Surface Anionic Groups Research Articles

Unveiling the role of counter-anions in amorphous transition metal-based oxygen evolution electrocatalysts

At the initial stage of the oxygen evolution reaction (OER) most electrocatalysts undergo structural and chemical surface reconstruction. While this reconstruction strongly influences their performance, it is frequently overlooked. Herein, we analyze the role of the oxidized anions, which is particularly neglected in most previous works. We introduce a range of different anionic groups (Cl-, CH3COO-, NO3-, SO42-) on the surface of an amorphous ZnCoxNiyOz catalyst by a facile proton etching and ion exchange method from a ZIF-8 self-sacrificial template. The structural and chemical properties of the obtained set of materials are thoroughly analysed and correlated with their electrocatalytic performance to study the effect of surface anionic groups, phase transition, metal leaching and defect generation on OER activity. Exploiting the control possibilities provided by the synthesis method here described and employing the uncovered property-performance correlations, the electrocatalyst is optimized. As a result, we produce ZnCo1.25Ni0.73Ox-SO4 catalysts with outstanding OER performances, including a low overpotential of 252 mV at 10 mA cm−2 with a small Tafel slope of 41.6 mV dec−1. Furthermore, this catalyst exhibits remarkable stability with negligible overpotential variation for 100 h. The excellent catalytic properties are rationalized using density functional theory calculations, showing that the surface-adsorbed anions, particularly SO42−, can stabilize the OOH* intermediate, thus enhancing the OER activity. This work offers new insight into the roles of metal leaching and surface-adsorbed anions in the OER progress and facilitates the rational design of highly-efficient electrocatalysts for OER.

An enhanced kinetics and ultra-stable zinc electrode by functionalized boron nitride intermediate layer engineering

The current application of zinc (Zn) anode for aqueous Zn-ion batteries (AZIBs) is faced with several challenges, such as the Zn dendrite growth, hydrogen evolution reaction and by-product generation. Here, an intermediate layer of sulfonate group modified boron nitride nanosheets (S-BN) has been rationally designed and harnessed to regulate Zn plating/stripping behavior and mitigate the side reaction with electrolyte. Benefiting from the nanoscale cavities and surface anionic charge groups, the S-BN intermediate layer endows a dendrite-free electrodeposition behavior via an advanced desolvation process and even interface electronic field. As expected, the S-BN@Zn symmetrical cell enables long-term cycling of 2500 h under 2 mAh·cm−2 with a small plating/stripping overpotential of around 45 mV. When coupled with Na2V6O16·1.63H2O (NVO) cathode, the S-BN@Zn/NVO battery can operate stably up to 1200 cycles, implying the superior durability of S-BN@Zn anode. Accordingly, this novel Zn diffusion intermediate layer provides a promising approach to significantly enhance the anode electrochemical performance of AZIBs.

Acid-Free Preparation of Cellulose Nanocrystals by TEMPO Oxidation and Subsequent Cavitation.

Softwood bleached kraft pulp (SBKP) and microcrystalline cellulose (MCC) were oxidized using a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated system. The TEMPO-oxidized SBKP prepared with 10 mmol/g NaClO (SBKP-10) had a higher mass recovery ratio and higher carboxylate content than the other prepared celluloses including the TEMPO-oxidized MCCs. The SBKP-10 was then exposed to cavitation-induced forces through sonication in water for 10-120 min to prepare aqueous dispersions of needle-like TEMPO-oxidized cellulose nanocrystals (TEMPO-CNCs) with homogeneous width of 3.5 to 3.6 nm and average lengths of ∼200 nm. The average chain lengths of the cellulose molecules that make up the TEMPO-CNCs were less than half the average lengths of the TEMPO-CNCs. Compared with conventional CNCs prepared by acid hydrolysis, the TEMPO-CNCs prepared by the acid-free and dialysis-free process exhibited higher mass recovery ratios, significantly higher amounts of surface anionic groups, and smaller and more homogeneous widths.

A Solid-State Single-Ion Conductor for Lithium Batteries Based on Anionic Nanoparticles of Fluorinated Titania

Nowadays, among the most challenging classes of materials for the development of high-energy density lithium batteries are electrolytes and high-capacity cathode materials [1]. A considerable interest is attracted by metallic lithium anode-based Li-S and Li-air batteries because of their high specific capacity [2]. Nevertheless, the use of a metallic lithium anode compromises the chemical and electrochemical stability of the electrolyte. To address these drawbacks, a significant research effort is recently devoted to the design and preparation of new lithium-conducting electrolytes. Here, a new concept of electrolyte based on a solid-state lithium single-ion conductor is proposed, which opens new perspectives in the development of advanced lithium batteries [3]. The electrolyte is obtained by direct reaction of nanometric fluorinated TiO2 (FT) with molten metallic lithium, and consists of nanoparticles (NPs) with surface anionic groups neutralized by lithium cations. The resulting nanopowder is labelled LiFT® [4]. It should be highlighted that after functionalization, the conductivity of fluorinated TiO2 increases by more than four orders of magnitude. In this work, the structure of LiFT is elucidated by means of several techniques such as: Inductively-Coupled Plasma Atomic Emission Spectroscopy (ICP-AES); High-Resolution Transmission Electron Microscopy (HR-TEM), powder X-Ray Diffraction (XRD), Infrared Spectroscopy (FT-MIR and -FIR), electrochemical measurements and solid-state Magic-Angle Spinning-NMR (MAS-NMR) spectroscopy. XRD and HR-TEM measurements show that LiFT has the “core” structure of anatase, with Li cations present only in the external lithium-rich shell of NPs. Thus, no intercalation processes of Li+ in “core” LiFT NPs take place. In addition, it is demonstrated that lithium cations can migrate through grain boundaries of electrolyte NPs in a very effective way, achieving: 1) a room-temperature single-ion conductivity of about 3x10-4 Scm-1; 2) an excellent electrochemical stability; and 3) a high exchange current density. All these features, together with an easy synthesis process, which is based on precursors obtained from very cheap starting materials, make LiFT a very attractive material for application in several fields such as: a) all-solid-state lithium batteries; b) molten electrode lithium batteries; c) nanocomposite electrolytes and d) lithium-air batteries.[1] M. Armand, J.-M. Tarascon, Building better batteries, Nature. 451 (2008) 652–657.[2] P.G. Bruce, S.A. Freunberger, L.J. Hardwick, J.-M. Tarascon, Li-O2 and Li-S batteries with high energy storage., Nat. Mater. 11 (2012) 19–29.[3] F. Bertasi, K. Vezzù, E. Negro, S. Greenbaum, V. Di Noto, Single-ion-conducting nanocomposite polymer electrolytes based on PEG400 and anionic nanoparticles: Part 1. Synthesis, structure and properties, Int. J. Hydrogen Energy. (2013).[4] V. Di Noto, F. Bertasi, E. Negro, M. Piga, M. Bettiol, F. Bassetto, Solid-state electrolytes based on fluorine-doped oxides, PCT/IB2012/053542, 2013.

Probing the chemical and surface chemical modification of vessel cell walls during bleaching of eucalyptus pulp

Abstract Eucalyptus pulp is increasingly used for the manufacture of printing papers. However, its major drawback, the vessel picking, is still waiting for a solution. The detailed features and the characteristic behaviour of vessel elements (VEs) in pulp and paper processes are poorly understood. This study focusses on the chemistry, surface chemistry and morphology of eucalyptus VEs. These properties were followed through the changes introduced by different stages of elemental chlorine-free (ECF) bleaching, by studying separated VEs. Microprobe X-ray photoelectron spectroscopy (μ-XPS) and field emission-scanning electron microscopy (FE-SEM) were applied to elucidate the surface chemical composition and morphological ultrastructure, respectively. The bulk chemical composition was investigated among others by Py-GC/MS. Lignin was detected in vessels still after completed bleaching sequence, whereas the fibres were lignin-free. The vessel lignin was mainly composed by syringyl-type units. Surface coverage by lignin and amount of surface anionic groups were practically unaffected by bleaching. The vessel cell wall structure was observed to be layered in a complex way with no particular orientation of cellulose fibrils, and the different layers seemed to be exfoliated during different bleaching stages.

Studies on the fibre surfaces modified with xylan polyelectrolytes

Xylan was isolated from birch wood chips by using pressurized hot water extraction (PHWE). The extracted xylan was chemically modified yielding three different xylan derivatives (XDs): xylan sulfate (XS), carboxymethyl xylan (CMX) and xylan-4-[N,N,N-trimethylammonium]butyrate chloride (XTMAB). The structure and molecular weight of XDs was determined by using NMR spectroscopy and size exclusion chromatography (SEC). The potential utilization of xylan polyelectrolytes for modifying fibre surfaces was assessed by sorption experiments using bleached pine Kraft pulp as substrate. Polyelectrolyte titration method was chosen for estimating the amount of sorbed XDs onto the fibres. The cationic xylan derivative XTMAB had a strong interaction with fibres while the anionic derivatives did not show any sorption. X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS) were selected as advanced surface analyses for studying the amount of surface anionic groups and the surface distribution of the XTMAB. XPS and polyelectrolyte titration results suggested that the XTMAB is sorbed onto the fibre surfaces. ToF-SIMS imaging showed that XTMAB was evenly distributed on fibre surfaces.

Changes of anionic groups in alkaline peroxide-impregnated aspen chemithermomechanical pulp during subsequent alkaline peroxide bleaching

The effect of alkaline peroxide bleaching on the total anionic groups (AGs) and surface AGs in aspen chemithermomechanical pulp (CTMP) fibers was investigated. Alkaline treatment, especially alkaline peroxide bleaching resulted in the formation of new AGs and surface AGs in the CTMP fibers. The carboxylic groups in uronic acid units, including 4-O-methylglucuronic acid, galacturonic acid, and glucuronic acid units were the main contributors to the AGs in the fibers. However, the oxidized lignin accounting for more than 30% of the total AGs in the bleached CTMP fibers, was the main origin of the new AGs formed during the peroxide bleaching. In addition, the new AGs were also formed by extensive deesterification of the residual esterified uronic acids in pectins and lignin-carbohydrate complexes (LCCs). Although some uronic acid units were dissolved in the process water, both the total AGs and surface AGs in the fibers increased after alkaline peroxide bleaching.

Surface chemistry of deinked pulps as analysed by XPS and ToF‐SIMS

AbstractThe surface chemistry of recycled deinked pulps made from old newspaper (ONP) and mixed office waste (MOW) was investigated by XPS and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The short and the long fibre fractions of the pulps were separated and their differences in surface chemistry were assessed. The amount of surface anionic groups (SAG) and the surface coverage by carbohydrates, lignin and extractives were calculated from the XPS measurements. Metal traces were observed on feed pulps and the fines fractions of both ONP and MOW, some of them exposed after extraction. Only fines of ONP showed a quantifiable amount of surface extractives. The amount of surface lignin did not differ significantly between the ONP fractions. The method presented high values of surface lignin on MOW, especially fines fraction, which was considered, in fact, a measure of other surface contamination. There were no remarkable differences between the SAGs in the different fractions. Residual chemicals from paper converting, printing and deinking were detected on the fibre surfaces by ToF‐SIMS spectrometry. The distributions of trace metals (e.g. Fe, Al and Mg), pulp components and some common contaminants were assessed using ToF‐SIMS imaging. It was discovered that the fibre surfaces were covered by patchy ink residuals at raster sizes of 200 µm × 200 µm. A uniform layer of siloxanes and phthalates was also detected on every sample. The residual paper and printing chemicals can affect interactions in papermaking and reduce the fibre‐to‐fibre bonds in the recycled paper. Copyright © 2010 John Wiley & Sons, Ltd.

Controlled adsorption-desorption of cationic polymers on the surface of anionic latex particles

The complexation of anionic latex particles with two series of cationic copolymers is studied. The copolymers of the first series contain cationic and electroneutral (zwitter ion) hydrophilic units. The electrostatic adsorption of these copolymers on the surface of latex particles is accompanied by the formation of multiple salt bridges between cationic copolymer units and surface anionic groups. The dependence of ultimate adsorption on the molar fraction of cationic groups in copolymer α is described by a bell-shaped curve with a maximum at α = 0.05−0.10 and a long horizontal portion at α > 0.24. In terms of the adsorption theory of polyampholytes, such a pattern of the adsorption curve results from the compromise between the attraction of polymer chains to the surface induced by their polarization in the electric field of particles and the repulsion of like charged macromolecular units. The stability of complexes with the copolymers of the first series in water-salt media increases with an increase in α. The copolymers of the second series contain cationic and hydrophobic units. In this case, an increase in α is accompanied by a decrease in the amount of the adsorbed polymer throughout the studied α range (0.24–1). The complexes are stabilized not only via electrostatic interactions but also via hydrophobic interactions. A decrease in α decreases the role of electrostatics in stabilization of the complexes; however, this effect is compensated for by an increase in the number of hydrophobic contacts. This allows the stability of complexes to be preserved in concentrated water-salt solutions. The results of this study indicate that the stability of interfacial layers with the participation of cationic copolymers can be changed in a wide range by varying the ratio of ionic and electroneutral (hydrophilic or hydrophobic) comonomers in macromolecules.

Anionic groups on cellulosic fiber surfaces investigated by XPS, FTIR-ATR, and different sorption methods

Anionic groups (AGs) on different cellulosic fiber surfaces were investigated by methylene blue (MB) and polyelectrolyte (PE) sorption, X-ray photoelectron spectroscopy (XPS), and total attenuated reflectance infrared spectrometry (FTIR-ATR). The MB sorption isotherms fitted well the Langmuir equation that gave consistent estimations of sorption capacities. FTIR-ATR showed that MB molecules had extensive accessibility to the fiber wall pores. Estimation of surface AGs by PE sorption gave much higher values than a new method combining MB sorption and XPS measurements (MB-XPS). The surface AGs in different cellulosic fibers accounted for 1–3% of the total AG content as revealed by MB-XPS. It was suggested that PE molecules can penetrate the fiber wall and form loops or unattached segments at external fiber surfaces that disrupt the PE sorption stoichiometry. The competition of MB and PE for the anionic sites in papermaking was assessed and it was shown that MB ions have a much stronger affinity to AGs than PE molecules.

Observation of Cathodic Photocurrents at Nanocrystalline TiO2 Film Electrodes, Caused by Enhanced Oxygen Reduction in Alkaline Solutions

Nanocrystalline TiO2 (rutile and anatase) film electrodes usually show anodic photocurrents in aqueous electrolytes. Detailed photoelectrochemical studies have revealed that they also show cathodic photocurrents under particular conditions, e.g., in alkaline solutions containing dissolved oxygen under illumination from the TiO2-film side at short wavelengths such as 300 nm. The cathodic photocurrents appear in a potential region about 0.5∼0.9 V more positive than the flat-band potential (Ufb) of single-crystal n-TiO2 electrodes. It is shown that the appearance of the cathodic photocurrents can be attributed to efficient electron transfer from the conduction band of TiO2 particles to chemically adsorbed oxygen molecules, the density of which is largely increased in alkaline solutions through a charge-transfer interaction between surface anionic groups such as Ti−O- as an electron donor and oxygen molecules as an electron acceptor. The dependences of the cathodic and anodic photocurrents on the illumination wavelength, the illumination direction, the electrode potential, and the crystal form of TiO2 particles are discussed in relation with the photocatalytic activity of particulate TiO2 films.

Herpetomonas megaseliae: Effect of lipopolysaccharide on cell-surface anionogenic groups

Surface anionic groups ofHerpetomonas megaseliae, untreated or treated with lipopolysaccharides (LPS), were analyzed by cell electrophoresis and cytochemistry as well as by identification of sialic acid residues with the aid of thin-layer chromatography. LPS treatment of the trypanosomatids caused a marked decrease in the negative surface charge, as well as in binding to the cell surface of cationized ferritin, colloidal iron hydroxide, and Sendai virus particles. Incubation of LPS-treated and untreated flagellates with neuraminidase resulted in decrease of their mobility to the negative pole. The foregoing findings suggest that sialic acid residues are the major anionogenic groups exposed on the surface of this protozoon. Treatment with LPS markedly alters the nature and number of these residues. OnlyN-acetylneuraminic acid can be detected on untreated flagellates, whereasN-acetyl andN-glycolylneuraminic acid derivatives are found on the organisms exposed to LPS.

Changes in Cell Surface Anionogenic Groups Induced by Propranolol in Herpetomonas muscarum muscarum

The effects of propranolol (10(-3) mM) on the surface anionic groups of Herpetomonas muscarum muscarum were analysed by cell electrophoresis, by ultrastructural cytochemistry and by identification of sialic acids using paper chromatography. Differentiation of H. muscarum muscarum induced by propranolol treatment caused a significant increase in the net negative surface charge. Binding of cationized ferritin (CF) and colloidal iron hydroxide particles was observed at the cell surface of both untreated and propranolol-treated cells. In cells incubated in the presence of the drug the CF particles were distributed in all membrane regions. However, there were small areas where the particles were absent. In H. muscarum muscarum exposed to propranolol the density of residues of sialic acid per cell was higher, and the agglutinating activity with Sendai virus was more intense. However, the pattern of sialic acid, characterized by the presence of N-acetylneuraminic acid derivative, was not modified upon cell interaction with the drug. Treatment of both control and propranolol-treated protozoa with neuraminidase significantly reduced the surface charge. These findings suggest that sialic acid residues are the major anionogenic groups exposed on the surface of H. muscarum muscarum.

Changes in cell surface anionogenic groups during differentiation ofHerpetomonas samuelpessoai mediated by dimethylsulfoxide

The surface anionic groups of untreated or dimethyl sulfoxide (DMSO)-treated Herpetomonas samuelpessoai cells were analyzed by cell electrophoresis, ultrastructural cytochemistry, and identification of sialic acids using thin-layer chromatography. Differentiation of H. samuelpessoai induced by DMSO treatment caused a significant increase in the net negative surface charge. In flagellates exposed to DMSO, more cationized ferritin, colloidal iron hydroxide, and sendai virus particles bound to the cell surface. Treatment of both untreated and DMSO-treated flagellates with neuraminidase decreased markedly the EPM of cells to the cathodic pole. These findings suggest that sialic acid residues are the major anionogenic groups exposed on the surface of H. samuelpessoai. Thin-layer chromatography showed that N-acetyl and N,O-diacylneuraminic acids, in equal proportions, were present in H. samuelpessoai. However, N-acetylneuraminic acid predominates in DMSO-treated cells.

Surface Anionic Groups in Symbiote‐Bearing and Symbiote‐Free Strains ofCrithidia deanei1

ABSTRACTThe surface anionic groups of symbiote‐bearing and symbiote‐free strains ofCrithidia deaneiwere compared by determining cellular electrophoretic mobility, by ultrastructural cytochemistry, and by identification of sialic acids by thin‐layer and gasliquid chromatography. Symbiote‐freeCrithidia deaneihas a highly negative surface charge (‐0.9984 μmċs‐1ċ V‐1ċ cm), which is slightly reduced (‐0.8527 μmċs‐1ċ V‐1ċ cm) by the presence of the endosymbiote. Treatment of both strains ofC. deaneiwith neuraminidase decreased significantly the electrophoretic mobility of cells toward the cathodic pole, indicating the existence of exposed sialic acid residues responsible for the negative charge on the protozoan cell surface. Thin‐layer and gas‐liquid chromatography showed thatN‐glycolyl‐ andN‐acetylneuraminic acids were present in both strains ofC. deanei.

The effect of neuraminidase- and ribonuclease-susceptible surface anionic groups on the aggregation of embryonic chick neural retina cells.

The role of cell surface charge in cellular interactions has been the subject of conflicting reports. The major contribution to the net cell surface negativity of all mammalian cells studied is made by the sialic acid moieties of the surface glycoproteins, while ribonuclease-susceptible sites have been shown to contribute to the lesser extent on some cell types. Experiments were done to determine whether these anionic groups at the cell periphery affect the aggregation and sorting behaviour of embryonic chick neural retina cells when cultured alone or in combination with embryonic heart cells. The net negative surface charge density, as determined by cell electrophoretic mobility, of neuraminidase- or ribonuclease-treated cells was significantly decreased immediately after incubation with the enzymes, and the treatment with neuraminidase resulted in a reduction in the binding of colloidal iron hydroxide particles at the cell surface. Both enzymes caused reduced aggregate size in gyratory shaker cultures of neural retina and mixed cell suspensions, and fewer neural retina cells adherent to microtest plate surfaces, but no differences were seen in their histological appearance or sorting pattern in mixed shaker culture. The results indicate that the neuraminidase- and ribonuclease-susceptible groups at the periphery of embryonic neural retina cells play a role in some aspects of cell contact behaviour in ways other than reduction in net negative surface charge.

The distribution and mobility of surface anionic groups of normal human oesophageal epithelium following interaction with cationized verritin.

Oesophageal epithelial cells from biopsies from normal patients showed the presence of randomly distributed anionic groups, mostly sialic acid on the cell membrane in fixed material shown by cationized ferritin. When biopsies were pulse labelled, patching occurred in all three cell layers. Patching was energy dependent and did not occur at 4 degrees C. Pulse labelled material incubated on an unlabelled medium showed progressive loss of cationized ferritin from the cell membrane. This was mostly into the medium, although some was internalized in membrane profiles. A second pulse of cationized ferritin produced further patching suggesting regeneration of cell membrane. Superficial cells were leaky, but their organelles were not.

An analysis of the effect of mono- and di-valent cations on the forces between charged lipid membranes with special reference to the grana thylakoids of chloroplasts

A numerical technique is applied to the investigation of salt effects on the electrostatic repulsion between lipid membranes with chargeable anionic groups. It is found that when such groups dissociate easily, the effects of mono- and divalent cations are antagonistic under low salt conditions. However, when the surface anionic groups have pK values closer to the bulk pH value, the effects are much more subtle. The results of the analysis are applied to explain experimental observations on chloroplast grana thylakoid membranes, but they may find more general use.

Thermotropic lateral translational motion of intramembrane particles in the inner mitochondrial membrane and its inhibition by artificial peripheral proteins.

Freeze fracturing and deep etching have been used to study thermotropic lateral translational motion of intramembrane particles and membrane surface anionic groups in the inner mitochondrial membrane. When the inner membrane is equilibrated at low temperature, the fracture faces of both halves of the membrane reveal a lateral separation between intramembrane particles and particle free, large smooth patches. Such separation is completely reversed through free lateral translational diffusion by reversing the temperature. The low temperature induced, particle-free, smooth membrane patches appear to represent regions of protein-excluding, ordered bilayer lipid which form during thermotropic liquid crystalline to gel state phase transitions. When polycationic ferritin is electrostatically bound to anionic groups exposed at the membrane surface at concentrations which inhibit the activities of cytochrome c oxidase and succinate permease, the bound ferritin migrates with intramembrane particles during the thermotropic lateral separation between the membrane particles and smooth patches. When bound polycationic ferritin is cross-bridged with native ferritin, an artificial peripheral protein lattice forms in association with the surface anionic groups and diminishes the thermotropic lateral translational motion of intramembrane particles in the membrane. These results reveal that the anionic groups of metabolically active integral proteins which are known to be exposed at the surface of the inner mitochondrial membrane migrate with intramembrane particles in the plane of the membrane under conditions which induce lipid-protein lateral separations. In addition, cross-bridging of the anionic groups through an artificial peripheral protein lattice appears to diminish such induced lipid protein lateral separations.

Regeneration of plasmalemma and surface properties in macrophages

The regeneration of surface anionic groups in mouse peritoneal macrophages was investigated by electron microscopy, using cationized ferritin (CF) as a tool for the localization and evaluation of negative charge density on the cell surface. In vitro interaction of living macrophages with CF resulted in removal of most anionic groups, either by concentration of their receptor sites to a part of the membrane which is subsequently internalized, or by detachment of the aggregated label from the surface. After incubation of macrophages lacking surface anionic groups in tissue culture medium without the ligand, regeneration of the binding capacity for CF took place within 3 h. The first regenerated parts of the membrane can be visualized within 1 h on the upper part of the adherent cells; there is a discontinuous coating of ferritin, with the lateral regions of the plasmalemma free of label. The attached CF particles on the regenerated membrane are closer to the membrane and their density is considerably higher than on the normal control macrophages. The results indicate that the turnover of the plasmalemma is regional and not dispersed; the mechanism involved is insertion of membrane patches into the pre-existing plasma membrane.