Structure and Chemical Reactivity of Y-Stabilized ZrO2 Surfaces: Importance for the Water-Gas Shift Reaction.

The surface structure and chemical properties of Y-stabilized zirconia (YSZ) have been subjects of intense debate over the past three decades. However, a thorough understanding of chemical processes occurring at YSZ powders faces significant challenges due to the absence of reliable reference data acquired for well-controlled model systems. Here, we present results from polarization-resolved infrared reflection absorption spectroscopy (IRRAS) obtained for differently oriented, Y-doped ZrO2 single-crystal surfaces after exposure to CO and D2O. The IRRAS data reveal that the polar YSZ(100) surface undergoes reconstruction, characterized by an unusual, red-shifted CO band at 2132 cm-1. Density functional theory calculations allowed to relate this unexpected observation to under-coordinated Zr4+ cations in the vicinity of doping-induced O vacancies. This reconstruction leads to a strongly increased chemical reactivity and water spontaneously dissociates on YSZ(100). The latter, which is an important requirement for catalysing the water-gas-shift (WGS) reaction, is absent for YSZ(111), where only associative adsorption was observed. Together with a novel analysis Scheme these reference data allowed for an operando characterisation of YSZ powders using DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy). These findings facilitate rational design and tuning of YSZ-based powder materials for catalytic applications, in particular CO oxidation and the WGS reaction.

Studying ZIF-8 SURMOF Thin Films with a Langatate Crystal Microbalance: Single-Component Gas Adsorption Isotherms Measured at Elevated Temperatures and Pressures.

Characterizing the adsorption behavior of thin films at technical operation ranges is highly relevant in order to obtain appropriate experimental parameters, as well as to evaluate their possible integration in multiple applications. Nonetheless, gathering such experimental data is not a trivial task. In the case of metal-organic framework thin films, a particular interesting class of highly porous coatings, determination of adsorption isotherms at elevated temperatures and pressures is not commonly reported. Using a custom-designed langatate crystal microbalance following the principle for piezoelectric microbalances, but under harsher conditions, allowed us to present adsorption equilibrium measurements on a zeolitic imidazolate framework-8 (ZIF-8) surface-mounted metal-organic framework (SURMOF) thin film at temperatures between 35 and 100 °C and at a pressure range up to 10 bars. The layer-by-layer liquid-phase epitaxy approach was used to deposit ZIF-8 SURMOF thin films on langatate crystals. X-ray diffraction, infrared reflection absorption spectroscopy, and scanning electron microscopy combined with energy dispersive X-ray mapping were used to gather deeper information on the ZIF-8 thin film growth. Single-component isotherms were collected for different gases of practical interest, that is, CO2, C2H6, C2H4, C3H8, and C3H6. The measurements were obtained at 35, 50, 75, and 100 °C at a gauge pressure range up to 10 bars. The collected data showed a clear preferential adsorption of ethane over ethylene, whereas only a slight difference was found between propane and propylene. Additionally, the experimental data allowed for the determination of adsorption equilibrium constants and saturation loadings of the ZIF-8 material as a thin SURMOF film, which is of great importance for its integration in multiple applications, such as sensor devices or in membrane-based separation.

Carbon-nanotube reinforcement of DNA-silica nanocomposites yields programmable and cell-instructive biocoatings.

Biomedical applications require substrata that allow for the grafting, colonization and control of eukaryotic cells. Currently available materials are often limited by insufficient possibilities for the integration of biological functions and means for tuning the mechanical properties. We report on tailorable nanocomposite materials in which silica nanoparticles are interwoven with carbon nanotubes by DNA polymerization. The modular, well controllable and scalable synthesis yields materials whose composition can be gradually adjusted to produce synergistic, non-linear mechanical stiffness and viscosity properties. The materials were exploited as substrata that outperform conventional culture surfaces in the ability to control cellular adhesion, proliferation and transmigration through the hydrogel matrix. The composite materials also enable the construction of layered cell architectures, the expansion of embryonic stem cells by simplified cultivation methods and the on-demand release of uniformly sized stem cell spheroids.

Synthesis, Transfer, and Gas Separation Characteristics of MOF-Templated Polymer Membranes.

This paper discusses the potential of polymer networks, templated by crystalline metal-organic framework (MOF), as novel selective layer material in thin film composite membranes. The ability to create mechanically stable membranes with an ultra-thin selective layer of advanced polymer materials is highly desirable in membrane technology. Here, we describe a novel polymeric membrane, which is synthesized via the conversion of a surface anchored metal-organic framework (SURMOF) into a surface anchored gel (SURGEL). The SURGEL membranes combine the high variability in the building blocks and the possibility to control the network topology and membrane thickness of the SURMOF synthesis with high mechanical and chemical stability of polymers. Next to the material design, the transfer of membranes to suitable supports is also usually a challenging task, due to the fragile nature of the ultra-thin films. To overcome this issue, we utilized a porous support on top of the membrane, which is mechanically stable enough to allow for the easy membrane transfer from the synthesis substrate to the final membrane support. To demonstrate the potential for gas separation of the synthesized SURGEL membranes, as well as the suitability of the transfer method, we determined the permeance for eight gases with different kinetic diameters.

Surface-Anchored Metal-Organic Frameworks as Versatile Resists for Gas-Assisted E-Beam Lithography: Fabrication of Sub-10 Nanometer Structures.

We demonstrate that surface-anchored metal-organic frameworks (SURMOFs) are extraordinary well-suited as resists for high-resolution focused electron beam induced processing (FEBIP) techniques. The combination of such powerful lithographic protocols with the huge versatility of MOF materials are investigated in respect to their potential in nanostructures fabrication. The applied FEBIP methods rely on the local decomposition of Fe(CO)5 and Co(CO)3NO as precursors, either by the direct impact of the focused electron beam (electron beam induced deposition, EBID) or through the interaction of the precursor molecules with preirradiated/activated SURMOF areas (electron beam induced surface activation, EBISA). We demonstrate the huge potential of the approach for two different types of MOFs (HKUST-1 and Zn-DPDCPP). Our "surface science" approach to FEBIP, yields well-defined deposits with each investigated precursor/SURMOF combination. Local Auger electron spectroscopy reveals clean iron deposits from Fe(CO)5; deposits from Co(CO)3NO contain cobalt, nitrogen, and oxygen. EBISA experiments were successful with Fe(CO)5. Remarkably EBISA with Co(CO)3NO does not result in deposit formation on both resists, making the process chemically selective. Most importantly we demonstrate the fabrication of "nested-L" test structures with Fe(CO)5 on HKUST-1 with extremely narrow line widths of partially less than 8 nm, due to reduced electron proximity effects within the MOF-based resists. Considering that the actual diameter of the electron beam was larger than 6 nm, we see a huge potential for significant reduction of the structure sizes. In addition, the role and high potential of loading and transport of the precursor molecules within the porous SURMOF materials is discussed.

Interaction of human plasma proteins with thin gelatin-based hydrogel films: a QCM-D and ToF-SIMS study.

In the fields of surgery and regenerative medicine, it is crucial to understand the interactions of proteins with the biomaterials used as implants. Protein adsorption directly influences cell-material interactions in vivo and, as a result, regulates, for example, cell adhesion on the surface of the implant. Therefore, the development of suitable analytical techniques together with well-defined model systems allowing for the detection, characterization, and quantification of protein adsorbates is essential. In this study, a protocol for the deposition of highly stable, thin gelatin-based films on various substrates has been developed. The hydrogel films were characterized morphologically and chemically. Due to the obtained low thickness of the hydrogel layer, this setup allowed for a quantitative study on the interaction of human proteins (albumin and fibrinogen) with the hydrogel by Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D). This technique enables the determination of adsorbant mass and changes in the shear modulus of the hydrogel layer upon adsorption of human proteins. Furthermore, Secondary Ion Mass Spectrometry and principal component analysis was applied to monitor the changed composition of the topmost adsorbate layer. This approach opens interesting perspectives for a sensitive screening of viscoelastic biomaterials that could be used for regenerative medicine.

Peptide-based SAMs that resist the adsorption of proteins.

In this paper we present a modular approach for the fabrication of surfaces to characterize protein-protein interactions. The approach is based on azido peptides with an optimized sequence which are then thiol-functionalized using an alkynyl thiol and "click" chemistry. From these peptide thiols we fabricated SAMs on gold to evaluate the protein resistance, using surface plasmon resonance spectroscopy, toward streptavidin, bovin serum albumin (BSA), and fibronectin.

Adsorption of benzene on coinage metals: a theoretical analysis using wavefunction-based methods.

The interaction of benzene with a Ag(111) surface has been determined using reliable ab initio electronic structure calculations. The results are compared to a recent detailed analysis of the interaction of benzene with copper and gold surfaces, thus making it possible to derive a consistent picture for the electronic structure changes encountered when benzene is brought into contact with the densely packed coinage metal surfaces. To avoid the problems encountered when the presently most frequently employed computational approach, density functional theory (DFT), is applied to adsorbate systems where dispersion (or van der Waals) forces contribute substantially, we use a wavefunction-based approach. In this approach, the weak van der Waals interactions, which are dominated by correlation effects, are described using second-order perturbation theory. The surface dipole moment and the work function changes induced upon adsorption are also discussed.