Water-induced reconstruction that affects mobile ions on the surface of calcite

Time-sequenced contact-force micrographs show that the (104) calcite cleavage surface reconstructs in humid air through pit formation and film growth. After 8 h at 80% relative humidity (RH), 50% to 80% of the surface is covered by islands that are flat-topped and 1-nm high. The lateral growth rates of individual islands are 4.2+/-0.4 nm min-1 in the 41 direction and 1.8+/-0.4 nm min-1 in the 48 direction, resulting in islands having distinct major and minor axes. On some samples, a contiguous, 1.5-nm-high film rapidly grows between the islands and the pits. The areal expansion rate of the film is 500 times faster than that of the islands. Gaps between the contiguous film and the islands expand and contract, which suggests that mass is exchanged between them and that both are loosely bound. Complementing the topographic images, polarization heights are simultaneously measured by polarization-force microscopy. The polarization heights of the islands and the contiguous film are -6 to -10 nm and -4 to -5 nm, respectively, compared to their respective topographic heights of +1.0 and +1.5 nm. Under our experimental conditions, the polarization heights are a surrogate for the local dielectric constant of the sample epsilon and arise from a convolution of the mobility and the density of surface ions. The polarization heights imply that epsilonsubstrate>epsilonfilm>epsilonisland. Changes in topographic and polarization heights at 20% and 50% RH suggest that the structures of the islands are in dynamic equilibrium with the adsorbed water. Our evidence suggests that the islands contain loosely bound water and may therefore be a hydrated calcium carbonate phase stabilized by the calcite surface.     

Reversible uptake of water on NaCl nanoparticles at relative humidity below deliquescence point observed by noncontact environmental atomic force microscopy

The behavior of NaCl nanoparticles as a function of relative humidity (RH) has been characterized using non-contact environmental atomic force microscopy (e-AFM) to measure the heights of particles deposited on a prepared hydrophobic surface. Cubic NaCl nanoparticles with sides of 35 and 80 nm were found to take up water reversibly with increasing RH well below the bulk deliquescence relative humidity (DRH) of 75% at 23(°)C, and to form a liquid-like surface layer of thickness 2 to 5 nm, with measurable uptake (>2 nm increase in particle height) beginning at 70% RH. The maximum thickness of the layer increased with increasing RH and increasing particle size over the range studied. The liquid-like behavior of the layer was indicated by a reversible rounding at the upper surface of the particles, fit to a parabolic cross-section, where the ratio of particle height to maximum radius of curvature increases from zero (flat top) at 68% RH to 0.7 ± 0.3 at 74% RH. These observations, which are consistent with a reorganization of mass on the solid NaCl nanocrystal at RH below the DRH, suggest that the deliquescence of NaCl nanoparticles is more complex than an abrupt first-order phase transition. The height measurements are consistent with a phenomenological model that assumes favorable contributions to the free energy of formation of a liquid layer on solid NaCl due both to van der Waals interactions, which depend partly upon the Hamaker constant, A(film), of the interaction between the thin liquid film and the solid NaCl, and to a longer-range electrostatic interaction over a characteristic length of persistence, ξ; the best fit to the data corresponded to A(film)= 1 kT and ξ = 2.33 nm.     

Zn2+ and Sr2+ adsorption at the TiO2 (110)-electrolyte interface: influence of ionic strength, coverage, and anions

The X-ray standing wave technique was used to probe the sensitivity of Zn2+ and Sr2+ ion adsorption to changes in both the adsorbed ion coverage and the background electrolyte species and concentrations at the rutile (alpha-TiO2) (110)-aqueous interface. Measurements were made with various background electrolytes (NaCl, NaTr, RbCl, NaBr) at concentrations as high as 1 m. The results demonstrate that Zn2+ and Sr2+ reside primarily in the condensed layer and that the ion heights above the Ti-O surface plane are insensitive to ionic strength and the choice of background electrolyte (with <0.1 A changes over the full compositional range). The lack of any specific anion coadsorption upon probing with Br-, coupled with the insensitivity of Zn2+ and Sr2+ cation heights to changes in the background electrolyte, implies that anions do not play a significant role in the adsorption of these divalent metal ions to the rutile (110) surface. Absolute ion coverage measurements for Zn2+ and Sr2+ show a maximum Stern-layer coverage of approximately 0.5 monolayer, with no significant variation in height as a function of Stern-layer coverage. These observations are discussed in the context of Gouy-Chapman-Stern models of the electrical double layer developed from macroscopic sorption and pH-titration studies of rutile powder suspensions. Direct comparison between these experimental observations and the MUltiSIte Complexation (MUSIC) model predictions of cation surface coverage as a function of ionic strength revealed good agreement between measured and predicted surface coverages with no adjustable parameters.     

Electrodynamic investigations of conduction processes in humid microcrystalline cellulose tablets

The conduction mechanism in microcrystalline cellulose (MCC) tablets at varying relative humidity (RH) has been investigated by using the techniques of low frequency dielectric spectroscopy and transient current analysis at room temperature. The dependence on RH on the measured conductivity and charge carrier density indicates that a high-power-law-exponent percolation process of cations being conducted on water molecules occupying available 6-OH units on the cellulose chains is the dominating dc conduction mechanism at RH below 3 wt % of moisture content. The experimentally observed decrease in charge carrier mobility with increasing moisture content shows that protons and H3O+ ions that are being blocked at empty 6-OH sites also contribute to the charge transport process in cellulose at low moisture contents.     

Control over wettability of polyethylene glycol surfaces using capillary lithography

We demonstrate that wettability of poly(ethylene glycol) (PEG) surfaces can be controlled using nanostructures with various geometrical features. Capillary lithography was used to fabricate PEG nanostructures using a new ultraviolet (UV) curable mold consisting of functionalized polyurethane with acrylate group (MINS101m, Minuta Tech.). Two distinct wetting states were observed depending of the height of nanostructures. At relatively lower heights (< 300 nm for 150 nm pillars with 500 nm spacing), the initial contact angle of water was less than 80 degrees and the water droplet easily invaded into the surface grooves, leading to a reduced contact angle at equilibrium (Wenzel state). At relatively higher heights (> 400 nm for 150 nm pillars with 500 nm spacing), on the other hand, the nanostructured PEG surface showed hydrophobic nature and no significant change in contact angle was observed with time (Cassie state). The presence of two wetting states was also confirmed by dynamic wetting properties and contact-angle hysteresis. The wetting transition from hydrophilic (bare PEG surface) to hydrophobic (PEG nanostructures) was described by the Cassie-Baxter equation assuming that enhanced hydrophobicity is due to the heterogeneous wetting mediated by an air pocket on the surface. The measured contact angles in the Cassie state were increased with increasing air fraction, in agreement with the theoretical prediction.     

Frequency tuning of long-wavelength VCSELs

Tuning properties of long-wavelength VCSELs have been studied experimentally, for the first time to our knowledge. Injection current and temperature tuning rates of two VCSELs operating near 1,512 and 1,577 nm have been measured using a Fabry-Perot etalon with free spectral range 0.056 cm(-1). A 100-Hz saw-tooth modulation with depths of modulation of approximately 10% or less was superimposed on a direct injection current (dc bias) to tune lasers in narrow spectral intervals (0.3-1.2 cm(-1)) around a central frequency set by the dc bias. The lasers have been found to be capable of being tuned faster at higher levels of dc bias. The enhancement factors were up to approximately 2 and approximately 3 for the 1,512- and 1,577-nm lasers, respectively, as compared with their tuning rates measured at the levels of the dc bias close to the threshold of lasing. A linear dependence between injection current tuning rates and the levels of dc bias has been observed. Temperature tuning coefficients have been proved to be independent of the laser heat sink temperature and of the dc bias. Frequency tuning curves were approximated with a second-order polynomial. The frequencies of more than 40 absorption lines of CO, CO(2), H(2)O and NH(3) known from spectral databases were compared with the calculated frequencies. The accuracy of the approximation was found to be within 0.2 cm(-1) for spectral intervals up to 38 cm(-1). The dependence of current tuning rates of the VCSELs on dc bias was shown to be taken into account for accurate analysis of absorption line profiles. The results obtained can be used for precise spectroscopic measurements with long-wavelength VCSELs.     

Facile fabrication of silver nanofin array via electroless plating

The fabrication of metallic nanostructures is one of the main issues in nanotechnology. This article describes the fabrication of a silver nanofin array by combining microlithography, electroless plating, and an etching technique. Fabricated Ag nanofins have a high aspect ratio (height/width = 10, width = 60 nm, height = 600 nm), and their widths and heights can be controlled by the period of electroless plating and the height of the original line pattern. An isolated Ag nanofin was proven to show metallic electrical conductivity. The current process provides a rapid and shape-designable fabrication method of metallic nanostructures.     

Sorption and distribution of226Ra in an electrolytic manganese dioxide column in the presence of other ions

Distribution of²²⁶Ra within a segmented electrolytic manganese dioxide (EMD) column was investigated under varying flow rates. Tests show uniform distribution of²²⁶Ra within the EMD column at higher flow rates, as compared to a lower flow rate whereby an apparent two stage sorption process is contributing to the sorption amount. The sorption of²²⁶Ra on EMD decreases from 57% to 14.2% over a short range of Ba²⁺ concentration (5–30 mg Ba²⁺ per 750.0 g solution) using flow rates of 200–300 ml min^–1. The sorption of²²⁶Ra on EMD decreases (58–15%) a consistent higher sorption of²²⁶Ra compared to¹³³Ba under all Ra:Ba ratios indicating the preference for Ra²⁺ ions.     

共聚焦拉曼光谱研究过饱和硝酸铵液滴中NH4+, NO3- 和H2O之间的相互作用

将硝酸铵液滴沉积在石英基底上,通过降低该液滴周围环境的相对湿度,测定了该液滴由低浓度直至过饱和状态下高信噪比的拉曼光谱.其中,相对湿度的变化可以精确控制液滴浓度的改变.在相对湿度(RH)由72.1%降低至37.9%的过程中,硝酸铵液滴v1-NO-3峰位保持在1048cm-1,半峰宽为10cm-1.该现象表明NO-3周围的水分子被NH4+取代后不会对v1-NO-3造成影响,说明水分子和NH4+所形成的氢键具有相同的强度.对2500-4000cm-1范围内的拉曼光谱进行成分分析,2890、3090、3140、3220、3402及3507cm-1分别被指认为NH+4伞状弯曲振动的泛频、NH+4伞状弯曲振动与摇摆振动的组合谱带、NH+4的对称伸缩振动、NH+4的反对称伸缩振动、水峰中强氢键成分和弱氢键成分.从拟合结果得出:强氢键在氢键结构中所占百分含量随液滴相对湿度的降低而减少,弱氢键所占百分含量随液滴相对湿度的降低而增加.该变化趋势是NO-3和NH+4之间复杂相互作用的结果.     

Apparent solubility of hydroxyapatite in aqueous medium and its influence on the morphology of nanocrystallites with precipitation temperature

Two differing wet-chemical synthesis routes, Ca(OH)2 + H3PO4 and CaCl2 + Na3PO4/NaOH, were used to prepare hydroxyapatite (HA) at various temperatures ranging from 30 to 95 degrees C. The electrical conductivity of the solution was measured at regular intervals of time during H3PO4 and Na3PO4 addition to the suspension/solution containing Ca2+ ions. The rate of change of conductivity is used to note the end point of the reaction. X-ray diffraction of the dried, precipitated particles revealed HA as the predominant phase, and the FTIR spectroscopy studies indicated the presence of CO3(2-) groups which substituted PO4(3-) groups in the HA lattice (B-type). FESEM observations revealed that the aspect ratio of the particles decreased with increasing precipitation reaction temperature in one system [Ca(OH)2 + H3PO4] and in the other system it increased with increasing temperature. The changes in the morphology with temperature were analyzed through conductivity measurements and the thermochemical properties of the reaction systems. Conductivity measurements showed that the concentration of dissolved ions at the end point of the reaction between Ca(OH)2 and H3PO4 increased, indicating an increased apparent solubility of HA with increasing temperature, whereas the end-point conductivity did not increase noticeably in the other reaction system.     

Synthesis of poly(hydroxamic acid) ligand from polymer grafted corn‐cob cellulose for transition metals extraction

Poly(hydroxamic acid) ligand was synthesized using ester functionalities of cellulose‐graft‐poly(methyl acrylate) copolymer, and products are characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, high‐resolution transmission electron microscopy, and X‐ray photoelectron spectroscopy analysis. The poly(hydroxamic acid) ligand was utilized for the sensing and removal of transition metal ions form aqueous solutions. The solution pH is found a key factor for the optical detection of metal ions, and the reflectance spectra of the [Cu‐ligand]ⁿ⁺ complex were observed to be the highest absorbance 99.5% at pH 6. With the increase of Cu²⁺ ion concentration, the reflectance spectra were increased, and a broad peak at 705 nm indicated that the charge transfer (π‐π transition) complex was formed. The adsorption capacity with copper was found to be superior, 320 mg g^?1, and adsorption capacities for other transition metal ions were also found to be good such as Fe³⁺, Mn²⁺, Co³⁺, Cr³⁺, Ni²⁺, and Zn²⁺ were 255, 260, 300, 280, 233, and 223 mg g^?1, respectively, at pH 6. The experimental data show that all metal ions fitted well with the pseudo‐second‐order rate equation. The sorption results of the transition metal ions onto ligand were well fitted with Langmuir isotherm model (R² > 0.98), which implies the homogenous and monolayer character of poly(hydroxamic acid) ligand surface. Eleven cycles sorption/desorption process were applied to verify the reusability of this adsorbent. The investigation of sorption and extraction efficiency in each cycle indicated that this new type of adsorbent can be recycled in many cycles with no significant loss in its original detection and removal capability. Copyright © 2016 John Wiley & Sons, Ltd.     

Physicochemical characterization of the retardation of aqueous Cs+ ions by natural kaolinite and clinoptilolite minerals

The aim of this study was to carry out kinetic, thermodynamic, and surface characterization of the sorption of Cs+ ions on natural minerals of kaolinite and clinoptilolite. The results showed that sorption followed pseudo-second-order kinetics. The activation energies were 9.5 and 13.9 kJ/mol for Cs+ sorption on kaolinite and clinoptilolite, respectively. Experiments performed at four different initial concentrations of the ion revealed that the percentage sorption of Cs+ on clinoptilolite ranged from 90 to 95, compared to 28 to 40 for the kaolinite case. At the end of a 1 week period, the percentage of Cs+ desorption from clinoptilolite did not exceed 7%, while it amounted to more than 30% in kaolinite, indicating more stable fixation by clinoptilolite. The sorption data were best described using Freundlich and D-R isotherm models. Sorption showed spontaneous and exothermic behavior on both minerals, with deltaH(0) being -6.3 and -11.4 kJ/mol for Cs+ uptake by kaolinite and clinoptilolite, respectively. Expanding the kaolinite interlayer space from 0.71 to 1.12 nm using DMSO intercalation, did not yield a significant enhancement in the sorption capacity of kaolinite, indicating that the surface and edge sites of the clay are more energetically favored. EDS mapping and elemental analysis of the surface of kaolinite and clinoptilolite revealed more intense signals on the surface of the latter with an even distribution of sorbed Cs+ onto the surfaces of both minerals.     

Adsorption of nickel on synthetic hydroxyapatite from aqueous solutions

The sorption of nickel on synthetic hydroxyapatite was investigated using a batch method and radiotracer technique. The hydroxyapatite samples used in experiments were a commercial hydroxyapatite and hydroxyapatite of high crystallinity with Ca/P ratio of 1.563 and 1.688, respectively, prepared by a wet precipitation process. The sorption of nickel on hydroxyapatite was pH independent ranging from 4.5 to 6.5 as a result of buffering properties of hydroxyapatite. The adsorption of nickel was rapid and the percentage of Ni sorption on both samples of hydroxyapatite was >98 % during the first 15–30 min of the contact time for initial Ni²⁺ concentration of 1 × 10^?4 mol dm^?3. The experimental data for sorption of nickel have been interpreted in the term of Langmuir isotherm and the value of maximum sorption capacity of nickel on a commercial hydroxyapatite and hydroxyapatite prepared by wet precipitation process was calculated to be 0.184 and 0.247 mmol g^?1, respectively. The sorption of Ni²⁺ ions was performed by ion-exchange with Ca²⁺ cations on the crystal surface of hydroxyapatite under experimental conditions. The competition effect of Co²⁺ and Fe²⁺ towards Ni²⁺ sorption was stronger than that of Ca²⁺ ions. NH₄ ⁺ ions have no apparent effect on nickel sorption.     

Informing the improvement of forest products durability using small angle neutron scattering

A better understanding of how wood nanostructure swells with moisture is needed to accelerate the development of forest products with enhanced moisture durability. Despite its suitability to study nanostructures, small angle neutron scattering (SANS) remains an underutilized tool in forest products research. Nanoscale moisture-induced structural changes in intact and partially cut wood cell walls were investigated using SANS and a custom-built relative humidity (RH) chamber. SANS from intact wood sections cut from each primary wood orientation showed that although wood scattered anisotropically across 1.3–600 nm length scales, measurement of elementary fibril spacing and low-q surface scattering were independent of orientation. Water sorption caused spacing between elementary fibrils to increase with RH, and this swelling accounted for over half the transverse swelling in S2 secondary wood cell walls. Elementary fibril spacing in longitudinally cut wood cells, which were designed to mimic cells near wood-adhesive bondlines, was greater than the spacing in intact cells above 90 % RH. This suggested that some cell wall hoop constraint from the S1 and S3 cell wall layers on the S2 layer was released by cutting the cells. Furthermore, increased spacing between elementary fibrils may also create diffusion channels that are hypothesized to be responsible for the onset of fungal decay in wood. Protocols were established to use SANS in future research to study adhesives and protection treatments to improve moisture durability in forest products.     

Theoretical Studies on the Ground State and Excited State of 2,70-(Ethylene)-bis-8-hydroxyquinoline

Dielectric relaxation method was employed to study the properties of oxygen ion diffusion and phase transition in the oxide-ion conductors (La1-xLnx)2Mo2O9 (Ln=Nd, Gd, x=0.05-0.25). Two dielectric loss peaks were observed: peak Pd at about 600 K and peak Ph around 720 K. Peak Pd is a relaxational peak and associated with the short-range diffusion of oxygen ions, while peak Ph hardly changes its position and dramatically decreases in height with increasing frequency, exhibiting non-relaxational nature. With increasing Ln3+ concentration, the heights of peak Ph and Pd increase at first and then decrease after passing a maximum at 15% doping. It is suggested that peak Ph is related to the phase transition of a static disordered state to a dynamic disordered state in oxygen ions/vacancies distribution. It is found that the 15%Gd or 15%Nd doped La2Mo2O9 samples exhibit the highest conductivity in accordance with the highest height of peak Pd at this doping content.     

Nanometer-size cluster formation in alkali-metal-doped fullerene layers

Kinetic Monte Carlo methods have been used to simulate structural transformations in fullerene layers during electrochemical intercalation with alkali-metal ions (A). Special attention is paid to the thermodynamic stability of the A(x)C(60) phases. The calculations point out a phase separation in the doped fullerene layer into alkali-metal-rich and alkali-metal-depleted areas at room temperature. The final state is represented by two phases which coexist as a stable fine mixture of nanoscale particles. The instability of homogeneous layers has potentially critical impact on their electrical properties and can explain the formation of nanostructures (20-50 nm) at the fullerene-electrolyte interface. Rb(3)C(60) clusters are predicted to be larger than K(3)C(60) ones for equal mean alkali-metal concentrations. Experimental data on electrochemical metal deposition on alkali-metal-doped fullerene substrates-in particular, atomic force microscopy measurements-are also consistent with the model proposed.     

Water sorption and electrical/dielectric properties of organic-inorganic polymer blends

Organic-inorganic polymer blends (OIPB) were obtained by reaction of organic and inorganic oligomers. The organic oligomer was synthesized with 2,4-toluene diisocyanate (TDI) and oligooxypropylene glycols (OPG) with various molecular weights (MW). The inorganic component was a water solution of sodium silicate. The OIPB obtained are hydrophilic and have great water sorption ability (the relative weight of sorbed water reaches 2000 %). The kinetics of water sorption and the changes of electrical conductivity during sorption were studied. Sorption ability, and mechanical, electrical and dielectric properties of OIPB depend on molecular weight of OPG: conductivity increases with increasing MW, whereas the sorption ability correlates with the mechanical properties. The influence of the inorganic phase content on the electrical and dielectric properties was studied as well.     

Reductive deposition of Rh nanostructures on n-type porous silicon: X-ray absorption and X-ray excited optical luminescence studies

22Porous silicon (PS) prepared from an n-type Si(100) wafer was utilized as a reducing agent and a nanosubstrate for the reduction of rhodium complex ions [RhCl6]3- from aqueous solution to metallic Rh nanostructures on the surface of the n-type PS. The morphology and the electronic properties of the PS layers as well as the rhodium nanostructures were studied by field emission scanning electron microscopy, X-ray absorption fine structures spectroscopy, and X-ray excited optical luminescence (XEOL). The average particle size of Rh nanostructures on PS was estimated to be approximately 7 nm by the X-ray diffraction pattern. The specificity ofXEOL allowed for the investigation of the effect of Rh nanostructures on the optical properties of PS.     

Study of interaction between nitrogen DBD plasma-treated viscose fibers and divalent ions Ca2+ and Cu2+

Viscose fibers were treated with atmospheric pressure dielectric barrier discharge (DBD) plasma obtained in nitrogen in order to activate the fiber surface prior to sorption of the divalent ions Ca²⁺ and Cu²⁺. Methylene blue sorption was used for estimation of carboxyl group formation on the surface after DBD plasma treatment, through the degree of fabric staining (K/S). Sorption of divalent ions was performed from solutions of each individual ion and from solutions of calcium and copper in succession onto untreated and plasma-treated viscose samples. The quantity of sorbed metal was determined from the neutralization and iodometric titration method. Scanning electron microscopy coupled with energy dispersive X-ray analysis was used for fiber morphology and surface characterization before and after plasma treatment, and after metal ions sorption. Experiments revealed copper microparticles formation on the fiber surface when sorption of copper was performed on samples with bonded calcium. Further analysis confirmed that for growth of copper particles, both calcium ions and nitrogen DBD plasma pretreatments are necessary.