Orientation of reduced graphene oxide in composite coatings.

Composite coatings containing reduced graphene oxide (rGO) and 3-(aminopropyl)triethoxysilane functionalised rGO (APTES-rGO) were prepared by sol-gel technology and deposited on Al 2024 T-3. Covalent functionalisation of GO by APTES occurred by formation of amide bonds, accompanied by GO reduction. The thin sheets were retained. The hydrophilicity of the coating increased when APTES-rGO was added. The opposite was observed when GO was added. A key finding is that the rGO flakes agglomerate and lie in a random orientation in the coating, whereas the APTES-rGO flakes are more evenly distributed in the matrix and appear to lie along the plane of the substrate.

High-performance fixed-bed in situ mass analyzer-ISMA.

We demonstrate a newly developed high-performance fixed-bed reactor combined with an in situ mass analyzer (ISMA). The ISMA is particularly relevant to sub-second time-resolved studies where mass changes occur due to, e.g., chemical reactions and process conditions such as choice of solid, temperature, gas atmosphere, and pressure. The mass is determined from the optically measured oscillation frequency of a quartz element, yielding a mass resolution below 10 µg-typically 2-3 µg-for samples up to ∼500 mg. By placing the quartz element and optical sensor inside stainless steel pipes and providing heat from the outside, the instrument is applicable up to ∼62 bars and 700 °C. By surrounding this core part of the instrument with a suitable feed system and product analysis instruments, in combination with computer control and logging, time-resolved studies are enabled. The instrument with surrounding feed and product analysis infrastructure is fully automated. Emphasis has been put on making the instrument robust, safe, operationally simple, and user-friendly. We demonstrate the ISMA instrument on selected samples.

Graphene Oxide-Based Silico-Phosphate Composite Films for Optical Limiting of Ultrashort Near-Infrared Laser Pulses.

The development of graphene-based materials for optical limiting functionality is an active field of research. Optical limiting for femtosecond laser pulses in the infrared-B (IR-B) (1.4-3 µm) spectral domain has been investigated to a lesser extent than that for nanosecond, picosecond and femtosecond laser pulses at wavelengths up to 1.1 µm. Novel nonlinear optical materials, glassy graphene oxide (GO)-based silico-phosphate composites, were prepared, for the first time to our knowledge, by a convenient and low cost sol-gel method, as described in the paper, using tetraethyl orthosilicate (TEOS), H3PO4 and GO/reduced GO (rGO) as precursors. The characterisation of the GO/rGO silico-phosphate composite films was performed by spectroscopy (Fourier-transform infrared (FTIR), Ultraviolet-Visible-Near Infrared (UV-VIS-NIR) and Raman) and microscopy (atomic force microscopy (AFM) and scanning electron microscope (SEM)) techniques. H3PO4 was found to reduce the rGO dispersed in the precursor's solution with the formation of vertically agglomerated rGO sheets, uniformly distributed on the substrate surface. The capability of these novel graphene oxide-based materials for the optical limiting of femtosecond laser pulses at 1550 nm wavelength was demonstrated by intensity-scan experiments. The GO or rGO presence in the film, their concentrations, the composite films glassy matrix, and the film substrate influence the optical limiting performance of these novel materials and are discussed accordingly.

The influence of acceptor and donor doping on the protonic surface conduction of TiO2.

The transport of protonic charge carriers along and within the pore surfaces of porous oxide matrices is of significant importance for many catalytic and electrochemical applications, with porous TiO2 being a candidate material both for photocatalytic applications and as an electronically conducting support for polymer-based electrochemical cells. This work investigates the effect of acceptor (Cr and Fe) and donor (Nb) doping on protonic surface conduction in porous TiO2 over a wide range of relative humidity, temperature and oxygen activity. Generally, we find that acceptor dopants on the surface counteract dissociation and reduce the mobility of protons, while donor dopants give rise to enhanced dissociation making protonic surface conduction the highest for donor-doped samples, contrary to conventional bulk proton conductors. Moreover, protonic surface conduction in Cr-doped TiO2 is significantly higher under oxidising conditions compared to reducing conditions, which we relate to the presence of a higher valent species such as Cr6+ on the surface under oxidising conditions, again emphasising that protonic surface conduction increases with higher-valent (donor) and more acidic cations present on the surface.

Linker conformation effects on the band gap in metal-organic frameworks.

In this work, we investigate how torsion in the middle aromatic ring on the terphenyldicarboxylate linker in UiO-68 affects the band gap. Furthermore, we incorporate the effect of monosubstitution on the linker (UiO-68-R; R = H, F, I, NH2, and NO2) in order to shed light on a possible route to tune the band gap by changing the torsional angle by substitutions. Our computations show that both the torsional angle and band gaps depend on the choice of the substituent, and it is, in fact, possible to tune the band gap through the substitution's effect of locking down the middle aromatic ring at different torsional angles, in combination with the substituents' electronic effects.

In situ infrared emission spectroscopy for quantitative gas-phase measurement under high temperature reaction conditions: an analytical method for methane by means of an innovative small-volume flowing cell.

We have used infrared emission spectroscopy (IRES) in order to perform in situ studies under flowing gas-phase conditions. When the small-volume cell developed herein is used, we can (1) observe emission spectra from a hot gas-phase sample having an effective volume much less than one milliliter, (2) observe spectra of typical molecular species present, and (3) observe spectra of the more important molecular species down to below 10% and in some cases even as low as 1%. In addition, an analytical method has been derived in order to conduct quantitative studies under typical reaction conditions. We show that simplifications can be made in the data acquisition and handling for a direct linear correlation between band intensity and concentration with only simple background correction. The practical lower limit for methane in the present setup is approximately 0.5-1% v/v depending on the selected temperature. Our data were collected at 500, 600, and 700 degrees C, respectively. The major features of the present cell design are fairly simple and basically formed by a quartz tube (outer diameter=6 mm, inner diameter=4 mm) inside a metal pipe and two tubular ceramic heaters. This simple setup has advantages and attractive features that have extended the application of IRES to new fields and, in particular, for in situ studies of hydrocarbon reactions at different residence times at high temperature.

An experimental and theoretical study of spin-spin coupling in chlorosilanes.

An experimental and theoretical study of the absolute value of the one-bond spin-spin coupling constant |(1)J(Si,H)| in SiH(n)Cl(4-n) (n = 0-4) dissolved in THF-d(8) is presented. We found |(1)J(Si,H)| to increase with an increasing number of chlorine substituents, and the quantitative changes were found to differ from the values previously reported for the same compounds dissolved in cyclohexane-d(12). We also report on the variations in |(1)J(Si,H)| as a function of temperature, which we found to be linearly temperature dependent for the chlorine-substituted silanes and temperature independent for SiH(4). Furthermore, the temperature dependence of |(1)J(Si,H)| varied between the different chlorosilanes. Solvent-solute interactions were studied by quantum chemical DFT calculations. The variations in chloro-silane bond lengths upon adduct formation and the different adduct interaction energies may explain the temperature dependences of the coupling constants.