Self-activation of catalyst and functionalization of metal surfaces

Why can solid surfaces promote a variety of chemical reactions? We supposed that active sites or active compounds are formed over the catalyst surface during catalysis or in pretreatment. Three topics are discussed from this viewpoint in this review. The first topic is an activation of inactive MoO_x film to super-active olefin metathesis catalyst, where Mo=CHR sites are prepared on MoO_x. A total mechanism for the productive and the cross metathesis of propene was firstly established on an activated catalyst by using deuterium labeled olefins. In the second topic, a new concept of quasi-compounds is discussed by using scanning tunneling microscopy (STM), and it is shown that the reaction of quasi-compounds yields (Cu)₆ cluster and (–Cu–O–) strings on Ag(110). In the third topic, a self-activation of Pt–Rh alloy and Pt/Rh bimetallic surfaces during the reaction of NO + H₂ is discussed by using single crystal surfaces. STM image showed that a Pt–Rh(100) surface is activated by reacting with oxygen where a specific array of Pt and Rh atoms is established. Formation of similar active sites on the other crystallographic surfaces is responsible for structure insensitive catalysis of Pt/Rh bimetallic surfaces.     

Thin metal films on quasicrystalline surfaces

Thin metal films with a thickness of one or over one monolayer formed on quasicrystalline surfaces were studied using reflection high-energy electron diffraction, X-ray photoelectron spectroscopy, X-ray photoelectron diffraction and scanning tunneling microscopy. The substrates were the 10f surface of d-Al–Ni–Co and the 5f surface of i-Al–Pd–Mn. The metals deposited were Au, Pt, Ag and In. None of these metals forms any ordered layer by deposition onto clean quasicrystalline surfaces. However, if a submonolayer of In is present atop the 10f surface, an epitaxial layer of multiply-twinned AuAl₂ crystals is formed by Au deposition and subsequent annealing. This is also the case for Pt deposition, but not for Ag deposition. Although the surfactant effect of In is also observed in the case of Au deposition on the 5f surface of i-Al–Pd–Mn, the ordered layer formed is a film of Au–Al alloy with icosahedral symmetry. No ordered films are formed by Pt or Ag deposition onto the 5f surface, regardless of the presence of an In-precovered layer. A Sn film monolayer induced by surface diffusion was also studied.     

Electro-switchable surfaces for heavy metal waste treatment: Study of polyacrylic acid films grafted on gold surfaces

This paper focuses on using electrochemical-pH-switchable polymer films as active surfaces for heavy metal waste treatment. Polyacrylic acid (PAA) was grafted at open air and room temperature on gold substrates. As a broad-range chelating material, PAA can capture heavy metal ions at low concentration. The release of the metal ions from the grafted-PAA film was obtained under electro-induced-acidification by applying an anodic potential at the electrode to promote a localized water electrolysis. Such electrochemical-switchable films can be part of a secondary step-treatment after conventional ion exchange process or precipitation for treatment of aqueous effluents in order to reach very low concentration in heavy metal ions without production of secondary effluents.     

Microanalysis of corrosion films on metal surfaces by Raman spectroscopy

Summary The chemical composition of corrosion films on the surface of metals used in electrical microrelays has been studied by Raman spectroscopy. On the surface of a zinc coated armature one formate species could be detected whereas on the surface of a spring composed of a copper-nickel-zinc alloy the formation of two different formate species was observed. The above formate formation resulted from contamination of the used lubricant by formic acid.

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Mikroanalyse von Korrosionsfilmen auf Metalloberflächen mit Hilfe der Raman-Spektroskopie

Zusammenfassung Die chemische Zusammensetzung von Korrosionsfilmen auf der Oberfläche von Metallen aus elektrischen Mikrorelais wurde mit Hilfe der Ramanspektroskopie untersucht. Auf der Oberfläche eines verzinkten Ankers wurde Formiat festgestellt und auf der Oberfläche einer Feder aus einer Kupfer-Nickel-Zink-Legierung wurden zwei verschiedene Arten Formiat nachgewiesen. Die Bildung dieser Formiate ergab sich aus der Verunreinigung eines Schmiermittels mit Ameisensäure.

     

Molecular-level functionalization of electrode surfaces. An overview

Electrochemical reactions occur at electrode/electrolyte interfaces. Hence, manipulation and design of electrochemical interfaces accompanied by surface modifications have assumed vital importance. Molecular level modification, either at the monolayer or multilayer level of electrode surfaces and leading to functionalization of electrodes, is being actively pursued by researchers. Modification based on the self-assembled monolayer approach has enabled electrodes to acquire molecular recognition and molecular electronic characteristics. Functionalization of electrode surfaces using polymeric materials and enzymes has facilitated electrodes in exhibiting properties like catalysis, molecular recognition, electrochromism and birefringence. The results of such molecular level functionalization studies of electrode surfaces carried out recently in our laboratories are presented in this overview. Besides, some representative results reported from elsewhere are also included.     

Photopolymerization of metal nanoparticles on multiwall carbon nanotubes

A facile method for the functionalization of multiwall carbon nanotubes (MWCNT) by photopolymerization of 5-mercapto-2,2'-bithiophene modified metal (Au or Ag) nanoparticles on the surface of the MWCNT is developed.     

Molecular-level functionalization of electrode surfaces

An ultra-thin film of functional molecule(s) can be deposited on an electrode, which then serves as a device to amperometrically monitor compounds of biological interest. The methods of surface functionalization, mostly on tin oxide (SnO₂) electrodes, include: chemical modification (covalent bond formation between the surface OH group with a functional group of a molecule); the Langmuir-Blodgett technique, where the NH₂ group of a long-chain alkylamine is bound to an enzyme via a small dialdehyde molecule as spacer; and electropolymerization of pyrrole in an electrolyte containing a single enzyme or a sequentially operating bienzyme system. The results of such investigations by the author’s group are presented.     

Photopolymerization of liquid carbon disulfide produces nanoscale polythiene films.

Broad band solar or 300--400 nm irradiation (Hg--Xe arc source) of liquid-phase carbon disulfide produces a new carbon--sulfur polymer with the approximate (n = 1.04--1.05) stoichiometry (CS(n))(x). The polymer, from here on called (CS)(x), forms as a approximately 200 nm thick transparent golden membrane as measured by SEM and AFM techniques. IR spectra for this polymer show some similarities with those obtained for the gas-phase photopolymerized (CS(2))(x) and the high-pressure-phase polymer of CS(2), called Bridgman's Black. The observed FT-IR absorptions of (CS)(x) include prominent features at 1431 (s, br), 1298 (m), 1250 (ms), and 1070 cm(-1) (m). In contrast to previous proposals for (CS(2))(x), (13)C labeling and model compound studies of alpha-(C(3)S(5))R(2) and beta-(C(3)S(5))R(2) (R = methyl or benzoyl) suggest that the absorption at 1431 cm(-1) and those at 1298 and 1250 cm(-1) are indicative of carbon--carbon double bonds and carbon--carbon single bonds, respectively. The molecular structure of alpha-(C(3)S(5))(C(O)C(6)H(5))(2), determined at -84 degrees C, belongs to space group P1, with a = 7.486(5) A, b = 13.335(11) A, c = 17.830(13) A, alpha = 105.60(6) degrees, beta = 95.32(6) degrees, gamma = 90.46(6) degrees, Z = 4, V = 1706(2) A(3), R = 0.0785, and R(w) = 0.2323. With use of electron and chemical ionization mass spectrometry, C(4)S(6) and C(6)S(7) were identified as the dominant soluble molecular side-products derived from a putative ethylenedithione (S==C==C==S) precursor. Atomic force microscopy (AFM) provided surface topology information for the thin film (CS)(x) and revealed features that suggested the bulk material is formed from small polymer spheres 20--50 nm in size. Both (CS(2))(x) and (CS)(x) are extensively cross-linked through disulfide linkages and both materials show strong EPR resonances (g > 2.006) indicative of sulfur-centered radicals from incomplete cross-linking. A polymerization mechanism based on the intermediacy of S(2)C=CS(2) is proposed.     

Single-step covalent functionalization of polylactide surfaces

A single-step, nondestructive, and versatile technique for the grafting and chemical surface modification of biodegradable polymers such as polylactide is described. The substrates are subjected to the vapor phase of any of three investigated vinyl monomers: acrylamide, maleic anhydride, and N-vinylpyrrolidone, and grafting is induced by photoinitiation of benzophenone under solvent free conditions. The modified surfaces exhibit higher wettability, and the grafting is verified by X-ray photoelectron spectroscopy, attenuated total reflection Fourier-transform IR, contact-angle measurements, and scanning electron microscopy. The graft-chain pendant groups remain functional and can subsequently be modified so that a tailor-made surface with desired properties may be achieved.     

Monolayer-derivative functionalization of non-oxidized silicon surfaces

This article describes a variety of monolayers anchored directly onto silicon surfaces without an oxide interlayer, their formation mechanisms, their technological applications, and our personal views on the future prospects for this field. The chemical modification of non-oxidized silicon surfaces utilizing monolayers was first reported in 1993. The basic finding that a non-oxidized silicon surface could be neutralized with alkyl chains through direct covalent linkage, i.e., silicon-carbon, has offered chemical scientists ease of handling even in an ambient environment and, thus, research has been predictably focused on forming anti-stiction coating films for nano- and micro-electromechanical systems (NEMS/MEMS). Such surface reforming has also been achieved by using other monolayers, which form interfacial bonds, e.g., silicon-nitrogen and silicon-oxygen. The resultant monolayer surfaces are useful for silicon-based applications including molecular electron transfer films, monolayer templates, molecular insulators, capsulators, and bioderivatives. Such monolayers are applicable not only for surface modification, but also for manipulating individual nanomaterials. By modifying the terminal groups of monolayers with nanomaterials including nanocrystals and biomolecules, the nanomaterials can remarkably be immobilized directly onto non-oxidized silicon surfaces based on the formation mechanisms of the monolayer. Such immobilizations will revolutionize the analysis of the specific features and capabilities of individual nanomaterials. Furthermore, the path will be opened for the development of more advanced monolayer-derived chip technology. To achieve this goal, it is extremely important to thoroughly understand the functionalization processes on silicon, since the resultant internal structures and properties of monolayer-derivative silicon may strongly depend on their course of formation.     

Vinyl polymerization by metal complexes. XXV. Photopolymerization of vinyl monomers by porphyrin–iron(III) complex

Photopolymerization of methyl methacrylate was studied in the presence of the system of the tetraphenylporphine–iron(III) complex, free amine, and carbon tetrachloride at 0°C in methanol solution. It was found that the activity of the complex for polymerization does not depend upon the structure of the free amines added. The effect of the polymeric amines on the polymerization was also examined. The photochemical reaction process among the iron(III) complex, amine, and carbon tetrachloride was followed also under similar conditions by ultraviolet and visible spectroscopy. The scheme for the initiation species presented is supported by the results on the posteffect of the photopolymerization.     

Zerovalent metal polymer composites. III. Metallization of metal oxide surfaces with the aid of metallized functional polymer microdispersions

The adsorption of poly[N-(m- and p-vinylbenzyl)-N,N,N-trimethylammonium tetrachloropal-ladate] complex on inorganic oxide surfaces followed by reduction of the palladium salt to form a catalytically active zerovalent metal polymer composite dispersed on the oxide surface and further deposition of transition metals, e.g., nickel, cobalt, and copper, by “additive” or “subtractive” deposition from electroless plating solutions is described. γ-Ferric oxide was used as a template for such intermetallic replacement reactions, providing materials with controlled amounts of metal. Multimetallic catalysts based on aluminum oxide, zinc oxide, lanthanum oxide, magnesium oxide, and silica were prepared. Iron oxide modified by subtractive deposition of rhodium and iridium on nickel-clad iron oxide were evaluated in Fischer–Tropsch carbonylation reactions leading from synthesis gas to alkanols.     

Tailor-made functionalization of silicon nitride surfaces

This communication presents the first functionalization of a hydrogen-terminated silicon-rich silicon nitride (Si3Nx) surface with a well-defined, covalently attached organic monolayer. Properties of the resulting monolayers are monitored by measurement of the static water contact angle, X-ray photoelectron spectroscopy (XPS), and infrared reflection absorption spectroscopy (IRRAS). Further functionalization was performed by reaction of Si3Nx with a trifluoroethanol ester alkene (CH2=CH-(CH2)8CO2CH2CF3) followed by basic hydrolysis to afford the corresponding carboxylic acid-terminated monolayer with hydrophilic properties. These results show that Si3Nx can be functionalized with a tailor-made organic monolayer, has highly tunable wetting properties, and displays significant potential for further functionalization.     

Photopolymerization of poly(ethylene glycol) diacrylate on eosin-functionalized surfaces

We describe a new method that allows photopolymerization of hydrogels to occur on surfaces functionalized with eosin. In this work, glass and silicon surfaces were derivatized with eosin and photopolymerization was carried out using visible light (514 nm). This mild condition may have advantages over methods that use ultraviolet (UV) light (e.g., for encapsulation of cells and proteins, in drug screening, or in biosensing applications). The hydrogel formed on the modified surface is remarkably stable for an extended period of time. The resultant hydrogel was hydrated for more than 18 months without suffering delamination from the substrate surface. This strongly suggests covalent attachment of the hydrogel to the surface. Contact angle titration measurements and X-ray photoelectron spectroscopy analysis of eosin surfaces before and after irradiation in the presence of triethanolamine suggest that the eosin radical is responsible for the covalent attachment of the gel onto the substrate surface. This method allows for 2-D patterning of hydrogels, which is demonstrated here using the microcontact printing technique. However, noncontact photolithography could be used to form similar patterns by directing light through a mask. This method can be easily implemented to form arrays of fluorophores and proteins in situ.     

Surface functionalization of polystyrene latex particles with a liposaccharide monomer

Emulsifier-free latexes with immobilized carbohydrate residues have been prepared by batch or seed (co)polymerization of styrene in the presence of 11-(N-p-vinylbenzyl)amido undecanoyl maltobionamide (LIMA). The critical micelle concentration and the molecular surface area of LIMA were determined by surface tension and fluorescence measurements. Batch polymerization of LIMA with styrene was first performed using potassium persulfate, proving the efficiency of LIMA as emulsifier. Seed copolymerization was then investigated using polystyrene seed particles with varying experimental conditions (especially the LIMA surface coverage). Material balance of LIMA between aqueous phase and particles was obtained by separating both phases by ultracentrifugation and it was found that the surfaceactive monomer is preferentially on or in the particle (nearly 100% in batch and at most 70% in seed copolymerization). The presence of the carbohydrate residues at the particle surface was directly evidenced by ¹H-nuclear magnetic resonance, electron spectroscopy for chemical analysis and electrophoretic mobility.     

Characterization of metal oxide surfaces and thin semiconductor films by inelastic electron tunneling spectroscopy.

Inelastic electron tunneling spectroscopy (IETS) is a unique surface and interface analytical technique using electron tunneling through a metal/insulator/metal tunneling junction at cryogenic temperatures. It gives the vibrational spectrum of a very thin (nm) insulator film and the adsorbed species on it. The high sensitivity, good resolution, and wide spectral range inherent in IETS enable us to analyze the surface and interface of the insulator in detail. The tunneling junction is a good model system for oxide catalysts, electronic devises, and solid state sensors. Information about the surfaces of alumina and magnesia, the adsorption states and chemical reactions of adsorbed species occurring on these oxides can be obtained through an analysis of the tunneling spectra. The structures and properties of evaporated thin semiconductor films can also be studied. In this review, the surface characterization of alumina and magnesia, the adsorption and surface reactions of organic acids, esters, amides, and nitryls on these oxides, and the characterization of thin evaporated films of Si, Ge, and the oxides are summarized.     

Fullerene adlayers on various single-crystal metal surfaces prepared by transfer from L films

Fullerene adlayers prepared by the simple Langmuir-Blodgett (LB) method onto various well-defined single-crystal metal surfaces were investigated by in situ scanning tunneling microscopy (STM). The surface morphologies of fullerene adsorbed onto metal surfaces depended largely on the adsorbate-substrate interactions, which are governed by the types of surfaces. Too weak adsorption of C60 molecules onto iodine-modified Au(111) (I/Au(111)) allows surface migration of the molecules, and then, STM cannot visualize the C60 molecules. Stronger and appropriate adsorption onto bare Au(111) leads to highly ordered arrays relatively easily due to the limited surface migration of C60. On iodine-modified Pt(111) (I/Pt(111)) and bare Pt(111) surfaces, which have stronger adsorption, randomly adsorbed molecular adlayers were observed. Although C60 molecules on Au(111) were visualized as a featureless ball due to the maintenance of the rapid rotational motion (perturbation) of C60 on the surface at room temperature, those on I/Pt(111) revealed the intramolecular structures, thus indicating that the perturbation motion of molecules on the surface was prohibited.     

A citric acid-derived ligand for modular functionalization of metal oxide surfaces via "click" chemistry

Citric acid is a widely used surface-modifying ligand for growth and processing of a variety of nanoparticles; however, the inability to easily prepare derivatives of this molecule has restricted the development of versatile chemistries for nanoparticle surface functionalization. Here, we report the design and synthesis of a citric acid derivative bearing an alkyne group and demonstrate that this molecule provides the ability to achieve stable, multidentate carboxylate binding to metal oxide nanoparticles, while also enabling subsequent multistep chemistry via the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The broad utility of this strategy for the modular functionalization of metal oxide surfaces was demonstrated by its application in the CuAAC modification of ZnO, Fe(2)O(3), TiO(2), and WO(3) nanoparticles.     

Studies on monomer reactivity ratios. III. Comparison of various mathematical models

Seven mathematical models for the treatment of monomer reactivity ratios in free-radical copolymerization are compared from the viewpoint of their relative simplicity, accuracy, and the number of parameters necessary for their use. It is concluded that the electronegativity and charge-transfer models proposed in previous papers represent the best compromise for routine usage if quantitative accuracy is the primary concern.     

Investigation of Biopag films adsorbed on metal and ceramic surfaces by X-ray photoelectron spectroscopy

Using X-ray photoelectron spectroscopy, it was found that the treatment of aluminum, nickel, and ceramic surfaces with a 1% Biopag aqueous solution (Biopag, poly(hexamethylene guanidine chloride)), was synthesized at the Institute of Ecological and Technological Problems in accordance with TU (Specifications) 9392-020-41547288-02) results in the formation of thin polymer films on the surfaces. The chemical composition of the films was determined. It was shown that the chemical composition of the films is changed on long standing in air. Microbiological tests were carried out, and the minimum suppressing concentration toward Pseudomonas aeruginosa was determined. It was shown that the Biopag films aged for 6 months retain up to 84% of their initial activity.