.4836(2) Å, β = 101.207(2)°) featuring distorted octahedra [TiS6] and bicapped trigonal prisms [US8]. Interatomic distances and X-ray photoelectron spectra indicate tetravalent uranium. Disordered U36Lu21S93I3 represents a new structure type (R3¯m, 13.3841(2) Å, 20.6447(2) Å) with an average crystal structure exhibiting square antiprisms [LuS8], bi- and tricapped trigonal prisms [US8] and [US9] and distorted octahedra [IU6]. Lutetium and sulfur atoms are disordered similar to Ce53Fe12S90X3, La53Fe12S90X3 (X = Cl, Br, I) and La52Fe12S90. This might be caused by positional shifts of iodine atoms away from the center of the polyhedron, thus avoiding unusually long U–I distances and severely disrupting the order of neighboring lutetium and sulfur atoms. The results of chemical analyses (ICP-MS, EDX), electron microscopy (TEM) and X-ray photoelectron spectroscopy support the composition and crystal structure of U36Lu21S93I3 and indicate mixed valency of uranium and charge balance according to the crystal chemical formula (U+III)18(U+IV)18(Lu+III)21(S-II)93(I–I)3.

Effects of Gd2O3 additives on microscopical morphology of ZrB2-SiC sintering ceramic system: Insights for electron transpiration cooling

By manipulating the work function, the dissipation of thermal energy on the material surface can be regulated through Electron Transpiration Cooling (ETC) mechanism. The doping of rare-earth oxide serves as an effective approach for reducing the work function, whereas there is still a lack of comprehensive research into the microstructural morphology of the rare-earth oxides and their correlations with the modifications of the work functions. This study investigates the detailed microscopical structure of Gd2O3 in the ultrahigh-temperature ceramic system (ZrB2-20 vol%SiC). Semi-quantitative composition analyses based on X-ray photoelectron spectra indicate that an increased doping concentration of Gd2O3 is beneficial for the formation of a single solid-state Gd0.18Zr0.82O1.91 phase of ZrB2-SiC system. Atomic-scale scanning transmission electron microscopy (STEM) analyses suggest that Gd2O3 is enriched at the interfaces between SiC and ZrB2 matrix with a nanoscale fibrous morphology composed of alternated Gd2O3 crystals and pores, rendering a continuous microstructure throughout the entire system. This peculiar microstructural morphology is anticipated to facilitate its diffusion along the grain boundary and the formation of Gd2O3 nanolayers at the surface region below the melting points of the ceramic matrix, which can efficiently lower the material work function and reduce the emission energy of the surface electrons during thermal emission through ETC mechanism. The composite with 10 vol% Gd2O3 induces a reduction of the averaged work function of ∼0.49 eV before preforming the thermionic emission experiments. Our results provide valuable insights into the impacts of rare-earth oxide on the ZrB2-SiC matrix, as well as shed light on the feasibility of the ETC mechanism through the efficient design of thermal protection materials.

The selective adsorption of Ni2+ over Co2+ from aqueous solutions in surface functionalized metal–organic frameworks

In this study, two metal-organic frameworks (MOFs), zirconium (IV)-based MOF-808 and chromium (III)-based MIL-101 were investigated for the selective adsorption of nickel (Ni2+) over cobalt (Co2+) and the role of the nitrogen (N)-containing functional groups was evaluated using pyrazole (PyC) and amine (–NH2). Selective adsorption and adsorption rates were quantified using batch adsorption experiments. The post-reaction MOFs after Co2+ and Ni2+ adsorption were characterized with attenuated total reflectance Fourier transform infrared (ATR-FTIR) and X-ray photoelectron (XPS) spectroscopies to identify the active adsorption sites and to infer the adsorption mechanism. The overall adsorption of Co2+ and Ni2+ by MOF-808 and MIL-101 increased after their surface functionalization with PyC and –NH2. However, selective Ni2+ adsorption was only observed with MOF-808-PyC. The pseudo-second-order model fit to the kinetic adsorption data suggests chemically driven adsorption of Co2+ and Ni2+ onto all examined MOFs. The ATR-FTIR and XPS analyses of MOFs with adsorbed Co2+ and Ni2+ indicate that the N sites in PyC and –NH2 are the reactive sites. ATR-FTIR analyses of aqueous PyC solutions with metal cations show a greater shift in the N–H vibrational band of PyC when interacting with Ni2+ compared to Co2+, which is linked to a stronger interaction between Ni2+ and PyC, resulting in the Ni2+ selectivity by PyC-functionalized MOF-808. We propose that PyC, as a π-acceptor ligand, exhibits greater affinity for Ni2+ compared to Co2+ due to i) the greater electronegativity of Ni2+ and ii) the greater stability of Ni2+complex with PyC ligand based on the Irving-Williams series and ligand field stabilization energy based on the electron configuration differences between Co2+ (3d7) and Ni2+ (3d8).

Graphene incorporated zinc oxide hybrid nanofluid for energy-efficient heat transfer application: A thermal lens study

The work focuses on the development of a hybrid nanofluid (NF) comprising zinc oxide-graphene (ZG) to address heat transfer (HT) limitations in thermal systems. The study employs a highly sensitive mode-mismatched dual-beam thermal lens (MDTL) method to analyze the lattice dislocation-induced thermal diffusivity (D) modifications of the hybrid NF. The hybrid composite (HC) is synthesized by solid-state mixing and annealing of ZG. The formation of ZG hybrid composites is revealed through X-ray diffraction (XRD), Fourier transform infrared, X-ray photoelectron, and Raman spectroscopic analyses. The structural dislocations present in the HC are understood from XRD and Raman analyses. Ultraviolet-visible and photoluminescence spectroscopic studies revealed the optical properties of the samples. The MDTL study is carried out by preparing the NFs of the synthesized samples in the base fluid, ethylene glycol (EG), and reveals the impact of crystallite defects on the thermal characteristics of the synthesized composites. Thus, the study suggests the potential capability of ZG composites in tuning the thermal behaviour of EG for HT applications.