Near-edge X-ray Adsorption Fine Structure Research Articles

Multivariate and multi-interface insights into carbon and energy recovery and conversion characteristics of hydrothermal carbonization of biomass waste from duck farm

High lipid, high nitrogen duck manure (DM) with high lipid, high lignocellulosic litter materials (LM) are the main wet biomass wastes from duck farms and both are naturally abundant carbon resources. The synthesis of duck farming biomass waste into carbon-rich materials for high value utilization by hydrothermal carbonization (HTC), which can directly treat wet biomass, has not been investigated. In this study, the physicochemical properties of hydrochar derived from co-HTC of DM and LM and its carbon and energy recovery patterns were systematically investigated under multivariate conditions of raw materials ratios, solids contents, temperatures and residence times. The application of synchrotron-based near-edge X-ray adsorption fine structure technique (C K-edge NEXAFS) combined with gas chromatography-mass spectrometry (GC–MS) to the hydrochar and hydrothermal liquid, respectively. At multiple interfaces provided an in-depth analysis of the important material transformations of the co-HTC process and the structure of the hydrochar. Extending residence time (180 min) and increasing LM ratio (M@4%) in co-HTC reaction of DM and LM is beneficial to achieve hydrochar containing higher carbon content (44.84%) at lower reaction temperatures (180 °C). The heating value (HHV) of the hydrochar ranges between 17.12 and 25.05 MJ/kg. The carbon recovery rate of the co-HTC of DM and LM all exceeded 55% and was more closely related to the carbon content of the hydrochar than to its yield. Additionally, the model ERR=0.97±0.01CRR+2.40±0.71 (R2 = 0.99, P < 0.01) was developed to predict energy recovery rate (ERR) based on carbon recovery rate (CRR). Esters were an important intermediate during co-HTC of DM and LM, and the derived hydrochar consisted of a wide range of polycyclic aromatic hydrocarbons, alkanes and N-aromatic heterocycles as well as polyfuran, pyrrole and pyridine structures.

The cation effect on adsorption of surfactant in the froth flotation of low-grade diasporic bauxite

Froth flotation has been proved to be the economic way to upgrade the low-grade diasporic bauxites by desilication of kaolinite. However, the recovery rate of diaspore varied significantly in industry due to water quality (cations) and the mechanism remains unknown. This report investigates the effect of common water hardness cations (Ca2+ and Mg2+) on the recovery of diaspore and kaolinite using micro-flotation at various pH values. The results show that adding Ca2+ significantly enhanced the diaspore recovery rate even under acidic conditions (pH = 4–7). In contrast, adding Mg2+ reduced the diaspore recovery rate to below 50% when the pH value was between 8 and 9 while adding Ca2+ increase the recovery rate to above 95%. In addition, adding either cation shows minimal change to the recovery of kaolinite. The mechanism has been revealed by thermodynamics speciation, zeta potential and synchrotron-based near edge X-ray adsorption fine structure (NEXAFS) spectroscopy. The change of both dipole-dipole interaction and hydrogen bonding plays a vital role on this cation effect.

Oxygen Functionalization of Hexagonal Boron Nitride on Ni(111).

The interaction of single-layer hexagonal boron nitride (h-BN) on Ni(111) with molecular oxygen from a supersonic molecular beam led to a covalently bonded molecular oxygen species, which was identified as being between a superoxide and a peroxide. This is a rare example of an activated adsorption process leading to a molecular adsorbate. The amount of oxygen functionalization depended on the kinetic energy of the molecular beam. For a kinetic energy of 0.7 eV, an oxygen coverage of 0.4 ML was found. Near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy revealed a stronger bond of h-BN to the Ni(111) substrate in the presence of the covalently bound oxygen species. Oxygen adsorption also led to a shift of the valence bands to lower binding energies. Subsequent temperature-programmed X-ray photoelectron spectroscopy revealed that the oxygen boron bonds are stable up to approximately 580 K, when desorption, and simultaneously, etching of h-BN set in. The experimental results were substantiated by density functional theory calculations, which provided insight to the adsorption geometry, the adsorption energy and the reaction pathway.

ZnO Functionalization: Metal–Dithiol Superstructures on ZnO(0001) by Self-Assembly

We present a study of the functionalization of a monocrystalline ZnO surface using aromatic dithiols. The aim is to obtain a sulfur-terminated self-assembled monolayer (SAM), which is then used for creation of further molecular superstructures with intercalated metal atoms. These metal-molecule self-assembled structures are characterized by high-resolution X-ray photoelectron spectroscopy (XPS) and near edge X-ray adsorption fine structure (NEXAFS) measurements. Formation of a 5,5- bis(mercaptomethyl)-2,20- bipyridine (BPD) SAM on ZnO(0001) is demonstrated using a protocol developed by us earlier for dithiol assembly on gold, allowing production of standing-up SAMs with free SH groups. Thereafter the formation of a metal intercalated dithiol super lattice is achieved by first grafting metal atoms (Ag or Ni) and then attaching a second BPD molecular layer. Metal atoms bind to both sulfur and the pyridine nitrogens within the SAM. Clear changes in the valence band region near the Fermi level are observed, a...

Spectromicroscopy of C60 and azafullerene C59N: Identifying surface adsorbed water.

C60 fullerene crystals may serve as important catalysts for interstellar organic chemistry. To explore this possibility, the electronic structures of free-standing powders of C60 and (C59N)2 azafullerenes are characterized using X-ray microscopy with near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy, closely coupled with density functional theory (DFT) calculations. This is supported with X-ray photoelectron spectroscopy (XPS) measurements and associated core-level shift DFT calculations. We compare the oxygen 1s spectra from oxygen impurities in C60 and C59N, and calculate a range of possible oxidized and hydroxylated structures and associated formation barriers. These results allow us to propose a model for the oxygen present in these samples, notably the importance of water surface adsorption and possible ice formation. Water adsorption on C60 crystal surfaces may prove important for astrobiological studies of interstellar amino acid formation.

Formation and Stability of Phenylphosphonic Acid Monolayers on ZnO: Comparison of In Situ and Ex Situ SAM Preparation.

Self-assembled monolayers (SAMs) enable an electronic interface tailoring of conductive metal oxides and offer an alternative to common transparent electrodes in optoelectronic devices. Here, the influence of surface orientation and pretreatment on the formation and stability of SAMs has been studied for the case of phenylphosphonic acid (PPA) on ZnO single crystals. Using thermal desorption spectroscopy (TDS), X-ray photoelectron spectroscopy (XPS), near-edge X-ray adsorption fine structure spectroscopy (NEXAFS) and density-functional theory (DFT) calculations, the thermal stability and orientational ordering of PPA-SAMs on the polar and mixed-terminated ZnO surfaces were analyzed. On all surfaces, PPA-SAMs remain stable up to 550 K, while at higher temperatures a C-P bond cleavage and dissociative desorption takes place yielding two distinct desorption peaks. Based on DFT calculations, these desorption channels are attributed to protonated and deprotonated chemisorbed PPA molecules, which can be related to tri- and bidentate species, hence allowing to determine their relative abundance from the intensity ratio. Beside immersion, an alternative monolayer preparation based on vacuum deposition in combination with controlled desorption of excess multilayers is demonstrated. This enables a SAM preparation on bare ZnO surfaces without any precoating due to exposure to ambient air, which is further compared with SAM formation on intentionally hydroxylated substrates. Corresponding TDS data indicate that initial hydroxylation favors the formation of tridentate and deprotonated bidentate, while the OMBD preparation on bare surfaces yields a larger fraction of protonated bidentate species. The orientation of PPA molecules adopted in the SAMs was determined from the dichroism of K-edge NEXAFS measurements and reveals an almost upright orientation for the deprotonated species, while a slight tilting is obtained for monolayer films with a large fraction of protonated bidentate molecules.

Transformation of metallic boron into substitutional dopants in graphene on6H−SiC(0001)

We investigate the development of the local bonding and chemical state of boron atoms during the growth of B-doped graphene on $6H\text{\ensuremath{-}}\mathrm{SiC}(0001)$. Photoemission experiments reveal the presence of two chemical states, namely, boron in the uppermost SiC bilayers and boron substituted in both the graphene and buffer layer lattices. We demonstrate the participation of the dopant in the $\ensuremath{\pi}$ electron system of graphene by the presence of the ${\ensuremath{\pi}}^{*}$ resonance in the near edge x-ray adsorption fine structure (NEXAFS) recorded at the B $K$-edge. The experimental findings are supported by NEXAFS simulations.

Surface Analytical Study of Poly(acrylic acid)-Grafted Microparticles (Beads): Characterization, Chemical Derivatization, and Quantification of Surface Carboxyl Groups

We report a surface analytical study of poly(methyl methacrylate) (PMMA) microparticles (beads) with a grafted shell of poly(acrylic acid) (PAA) with thicknesses up to 4 nm using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy. These polymer microparticles were analyzed before and after reaction of the surface carboxyl (CO2H) groups with 2,2,2-trifluoroethylamine (TFEA) to gain a better understanding of methods with use of covalently bound probe molecules for surface group analysis. The results obtained with chemical derivatization XPS using TFEA are discussed in terms of surface quantification of reactive CO2H groups on these PAA-coated microparticles. A labeling yield of about 50% was found for TFEA-derivatized particles with amounts of surface-grafted CO2H groups of 99 μmol/g or more, which is consistent with predicted reaction yields for homogeneous...

Converting leguminous green manure into biochar: changes in chemical composition and C and N mineralization

Leguminous green manure is an important source of nitrogen (N) and carbon (C) in cropping systems. The fast turnover of leguminous green manure enables it to release N quickly, but limits its effectiveness in maintaining soil organic C content. Converting leguminous green manure into biochar facilitates its use as a soil amendment. In this study, we assessed how the conversion of leguminous green manure (Sesbania roxburghii) into biochar altered its chemical composition and subsequent C and N mineralization. Biomass was charred along a temperature gradient from 200 to 500°C. Using nuclear magnetic resonance and near-edge X-ray adsorption fine structure spectroscopy, we found that both C and N became enriched in aromatic and heterocyclic aromatic structures in biochar, and this structural change led to a reduction in C and N mineralization rates. The mineralized C decreased from 32.7% of the added C of raw biomass to <0.5% of that of biochar at charring temperatures above 400°C. N release shifted from N mineralization in raw biomass to N immobilization at charring temperatures at 500°C. As such, soil amended with biochar produced at charring temperatures exceeding 400°C demonstrated a 25% decrease in dry shoot biomass compared with unamended soil. The results indicated that the C stability of leguminous green manure can be achieved by converting raw material into biochar, but that the charring process may limit it to providing N.

Carbon adsorption onto Fe oxyhydroxide stalks produced by a lithotrophic iron‐oxidizing bacteria

Iron (Fe)-oxidizing bacteria have the potential to produce morphologically unique structures that may be used as biosignatures in geological deposits. One particular example is Mariprofundus ferrooxydans, which produces extracellular twisted ribbon-like stalks consisting of ferrihydrite, co-located with organic and inorganic elements. It is currently thought that M.ferrooxydans excrete and co-precipitate polysaccharides and Fe simultaneously; however, the cellular production of these polysaccharides has yet to be confirmed. Here, we report on a time-series study that used scanning transmission X-ray microscopy and C 1s and Ca 2p near-edge X-ray adsorption fine structure spectroscopy to investigate production of polysaccharides over the growth cycle of M.ferrooxydans. The production and morphology of twisted iron stalks were consistent with previous observations, but unexpectedly, in the log phase, the carbon content of the stalks was extremely low. It was not until stationary growth phase that a significant component of carbon was detected on the stalks. During the log phase, low levels of carbon, only detectable when the stalks were thin, suggested that M.ferrooxydans produce an extracellular polysaccharide template onto which the Fe precipitates. By stationary phase, the increased carbon association with the stalks was a result of adsorption of organic compounds that were released during osmotic shock post-stalk production. In the environment, elevated concentrations of DOC could adsorb onto the Fe stalks as well as a number of other elements, for example, Si, P, Ca, which, by preventing chemical interactions between the Fe nanoparticles, will prevent structural deformation during recrystallization and preserve the structure of these filaments in the rock record.

NEXAFS study of electron beam irradiated PET

One of the most promising methods for surface property modification is electron beam irradiation, which can create new chemical groups on surfaces. In this study we investigated the surface functionalisation of polyethylene terephthalate (PET), a commonly used polymer material with many applications. The changes in surface properties were examined after electron beam irradiation with near edge X-ray adsorption fine structure (NEXAFS). The angle dependent NEXAFS spectra measured at the C K-edge of PET exhibit good directionality with a tilting angle α of 31.0°. As the duration of the electron beam irradiation is increased, new chemical bonding is induced on the surface and the angle dependence of PET disappears, which are results of the breaking of the C=C π* bonds.

Advanced Techniques for the Characterization of Surface Structure in Polymer Thin Films and Coatings

This review demonstrates the importance of advanced characterization techniques, such as X-ray photoelectron spectroscopy (XPS) and near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy, in accurately determining the composition/morphology of polymeric thin films. The ability to relate structure with surface properties has the potential to benefit a wide variety of science and engineering fields with direct application to the polymer coating, lithography and solar cell industries. Further advances in such areas will build on these characterization techniques and other microscopy, probe and scattering methods to allow real-time monitoring of the evolution of surface structure during processing and/or annealing. The ultimate goal of these methods is the accurate design of tunable, multifunctional surfaces.

CVD Graphene as Interfacial Layer to Engineer the Organic Donor–Acceptor Heterojunction Interface Properties

We demonstrate the use of chemical-vapor-deposited (CVD) graphene as an effective indium-tin-oxide (ITO) electrode surface modifier to engineer the organic donor-acceptor heterojunction interface properties in an inverted organic solar cell device configuration. As revealed by in situ near-edge X-ray adsorption fine structure measurement, the organic donor-acceptor heterojunction, comprising copper-hexadecafluoro-phthalocyanine (F16CuPc) and copper phthalocyanine (CuPc), undergoes an obvious orientation transition from a standing configuration (molecular π-plane nearly perpendicular to the substrate surface) on the bare ITO electrode to a less standing configuration with the molecular π-plane stacking adopting a large projection along the direction perpendicular to the electrode surface on the CVD graphene-modified ITO electrode. Such templated less-standing configuration of the organic heterojunction could significantly enhance the efficiency of charge transport along the direction perpendicular to the electrode surface in the planar heterojunction-based devices. Compared with the typical standing organic-organic heterojunction on the bare ITO electrode, our in situ ultraviolet photoelectron spectroscopy experiments reveal that the heterojunction on the CVD graphene modified ITO electrode possesses better aligned energy levels with respective electrodes, hence facilitating effective charge collection.

Probing the Orientation of Electrostatically Immobilized Protein G B1 by Time-of-Flight Secondary Ion Spectrometry, Sum Frequency Generation, and Near-Edge X-ray Adsorption Fine Structure Spectroscopy

To fully develop techniques that provide an accurate description of protein structure at a surface, we must start with a relatively simple model system before moving to increasingly complex systems. In this study, X-ray photoelectron spectroscopy (XPS), sum frequency generation spectroscopy (SFG), near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy, and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to probe the orientation of Protein G B1 (6 kDa) immobilized onto both amine (NH(3)(+)) and carboxyl (COO(-)) functionalized gold. Previously, we have shown that we could successfully control orientation of a similar Protein G fragment via a cysteine-maleimide bond. In this investigation, to induce opposite end-on orientations, a charge distribution was created within the Protein G B1 fragment by first substituting specific negatively charged amino acids with neutral amino acids and then immobilizing the protein onto two oppositely charged self-assembled monolayer (SAM) surfaces (NH(3)(+) and COO(-)). Protein coverage, on both surfaces, was monitored by the change in the atomic % N, as determined by XPS. Spectral features within the SFG spectra, acquired for the protein adsorbed onto a NH(3)(+)-SAM surface, indicates that this electrostatic interaction does induce the protein to form an oriented monolayer on the SAM substrate. This corresponded to the polarization dependence of the spectral feature related to the NEXAFS N(1s)-to-π* transition of the β-sheet peptide bonds within the protein layer. ToF-SIMS data demonstrated a clear separation between the two samples based on the intensity differences of secondary ions stemming from amino acids located asymmetrically within Protein G B1 (methionine: 62 and 105 m/z; tyrosine: 107 and 137 m/z; leucine: 86 m/z). For a more quantitative examination of orientation, we developed a ratio comparing the sum of the intensities of secondary-ions stemming from the amino acid residues at either end of the protein. The 2-fold increase in this ratio, observed between the protein covered NH(3)(+) and COO(-) SAMs, indicates opposite orientations of the Protein G B1 fragment on the two different surfaces.

Effect of Gap States on the Orientation-Dependent Energy Level Alignment at the DIP/F16CuPc Donor–Acceptor Heterojunction Interfaces

The interface properties of organic–organic heterojunctions (OOHs) between diindenoperylene (DIP) and copper hexadecafluorophthalocyanine (F16CuPc), including interface morphology, molecular orientation, and energy level alignment, have been investigated systematically by atomic force microscopy, in situ ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), and synchrotron-based near-edge X-ray adsorption fine structure (NEXAFS) measurements. As revealed by NEXAFS measurements, DIP molecules adopt the standing orientation on the standing F16CuPc on the SiO2 substrate, while they have the lying-down configuration on the flat-lying F16CuPc on the highly oriented pyrolytic graphite substrate. From the UPS and XPS studies, there is a large interfacial charge transfer and a band-bending-like behavior in the standing DIP/F16CuPc OOHs, while the vacuum level is almost aligned at the lying-down DIP/F16CuPc OOH interface. We propose that the defects-induced gap states have a crucial...

Uracil on Cu(110): A quantitative structure determination by energy-scanned photoelectron diffraction

The local adsorption site of the nucleobase uracil on Cu(110) has been determined quantitatively by energy-scanned photoelectron diffraction (PhD). Qualitative inspection of the O 1s and N 1s soft x-ray photoelectron spectra, PhD modulation spectra, and O K-edge near-edge x-ray adsorption fine structure indicate that uracil bonds to the surface through its nitrogen and oxygen constituent atoms, each in near atop sites, with the molecular plane essentially perpendicular to surface and aligned along the close packed [110] azimuth. Multiple scattering simulations of the PhD spectra confirm and refine this geometry. The Cu-N bondlength is 1.96 ± 0.04 Å, while the Cu-O bondlengths of the two inequivalent O atoms are 1.93 ± 0.04 Å and 1.96 ± 0.04 Å, respectively. The molecule is twisted out of the [110]direction by 11 ± 5°.

New Insights into the Substrate–Plasma Polymer Interface

We describe a new method to characterize the underside (substrate interface) of plasma polymer (PP) thin films via their simple delamination from a sodium chloride single crystal substrate. By depositing the PP film onto an ionic bonded surface such as a sodium chloride crystal, the PP films investigated were easily delaminated from the substrate. Two plasma polymer films deposited from 1-bromopropane (BrPP) and allylamine (AAPP) were used to exemplify this new technique. The top- and underside (substrate-plasma polymer interface) of the films were examined by X-ray photoelectron spectroscopy (XPS) and synchrotron-based near edge X-ray adsorption fine structure (NEXAFS) spectroscopy. The results demonstrate that both films exhibit heterogeneous film structures with their chemical composition and levels of unsaturated species. The underside of both the BrPP and the AAPP films exhibited higher concentrations of oxygen, while their topsides contained higher levels of unsaturated species. These results provide useful insights into the BrPP and AAPP film formation and the chemistry. The delamination technique provides a simple method to analyze the early stages of film chemistry for plasma polymer thin films. Furthermore, this approach opens new opportunities for additional studies on the mechanisms and fundamentals of plasma polymer thin film formation with various monomers.

Temporal Evolution of Benzenethiolate SAMs on Cu(100)

The structure and thermal stability of self-assembled monolayers (SAMs) of benzenethiolate (BT) on Cu(100) have been studied by means of thermal desorption spectroscopy (TDS), scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), UV photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), and near-edge X-ray adsorption fine structure spectroscopy (NEXAFS). Vapor deposition at room temperature yields a well-ordered, densely packed c(6 × 2) saturation structure. At room temperature, this film is, however, metastable and transforms via partial decomposition by cleavage of the S-C bond into a less densely packed layer that reveals a coexisting p(2 × 2) phase. Such a transition occurs on a time scale of several days and is accompanied by a reduction of the work function change with respect to the bare Cu(100) surface from Δϕ = -0.9 eV for a freshly prepared saturated layer to -0.5 eV for an aged film. TDS experiments exhibit the presence of two distinct desorption channels (dissociative and intact desorption) occurring at different temperatures that reflects a variation of the local Cu-S interaction strength of BT at differently coordinated adsorption sites. Heating to above room temperature causes a rapid degradation and continuous thinning of BT films whereas above 500 K all thiolate species have desorbed or dissociated, leaving a sulfide overlayer behind that is accompanied by a substrate reconstruction. Interestingly, the upright orientation of BT adopted in the saturated monolayer remains almost identical upon heating and demonstrates the absence of downward tilting upon thermally induced thinning of the film.

P‐195L: Late‐News Poster: Effect of the Surface Anisotropy of a Rubbed Polyimide Film on Liquid Crystal Alignment Properties

AbstractMorphological and molecular orientational anisotropies of a rubbed polyimide film, which is a general alignment layer in a mass production of the 42″ IPS‐mode LCD, were analyzed. The results of our AFM (Atomic Force Microscopy) and XRR (X‐ray Reflectivity) measurements of rubbed polyimide surface didn't show any morphological anisotropy between parallel and perpendicular to a rubbing direction. On the other hand, orientational anisotropy of polyimide chains on their surface was observed by a NEXAFS (Near Edge X‐ray Adsorption Fine Structure) analysis. The reason for this is that the hardness of a polyimide film and the rubbing process in LCD manufacturing were optimized to minimize a rubbing scratch, which deteriorates an image quality if any. From these results, we imply that only molecular orientation without any morphological anisotropy at the polyimide surface is enough to attain LC (Liquid Crystal) alignment ability for currently mass‐produced IPS‐mode LCD products. In order to reveal the effect of molecular anisotropy on LC alignment properties, we enhanced the orientational anisotropy of polyimide chains by changing their molecular structures. We then confirmed that the increase of the orientational anisotropy could improve contrast ratio of a 42″ IPS‐mode LCD TV.

Tetra-σ bonding adsorption of pyridine on Si(1 0 0)-2 × 1

We studied adsorption of pyridine on Si(1 0 0) at room temperature using high resolution photoemission spectroscopy (PES) and near edge X-ray adsorption fine structure (NEXAFS) in the partial electron yield (PEY) mode. The Si 2p, C 1s, N 1s spectra of pyridine on Si(1 0 0) showed that pyridine is chemisorbed on Si(1 0 0)-2 × 1 through the formation of the tetra-σ-bonded structure with the N atom and three C atoms. NEXAFS was conducted to characterize the adsorption geometry of pyridine on Si(1 0 0). The π* orbital of C C bond showed a good angle dependence in C K-edge NEXAFS spectra, and we were able to estimate the adsorption angle between chemisorbed pyridine of C C bond and the Si(1 0 0) surface using an analytical solution of NEXAFS intensity. We find the coexistence of two different tight bridges with the adsorption angles 42 ± 2° and 45 ± 2° with almost equal abundance.