Inorganic Oxide Surfaces Research Articles

Reverse atom transfer radical graft polymerization of 4‐vinylpyridine onto inorganic oxide surfaces

AbstractThin poly(4‐vinylpyridine) films terminally anchored onto nonporous inorganic oxide substrates were synthesized by aqueous phase reverse atom transfer radical graft polymerization (ATRGP). Surface initiators were immobilized on the inorganic substrate surface by chemically attaching glycidoxytrimethoxy silane onto the substrates followed by conversion of the glycidoxy silane into azobis silane by a reaction with 4,4′‐azobis(4‐cyanovaleric acid). Reverse ATRGP of 4‐vinylpyridine onto the active surface azo sites was carried out in a 1‐methyl‐2‐pyrrolidone/water solvent mixture using CuCl2/2,2′‐bipyridine as the catalyst‐ligand complex with initial monomer concentration [M]0 = 2.32M at 90°C. Controlled radical polymerization was achieved at catalyst to initiator molar ratios of 2 : 1 and 3 : 1, with a catalyst to ligand molar ratio of 1 : 2. Controlled polymerization was indicated by a first‐order rate of polymerization kinetics, with respect to monomer conversion at the surface and in solution, the linear increase of the P4VP graft yield with time, and a low polydispersity index (PDI < 1.40). The highest graft yield of 8 mg/m2 was achieved at a 3 : 1 catalyst to initiator molar ratio which corresponded to a number‐average molecular weight of 11,500 g/mol, surface density of 0.69 μmol/m2, and a polydispersity index of 1.28. AFM surface analysis of the grafted polymer films, prepared by reverse ATRGP of 4VP, revealed a decrease in the RMS surface roughness (RRMS = 1.04 nm) and feature size (feature diameter = 20–45 nm), relative to uncontrolled free radical graft polymerization (RRMS = 1.42 nm; feature diameter = 60–145 nm), thereby providing an additional indication that a denser and controlled reaction was achieved via reverse ATRGP. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Forms of Iron and Their Association with Soil Properties in Four Soil Taxonomic Orders of Arid and Semi‐arid Soils of Punjab, India

Profiles of arid and semi‐arid zones soils of Punjab, northwestern India, were investigated for different forms of iron (Fe): total Fe, diethylenetriamine penta‐acetic acid (DTPA)–extractable Fe, soil solution plus exchangeable Fe, Fe adsorbed onto inorganic sites and oxide surfaces, and Fe bound by organic sites. Irrespective of the different fractions of Fe present, its content was higher in the fine‐textured Alfisols and Inceptisols than in the coarse‐textured Entisols and Aridisols. Lower content of total Fe was observed in the surface horizon and then increased in the subsurface horizons, whereas no set pattern was observed in Entisols. Also, irrespective of the soil orders, the contents of different forms of Fe were higher in the surface horizon and then decreased by depth. None of the forms of Fe exhibited any consistent pattern of distribution. Organic matter and the content of clay and silt fractions had a strong bearing on the distribution of forms of Fe. Based on a linear coefficient of correlation, the soil solution plus exchangeable Fe adsorbed onto inorganic sites and DTPA‐extractable Fe increased with increase in soil organic carbon but decreased with increase in soil pH and calcium carbonate content. Total Fe increased with increase in cation exchange capacity (CEC) and clay and silt content. The results also revealed that there was equilibrium in different fractions of this element. Among the different Fe forms, Fe bound by organic sites, water‐soluble plus exchangeable Fe, and Fe adsorbed onto oxides (amorphous surfaces) were positively correlated with the DTPA‐extractable Fe. Though some forms are interrelated, none of the forms had any relationship with the total Fe.

The deposition of osmium carbonyl clusters onto inorganic oxide surfaces: A ToF-SIMS and IR spectroscopic study of the surface species

The interaction between the osmium clusters [Os 3(CO) 12], [Os 3(CO) 10(μ-H) 2], [Os 3(CO) 10(μ-H)(μ-OH)], and a series containing a free functional group, viz., [Os 3(CO) 10(μ-H)(μ- S ∧ EH )] (where = alkyl ∧ chain or an aromatic ring, E = COO, S or O), with SiO 2, ZnO and In 2O 3, was examined by ToF-SIMS and IR spectroscopy. While the interaction with the silica surface is mostly via an O atom or the functional group, the interaction with the ZnO and In 2O 3 surfaces is more complex.

Lipid redistribution in phosphatidylserine-containing vesicles adsorbing on titania

Lipid vesicles (liposomes) exhibit a wide range of behavior at inorganic (oxide) surfaces. A complete understanding of the vesicle-surface interactions, and of the ensuing transformations surface adsorbed liposomes undergo, has proven elusive. This is at least in part due to the large number of degrees of freedom of the system comprising vesicles with their molecular constituents, substrate surface, and electrolyte solution. The least investigated among these degrees of freedom are those intrinsic to the vesicles themselves, involving rearrangements of lipid molecules. In this study, the adsorption of two-component vesicles (phosphatidylcholine:phosphatidylserine) on titanium dioxide was investigated by dual polarization interferometry. Mixtures of these two lipids containing more than 20% of phosphatidylserine form supported bilayers on titania, with phosphatidylserine predominantly facing the surface of the oxide. The purpose of this investigation is to ascertain whether redistribution of phosphatidylserine occurs already in the adsorbing vesicles. Indeed, this was found to be the case. A possible mechanism of this process is discussed.

Self-Consistent Field Modeling of Adsorption from Polymer/Surfactant Mixtures

We report on the development of a self-consistent field model that describes the competitive adsorption of nonionic alkyl-(ethylene oxide) surfactants and nonionic polymer poly(ethylene oxide) (PEO) from aqueous solutions onto silica. The model explicitly describes the response to the pH and the ionic strength. On an inorganic oxide surface such as silica, the dissociation of the surface depends on the pH. However, salt ions can screen charges on the surface, and hence, the number of dissociated groups also depends on the ionic strength. Furthermore, the solvent quality for the EO groups is a function of the ionic strength. Using our model, we can compute bulk parameters such as the average size of the polymer coil and the surfactant CMC. We can make predictions on the adsorption behavior of either polymers or surfactants, and we have made adsorption isotherms, i.e., calculated the relationship between the surface excess and its corresponding bulk concentration. When we add both polymer and surfactant to our mixture, we can find a surfactant concentration (or, more precisely, a surfactant chemical potential) below which only the polymer will adsorb and above which only the surfactant will adsorb. The corresponding surfactant concentration is called the CSAC. In a first-order approximation, the surfactant chemical potential has the CMC as its upper bound. We can find conditions for which CMC < CSAC . This implies that the chemical potential that the surfactant needs to adsorb is higher than its maximum chemical potential, and hence, the surfactant will not adsorb. One of the main goals of our model is to understand the experimental data from one of our previous articles. We managed to explain most, but unfortunately not all, of the experimental trends. At the end of the article we discuss the possibilities for improving the model.

Formation, Stability, and Rheology of Particle Stabilized Emulsions: Influence of Multivalent Cations

Recently, it has been shown that hydrophilic colloidal silica particles (Ludox) can be rendered sufficiently hydrophobic to stabilize oil in water (O/W) emulsions simply by changing the pH of the suspending medium to ∼2, and such emulsions have been shown to display novel rheology (shear thickening) compared to conventional emulsions (Wolf et al. J. Rheol., 2007, 51, 465). However, while lowering pH can render nanosized silica (∼10 nm) sufficiently hydrophobic so as to stabilize O/W emulsions, this method does not appear to generalize to larger silica particles (∼200 nm). In this present study, we explore a different approach, which employs hydrophilic, (i.e., not surface modified) colloidal silica particles to stabilize O/W emulsions in the presence of a range of cations. It appears that certain cations at high pH (in particular La3+) will render various inorganic oxide surfaces more hydrophobic. As such this makes the combination of silica particles with appropriate concentrations of Lanthanum cations a...

FT-IR Investigation of the Thermal Decomposition of Poly(amidoamine) Dendrimers and Dendrimer−Metal Nanocomposites Supported on Al2O3 and ZrO2

The decomposition and removal of poly(amidoamine) (PAMAM) dendrimers from inorganic metal oxide surfaces frequently used as catalyst supports was investigated by the use of FT−IR spectroscopy. Spectra of fourth-generation hydroxyl-terminated PAMAM dendrimers (G4OH) on γ-Al2O3 were collected first at room temperature and were subsequently analyzed with all bands assigned to the vibrational frequencies of dendrimer functional groups. Bands corresponding to amide and ethylenic groups decrease in intensity upon heating at 150 °C, while new bands corresponding to surface carboxylate species appear in their stead. Thus, the process of dendrimer removal occurs in two stages: dendrimer decomposition to form adsorbed carboxylates followed by the removal of these carboxylates from the surface. The dendrimer generation (i.e., G3OH vs G4OH) does not affect the rate of this process. However, the temperature required for completion of the first stage rises with increasing G4OH weight loading. Other factors that influence the rate of overall dendrimer removal were found to include the type of gas-phase environment used and the presence or absence of metal species within the dendrimer. Specifically, an oxidizing environment, or the presence of either platinum or rhodium, facilitates complete dendrimer removal at lower temperatures. Finally, although the rate of dendrimer removal is very similar on both alumina and zirconia, the conformations of the adsorbed dendrimers on these supports are different.

Australian Colloid and Surface Science in 2007

This special issue of the Australian Journal of Chemistry comprises a selection of papers from the program of the Australian Colloid and Interface Symposium (ACIS), which was held at Coogee Beach, Sydney from 4 to 8 February 2007. The conference was chaired by Professor Roger Horn from the Ian Wark Research Institute at the University of South Australia. Over 240 scientists gathered at Coogee for this meeting, including 93 international guests from over 20 different countries and 150 Australians from almost every state inAustralia.The weather was excellent during the conference, but, as the conference attendees arrived at Coogee, unfortunately so too did about 6000 bluebottles, who also arrived to enjoy the beautiful local waters. Ironically, the bluebottles left at about the same time as the bulk of the conference delegates. The ACIS 2007 program highlighted current research in colloid and interface science from both fundamental and technological viewpoints, as well as highlighting some of the exciting new areas in which the discipline is having a substantial impact. This year’s themes were Spectroscopy and Scattering in Surface and Colloid Science (chaired by David Beattie, Ian Wark Research Institute, and Jim McQuillan, University of Otago), which drew attention to the opportunities for studying colloidal and interfacial interactions using either spectroscopic or scattering techniques, with the latter particularly focussed towards the Australian Synchrotron and the Opal Replacement Reactor. The theme of Surface Forces, Nanotribology and Biological Interactions (chaired by Michelle Gee, University of Melbourne, and Roger Horn, Ian Wark Research Institute) honoured the work of Professor Jacob Israelachvili (Fig. 1), including his seminal research in surface forces undertaken at the Australian National University in the late 1970s and early 1980s. The Inorganic Oxide Surfaces theme (chaired by George Franks, University of Melbourne, Jonas Addai-Mensah, Ian Wark Research Institute,

Spectroscopic evidences of EDTA interaction with inorganic supports during the preparation of supported metal catalysts

Chelating compounds (etylenediaminetetraacetic acid (EDTA)-type reagents) are broadly applied in many chemical processes. One of the possible applications is their use in the preparation of the catalysts. A short summary based on my own experience in the spectroscopic studies on chelating molecules interaction with the surface of inorganic oxides is presented. The application of spectroscopic techniques allow to describe the nature and type of interactions. Particularly, the experiments conducted by an infrared spectroscopy method deliver valuable information which is of great importance for the adsorption and catalytic investigations.

IR studies of EDTA alkaline salts interaction with the surface of inorganic oxides

The adsorption of alkaline salts of ethylenediaminetetraacetic acid (EDTA) on inorganic supports characterized by the different value of the isoelectric point of the surface (IEPS) has been investigated by transmission and photoacoustic (PA) FT-IR. The IR spectra in the 1800–1200 cm −1 region of the supported complexones are different from those of the unsupported compounds. The results obtained imply that the observed changes in the properties of adsorbed complexones are mainly due to interaction of the carboxyl groups of chelate molecule with inorganic oxide hydroxyl groups. The models of those interactions have been proposed. The IEPS value has a noticeable influence on the nature of the interactions observed. Based on the experimental data the ability of inorganic oxide interaction with the chelate molecule can be presented as follows: V 2O 5 < SiO 2 < TiO 2 < MgO < Al 2O 3 < ZrO 2-La < ZrO 2.

The Surface of Inorganic Oxides or Zeolites as a Nonconventional Reaction Medium for the Selective Synthesis of Metal Carbonyl Complexes and Clusters

AbstractFor Abstract see ChemInform Abstract in Full Text.

The surface of inorganic oxides or zeolites as a nonconventional reaction medium for the selective synthesis of metal carbonyl complexes and clusters.

The surface of inorganic oxides or zeolites as a nonconventional reaction medium for the selective synthesis of metal carbonyl complexes and clusters.

On the interaction of Schrock Mo–alkylidene complexes with the surface of inorganic oxides

This work describes the reactivity of Schrock-type alkylidenemolybdenum(VI) complexes, Mo(=CHCPhMe 2)(=NAr)(O tBu) 2, I, or Mo(=CHCPhMe 2)(=NAr)[OCMe(CF 3) 2] 2, II, with the surface of silica, silica–alumina and niobia. In situ FT-IR studies suggest that I and II are attached to the surface of silica via a Lewis acid base adduct; on silica–alumina, an OH addition to the MoN bond seems to take place. Grafting of I and II causes a decrease in their intrinsic catalytic activity as well as a change in the stereoselectivity of II in ROMP of norbornene.

Heterogenizing Homogeneous Catalysis Using Molecular Self-Assembly of Long Alkane Chain Phosphines Bound to Rh(I) Complexes

Long alkane chain hydrocarbons terminated with OH and PPh2 groups, HO−(CH2)n−PPh2 (n = 10−12) were self-assembled on inorganic oxide surfaces via acid−base hydrolysis of surface-anchored [Si]−NEt2 groups with terminal OH moieties and subsequently used to covalently anchor Rh(I) complexes. Similar thin films can also be prepared from [Si]−NEt2 and RhCl(1,5-C8H12)[PPh2(CH2)nOH]. The functionalized surfaces were characterized using solid-state NMR, contact angle goniometry, ellipsometry, X-ray photoelectron spectroscopy, and FT-IR. The self-assembled organometallic thin films were found to be highly active in catalyzing hydrogenation of tolan. Surface-bound Rh(I) catalyst is stable and can be recycled, while the homogeneous analogue decomposes under similar catalytic reaction conditions.

Article

The hydrolysis of surface-bound basic tin-amide moieties with acidic protons of alkynyl chromophores leads to molecular self-assembly of a variety of rigid-rod alkynes on inorganic oxide surfaces such as glass, quartz, and single crystal silicon. Characterization of these newly developed thin films was achieved by contact-angle goniometry, FTIR-ATR, ellipsometry, and X-ray photoelectron spectroscopy, which indicate that these thin films are densely packed. Comparative molecular mechanics modeling studies on unbound and chemisorbed -Sn-Ctriple bondC-H monomer, dimer, trimer, and a 12 × 12 (144 molecule) model substrate, suggest that surface anchoring of Sn-alkynyl units is essential for highly ordered thin-film structures that can effect topochemical polymerization. Preliminary MO calculations on a 4 × 4 model show conjugated molecular orbitals through the system.Key words: molecular self-assembly, rigid-rod alkynes, acid-base hydrolysis, tin-alkynyl thin films, molecular mechanics modeling studies, topochemical polymerization, molecular orbitals.

Effective Viscosity of Polymer Solutions: Relation to the Determination of the Depletion Thickness and Thickness of the Adsorbed Layer of Cellulose Derivatives

The diffusion of silica particles with radii ranging from 12 to 510 nm in dilute solutions of carboxymethyl cellulose (Mw= 180 to 1200 kg mol−1,cCMC= 5 to 1000 mg l−1) was investigated by means of dynamic light scattering at pH 5 in 0.01 mol l−1NaCl. The viscosity of the polymer solution as experienced by the silica probes (the “microscopic” or effective viscosity, ηeff) differs from the viscosity as determined by capillary viscometry (ηp). For small particles ηeffnearly equals the viscosity of the solvent (η0). The effective viscosity increases with the size of the probe particles and the polymer concentration but remains less than ηp. The effective viscosity is interpreted in terms of a model in which the particle is surrounded by a layer of polymer free solution (η = η0). The thickness of the polymer-free layer is assumed to be equal to the thickness of the depletion layer (λd). Applying this model, a decrease in λdas a function of CMC concentration is observed. At low concentration λdequals the radius of gyration. The hydrodynamic layer thickness (δh) of cellulose derivatives (carboxymethyl cellulose and hydroxyethyl cellulose) adsorbed on inorganic oxide surfaces (α-Fe2O3and SiO2) is also investigated by dynamic light scattering. Upon using ηpmaxima in δhare found. However, these maxima are a consequence of an incorrect choice of the viscosity. When the viscosity is used as obtained from inert probe diffusion, no anomalies are observed.

Acid−Base Hydrolytic Chemistry Route to Thin Films Containing Terminal Donor Ligands and Organometallic Complexes for Heterogenization of Metal Complex Catalysis

A general synthetic approach based on the hydrolysis of R‘3Si−NR2 with organic compounds containing acidic protons, to construct thin films of donor ligands on inorganic oxide surfaces that are sub...

Kinetics of the heterogeneous reaction CO + O → CO2 on inorganic oxide and water ice surfaces: Implications for the Martian atmosphere

The heterogeneous reaction CO + O → CO2 on water ice and various inorganic oxide (SiO2, Al2O3, Fe2O3, Fe3O4, CaO, MgO, and TiO2) surfaces has been investigated in order to evaluate the proposition that this heterogeneous reaction may contribute to the CO2 stability in the Martian atmosphere. The reaction probabilities were measured at both 196 K and 294 K by using a fast flow‐tube reactor coupled to an electron‐impact ionization mass spectrometer. The atomic oxygen was generated by passing a mixture of O2 and He through a microwave discharge at a side‐arm inlet and then allowed to react with CO over these substrates in the reactor. The reaction product, CO2, was monitored as a function of time at the downstream end of the flow‐tube reactor. The measured reaction probabilities were determined from the growth rates of CO2 signal and were found to range from 1.6 × 10−7 to 1.0 × 10−5 on the basis of the geometric area of the reactor. If we adopt a typical reaction probability of 5 × 10−7 for the heterogeneous CO + O reaction on Martian aerosols at 196 K, a simple calculation suggests that this mechanism plays a negligible role in CO2 recycling as compared to that of the homogeneous CO + OH reaction.

Comparison of the partitioning behaviours of yttrium, rare earth elements, and titanium between hydrogenetic marine ferromanganese crusts and seawater

In order to evaluate details of the partitioning behaviours of Y, rare earth elements (REEs), and Ti between inorganic metal oxide surfaces and seawater, we studied the distribution of these elements in hydrogenetic marine ferromanganese (Fe-Mn) crusts from the Central Pacific Ocean. Nonphosphatized Fe-Mn crusts display shale-normalized rare earths and yttrium (REY SN ) patterns (Y inserted between Dy and Ho) that are depleted in light REEs (LREEs) and which show negative anomalies for Y sn , and positive anomalies for La SN , Eu SN , Gd SN , and in most cases, Ce sn. They show considerably smaller Y/ Ho ratios than seawater or common igneous and clastic rocks, indicating that Y and Ho are fractionated in the marine environment. Compared to P-poor crusts, REY SN patterns of phosphatized Fe-Mn crusts are similar, but yield pronounced positive Y sn anomalies, stronger positive La SN anomalies, and enrichment of the HREEs relative to the MREEs. The data suggest modification of REY during phosphatization and indicate that studies requiring primary REY distributions or isotopic ratios should be restricted to non-phosphatized (layers of) Fe-Mn crusts. Apparent bulk coefficients, K d m, describing trace metal partitioning between nonphosphatized hydrogenetic Fe-Mn crusts and seawater, are similar for Pr to Eu and decrease for Eu to Yb. Exceptionally high values of K D Ce, which are similar to those of Ti, result from oxidative scavenging of Ce and support previous suggestions that Ce (IV) is a hydroxide-dominated element in seawater. Yttrium and Gd show lower K D values than their respective neighbours in the REY series. Results of modelling the exchange equilibrium between REY dissolved in seawater and REY sorbed on hydrous Fe-Mn oxides corroborate previous studies that suggested the surface complexation of REY can be approximated by their first hydroxide binding constant. Negative “anomalies” occur for stabilities of bulk surface complexes of Gd, La, and particularly Y. The differences in inorganic surface complex stability between Y and Ho and between Gd and its REE neighbours are similar to those shown by the stabilities of complexes with aminocarboxylic acids and are significantly larger than those shown by stabilities of complexes with carboxylic acids. Hence, sorption of Y and REEs onto hydrous Fe-Mn oxides may contribute significantly to the positive Y SN and Gd SN anomalies in seawater.

Heterogenizing homogeneous catalysis

A new method for heterogenizing homogeneous catalysts involving simple acid–base hydrolytic chemistry on inorganic oxide surfaces is described. It provides easy access to thin films containing terminal amine and phosphine donor ligands, which are precursors to a variety of oriented organometallic surfaces (see figure; L =CO, PR3). Opportunities for the development of tailor‐made active and selective catalysts are discussed. magnified image