Electrochemically generated super-hydrophilic surfaces

The control of surface wettability of indium tin oxide (In2O3-SnO2) coated glass surfaces is studied. We report here the first observation of purely electrochemical generation of super-hydrophilic surfaces at In2O3-SnO2 electrodes in the absence of an ultraviolet illumination source. This is achieved by the application of high anodic potentials for a prolonged period. Such surfaces are reversibly converted back to their original hydrophobic state on storage in air (one or two days) or water (a week)(and vice versa). The unique character of these surfaces can be attributed to the surface structure of the hydrophilic phase.     

Size control for two-dimensional iron oxide nanodots derived from biological molecules

We demonstrated the fabrication of size-controlled two-dimensional iron oxide nanodots derived from the heat treatment of ferritin molecules self-immobilized on modified silicon surfaces. Ferritin molecules were immobilized onto 3-aminopropyltrimethoxysilane (3-APMS)-modified silicon surfaces by electrostatic interactions between negatively charged amino acids of ferritin molecules and amino terminal functional groups of 3-APMS. Heat treatments were performed at 400 degrees C for 60 min to fabricate two-dimensional nanodots based on ferritin cores. XPS and FT-IR results clearly indicate that ferritin shells were composed of amino acids and 3-APMS modifiers on silicon surfaces were eliminated by heat treatment. Nanodots on substrate surfaces corresponded to iron oxides. The size of nanodots was tunable in the range of 0-5 (+/-0.75) nm by in situ reactions of iron ion chelators with ferritin molecules immobilized on substrates before heat treatment.     

Improved scheme for the analysis of high-purity talc

An improved method is proposed for the determination of silica, magnesium oxide, R(2)O(3), ferric oxide, calcium oxide, and aluminium oxide in high-purity talc. In the method for silica and magnesium oxide, the sample is fused with sodium carbonate and the cooled melt is dissolved with perchloric acid in such a manner that it floats free from the crucible (in previous schemes for the analysis of talc there are frequently mechanical losses due to the difficulty of removing the magnesium silicate melt from the crucible). The solution is then evaporated to fumes of perchloric acid and the silica is filtered off and ignited. The magnesium oxide is determined in the filtrate by precipitation as magnesium ammonium phosphate and a correction is made for the calcium which is precipitated along with the magnesium ammonium phosphate. R(2)O(3) is determined after treatment of the sample with nitric and hydrofluoric acids and evaporation to fumes of perchloric acid. Iron oxide and calcium oxide are determined by atomic absorption, after treatment with nitric and hydrofluoric acids and evaporation to fumes of perchloric acid. Al(2)O(3) is calculated by difference.     

Benzoic and aliphatic carboxylic acid monomolecular layers on oxidized GaAs surface as a tool for two-dimensional photonic crystal infiltration

The possibility of using surface-adsorbed monolayers on oxidized GaAs single crystals is investigated to explore liquid crystal (LC) wettability and alignment. A technological process is developed to chemically activate the GaAs surface with a view to perform the infiltration of tunable two-dimensional (2-D) photonic crystals with LC materials. We demonstrate a vapor growth method to fabricate self-organized monolayers of carboxylated derivatives on plasma-activated surfaces. Our monolayers strongly increase the wettability of liquid crystal surfaces and may be helpful in achieving the infiltration of 2-D GaAs photonic crystals. Two types of molecular families were studied in this work: benzoic acids and fatty acids. Para-substituted benzoic acids with a wide range of electrical dipoles allow adsorption to be followed by measuring the surface potential of the grafted substrates using the Kelvin probe technique. These model compounds yield important information on the grafting conditions and the stability of the layers. Surface-adsorbed fatty acids are well-known to produce hydrophobic surfaces. The water contact angles measured on modified GaAs surfaces are equivalent to the ones measured on classical alkanethiol layers on gold.     

Reactive landing of gas-phase ions as a tool for the fabrication of metal oxide surfaces for in situ phosphopeptide enrichment

Zirconium, titanium, and hafnium oxide-coated stainless steel surfaces are fabricated by reactive landing of gas-phase ions produced by electrospray ionization of group IVB metal alkoxides. The surfaces are used for in situ enrichment of phosphopeptides before analysis by matrix-assisted laser desorption ionization (MALDI) mass spectrometry. To evaluate this method we characterized ZrO₂ (zirconia) surfaces by (1) comparison with the other group IVB metal oxides of TiO₂ (titania) and HfO₂ (hafnia), (2) morphological characterization by SEM image analysis, and (3) dependence of phosphopeptide enrichment on the metal oxide layer thickness. Furthermore, we evaluated the necessity of the reactive landing process for the construction of useful metal oxide surfaces by preparing surfaces by electrospray deposition of Zr, Ti, and Hf alkoxides directly onto polished metal surfaces at atmospheric pressure. Although all three metal oxide surfaces evaluated were capable of phosphopeptide enrichment from complex peptide mixtures, zirconia performed better than hafnia or titania as a result of morphological characteristics illustrated by the SEM analysis. Metal oxide coatings that were fabricated by atmospheric pressure deposition were still capable of in situ phosphopeptide enrichment, although with inferior efficiency and surface durability. We show that zirconia surfaces prepared by reactive landing of gas-phase ions can be a useful tool for high throughput screening of novel phosphorylation sites and quantitation of phosphorylation kinetics.     

Porphyrins bearing arylphosphonic acid tethers for attachment to oxide surfaces

Synthetic molecules bearing phosphonic acid groups can be readily attached to oxide surfaces. As part of a program in molecular-based information storage, we have developed routes for the synthesis of diverse porphyrinic compounds bearing phenylphosphonic acid tethers. The routes enable (1) incorporation of masked phosphonic acid groups in precursors for use in the rational synthesis of porphyrinic compounds and (2) derivatization of porphyrins with masked phosphonic acid groups. The precursors include dipyrromethanes, monoacyldipyrromethanes, and diacyldipyrromethanes. The tert-butyl group has been used to mask the dihydroxyphosphoryl substituent. The di-tert-butyloxyphosphoryl unit is stable to the range of conditions employed in syntheses of porphyrins and multiporphyrin arrays yet can be deprotected under mild conditions (TMS-Cl/TEA or TMS-Br/TEA in refluxing CHCl(3)) that do not cause demetalation of zinc or magnesium porphyrins. The porphyrinic compounds that have been prepared include (1) A(3)B-, trans-AB(2)C-, and ABCD-porphyrins that bear a single phenylphosphonic acid group, (2) a trans-A(2)B(2)-porphyrin bearing two phenylphosphonic acid groups, (3) a chlorin that bears a single phenylphosphonic acid group, and (4) a porphyrin dyad bearing a single phenylphosphonic acid group. For selected porphyrin-phosphonic acids, the electrochemical characteristics have been investigated for molecules tethered to SiO(2) surfaces grown on doped Si. The voltammetric behavior indicates that the porphyrin-phosphonic acids form robust, electrically well-behaved monolayers on the oxide surface.     

Infrared spectroscopic studies of siderophore-related hydroxamic acid ligands adsorbed on titanium dioxide

The adhesion of bacteria to metal oxide and other mineral surfaces may involve bacterial siderophores, many of which contain hydroxamic acid (Ha) ligands. The adsorption behavior of the siderophore-related ligands acetohydroxamic acid, N-methylformohydroxamic acid, N-methylacetohydroxamic acid, and 1-hydroxy-2-piperidone on titanium dioxide thin films has been investigated using in situ ATR-IR spectroscopy with variation of concentration and pH. All the ligands were found to adsorb strongly on the TiO2 surface as hydroxamate ions and form bidentate surface complexes. Vibrational modes involving C=O stretching and N-O stretching of these ligands were assigned by comparing observed IR spectra with those calculated by the density functional method at the B3LYP/6-31+G(d) level. Calculated spectra of the complex [Ti(Ha)(OH)4]-, used to model the TiO2 surface, were compared with observed spectra of adsorbed hydroxamic acids. These results suggest that hydroxamic acid ligands in siderophores would be expected to bind to metal (oxide) and mineral surfaces during bacterial adhesion processes.     

Theory of oxides surfaces, interfaces and supported nano-clusters

Oxides surfaces and thin films are finding continuous new technological applications and represent an important class of systems in materials science. Today we assist to a considerable effort to characterize the surfaces and the interfaces of oxide materials at an atomistic level. The intense experimental activity in this field has stimulated a parallel computational activity based on high-quality first principle calculations. In this review we focus our attention on the properties of oxide surfaces, and we describe the main factors that contribute to determine their behaviour: (1) nature of the bonding and electronic structure of the oxide; (2) surface morphology and defectivity; (3) doping and functionalization; (4) redox properties; (5) nano-dimensionality (e.g. in ultra-thin films). We also show how each of these parameters can affect the properties of supported metal atoms and nano-particles.     

Self-assembly and oligomerization of alkyne-terminated molecules on metal and oxide surfaces

We report the self-assembly and subsequent oligomerization of organic molecules based on terthiophenes bearing a terminal alkyne moiety. Molecules with thioacetate and phosphonic acid functional groups were synthesized, enabling molecular self-assembly on metal (Au and Pd) and metal oxide [Al(2)O(3), HfO(2), and indium tin oxide (ITO)] surfaces, respectively. The molecules were assembled from solution and then oligomerized using either 2,5-norbornadiene-rhodium(I) chloride dimer or UV light. UV-vis and infrared absorption spectroscopies and electrochemical techniques show that the molecules assemble to form dense monolayers on the substrate surfaces and oligomerize under the action of a catalyst or UV light.     

High-resolution soft X-ray photoelectron spectroscopic studies and scanning auger microscopy studies of the air oxidation of alkylated silicon(111) surfaces

High-resolution soft X-ray photoelectron spectroscopy was used to investigate the oxidation of alkylated silicon(111) surfaces under ambient conditions. Silicon(111) surfaces were functionalized through a two-step route involving radical chlorination of the H-terminated surface followed by alkylation with alkylmagnesium halide reagents. After 24 h in air, surface species representing Si(+), Si(2+), Si(3+), and Si(4+) were detected on the Cl-terminated surface, with the highest oxidation state (Si(4+)) oxide signal appearing at +3.79 eV higher in energy than the bulk Si 2p(3/2) peak. The growth of silicon oxide was accompanied by a reduction in the surface-bound Cl signal. After 48 h of exposure to air, the Cl-terminated Si(111) surface exhibited 3.63 equivalent monoleyers (ML) of silicon oxides. In contrast, after exposure to air for 48 h, CH(3)-, C(2)H(5)-, or C(6)H(5)CH(2)-terminated Si surfaces displayed <0.4 ML of surface oxide, and in most cases only displayed approximately 0.20 ML of oxide. This oxide was principally composed of Si(+) and Si(3+) species with peaks centered at +0.8 and +3.2 eV above the bulk Si 2p(3/2) peak, respectively. The silicon 2p SXPS peaks that have previously been assigned to surface Si-C bonds did not change significantly, either in binding energy or in relative intensity, during such air exposure. Use of a high miscut-angle surface (7 degrees vs < or =0.5 degrees off of the (111) surface orientation) yielded no increase in the rate of oxidation nor change in binding energy of the resultant oxide that formed on the alkylated Si surfaces. Scanning Auger microscopy indicated that the alkylated surfaces formed oxide in isolated, inhomogeneous patches on the surface.     

Surface-catalyzed chlorine and nitrogen activation: mechanisms for the heterogeneous formation of ClNO, NO, NO2, HONO, and N2O from HNO3 and HCl on aluminum oxide particle surfaces

It is well-known that chlorine active species (e.g., Cl(2), ClONO(2), ClONO) can form from heterogeneous reactions between nitrogen oxides and hydrogen chloride on aerosol particle surfaces in the stratosphere. However, less is known about these reactions in the troposphere. In this study, a potential new heterogeneous pathway involving reaction of gaseous HCl and HNO(3) on aluminum oxide particle surfaces, a proxy for mineral dust in the troposphere, is proposed. We combine transmission Fourier transform infrared spectroscopy with X-ray photoelectron spectroscopy to investigate changes in the composition of both gas-phase and surface-bound species during the reaction under different environmental conditions of relative humidity and simulated solar radiation. Exposure of surface nitrate-coated aluminum oxide particles, from prereaction with nitric acid, to gaseous HCl yields several gas-phase products, including ClNO, NO(2), and HNO(3), under dry (RH < 1%) conditions. Under humid more conditions (RH > 20%), NO and N(2)O are the only gas products observed. The experimental data suggest that, in the presence of adsorbed water, ClNO is hydrolyzed on the particle surface to yield NO and NO(2), potentially via a HONO intermediate. NO(2) undergoes further hydrolysis via a surface-mediated process, resulting in N(2)O as an additional nitrogen-containing product. In the presence of broad-band irradiation (λ > 300 nm) gas-phase products can undergo photochemistry, e.g., ClNO photodissociates to NO and chlorine atoms. The gas-phase product distribution also depends on particle mineralogy (Al(2)O(3) vs CaCO(3)) and the presence of other coadsorbed gases (e.g., NH(3)). These newly identified reaction pathways discussed here involve continuous production of active ozone-depleting chlorine and nitrogen species from stable sinks such as gas-phase HCl and HNO(3) as a result of heterogeneous surface reactions. Given that aluminosilicates represent a major fraction of mineral dust aerosol, aluminum oxide can be used as a model system to begin to understand various aspects of possible reactions on mineral dust aerosol surfaces.     

Adsorption of 2-chloropyridine on oxides--an infrared spectroscopic study

The adsorption of 2-chloropyridine on SiO(2), TiO(2), ZrO(2), SiO(2)-Al(2)O(3) and H-mordenite has been studied by IR spectroscopy. The different modes of interaction with oxide surfaces, i.e. hydrogen-bonding and adsorption at Br?nsted or Lewis acid sites, was modelled by ab initio calculations at the B3LYP/DZ+(d) level. Adsorption on SiO(2) results in hydrogen bonding to surface hydroxyl groups, whereas the spectra obtained following adsorption on TiO(2) and ZrO(2) display evidence for electron transfer at Lewis acidic surface sites. Protonation of 2-chloropyridine at Br?nsted acidic sites was detected only for adsorption on SiO(2)-Al(2)O(3) and H-mordenite, indicating the presence of Br?nsted acidic sites on these oxide surfaces with pK(a) values 相似文献   

Structural and Energetic Nonuniformities of Pyrocarbon-Mineral Adsorbents

Several series of pyrocarbon-mineral adsorbents (carbosils) were studied using the nitrogen adsorption method to compute structural and energetic parameters within the scope of overall adsorption isotherm approximation applying a regularization procedure with consideration for surface heterogeneity. A portion of pyrocarbon deposits (graphene clusters) fills mesopores of the oxide supports, but another portion represents relatively large nonporous pyrocarbon globules formed on the outer surfaces of the oxide matrices. Contributions of these two types of pyrocarbon deposits depend on the nature of oxide matrices and carbonized precursors. The characteristics of pyrocarbon formed on the silica (silica gel, fumed silica) surfaces differ from those for deposits prepared on the surfaces of titania/silica and alumina/silica or by the pyrolysis of metal acetylacetonates (Zr(AcAc)(4), TiO(AcAc)(2), Ni(AcAc)(2), Zn(AcAc)(2), Cr(AcAc)(3), Co(AcAc)(2)) on mesoporous silica gel. The structural and energetic characteristics estimated using the adsorption method with consideration for the adsorbent heterogeneity are fruitful for comparative analysis of the (1)H NMR spectra of water adsorbed on carbosils from the gas phase or unfrozen in the aqueous suspensions at T < 273 K. Copyright 2001 Academic Press.     

Creating mixed Fe/Al coatings on planar gamma-Al2O3 surfaces

Insufficient understanding of the interactions of reactive phases (e.g., Fe and Al oxides) with minerals, other reactive phases and sorbing species has made predicting and modeling metal sorption on natural sediment surfaces difficult. This work develops a method to create mixed Fe/Al planar oxide surfaces by coating well-characterized planar gamma-Al2O3 with ferric iron. The objective is to closely control the Fe/Al ratio as well as the distribution of Fe on the planar surface. Effects of starting Fe(III) concentration, reaction time and number of coating sequences were examined using XPS and ToF-SIMS. No observable trend was seen in Fe/Al ratios by varying the starting Fe(III) concentration or reaction time. For both 4- and 14-day reactions, lower concentrations of Fe(III) produced oxide phases with a homogeneous distribution of Fe at the surface as detected by ToF-SIMS. ToF-SIMS Fe elemental maps of the oxide phases resulting from the highest Fe(III) concentration showed areas of localized Fe deposition. A sequential coating procedure allowed for a closer control of the concentration and spatial distribution of Fe(III) in the resulting oxide phase. This work provides methodology that can be used to create Fe/Al oxide phases whose Fe/Al content can be controlled for use in subsequent sorption studies to better understand the effects of mixed phase oxides on metal ion uptake.     

Chemical force microscopy investigation of phosphate adsorption on the surfaces of iron(III) oxyhydroxide particles

Phosphate-modified AFM tips were prepared by the deposition of self-assembled monolayers (SAMs) of bis(11-thioundecyl) phosphate on Au-coated silicon nitride cantilevers. The properties of the PO(2)H-terminated SAMs were investigated by studying the pH-dependent force interactions of the tips with phosphate- and carboxylic acid-terminated SAM control surfaces. The PO(2)H functional groups had a pK(a) of approximately 5.0. A chemical force microscopy (CFM) study was conducted on the interactions between the probes and the surfaces of hydrous ferric oxide particles prepared in our laboratory by hydrolytic precipitation from FeCl(3). The forces between PO(2)H probes and the hydrous ferric oxide surfaces were seen to exhibit a strong pH dependence, with maximum attractive forces occurring for pH values between 5 and 8. The effects of postprecipitation of the hydrous ferric oxide colloids with orthophosphate, H(2)PO(4)(-), dimethylphosphate, (CH(3)O)(2)PO(2)H (DMP), and tannic acid (TA) on the adhesive interactions between the PO(2)H tips and the solids were also investigated. Attenuated total reflectance infrared spectroscopy (ATR-IR) was used to verify the presence of surface-adsorbed species and zeta potentiometric measurements to determine surface charge on the colloids. We show that the method of chemical force titration using phosphate-terminated tips can differentiate between these various colloids and that it shows promise as a general method for studying this environmentally important class of compounds.     

Natural Cellulose Derived Nanocomposites as Anodic Materials for Lithium‐Ion Batteries

Bio‐inspired synthetic method provides an effective shortcut to fabricate functional nanostructured materials with specific morphologies and designed functionalities. Natural cellulose substances (e. g., commercial laboratory cellulose filter paper) possesses unique three‐dimensionally cross‐linked porous structures and abundant functional groups for the functional modification on the surfaces. The deposition of metal oxide gel film on the surfaces of the cellulose nanofibers is facilely to be achieved through the surface sol‐gel process, resulting in metal oxide replicas of the initial cellulose substance or metal‐oxide/carbon nanocomposites. Moreover, the as‐deposited metal oxide gel films coated on the cellulose fiber surfaces provide ideal platforms for the further formation of specific functional assemblies, and eventually to the corresponding nanocomposite materials. Based on this methodology, various nanostructured composites were prepared and employed as anodic materials for lithium‐ion batteries, including metal‐oxides‐based (such as SnO₂, TiO₂, MoO₃, Fe_xO_y, and SiO₂) and Si‐based composites, as summarized in this personal account. Benefiting from the unique hierarchically porous network structures and the synergistic effects among the composite components of the anodic materials, the transfer of electrons/ions is accelerated and the structural stability of the electrode is enhanced, leading to the improved lithium storage performances and promoted cycling stability.     

'Shape effects' in metal oxide supported nanoscale gold catalysts

We report the activity of shape-controlled metal oxide (CeO(2), ZnO and Fe(3)O(4)) supported gold catalysts for the steam reforming of methanol (SRM) and the water gas shift (WGS) reactions. Metal oxide nanoshapes, prepared by controlled hydrolysis and thermolysis methods, expose different crystal surfaces, and consequently disperse and stabilize gold differently. We observe that similar to gold supported on CeO(2) shapes exposing the {110} and {111} surfaces, gold supported on the oxygen-rich ZnO {0001} and Fe(3)O(4) {111} surfaces shows higher activity for the SRM and WGS reactions. While the reaction rates vary among the Au-CeO(2), Au-ZnO and Au-Fe(3)O(4) shapes, the apparent activation energies are similar, indicating a common active site. TPR data further indicate that the reaction lightoff coincides with the activation of Au-O-M species on the surface of all three oxide supports evaluated here. Different shapes contain a different number of binding sites for the gold, imparting different overall activity.     

Synthesis and characterisation of Gd2O3 nanocrystals functionalised by organic acids

Nanocrystals of Gd2O3 have been prepared by various methods, using, e.g., trioctylphosphine oxide (TOPO), diethylene glycol (DEG) or glycine. The crystalline particles were of sizes 5 to 15 nm. Different carboxylic acids, e.g., oleic acid or citric acid, were adsorbed onto the surface of the particles made with DEG. IR measurements show that the molecules coordinate to the Gd2O3 surface via the carboxylate group in a bidentate or bridging manner. The organic-acid/particle complexes were characterised by XRPD, TEM, FTIR, Raman, and XPS.     

Probing enantioselectivity on chirally modified Cu(110), Cu(100), and Cu(111) surfaces

Temperature programmed desorption methods have been used to probe the enantioselectivity of achiral Cu(100), Cu(110), and Cu(111) single crystal surfaces modified by chiral organic molecules including amino acids, alcohols, alkoxides, and amino-alcohols. The following combinations of chiral probes and chiral modifiers on Cu surfaces were included in this study: propylene oxide (PO) on L-alanine modified Cu(110), PO on L-alaninol modified Cu(111), PO on 2-butanol modified Cu(111), PO on 2-butoxide modified Cu(100), PO on 2-butoxide modified Cu(111), R-3-methylcyclohexanone (R-3-MCHO) on 2-butoxide modified Cu(100), and R-3-MCHO on 2-butoxide modified Cu(111). In contrast with the fact that these and other chiral probe/modifier systems have exhibited enantioselectivity on Pd(111) and Pt(111) surfaces, none of these probe/modifier/Cu systems exhibit enantioselectivity at either low or high modifier coverages. The nature of the underlying substrate plays a significant role in the mechanism of hydrogen-bonding interactions and could be critical to observing enantioselectivity. While hydrogen-bonding interactions between modifier and probe molecule are believed to induce enantioselectivity on Pd surfaces (Gao, F.; Wang, Y.; Burkholder, L.; Tysoe, W. T. J. Am. Chem. Soc. 2007, 129, 15240-15249), such critical interactions may be missing on Cu surfaces where hydrogen-bonding interactions are believed to occur between adjacent modifier molecules, enabling them to form clusters or islands.     

Simultaneous determination of mercapturic acids derived from ethylene oxide (HEMA), propylene oxide (2-HPMA), acrolein (3-HPMA), acrylamide (AAMA) and N,N-dimethylformamide (AMCC) in human urine using liquid chromatography/tandem mass spectrometry

Mercapturic acids are highly important and specific biomarkers of exposure to carcinogenic substances in occupational and environmental medicine. We have developed and validated a reliable, specific and very sensitive method for the simultaneous determination of five mercapturic acids derived from several high-production chemicals used in industry, namely ethylene oxide, propylene oxide, acrylamide, acrolein and N,N-dimethylformamide. Analytes are enriched and cleaned up from urinary matrix by offline solid-phase extraction. The mercapturic acids are subsequently separated by means of high-performance liquid chromatography on a Luna C8 (2) column and specifically quantified by tandem mass spectrometric detection using isotopically labelled analytes as internal standards. The limits of detection (LODs) for N-acetyl-S-2-carbamoylethylcysteine (AAMA) and N-acetyl-S-2-hydroxyethylcysteine (HEMA) were 2.5 microg/L and 0.5 microg/L urine, while for N-acetyl-S-3-hydroxypropylcysteine (3-HPMA), N-acetyl-S-2-hydroxypropylcysteine (2-HPMA) and N-acetyl-S-(N-methylcarbamoyl)cysteine (AMCC) it was 5 microg/L. These LODs were sufficient to detect the background exposure of the general population. We applied the method on spot urine samples of 28 subjects of the general population with no known occupational exposure to these substances. Median levels for AAMA, HEMA, 3-HPMA, 2-HPMA and AMCC in non-smokers (n = 14) were 52.6, 2.0, 155, 7.1 and 113.6 microg/L, respectively. In smokers (n = 14), median levels for AAMA, HEMA, 3-HPMA, 2-HPMA and AMCC were 243, 5.3, 1681, 41.7 and 822 microg/L, respectively. Due to the simultaneous quantification of these mercapturic acids, our method is well suited for the screening of workers with multiple chemical exposures as well as the determination of the background excretion of the general population.