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1.
Phys Chem Chem Phys ; 2020 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-32051998

RESUMO

Morphological control of gold nanocrystals is important as their catalytic and optical properties are highly shape dependent. In this paper we report the shapes of gold nanocrystals which deviate from the equilibrium Wulff shape due to the influence of the SrTiO3 single crystal substrates. The gold crystals are characterized by scanning tunneling microscopy (STM) and scanning electron microscopy (SEM). The nanocrystals have an equilibrium shape of a truncated octahedron with {111} and {001} facets. On all three substrate surfaces, i.e., SrTiO3(001)-(2 × 1), SrTiO3(001)-c(4 × 2), and SrTiO3(111)-(4 × 4) + (6 × 6), the height-to-width ratio of the gold crystals is not a constant as would be expected for equilibrium crystals, but instead it increases with crystal height. We propose that as the crystals increase in size, their aspect ratio heightens to relax the interfacial strain. The ratio between the {111} and {001} surface areas of our gold crystals is found to differ on the three substrates, which we speculate is due to the selective adsorption of surfactants on the {111} and {001} gold facets resulting from the different substrate surfaces. Reentrant facets of gold crystals that should be present according to their Wulff shape are not observed because these concave sites typically grow out due to kinetic considerations. This study demonstrates the significant effect of the crystal facet termination and surface reconstruction of an oxide substrate on the shape of supported gold nanocrystals.

2.
Chemphyschem ; 20(5): 745-751, 2019 03 04.
Artigo em Inglês | MEDLINE | ID: mdl-30614177

RESUMO

Metal-organic frameworks (MOFs) are very promising host materials for nanoscale guest materials. However, some MOFs such as MIL-53 are known to undergo phase transitions which can complicate the guest particle size control. In this study, Pd nanoparticles embedded in Al-MIL-53 were synthesised via (a) electrodeposition and (b) gas-phase reduction. A thorough structural investigation revealed that each synthesis method most likely favoured a different phase of Al-MIL-53, presenting the possibility of MOF phase selection as a technique for size control of embedded nanoparticles. For the first time, we hereby report the use of pair distribution function analysis to successfully investigate the structure and morphology of guest particles embedded in a MOF host.

3.
Phys Chem Chem Phys ; 18(4): 2488-94, 2016 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-26697927

RESUMO

The electrochemical behaviour of highly toxic hydrogen chloride (HCl) gas has been investigated in six room temperature ionic liquids (RTILs) containing imidazolium/pyrrolidinium cations and range of anions on a Pt microelectrode using cyclic voltammetry (CV). HCl gas exists in a dissociated form of H(+) and [HCl2](-) in RTILs. A peak corresponding to the oxidation of [HCl2](-) was observed, resulting in the formation of Cl2 and H(+). These species were reversibly reduced to H2 and Cl(-), respectively, on the cathodic CV scan. The H(+) reduction peak is also present initially when scanned only in the cathodic direction. In the RTILs with a tetrafluoroborate or hexafluorophosphate anion, CVs indicated a reaction of the RTIL with the analyte/electrogenerated products, suggesting that these RTILs might not be suitable solvents for the detection of HCl gas. This was supported by NMR spectroscopy experiments, which showed that the hexafluorophosphate ionic liquid underwent structural changes after HCl gas electrochemical experiments. The analytical utility was then studied in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][NTf2]) by utilising both peaks (oxidation of [HCl2](-) and reduction of protons) and linear calibration graphs for current vs. concentration for the two processes were obtained. The reactive behaviour of some ionic liquids clearly shows that the choice of the ionic liquid is very important if employing RTILs as solvents for HCl gas detection.

4.
Sensors (Basel) ; 15(10): 26866-76, 2015 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-26506358

RESUMO

Commercially available Pt screen printed electrodes (SPEs) have been employed as possible electrode materials for methylamine (MA) and hydrogen chloride (HCl) gas detection. The room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][NTf2]) was used as a solvent and the electrochemical behaviour of both gases was first examined using cyclic voltammetry. The reaction mechanism appears to be the same on Pt SPEs as on Pt microelectrodes. Furthermore, the analytical utility was studied to understand the behaviour of these highly toxic gases at low concentrations on SPEs, with calibration graphs obtained from 10 to 80 ppm. Three different electrochemical techniques were employed: linear sweep voltammetry (LSV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV), with no significant differences in the limits of detection (LODs) between the techniques (LODs were between 1.4 to 3.6 ppm for all three techniques for both gases). The LODs achieved on Pt SPEs were lower than the current Occupational Safety and Health Administration Permissible Exposure Limit (OSHA PEL) limits of the two gases (5 ppm for HCl and 10 ppm for MA), suggesting that Pt SPEs can successfully be combined with RTILs to be used as cheap alternatives for amperometric gas sensing in applications where these toxic gases may be released.

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