Modulating the effective ionic radii of trivalent dopants in ceria using a combination of dopants to improve catalytic efficiency for the oxygen evolution reaction.

Aliovalent doping in ceria and defect engineering are important aspects in tuning the properties of ceria for advanced technological applications, especially in the emerging field of electrocatalytic water-splitting for harvesting renewable energy. However, the ambiguity regarding the choice of dopants/co-dopants and ways to deal with the size difference between dopants and lattice hosts remains a long-standing problem. In this study, ceria was aliovalently codoped with Sc3+ and La3+ while keeping the total concentration of dopants constant; the ionic radius of the former is smaller and that of the latter is larger than Ce4+. Variations in the relative amounts of these dopants helped to modulate the effective ionic radii and match that of the host. A systematic study on the role of these aliovalent dopants in defect evolution in ceria and in modulating the Ce3+ fraction using powder XRD, Rietveld refinement, positron annihilation lifetime spectroscopy, X-ray photoelectron spectroscopy, Eu3+ photoluminescence, and Raman spectroscopy is presented here. The evolved defects and their dependence on subtle factors other than charge compensation are further correlated with their electrocatalytic activity towards oxygen evolution reaction (OER) in alkaline medium. The catalyst with an optimum defect density, maximum Ce3+ fraction at the surface and the least effective ionic radius difference between the dopants and the host demonstrated the best performance towards the OER. This study demonstrates how effective ionic radius modulation in defect-engineered ceria through a judicious choice of codopants can enhance the catalytic property of ceria and provides immensely helpful information for designing ceria-based heterogeneous catalysts with desired functionalities.

DFT stimulation and experimental insights of chiral Cu(II)-salen scaffold within the pocket of MWW-zeolite and its catalytic study.

A Cu(II)-salen complex encapsulated in MWW-framework as an efficient chiral organocatalyst was developed for the synthesis of 3,4-dihydropyrimidin-2-(1H)-one (DHPMs) derivatives via an asymmetric pathway. In order to confirm its structural properties, single-crystal X-ray diffraction, powder XRD, BET, XPS, FE-SEM, EDX, UV-Vis, and FTIR spectra were used. Using computer-assisted DFT calculations, the Cu(II)-salen complex has been fine-tuned to fit into the pocket of the porous MWW support while keeping its chirality. This organocatalyst was shown to be a potent catalyst for the formation of the desired DHPMs product under short reaction times. Furthermore, this green protocol allows rapid and simple isolation of active MWW-trapped Cu(II)-salen scaffolds and its reusability in at least five consecutive runs without losing much of its activity.

Process temperature-dependent interface quality and Maxwell-Wagner interfacial polarization in atomic layer deposited Al2O3/TiO2 nanolaminates for energy storage applications.

Considering the excellent tunability of electrical and dielectric properties in binary metal oxide based multi-layered nanolaminate structures, a thermal atomic layer deposition system is carefully optimized for the synthesis of device grade Al2O3/TiO2 nanolaminates with well-defined artificial periodicity and distinct interfaces, and the role of process temperature in the structural, interfacial, dielectric and electrical properties is systematically investigated. A marginal increase in interfacial interdiffusion in these nanolaminates, at elevated temperatures, is validated using X-ray reflectivity and secondary ion mass spectrometry studies. With an increase in deposition temperature from 150 to 300 °C, the impedance spectroscopy measurements of these nanolaminates exhibited a monotonic increment in dielectric constant from ∼95 to 186, and a decrement in dielectric loss from ∼0.48 to 0.21, while the current-voltage measurements revealed a subsequent reduction in leakage current density from ∼2.24 × 10-5 to 3.45 × 10-7 A cm-2 at 1 V applied bias and an improvement in nanobattery polarization voltage from 100 mV to 700 mV, respectively. This improvement in dielectric and electrical properties at elevated processing temperature is attributed to the reduction in impurity content along with the significant enhancement in sublayer densities and the conductivity contrast driven Maxwell-Wagner interfacial polarisation. Additionally, the devices fabricated at 300 °C exhibited a higher capacitance density of ∼22.87 fF µm-2, a low equivalent oxide thickness of ∼1.51 nm, and a low leakage current density of ∼10-7 A cm-2 (at 1 V bias), making this nanolaminate a promising material for high-density energy storage applications. These findings highlight the ALD process temperature assisted growth chemistry of Al2O3/TiO2 nanolaminates for superior dielectric performance and multifaceted applications.

Structural investigation of Ayurveda Lauha (Iron) Bhasma.

In Ayurveda, 'Lauha' (Iron) Bhasma is primarily used to cure diseases related to iron deficiency in humans. It is produced from purified raw metallic iron using a combination of multi-step traditional preparation processes described in the Ayurveda literature. Here, we present the results of structural investigation performed on the medicinal grade 'Lauha' Bhasma using various X-ray based techniques. Our results indicate that after several rounds of heating and cooling in specific conditions following the Ayurvedic preparation procedure, metallic iron eventually converts to a natural iron-oxide mineral belonging to the magnetite group. Scanning electron microscopy (SEM) and X-ray standing wave assisted fluorescence measurements carried out on powdered Bhasma specimen reveal that the magnetite micro-particles in the Bhasma specimen are usually present in the form of agglomerates of nano-particles. We anticipate that the Ayurvedic Lauha Bhasma has great potential for noninvasive localized target killing of cancer cells, particularly in sensitive parts of the human body such as the brain, spinal cord, and lungs, via necrosis by application of an alternating external magnetic field or photo electron generation through X-rays.

Boron carbide thin film surface characterization after graphitic carbon removal using low-pressure oxygen gas RF plasma.

B 4 C-coated thin film mirrors are used in high brilliance synchrotron and x-ray free electron laser beamlines due to their low absorption coefficient and high thermal stability. As in the case of gold, platinum, and other thin film mirrors, B 4 C-coated mirrors also are affected due to synchrotron radiation-induced carbon contaminations in beamlines. In the present study, a graphitic carbon (C) layer deposited on top of boron carbide (B x C) thin film surface is removed by five successive oxygen radio frequency (RF) plasma exposures (RF power, 10 W; O 2 flow, 30 sccm; exposure time, 10 min each). Before and after the carbon layer removal, structural and compositional properties of the B x C/C bilayer are characterized by soft x-ray reflectivity, x-ray photoelectron spectroscopy, grazing angle x-ray diffraction, and Raman spectroscopy techniques. Characterization results reveal that in the first four exposures the carbon layer thickness decreases continuously without affecting the B x C layer properties; however, in the fifth exposure, the carbon layer is completely removed along with a partial etching of the B x C layer too.

Oxygen vacancy and valence engineering in CeO2 through distinct sized ion doping and their impact on oxygen reduction reaction catalysis.

Defect tuning in ceria to enhance its catalytic properties is a subject of great interest for the scientific community owing to the growing demand for catalytic materials in drug, automobile and chemical industries. Doping induced defect engineering was found to be one of the most sought out strategies particularly in oxides for achieving multifunctionality. Here, in this study, we have doped ceria with distinct sized trivalent rare-earth ions, namely, Y3+, Eu3+ and La3+, using combustion techniques. Positron annihilation lifetime spectroscopy (PALS) suggested enhanced defect density with doping in general and higher concentration of oxygen vacancies in La3+ doped ceria compared to Y3+ and Eu3+ counterparts. X-ray photoelectron spectroscopy (XPS) suggested the existence of both Ce3+ and Ce4+, with the former having higher fraction in CeO2:La3+ compared to CeO2:Y3+. The electron transfer resistance (Rct) reduced in all the doped samples when compared to undoped ceria and they demonstrated improved catalytic activity towards the oxygen reduction reaction (ORR). The highest reduction in Rct was seen in the 5% La doped sample owing to the very high concentration of oxygen vacancies and Ce3+/Ce4+ ratio and CeO2:5.0% La3+ showed the best performance towards ORR electrocatalysis. The studies are expected to help in further tuning the catalysts in terms of dopant concentrations, and in future work, the strategy will be to control the Ce3+/Ce4+ ratio and see its implication in both catalytic and magnetic applications.

g-C3N4/Ca2Fe2O5 heterostructures for enhanced photocatalytic degradation of organic effluents under sunlight.

g-C3N4/Ca2Fe2O5 heterostructures were successfully prepared by incorporating g-C3N4 into Ca2Fe2O5 (CFO). As prepared g-C3N4/CFO heterostructures were initially utilized to photodegrade organic effluent Methylene blue (MB) for optimization of photodegradation performance. 50% g-C3N4 content in CFO composition showed an enhanced photodegradation efficiency (~ 96%) over g-C3N4 (48.15%) and CFO (81.9%) due to mitigation of recombination of photogenerated charge carriers by Type-II heterojunction. The optimized composition of heterostructure was further tested for degradation of Bisphenol-A (BPA) under direct sunlight, exhibiting enhanced photodegradation efficiency of about 63.1% over g-C3N4 (17%) and CFO (45.1%). The photoelectrochemical studies at various potentials with and without light illumination showed significant improvement in photocurrent response for g-C3N4/Ca2Fe2O5 heterostructures (~ 1.9 mA) over CFO (~ 67.4 µA). These studies revealed efficient solar energy harvesting ability of g-C3N4/Ca2Fe2O5 heterostructures to be utilized for organic effluent treatment.

Carbon removal from a mirror-like gold surface by UV light, RF plasma, and IR laser exposure: a comparative study.

A decrease in photon intensity due to carbon contamination on optical elements is a serious issue in synchrotron radiation (SR) beamlines. Photon intensity can be regained by refurbishment of optical elements using suitable techniques. In the literature, three suitable techniques [radio frequency (RF) plasma, ultraviolet (UV) radiation (λ=172nm), and infrared (IR) laser (λ=1064nm) exposure] are reported to remove carbon contaminations from optical elements. These techniques are used independently to remove carbon, and, to the best of our knowledge, no systematic study is available on their relative efficiencies and effects on a mirror surface. We have applied these techniques independently for removal of carbon contamination from a gold surface, and detailed surface characterizations are carried out using soft x-ray reflectivity, x-ray photoelectron spectroscopy, Raman spectroscopy, and atomic force microscopy techniques. Characterization results suggest that all three techniques are capable of removing carbon contamination with certain limitations. Here, detailed relative effects on a gold surface after cleaning experiments with three techniques are discussed.

Influence of Eu3+ on the Structure and Photophysical Properties in (Y,Gd)F3 Nanophosphors.

The scientific community has shown a growing interest in relating to the lanthanide based luminescent materials and it has made an effort to develop them. Among these several luminescent materials, we have proposed to developed (Y,Gd)F3 nanophosphors doped with distinct of Eu3+ concentrations using modified hydrothermal process. The effect of co-doping of rare earth activators to the host lattice structure and morphology are investigated using different analytical techniques. The diffuse reflectance spectra reveal a tuning of optical band gap due to substitutions. From the extensive XPS analysis, Gd and Eu are found to be in a stable ionic state of +3 which is replacing Y3+ in YF3 host. Photoluminescence emission spectra of the nanophosphors are excited by near ultraviolet (UV, 393 nm) excitation. From photoluminescence study, the intensity variation is observed for emission peak at 591 nm and fluorescence quenching occurs at higher doping level. This effect subsequently explained on the frame work of local symmetry and nonradiative transfer among multipole-multipole interaction. At 393 nm excitation Eu3+ (2, 3, 5, 7, 10 at %) doped (Y, Gd) F3 show CIE chromaticity coordinates shifted to red regions with increase in Eu doping levels. Because of the longer decay time these phosphors can be used for bio-labeling and other similar applications.

Probing structural and photophysical features of Eu3+ activated NaCdPO4 orthophosphate phosphor.

A series of Eu3+ doped NaCd1-xPO4: x Eu3+ (0 ≤ x ≤ 0.1) phosphors were synthesized and a systematic investigation of structural, morphological, optical and photophysical properties were carried out. Structural characteristics were analyzed both qualitatively as well as quantitatively to establish the phase purity, supported by FTIR and Raman spectroscopy methods. The valance state of the dopant, as well as surface elemental compositions were investigated by XPS technique. The optical characteristics were analyzed by employing UV-Visible DRS, which shows that the host bandgap is getting broadened upon doping as a result of the Burstein-Moss (BM) effect. Eu3+ doped phosphor exhibits emissions rich in red (617 nm) under suitable excitations at 393 nm while the optimal doping concentration was found to be around x = 0.06. The effective non-radiative transfer of energy from host to activator is governed by the dominant dipole-dipole transitions. The hypersensitive transition line 5D0 â†’ 7F2 is observed owing to the induced electric dipole (ED) transition of Eu3+ centered at 617 nm. Local site symmetry has been analyzed to ascertain the environment around Eu3+ and presence of any non-equivalent cation sites. The concentration quenching effect of phosphors was explained on the basis of Dexter's theory and charge compensation mechanism. The Commission Internationale de l'Eclairage (CIE 1931) chromaticity coordinates for the prepared phosphors were estimated and found to lie in the red region of color space. The photoluminescence decay time was measured for the most intense emission line 5D0 â†’ 7F2 at 617 nm under 393 nm excitation and the results indicate that Eu3+ activated NaCdPO4 can be a suitable red phosphor for white LED using UV-LED chip owing to it's near UV-excitation characteristics.

Electrochemical reduction of CO2 to ethylene on Cu/Cu x O-GO composites in aqueous solution.

Here, we present fabrication of Graphene oxide (GO) supported Cu/Cu x O nano-electrodeposits which can efficiently and selectively electroreduce CO2 into ethylene with a faradaic efficiency (F.E) of 34% and a conversion rate of 194 mmol g-1 h-1 at -0.985 V vs. RHE. The effect of catalyst morphology, working electrode fabricational techniques, the extent of metal-GO interaction and the oxide content in Cu/Cu x O, was studied in detail so as to develop a protocol for the fabrication of an active, stable and selective catalyst for efficient electro-production of ethylene from CO2. Moreover, a detailed comparative study about the effect of the GO support, and the nature of the cathodic collection substrate used for the electro-deposition is presented.

Depth-resolved compositional analysis of W/B4C multilayers using resonant soft X-ray reflectivity.

W/B4C multilayers (MLs) consisting of ten layer pairs with varying boron carbide layer thicknesses have been investigated. The ML structures were characterized using grazing-incidence hard X-ray reflectivity (GIXR), resonant soft X-ray reflectivity (RSXR), hard X-ray photoelectron spectroscopy (HAXPES) and X-ray absorption near-edge spectroscopy (XANES). Depth-resolved spectroscopic information on the boron carbide layer in W/B4C MLs was extracted with sub-nanometre resolution using reflectivity performed in the vicinity of the B K-edge. Interestingly, these results show that the composition of boron carbide films is strongly dependent on layer thicknesses. HAXPES measurements suggest that most of the boron is in the chemical state of B4C in the multilayer structures. XANES measurements suggest an increase in boron content and C-B-C bonding with increase in boron carbide layer thickness.

HAXPES beamline PES-BL14 at the Indus-2 synchrotron radiation source.

The Hard X-ray Photo-Electron Spectroscopy (HAXPES) beamline (PES-BL14), installed at the 1.5 T bending-magnet port at the Indian synchrotron (Indus-2), is now available to users. The beamline can be used for X-ray photo-emission electron spectroscopy measurements on solid samples. The PES beamline has an excitation energy range from 3 keV to 15 keV for increased bulk sensitivity. An in-house-developed double-crystal monochromator [Si (111)] and a platinum-coated X-ray mirror are used for the beam monochromatization and manipulation, respectively. This beamline is equipped with a high-energy (up to 15 keV) high-resolution (meV) hemispherical analyzer with a microchannel plate and CCD detector system with SpecsLab Prodigy and CasaXPS software. Additional user facilities include a thin-film laboratory for sample preparation and a workstation for on-site data processing. In this article, the design details of the beamline, other facilities and some recent scientific results are described.