XANES Research Articles

In-Situ Scanning Transmission X-Ray Microscopy Studies of MnO2-Based Supercapacitor Electrodes

Supercapacitors (SCs) as energy storage devices provide higher energy density than conventional capacitors and higher power density than batteries1. Understanding how charge is efficiently stored in the electrodes or across the electrolyte/electrode interface is key to developing advanced SC electrodes. Scanning transmission x-ray microscopy (STXM) studies2 have been used to investigate MnO2 based supercapacitor electrodes using a novel three-electrode based in-situ flow electrochemical device (Fig. 1)3, 4. Near-edge X-ray absorption fine structure (NEXAFS) spectra of MnO2 films in-situ deposited and subjected to several different electrochemical processes were measured with high spatial resolution at the Mn L3 and O K edges (Fig. 2) at both working electrode (WE) and counter electrode (CE) regions. In this work, the redox state changes associated with pseudocapacitance during charging/discharging processes in a potential window of -0.5 VAu to +0.9 VAu (+0.1 VRHE to +1.5 VRHE) have been investigated. The spectroscopic data and quantitative chemical mapping by in-situ STXM measurements demonstrated that an as-electrodeposited MnO2 film was reduced to both Mn3+ and Mn2+ oxidation states through a reversable Mn4+ ↔ Mn3+/Mn2+ redox reaction. A significant change from a quasi-uniform MnO2 film to a dendritc MnO2 structure was observed during discharging at +1.5 VRHE (Fig. 3, Fig. 4) corresponding to redeposition of Mn2+ dissolved into electrolyte during the reduction process5. In-situ STXM measurements at the CE showed there is deposition of MnO2 during the reduction reaction (charging process) at +0.1 VRHE. Mn L3 features of Mn2+ appeared in the electrolyte region during the reduction process and disappeared during the oxidation process, confirming the dissolution/redeposition mechanism. We have developed a novel and versatile platform for in situ studies of electrochemical processes, including supercapacitors, batteries, and electro-catalysts3, 4. References A. G. Olabi, Q. Abbas, A. Al Makky, and M. A. Abdelkareem, Energy, 248 123617 (2022). K. V. Kaznatcheev, C. Karunakaran, U. D. Lanke, S. G. Urquhart, M. Obst, and A. P. Hitchcock, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 582 (1), 96-99 (2007). A. P. Hitchcock, C. Zhang, H. Eraky, L. Shahcheraghi, F. Ismail, and D. Higgins, Microscopy and Microanalysis, 27 (S2), 59-60 (2021). C. Zhang, N. Mille, H. Eraky, S. Stanescu, S. Swaraj, R. Belkhou, D. Higgins, and A. Hitchcock, (2023). T.-H. Wu, Y.-Q. Lin, Z. D. Althouse, and N. Liu, ACS Applied Energy Materials, 4 (11), 12267-12274 (2021). Figure 1

Investigating the Molecular Orientation and Thermal Stability of Spiro-OMeTAD and Its Dopants By Near Edge X-Ray Absorption Fine Structure

This work describes the utilization of near edge X-ray absorption fine structure (NEXAFS) to investigate the hole transporting material (HTM) 2,2ʹ,7,7ʹ-tetrakis(N,N-di-p-methoxyphenylamine)- 9,9ʹ-spirobifluorene (Spiro-OMeTAD) and its most common dopants, lithium bis-(trifluoromethylsulfonyl) imide (LiTFSI), 4-tert-butylpiridine (tBP) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ). Utilizing angle resolved NEXAFS, the orientation of the molecules on the surface can be observed. The data suggests it is difficult to determine any orientational preference for Spiro-OMeTAD deposited on a surface due to the 3D propeller-like geometry of this molecule. Both doped and undoped samples show thermal stability beyond the glass transition temperature of the molecules. Significant changes to the Spiro-OMeTAD spectra were observed with the addition of the dopants, in particular the C K-edge. Differences are also observed in the valence band spectra when dopants are added. It is also demonstrated how the doping combination of LiFTSI with tBP and, F4-TCNQ act as p-type dopants by altering the position of the HOMO levels. The F4-TCNQ induces a larger change in the HOMO levels when compared to the LiTFSI and tBP. These results are important to increase our understanding of Spiro-OMeTAD and the effect dopants have on this material for next generation solar cells.

Highly Durable Electrocatalyst with Low-Loading Pt-Co Dispersed over Graphene Nanofiber for Oxygen Reduction Reaction Under PEMFC Condition

Proton exchange membrane fuel cell (PEMFC) has been demonstrated as a highly efficient energy conversion technology. The sluggish oxygen reduction reaction (ORR) at the fuel cell cathode requires 3 to 5 times more catalysts than the hydrogen oxidation reaction at the anode (1). Currently, platinum is still the catalyst material of choice. However, the heavy use of scarce Pt in the electrodes represents a major cost barrier to the commercialization of PEMFCs. Tremendous efforts have been dedicated to reduce or remove Pt usage through the development of Pt-transition metal catalysts, as highlighted recently by dealloyed PtNi (2), Mo-doped PtNi(3), and ordered PtCo (4); or through the development of transition metals-nitrogen-carbon based PGM-free catalysts (5, 6).In the fuel cell, catalysts should be highly dispersed over the electrode surface to be easily accessible by the reactants, especially at the high fuel cell current density where a large influx of O2 must be converted. For the Pt alloy catalyst of large crystallites, there won’t be enough crystallites available to spread over the electrode surface to encounter the incoming O2 if the total loading of platinum has to be maintained ultralow. Furthermore, unprotected Pt nano-alloys may lose their nanostructure and crystallinity from the dissolution and agglomeration during the ORR process. The PGM-free catalysts, on the other hand, have high catalytic site density with uniform distribution when prepared by homogenous precursors such as metal-organic framework or porous organic polymer, rendering them highly efficient in interacting with O2 flux. Their key drawback, however, is the poor stability operated under PEMFC condition.In this presentation, we will describe a method of preparing highly active yet stable electrocatalysts containing ultralow Pt content using polymer fiber containing cobalt zeolitic imidazolate framework as precursor. The new catalyst contains Pt-Co nanoparticels situated over the PGM-free catalystically active support (7,8). The ORR activities of the new catalyst was first tested in O2 saturated acidic electrolyte by rotating ring disk electrode (RRDE) before fabricated into the membrane electrode assembly (MEA) and evaluated under fuel cell operating condition. The synergistic catalysis between PtCo NPs and the PGM-free active substrate led to an unprecedented oRR performance in both RRDE and fuel cell. For example, the fuel cell test demonstrated a mess activity of 2.43 A/mgPt for the new catalysts and > 80% retention of the initial mass activity after 60000 continuous voltage cycles from 0.6 – 1.0 V.The characterizations of the fresh and the post-electrochemical test samples were investigated by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), x-ray absorption near-edge structure (XANES), extended x-ray absorption fine structure (EXAFS), transmission electron microscopy (TEM), Raman spectroscopy and BET surface analysis. We also performed DFT calculation on the ORR thermodynamic barriers over both Pt-Co NPs and PGM-free site as the descriptors for reaction pathway. The results reveal that the synergistic interaction between Pt-Co and PGM active substrate contribute significantly to both activity and durability enhancements.Acknowledgments:This work was supported by Argonne National Laboratory through Maria Goeppert Mayer Fellowship, US; Overseas Outstanding Youth Fund project, shanghai Jiao Tong university, Shanghai, China, State Key Laboratory of Metal Matrix Composites, shanghai Jiao Tong university, Shanghai, China. The works performed at Argonne National Laboratory’s Center for Nanoscale Materials and Advanced Photo Source, and Hydrogen research center, shanghai Jiao Tong university.Reference: H. A. Gasteiger, N. M. Markovic, Just a Dream-or Future Reality? Science 324, 48-49 (2009).B. Han et al., Record activity and stability of dealloyed bimetallic catalysts for proton exchange membrane fuel cells. Energy & Environmental Science 8, 258-266 (2015).X. Huang et al., High-performance transition metal–doped Pt3Ni octahedra for oxygen reduction reaction. Science 348, 1230-1234 (2015).D. Wang et al., Structurally ordered intermetallic platinum-cobalt core-shell nanoparticles with enhanced activity and stability as oxygen reduction electrocatalysts. Nat Mater 12, 81-87 (2013).L. Chong et al., Investigation of Oxygen Reduction Activity of Catalysts Derived from Co and Co/Zn Methyl-Imidazolate Frameworks in Proton Exchange Membrane Fuel Cells. ChemElectroChem 3, 1541-1545 (2016).J. Shui, C. Chen, L. Grabstanowicz, D. Zhao, D. J. Liu, Highly efficient nonprecious metal catalyst prepared with metal-organic framework in a continuous carbon nanofibrous network. Proc Natl Acad Sci U S A 112, 10629-10634 (2015).L. Chong et al., Ultralow-loading platinum-cobalt fuel cell catalysts derived from imidazolate frameworks. Science, (2018).L. Chong et al., Highly durable fuel cell electrocatalyst with low-loading Pt-Co nanoparticles dispersed over single-atom Pt-Co-N-graphene nanofiber. Chem Catalysis 3, 100541.

On the splitting of the surface plasmon resonance band of gold nanopillars developed on rippled Si surface

In this work, we reported split surface plasmon resonance (SPR) bands originated from the Au nanopillars developed on rippled Si substrates. This is the first report of gold SPR splitting on a pre-structured Si surface. The Si surface was subjected to a bombardment of Ar ions to fabricate ripples on the surface. A 5 nm thin layer of Au was then deposited on the rippled surface, and the SPR was studied using UV–visible spectroscopy. Further, X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure spectroscopy (EXAFS) were used to characterize the prepared samples. The AFM confirmed that the deposited gold is in nanopillar form, and the rippled surface governs the growth, shape, and size of gold nanopillars. A large aspect ratio has been observed for the nanopillars, resulting in a red-shifted and split SPR band. The experimental XANES of Au L3-edge were successfully mimicked by simulated XANES, confirming the existence and signature of the nanostructure. For the first time, the local structure information of Au nanopillars constructed on rippled Si substrate has been obtained using the EXAFS approach in different directions and correlated with the plasmonic bands.

Soil phosphorus cycling across a 100-year deforestation chronosequence in the Amazon rainforest.

Deforestation of tropical rainforests is a major land use change that alters terrestrial biogeochemical cycling at local to global scales. Deforestation and subsequent reforestation are likely to impact soil phosphorus (P) cycling, which in P-limited ecosystems such as the Amazon basin has implications for long-term productivity. We used a 100-year replicated observational chronosequence of primary forest conversion to pasture, as well as a 13-year-old secondary forest, to test land use change and duration effects on soil P dynamics in the Amazon basin. By combining sequential extraction and P K-edge X-ray absorption near edge structure (XANES) spectroscopy with soil phosphatase activity assays, we assessed pools and process rates of P cycling in surface soils (0-10 cm depth). Deforestation caused increases in total P (135-398 mg kg-1 ), total organic P (Po ) (19-168 mg kg-1 ), and total inorganic P (Pi ) (30-113 mg kg-1 ) fractions in surface soils with pasture age, with concomitant increases in Pi fractions corroborated by sequential fractionation and XANES spectroscopy. Soil non-labile Po (10-148 mg kg-1 ) increased disproportionately compared to labile Po (from 4-5 to 7-13 mg kg-1 ). Soil phosphomonoesterase and phosphodiesterase binding affinity (Km ) decreased while the specificity constant (Ka ) increased by 83%-159% in 39-100y pastures. Soil P pools and process rates reverted to magnitudes similar to primary forests within 13 years of pasture abandonment. However, the relatively short but representative pre-abandonment pasture duration of our secondary forest may not have entailed significant deforestation effects on soil P cycling, highlighting the need to consider both pasture duration and reforestation age in evaluations of Amazon land use legacies. Although the space-for-time substitution design can entail variation in the initial soil P pools due to atmospheric P deposition, soil properties, and/or primary forest growth, the trend of P pools and process rates with pasture age still provides valuable insights.

Coupling electrokinetic technique with hydrothermal carbonization for phosphorus-enriched hydrochar production and heavy metal separation from sewage sludge

Hydrothermal carbonization is a promising treatment technology for wet organic solid wastes, due to its energy-efficient production of functionalized carbonaceous materials. However, the usage of sewage sludge (SS) derived hydrochar as phosphorus (P) fertilizer for agricultural soil is inhibited by the presence of heavy metals (HMs). Appropriate HM removal technology is required prior to its land application. In this study, an innovative FeCl3-assisted electrokinetic technique coupling with hydrothermal carbonization (FEK–HTC) is proposed to produce SS hydrochars with reduced HM content and increased P-retention. FEK–HTC treatment showed synergistic effects in terms of P retention and HM content reduction (56–64 % for Ni, Cu, and Zn). Furthermore, the toxicity of the remaining HMs was dramatically reduced, e.g., by 39.35 % in the case of Zn. Additionally, FEK–HTC transformed P species in hydrochars into highly bio-available form. Electrokinetic treatment resulted in decreased pH values of SS feedstock and promoted the solubilization and erosion of Ca-associated P, resulting in higher non-apatite inorganic phosphorus contents (12.47 to 23.19 mg·g−1) compared to hydrochars from untreated sludge. The P migration patterns during the FEK-HTC treatment were assessed based on the combined result of chemical extraction, 31P NMR, X-ray absorption near edge structure (XANES), and diffusive gradients in thin film (DGT). DGT analysis showed that the addition of treated hydrochars greatly increased the available P content in the soil. The results provide new insights into applying FEK-HTC technique for SS management.

In Situ Laser-Induced Breakdown Spectroscopy for Chromium Speciation Analysis Based on the Interactions of Oxygen-Containing Groups with Functionalized Co3O4-rGO: Evidence from Advanced Optical Techniques and Density Functional Theoretical Calculations under Electric Field.

Achieving accurate detection of different speciations of heavy metal ions (HMIs) in an aqueous solution is an urgent problem due to the different bioavailabilities and physiological toxicity. Herein, we nominated a novel strategy to detect HCrO4- and Cr(OH)2+ at a trace level via the electrochemical sensitive surface constructed by Co3O4-rGO modified with amino and carboxyl groups, which revealed that the interactions between distinct functional groups and different oxygen-containing groups of target ions are conducive to the susceptible and anti-interference detection. The detection sensitivities of 19.46 counts μg-1 L for HCrO4- and 13.44 counts μg-1 L for Cr(OH)2+ were obtained under optimal conditions, while the limits of detection were 0.10 and 0.12 μg L-1, respectively. Satisfactory anti-interference and actual water sample analysis results were obtained. A series of advanced optical techniques like X-ray photoelectron spectroscopy, X-ray absorption near-edge structure technology, and density functional theory calculations under an electric field demonstrated that chemical interactions between groups contribute more to the fixation of target ions than electrical attraction alone. The presence of oxygen-containing groups distinct from simple ionic forms was a critical factor in the selectivity and anti-interference detection. Furthermore, the valence cycle of Co(II)/(III) synergistically boosted the detection performance. This research provides a promising tactic from the microscopic perspective of groups' interactions to accomplish the precise speciation analysis of HMIs in the water environment.

An XAS study of Hg(II) sorption to Al-based drinking water treatment residuals

Drinking water treatment residuals (DWTRs) are produced from the coagulation and flocculation processes in conventional drinking water treatment. The abundant metal oxide content of these materials resulting from the use of coagulants, like alum and ferric chloride, has driven strong research interest into the reuse of DWTRs as sorptive materials. Using a suite of aluminum-based DWTRs, we provide new insights into Hg(II) sorption mechanisms. Experiments performed at circum-neutral pH show that sorption capacities are related to the amount of organic carbon/matter present in DWTRs. We found that carbon rich samples can scavenge about 9000 mg/kg of Hg, in contrast to 2000 mg/kg for lime based DWTRs. X-ray absorption spectroscopy (XAS) at the Hg L3 edge further characterizes mercury coordination. X-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) results point to a partial association of mercury with sulfur at low mass loadings, transitioning to a full association with oxygen/carbon at higher concentrations of sorbed Hg(II) and in DWTRs with limited sulfur content. These results suggest that sorption of Hg(II) is primarily controlled by the carbon/organic matter fraction of DWTRs, but not by the coagulants.

Optimizing the Electron Spin States of Na4Fe3(PO4)2P2O7 Cathodes via Mn/F Dual‐Doping for Enhanced Sodium Storage

AbstractA NASICON‐type Mn/F dual‐doping Na4Fe3(PO4)2P2O7 cathode material is successfully synthesized via a spray drying method. A medium‐spin of Fe is measured by DFT calculation, X‐ray absorption near edge structure (XANES), temperature‐dependent magnetization susceptibility (M−T) measurement, and electron paramagnetic resonance (EPR) tests. It indicates that the eg orbital occupation of Fe2+ can be finely regulated, thus optimizing the bond strength between the oxidation and reduction processes. Furthermore, from UV−vis DRS and four‐point probe conductivity measurements, it can be seen that, after adjusting the electron spin states, the band gap of the material has decreased from 1.01 to 0.80 eV, and the electronic conductivity has increased from 8.5 to 24.4 µS cm−1, thereby leading to competitive electrochemical performance. The as‐optimized Na4Fe3(PO4)2P2O7 displays both excellent rate performance (121.0 and 104.9 mAh g−1 at 0.1 C and 5 C, respectively) and outstanding cycling stability (88.5% capacity retention after 1000 cycles at 1 C). The results indicate that this low‐cost Mn/F dual‐doping Na4Fe3(PO4)2P2O7 cathode can be a competitive candidate material for sodium‐ion batteries.

Thorium speciation in ilmenite concentrates from the Mandena deposit, Madagascar: Implications for environmental remediation and thorium beneficiation

Placer ilmenite deposits are important sources for titanium dioxide production but are often radioactive due to elevated thorium and uranium contents, posing significant challenges to their upgrading and downstream commercial applications. In this contribution, we have investigated ilmenite concentrates containing 133 ppm Th and 12.8 ppm U from the Mandena deposit, Madagascar, using a wide range of analytical techniques: powder X-ray diffraction, electron microprobe analysis, quantitative evaluation of materials by scanning electron microscopy, inductively coupled plasma mass spectrometry, laser ablation inductively coupled plasma mass spectrometry, synchrotron X-ray absorption spectroscopy, microbeam synchrotron X-ray fluorescence mapping, and microbeam synchrotron Laue X-ray diffraction analysis. Our data show that monazite-(Ce), mainly as discrete grains, accounts for ∼55% of Th in the Mandena ilmenite concentrates. Thorianite hosting the remaining Th at ∼45% is revealed by synchrotron Th LIII edge X-ray absorption near-edge structure and extended X-ray absorption fine structure analyses and is correlated with the degree of ilmenite alteration. These results suggest that thorianite probably formed from the alteration of ilmenite and precipitated on the surface of altered ilmenite. The presence of monazite-(Ce) and thorianite in the Mandena ilmenite concentrates is further supported by principal component analysis of trace elements. Our results suggest that combined magnetic separation and acid leaching are effective for reducing the Th (and U) abundances in the Mandena ilmenite concentrates, via the removal of Th-bearing minerals. These findings have important implications for both Th remediation and beneficiation. Moreover, the precipitation of thorianite on the surface of altered ilmenite is an effective method for attenuating the common radionuclide Th in surficial environments.

Designing M13 Bacteriophage and Fe-Nanonest Self-Assembly System for Universal and Facile Preparation of Metal Single Atoms as Stable Mimicking Enzymes.

Metal single-atom catalysts (MSACs) possess multiple advantages in chemical synthesis; their efficient fabrication routes, however, remain a challenge to date. Here, an interdisciplinary design using M13 bacteriophage virus as a biotemplate to carry Fe nanoclusters, which we figuratively call "Fe-nanonests", is proposed to enable facile and versatile synthesis of MSACs. The feasibility and generality of this self-assembly method was demonstrated by the observation of six different metal single atoms (MSAs) including Ag, Pt, Pd, Zn, Cu, and Ni. With Pd as a representative, key factors dominating the fabrication were determined. The Pd single atoms exhibited excellent horseradish peroxidase (HRP)-like activity, which was further improved by 50% via genetic editing of the M13 pVIII protein terminals. Excellent stability was also observed in the quantification of acid phosphatase, a cancer predictor. X-ray absorption near-edge structure spectroscopy has been applied to the analysis of Pd single atoms as well, and the Pd-N4 coordination explained the mechanism of high HRP-like catalytic activity. The MSAs synthesized by the M13 phage and Fe-nanonest self-assembly method show promising prospects in non-cold-chain medical detection applications.

Elucidation of Surface Functional Groups Deposited by Electrochemical Surface Treatment of Discontinuous Carbon Fiber by NEXAFS and XPS.

Control of carbon fiber heteroatom (oxygen and nitrogen) functionalization using electrochemical oxidation is explored in a variety of electrolyte solutions. Results of X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy indicate that most electrolytes in aqueous and anodic conditions are limited to heteroatom surface content of no more than 13 atomic percent (at %) with a majority C-O and/or C-N moieties; the remaining moieties include an oxidative sequence of carbon (alcohol to ketone to carboxylate) and more complex O- and N-containing groups. The pH of the electrolyte solution was found to be crucial in controlling the ratio of the amount of oxygen to nitrogen functionalities, with the increased basicity of solution resulting in higher nitrogen deposition. The oxidative (and/or thermal) decomposition of many electrolytes during electrochemical treatment can have a major impact on functionalization through changes to pH. Oxidation of carbon fiber in some electrolyte solutions showed higher surface concentrations of heteroatoms (25-30 at %) than most electrolytes (13 at %). Mechanisms were proposed to explain how some electrolytes can exceed 13 at % of heteroatom deposition. Specifically, we hypothesized that electrolytes that contain organic ions with chelation capabilities and moieties that produce additional sites of functionalization can overcome that threshold.

Mechanism insight into highly efficient stabilization of Cd contaminated soils by steam flash heating

Soil cadmium (Cd) contamination is a world-wide challenge and chemical stabilization is the most used remediation strategy. To solve the disadvantages of high stabilizer dosage and cost, we innovated a cost-efficient steam flash heating (SFH) approach to chemically immobilize Cd in contaminated soils, which introduced high-pressure saturated water vapor into soil microstructure, broke their binding with soil particles and accelerated Cd reactions with stabilizers by ultrafast pressure release. Using calcium dihydrogen phosphate, potassium hydrogen phosphate or calcium carbonate as stabilizer, Cd stabilization efficiency was 10.4%, 13.4% and 17.1% higher by SFH than conventional chemical stabilization, and the lowest Cd content in leachate was 0.61 mg/L. Additionally, SFH approach averagely reduced 50.1 ± 7.29% of stabilizer dosage, 34.1% of cost, and 29.9% of CO2 emission. BCR sequential extraction results suggested that acid extractable Cd was preferentially transformed into residual Cd by SFH. Analysis of X-ray absorption near edge structure (XANES) documented that SFH treatment produced more stable Cd-minerals of Cd3(PO4)2, CaCO3-Cd, and CdCO3. Our findings proved the state-of-the-art SFH approach and uncovered its mechanisms to stabilize Cd in contaminated soils, offering a green and cost-efficient remediation alternative for heavy metal contaminated site management.

Phosphorus-enriched biochar from biogas residue of Eichhornia crassipes: transformation and release of phosphorus

Pyrolysis is an effective technology for treating and utilizing biogas residue. To explore the phosphorus (P) supply capacity of the biochar generated from biogas residue of Eichhornia Crassipes, the P speciation of E. crassipes biogas residue and biomass during pyrolysis (300–700 °C) was analyzed by combining sequential chemical extraction, 31P nuclear magnetic resonance (NMR) and P K-edge X-ray absorption near edge structure (XANES) spectroscopy. Pyrolysis treatment promoted the conversion of amorphous Ca-P phases in biogas residue and biomass into crystalline hydroxyapatite (HAP) phase, which matched the formation of stable HCl-P pools in the biochar derived from biogas residue (AEBs, 22.65–82.04%) and biomass (EBs, 13.08–33.52%) in the process of pyrolysis. Moreover, the total P contents in AEBs (19.43–28.92 mg g−1) were higher than that of EBs (3.41–5.26 mg g−1), indicating that AEBs had a great P reclamation potential. The P release kinetics from AEBs and EBs in water were evaluated via an incubation experiment for 360 h. The P release from both AEBs and EBs conformed to the pseudo-second order kinetics model (R2 > 0.93), but their P release behaviors were different. The P release of AEBs conformed to the diffusion-re-adsorption model, while that of EBs accorded with the diffusion-dissolution model. The diffusive gradients in thin-films (DGT) analysis showed that AEBs could significantly increase soil available P content as compared with EBs. Hence, the biochar produced from biogas residue of E. crassipes via pyrolysis has a good application potential as a P fertilizer.Graphical

Probing the Electronic Properties of Cu and CuO Thin Films via XANES utilizing Powder XRD System

This research introduces an alternative approach on materials characterization by developing an in-house X-ray Absorption Spectroscopy (XAS) system utilizing powder X-ray Diffraction (XRD) machine. The performance of the in-house XAS system was investigated by analysing the position of Cu K-edge and the absorption spectrum shape within the X-ray Absorption Near Edge Structure (XANES) region. Copper (Cu) based samples were used to test the performance of the system where Cu and Copper Oxide (CuO) thin film deposited on polyimide tape and silicon wafer (100) prepared through the deposition process carried out using RF Magnetron Sputtering machine. Phase confirmation analysis were conducted by XRD and the deposited films’ thickness were measured by Scanning Electron Microscope (SEM). The laboratory-based XAS measurement was carried out using Rigaku SmartLab X-ray Diffractometer configured for Bragg-Brentano (BB) measurement mode. Molybdenum (Mo) target was used to produce white X-rays by energizing it near 20 keV ±0.01 keV. XRD measurements on XRD and SEM analysis proves successful deposition of pure Cu and CuO thin films and the film thickness measured is 1.432 μm and 0.680 μm respectively. The conclusive findings of the laboratory-based XAS measurements indicate successful acquisition of XAS data with similar spectrum shape of experimental Cu and CuO XANES in comparison with theoretical data. Next, experimental XANES shows clear observation of Cu K-edge peaks for Cu thin film at 8.9737 keV, while Cu K-edge for CuO thin films is not observable. Lastly, there is also presence of significant XANES broadening and which then effect consequent peak shiftings.

Discovery and In Situ Crystallization Studies of Cerium-Based Metal-Organic Frameworks with V-Shaped Linker Molecules.

We report the discovery and characterization of two porous Ce(III)-based metal-organic frameworks (MOFs) with the V-shaped linker molecules 4,4'-sulfonyldibenzoate (SDB2-) and 4,4'-(hexafluoroisopropylidene)bis(benzoate) (hfipbb2-). The compounds of framework composition [Ce2(H2O)(SDB)3] (1) and [Ce2(hfipbb)3] (2) were obtained by using a synthetic approach in acetonitrile that we recently established. Structure determination of 1 was accomplished from 3D electron diffraction (3D ED) data, while 2 could be refined against powder X-ray diffraction (PXRD) data using the crystal structure of an isostructural La-MOF as the starting model. Their framework structures consist of chain-like inorganic building units (IBUs) or hybrid-BUs that are interconnected by the V-shaped linker molecules to form framework structures with channel-type pores. The composition of both compounds was confirmed by PXRD, elemental analysis, as well as NMR and IR spectroscopy. Interestingly, despite the use of (NH4)2[CeIV(NO3)6] in the synthesis, cerium ions in both MOFs occur exclusively in the + III oxidation state as determined by X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS). Thermal analyses reveal remarkably high thermal stabilities of ≥400 °C for the MOFs. Initial N2 sorption measurements revealed the peculiar sorption behavior of 2 which prompted a deeper investigation by Ar and CO2 sorption experiments. The combination with nonlocal density functional theory (NL-DFT) calculations adds to the understanding of the nature of the different pore diameters in 2. An extensive quasi-simultaneous in situ XANES/XRD investigation was carried out to unveil the formation of Ce-MOFs during the solvothermal syntheses in acetonitrile. The crystallization of the two Ce(III)-MOFs presented herein as well as two previously reported Ce(IV)-MOFs, all obtained by a similar synthetic approach, were studied. While the XRD patterns show time-dependent MOF crystallization, the XANES data reveal the presence of Ce(III) intermediates and their subsequent conversion to the MOFs. The addition of acetic acid in combination with the V-shaped linker molecule was identified as the crucial factor for the formation of the crystalline Ce(III/IV)-MOFs.

Tuning Coordination Structures of Zn Sites Through Symmetry-Breaking Accelerates Electrocatalysis.

Manipulating the coordination environment of individual active sites in a precise manner remains an important challenge in electrocatalytic reactions. Herein, inspired by theoretical predictions, a facile procedure to synthesize a series of symmetry-breaking zinc metal-organic framework (Zn-MOF) catalysts with well-defined structures is presented. Benefiting from the optimized coordination microenvironment regulated by symmetry-breaking, Zn-N2 S2 -MOF exhibits the best performance of nitrogen (N2 ) reduction reaction (NRR) with NH3 yield rate of 25.07±1.57µgh-1 cm-2 and Faradaic efficiency of 44.57±2.79% compared with reported Zn-based NRR catalysts. X-ray absorption near-edge structure shows that the symmetry-breaking distorts the coordination environment and modulates the delocalized electrons around the Zn sites, which favors the formation of unpaired low-valence Znδ+ , thereby facilitating the adsorption/activation of N2 . Theoretical calculations elucidate that low-valence Znδ+ in Zn-N2 S2 -MOF can effectively lower the energy barrier of potential determining step, promoting the kinetics and boosting the NRR activity. This work highlights the relationship between the precise coordination environment of metal sites and the catalytic activity, which offers insightful guidance for rationally designing high-efficiency electrocatalysts.

Electronic Structure Calculation of α-Al2X3 System (X = O, S) Based on R++Scan Functional

Due to the necessity of reducing the reliance on fossil fuels, several systems are considered to be alternative and/or additional support for the existing battery material. In this report, structural and electronic properties of aluminium oxide (Al2O3) and aluminium sulfide (Al2S3) with hexagonal symmetry (α-phase), are investigated by utilizing density functional theory technique based on r++SCAN functional. The calculated lattice parameter and insulating gap for both systems are well matched with previous experimental studies and display higher accuracy compared to the results from local density approximation (LDA) and generalized gradient approximation (GGA) studies. The calculated insulating gap values are 10.3 eV and 4.1 eV for α-Al2O3 and α-Al2S3 respectively. For α-Al2O3 system, we observed hybridized s-p-d orbital of Al-O in the conduction states, consistent with the interpretation of past X-ray Absorption Near Edge Structure (XANES) data. Finally, the bulk and young modulus for α-Al2O3 are determined to be 251 GPa and 423 GPa which is very close to the known experimental values of 280 GPa and 451 GPa.

Manifold projection image segmentation for nano-XANES imaging

As spectral imaging techniques are becoming more prominent in science, advanced image segmentation algorithms are required to identify appropriate domains in these images. We present a version of image segmentation called manifold projection image segmentation (MPIS) that is generally applicable to a broad range of systems without the need for training because MPIS uses unsupervised machine learning with a few physically motivated hyperparameters. We apply MPIS to nanoscale x-ray absorption near edge structure (XANES) imaging, where XANES spectra are collected with nanometer spatial resolution. We show the superiority of manifold projection over linear transformations, such as the commonly used principal component analysis (PCA). Moreover, MPIS maintains accuracy while reducing computation time and sensitivity to noise compared to the standard nano-XANES imaging analysis procedure. Finally, we demonstrate how multimodal information, such as x-ray fluorescence data and spatial location of pixels, can be incorporated into the MPIS framework. We propose that MPIS is adaptable for any spectral imaging technique, including scanning transmission x-ray microscopy, where the length scale of domains is larger than the resolution of the experiment.

X-ray absorption near-edge, terahertz and Raman spectroscopies evidence growth-orientation dependent cation order, phase transitions and spin–phonon coupling in half-metallic Ca2FeMoO6 thin films

The disorder due to anti-site cation distribution is intrinsic to the double perovskites wherein the crystal orientations of the substrate template are predicted to offer different degrees of cation order in thin film form. To demonstrate this effect, epitaxial thin films of half-metallic double perovskite Ca2FeMoO6 (CFMO) were prepared on (100) and (111) oriented LaAlO3 substrates in vacuum and nitrogen atmospheres. The findings using X-ray absorption near-edge structure, Terahertz (THz) and Raman spectroscopies, in combination with magnetization show that (111) epitaxial template effectively restricts the Fe–Mo anti-site cation disorder. A resultantly enhanced cation order in (111) films induces dramatic transformations in its properties as follows: (i) significantly enhanced ferromagnetic exchange interactions and saturation magnetization, (ii) a significant increase in the Curie temperatures, (iii) a metallic behavior down to much lower temperature (∼75 K) compared to that down to 200 K for (100) film, (iv) an enhanced spin–phonon coupling. The complex THz optical conductivity spectra evaluated in the framework of Drude and Drude–Smith phenomenological models and the temperature-dependent Raman data fitted to the Balkanski model corroborate well to indicate an enhanced cation order in (111) films. While this study establishes a dominant role of crystallographic orientation in the much-desired control of cation order in double perovskites, a demonstration of the same in room temperature half-metallic CFMO system could reinforce its technological utility both as active and passive components in emergent spintronic functionalities.