The low cost and high aspect ratio of kaolin has garnered attention toward its application as an oxygen barrier coating. The challenge associated with achieving oxygen barrier properties is, however, obtaining aligned kaolin platelets. We report a simple layer-by-layer (LBL) approach for obtaining highly oriented kaolin films on glass, silicon, and 304 steel substrates. The process involves sequential deposition of the substrates into suspensions containing cationic and anionic kaolin particulates. The cationic kaolin suspensions were generated by a slow addition of a dilute kaolin suspension into a highly concentrated solution of polydiallydimethylammonium chloride cationic polymer. This led to a stable suspension of kaolin particles with equal particle size but opposite sign of the zeta potential to that of the "as received" kaolin particles, which are inherently slightly anionic. To generate an anionic suspension of kaolin particles with enhanced anionic charge, the "as received" anionic kaolin particles were added to a solution containing sodium polyacrylate. This produced a kaolin suspension with a larger negative zeta potential and particle size comparable in magnitude to those of the cationic kaolin suspension. It is shown that this LBL approach provides a means of achieving controlled amounts of highly oriented kaolin particles deposited on various substrates. Analysis using SEM, IR spectroscopy, and X-ray diffraction (2θ scans and rocking curves) provided evidence of the kaolin platelets lying parallel to the various substrates.

Numerous studies show that sulfating titania narrows its band gap, facilitating longer-wavelength photochemistry, but there are contradictory reports on whether this improves or degrades UV photocatalysis and whether reactions proceed via electron-or hole-mediated pathways. The widely proposed role of sulfur is that it induces deep electron traps, which increase hole lifetimes. There is, however, no direct evidence for unoccupied states deep in the band gap. By contrast, transient absorption spectroscopy indicates that sulfur induces hole traps. We present experiments on sulfur-free and sulfated titania in which dissociation of hydrogen generates electrons that fill the lowest unoccupied states. The energy of these electrons relative to the conduction band minimum (CBM) was measured with diffuse reflectance spectroscopy in the infrared and UV-vis ranges. For all commercial sulfur-containing anatase materials, conversion of tridentate sulfate species into sulfur substituted on lattice sites occurred under highly oxidizing conditions above 400 degrees C and led to partially unoccupied states similar to 2.8 eV below the CBM. We assign this deep trap state to sulfur atoms substituted on a titanium lattice site with a formal charge of S5+ in non-stoichiometric TiO2+x, based on agreement between the experiment and the predicted UV- vis spectrum of Harb, Sautet, and Raybaud, using HSE06 density functional perturbation theory. Our band structure calculations demonstrate that titanium vacancies (or excess oxygen) are necessary to create partially unoccupied states, and X-ray diffraction Rietveld analysis confirms the existence of these vacancies. The partial occupancy of these states, along with sulfur's ability to switch oxidation states, explains their role as both electron (S5+ + e--* S4+) and hole (S5+ + h+-* S6+) traps, reconciling previous work. We discuss how relative rates of electron vs hole trapping can enhance or degrade activity depending on the pathway and the TiO2+x non-stoichiometry. We consider how increasing the dopant concentration can induce band bending or pin the Fermi level and shift the redox reactions that are thermodynamically accessible.

This paper describes a novel synthetic approach for the conversion of zero-valent copper metal into a conductive two-dimensional layered metal–organic framework (MOF) based on 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) to form Cu3(HHTP)2. This process enables patterning of Cu3(HHTP)2 onto a variety of flexible and porous woven (cotton, silk, nylon, nylon/cotton blend, and polyester) and non-woven (weighing paper and filter paper) substrates with microscale spatial resolution. The method produces conductive textiles with sheet resistances of 0.1–10.1 MΩ/cm2, depending on the substrate, and uniform conformal coatings of MOFs on textile swatches with strong interfacial contact capable of withstanding chemical and physical stresses, such as detergent washes and abrasion. These conductive textiles enable simultaneous detection and detoxification of nitric oxide and hydrogen sulfide, achieving part per million limits of detection in dry and humid conditions. The Cu3(HHTP)2 MOF also demonstrated filtration capabilities of H2S, with uptake capacity up to 4.6 mol/kgMOF. X-ray photoelectron spectroscopy and diffuse reflectance infrared spectroscopy show that the detection of NO and H2S with Cu3(HHTP)2 is accompanied by the transformation of these species to less toxic forms, such as nitrite and/or nitrate and copper sulfide and Sx species, respectively. These results pave the way for using conductive MOFs to construct extremely robust electronic textiles with multifunctional performance characteristics.

Au nanoparticles (NP) on TiO2 have been shown to be effective catalysts for selective oxidation reactions by using molecular oxygen. In this work, we have studied the influence of support morphology on the catalytic activity of Au/TiO2 catalysts. Two TiO2 anatase supports, a nanoplatelet-shaped material with predominantly the {001} facet exposed and a truncated bipyramidal-shaped nanoparticle with predominantly the {101} facet exposed, were prepared by using a nonaqueous solvothermal method and characterized by using DRIFTS, XPS, and TEM. Au nanoparticles were deposited on the supports by using the deposition-precipitation method, and particle sizes were determined by using STEM. Au nanoparticles were smaller on the support with the majority of the {101} facet exposed. The resulting materials were used to catalyze the aerobic oxidation of benzyl alcohol and trifluoromethylbenzyl alcohol. Support morphology impacts the catalytic activity of Au/TiO2; reaction rates for reactions catalyzed by the predominantly {101} material were higher. Much of the increased reactivity can be explained by the presence of smaller Au particles on the predominantly {101} material, providing more Au/TiO2 interface area, which is where catalysis occurs. The remaining modest differences between the two catalysts are likely due to geometric effects as Hammett slopes show no evidence for electronic differences between the Au particles on the different materials.

This paper describes the identification of specific host-guest interactions between basic gases (NH3, CD3 CN, and pyridine) and four topologically similar 2-dimensional (2D) metal-organic frameworks (MOFs) comprising copper and nickel bis(diimine) and bis(dioxolene) linkages of triphenylene-based ligands using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectroscopy (EPR), and powder X-ray diffraction (PXRD). This contribution demonstrates that synthetic bottom-up control over surface chemistry of layered MOFs can be used to impart Lewis acidity or a mixture of Bronsted and Lewis acidities, through the choice of organic ligand and metal cation. This work also distinguishes differences in redox activity within this class of MOFs that contribute to their ability to promote electronic transduction of intermolecular interactions. Future design of structure-function relationships within multifunctional 2D MOFs will benefit from the insights this work provides.

The Mg-catalyzed dehydrogenation of ethanol to yield acetaldehyde is an important step in the Lebedev reaction. In this work, we prepared a model MgO-SiO2 catalyst by impregnation of MgO onto an SBA-15 support and used this material to study the reaction kinetics of ethanol dehydrogenation to acetaldehyde. The rates of acetaldehyde and ethylene production were measured for ethanol partial pressures ranging from 0.92 to 5.25 kPa. Both rates are fractional order at 723 K, decreasing to nearly zero-order at 648 K. Consistent with the literature for MgO-SiO2 Lebedev catalysts, both basic sites and Lewis acidic sites were observed on this catalyst. The rates of both acetaldehyde and ethylene were inhibited by pyridine but not by 2,6-ditertbutylpyridine, suggesting that both reactions involve not only basic but also Lewis acidic sites. To elucidate the origin of this cooperativity, a microkinetic model was constructed using a recently published mechanism for the Lebedev reaction catalyzed by MgO. The model was fit to our data using four fitting parameters. The fitting suggests that adsorbed ethanol and hydrogen atoms have a weaker bond with mixed-oxide MgO-SiO2 catalysts than with bulk MgO catalysts, which we attribute experimentally to an increase in the number of moderate-strength Mg2+O2- site pairs formed at the expense of strongly basic MgO sites.

This work characterized the surface chemistry of a number of different titania samples including four commercial anatase samples, an anatase sample that we synthesized, the pyrogenic titania samples P25 and P90, and a commercial rutile sample. X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), were used to identified surface species that might interfere with the acid/base properties of the surface hydroxyls. All commercial anatase samples were contaminated by sulfur, which diminished their effectiveness as metal oxide supports for heterogeneous catalysis and has implications for their utility as photocatalysts. Hydrogen-bonded surface hydroxyls remained after calcination up to 400 degrees C for all anatase samples, in contrast to rutile and the pyrogenic titania materials P25 and P90, in which they were eliminated. Ru(0) catalysts on titania without hydrogen-bonded surface hydroxyls showed enhanced C-O hydrogenolysis selectivity in the presence of water while Ru(0) catalysts on titania with hydrogen-bonded surface hydroxyls showed diminished selectivity in water, suggesting that surface hydrophilicity is important for this reaction. Heteroepitaxy between rutile RuO2 and rutile TiO2 is not essential for the creation of small evenly-spaced supported Ru(0) nanoparticles, which are important in many catalytic reactions. (C) 2019 Elsevier Ltd. All rights reserved.

The surface reactivity of TiO2 is often governed by hydroxyl groups. Fourier transform infrared (FTIR) spectroscopy is the most commonly used method to study surface hydroxyls. However, interpretation of the observed bands of powder samples is not straightforward. In this work, we propose a facet-specific assignment of the surface hydroxyls of pyrogenic TiO2 (commonly known as P25 and P90) by comparison between experimentally observed FTIR bands of P90, rutile, and anatase with calculated vibrational frequencies for well-defined surface facets using density functional theory. Titania was calcined for extended periods in extremely dry O-2 to remove carbonates and water for diffuse reflectance infrared spectroscopy measurements of the most thermally stable hydroxyls remaining in the 300-400 degrees C range. Reactions of the dehydroxylated surfaces with H-2(D-2) provided further insight into hydroxyl formation. Theoretical assignments of hydroxyls were based on the calculated thermal stability of hydroxyls to dehydroxylation, agreement with calculated frequencies [scaled to be consistent with the experimental bridging hydroxyl frequency on rutile TiO2(110)], and the thermodynamic stability of the specific facets. Our assignments, combined with previous results, show that terminal and bridging hydroxyl frequencies overlap; therefore, the common assumption that terminal hydroxyls vibrate at higher frequencies is not valid.

This work uses multiple characterization techniques to show conclusively that the pyrogenic TiO2 photocatalysts, P90 and P25, are made of discrete rutile and anatase nanoparticles and are not composed of a core of anatase with a rutile shell as some studies have posited. Atomic pair distribution (PDF) analysis of P90 demonstrates that the technique is capable of detecting and quantifying minority phases and particle morphology in heterogeneous titania mixtures, with important implications for further studies of shape-controlled nanoparticles with well-defined surface facets.

Chemiresistive metal oxide gas sensors based on materials including SnO2, ZnO, TiO2, and WO3 have been investigated extensively for a wide range of applications. The band bending model, based on the surface chemistry of highly reactive ionosorbed species (O-2(-) or O-) and the semiconducting material properties of SnO2, TiO2, and ZnO, adequately predicts the dependence of steady state response on target gas pressure and temperature for these materials. However, the assumptions associated with the band bending model are not valid for sensors based on reducible oxides such as WO3, MoO3, and V2O5, in which lattice oxygen reacts with adsorbed target gases creating oxygen vacancies which diffuse rapidly into the bulk and modulate the conductivity. Here, we develop a model that includes surface reactions and vacancy diffusion for the bulk conduction mechanism and describe characteristics of the sensor behavior that allow bulk conduction to be distinguished from the band bending transduction mechanism. We illustrate the predictions of the model regarding how the change in conductivity, Delta sigma, and response time, tau, depend on target gas pressure, temperature, and film thickness using well-characterized WO3 sensors, including epitaxially oriented polycrystalline thin films and nanorod structured glancing angle deposition (GLAD) films. The physical/chemical parameters of the model are determined in independent measurements. Expressions for the limiting cases in which tau is determined either by surface reactions or by bulk diffusion provide design criteria to predict the theoretical performance limits of sensors which operate via this transduction mechanism.

Traditional lignin pyrolysis generates a bio-oil with a complex mixture of alkyl-functionalized guaiacol and syringol monomers that have limited utility to completely replace phenol in resins. In this work, formate assisted fast pyrolysis (FAsP) of lignin yielded a bio-oil consisting of alkylated phenol compounds, due to deoxyhydrogenation, that was used to synthesize phenol/formaldehyde resins. A solvent extraction method was developed to concentrate the phenolics in the extract to yield a phenol rich monomer mixture. Phenolic resins were synthesized using phenol (phenol resin), FAsP bio-oil (oil resin), and an extract mimic (mimic resin) that was prepared to resemble the extract after further purification. All three phenolic sources could synthesize novolac resins with reactive sites remaining for subsequent resin curing. Differential scanning calorimetry and thermogravimetric analysis of the three resins revealed similar thermal and decomposition behavior of phenol and the mimic resins, while the oil resin was less stable. Resins were cured with hexamethylenetetramine and the mimic resin demonstrated improved curing energies compared to the oil resin. The adhesive strength of the mimic resin was found to be superior to that of the oil resins. These results confirmed that extracting a mixture of substituted aromatics from FAsP bio-oil could synthesize resins with properties similar to those from phenol and improved over the parent bio-oil. (C) 2017 Wiley Periodicals, Inc.

Bio-oil generated by the fast pyrolysis of biomass is an unstable material, undergoing chemical and physical transformations as the oil ages at room temperature. In this study, electrostatic precipitator. (ESP) pine wood-derived bio-oil, which contains less water and does not undergo phase-separation upon aging, was characterized following accelerated aging. Bulk oil properties (percent water and viscosity) were found to increase in ways similar to conventional bio-oils. The imaged and-aged bib-oil samples were characterized by gel permeation chromatography (GPC), solvent fractionation, solution C-13 NMR, gas chromatography/mass spectrometry (GC/MS), and chip-based nanoelectrospray ionization, liquid chromatography, quadrupole time-of-flight (nanoESI-LC-QTOF) MS/MS. Using the formation of the silyated derivatives to extend the range of detectable compounds, GC/MS analysis was used to identify specific compounds that showed:, elevated reactivity, extending the understanding of reactivity characteristics beyond the known reactivity of aldehydes and Some aromatics to distinguishing the reactivity of ring-conjugated aromatics and certain polyhydroxylated benzenes; specifically the 1,3-di-, 1,2,3-tri-, and 1,2,4-trihydroxy substituted compounds. To explain the enhanced reactivity of these compounds, we propose acid-catalyzed formation of quinone methides, as important intermediates. Additionally, we find significant changes to the composition of mono- and disaccharides, where specific monosaccharides (arabinose, xylose, and glucose) increased in concentration With aging and high reactivity was observed for certain sugars with furano-ring mass spectral characteristics. In contrast, we also found that three anhydrosugars (levoglucosan, mannosan, and galactosan) were largely stable-with respect to aging. High mass resolution nanoESI-LC/MS/MS analyses of peracetylated samples permitted the analysis and chromatographic separation of both lignin and carbohydrate-derived oil components and were used for the identification of a putative formaldehyde trihydroxybenzene dieter. This work provides further insights into chemically specific entities and the processes responsible for bio-oil aging.

3 mM p-nitrophenyldisulfide solutions in various solvents: (A) THF, (B) CH2Cl2, (C) (CH3)2CO (acetone), (D) CH3CN, (E) (CH3)2SO (DMSO). The picture for DMSO was taken approximately 1 min after mixing, all other solutions remain colorless at all times.

Catalytic reduction of pyrolyzed biomass is required to remove oxygen and produce transportation fuels, but limited knowledge of how hydrodeoxygenation (HDO) catalysts work stymies the rational design of more efficient and stable catalysts, which in turn limits deployment of biofuels. This work reports results from a novel study utilizing both isotopically labeled phenol (which models the most recalcitrant components of biofuels) with D2O and DFT calculations to provide insight into the mechanism of the highly efficient HDO catalyst, Ru/TiO2. The data point to the importance of interface sites between Ru nanopartides and the TiO2 support and suggest that water acts as a cocatalyst favoring a direct deoxygenation pathway in which the phenolic OH is replaced directly with H to form benzene. Rather than its reducibility, we propose that the amphoteric nature of TiO2 facilitates H-2 heterolysis to generate an active site water molecule that promotes the catalytic C-O bond scission of phenol. This work has clear implications for efforts to scale-up the hydrogen-efficient conversion of wood waste into transportation fuels and biochemicals.

Substituted phenols are the most recalcitrant oxygenates in conventional pyrolysis oils and the dominant oxygenates in lower-oxygen content, formate-assisted pyrolysis oils (FAsP). Ru catalysts with a wide range of dispersion on carbon, silica, alumina, and titania supports were synthesized, characterized and evaluated for hydrodeoxygenation (HDO) activity using phenol as a model compound. Metal content, phase, and particle size were determined with ICP-OES, EXAFS/XANES, and CO pulse chemisorption, respectively. High dispersion of ruthenium on the supports converts more phenol to products. The majority of catalysts predominantly catalyze the hydrogenation (HYD) route typical of noble metal catalysts. A highly dispersed Ru/TiO2 catalyst shows unusually high selectivity toward direct deoxygenation (DDO) and outstanding activity. We suggest that the DDO pathway on titania involves a bifunctional catalyst, where hydrogen creates reduced titania sites, created by hydrogen spillover, that interact strongly with the phenol hydroxyl group. (C) 2014 Elsevier B.V. All rights reserved.

The hydrothermal stability of mesoporous silica is critical for applications including catalytic processing of biofuels due to the presence of significant amounts of water. We have combined neutron diffraction intensity analysis with NLDFT analysis of nitrogen sorption isotherms to characterize the spatial distribution of the secondary pore network in SBA-15 following postcalcination hydrothermal treatment in both liquid and vapor phase water at temperatures from 115 to 155 degrees C under autogenous pressure. The results are consistent with a degradation mechanism in which silica dissolves from regions of small positive curvature, e.g., near the entrance to the secondary pores, and is redeposited deeper into the framework. Pore volumes decrease fastest for the micropores and more slowly for larger secondary mesopores. Under water treatment at 115 degrees C, the mesopore diameter increases and the intrawall void fraction decreases significantly. The behavior is similar for steam treatment but occurs more slowly. Differences in the chemical environment and transport limitations are discussed. At higher temperatures of 155 degrees C, pores in the region surrounding the mesopore are nearly eliminated, trapping water deeper in the matrix, which can be seen with neutron scattering but is inaccessible to nitrogen isotherm measurements.

The hydrodeoxygenation of 2-methoxyphenol (guaiacol) has been studied over a MoS2 catalyst supported on two activated carbons with marked differences in porosity and oxygen surface functionality. The catalysts were prepared by rotary evaporator impregnation and characterized by BET surface area and XPS, while the supports were characterized by TPD, PZC, FTIR, BET and XPS techniques. The reaction was studied in a batch reactor at 300°C and 5MPa. Activity differences on the carbon supports are correlated with the dispersion of MoS2. Greater abundance of surface oxygen (mainly carboxylic, quinonic and lactonic groups) on the support resulted in lower catalyst dispersion and lower HDO activity. The dispersion, textural properties and surface chemistry did not affect the nature of the MoS2 active sites.