Paul A. Sermon

Surface reactivity and bulk properties of ZrO2. Part 2.—Importance of homogeneity in the stabilisation of high surface area CeO2–ZrO2 aerogels

CeO2–ZrO2 aerogels (prepared by supercritical drying of the precursor hydrogels produced by either co-precipitation or deposition-precipitation) have been characterised in order to elucidate the effect of the structural homogeneity on the stability of their total surface areas at high temperatures. Co-precipitated aerogels (CPA) had larger and more crystalline particles but showed much higher surface areas than deposited-precipitated aerogels (DPA) after calcination at high temperatures (i.e. 1223 K). The difference originates, it is believed, from their surface structural homogeneity. Differential thermal analysis (DTA) and X-ray diffraction (XRD) revealed that the CPA aerogels had a homogeneous single-phase structure even after calcination at 1223 K, while transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and IR spectrascopy showed that the CPA samples were highly dispersed with homogeneous surfaces in the composition range studied. However, the DPA sample did not have the same homogeneity and appeared to form larger aggregates via inter-particulate contacts due to the high levels of cerium carbonates on their surfaces, which led to the presence of the monoclinic phase and a loss of surface area when the sample was calcined at high temperatures.

Scandium oxide nanoparticles produced from sol–gel chemistry

A new method to produce scandium oxide nanoparticles with dimensions <80xa0nm is reported. This method could be of great interest for homogeneous incorporation of scandium oxide in specific materials, and in the production of thin Sc2O3 films. Colloidal particles of oxo–hydroxo scandium were synthesised by the sol–gel method. The particle morphology was characterised by TEM analysis. The particles so formed were lozenge shaped platelets (ca. 66 × 37 × 4.5xa0nm) and were highly stable in suspension in alcoholic solution. The xerogel material was produced by slowly evaporating the solvent from the sol. Its thermal stability, structure and composition were deduced from XRD, TGA–DSC, N2-BET isotherms, 13C{1H} NMR CP MAS and FTIR investigations. The particle morphology was retained upon calcination at 773xa0K, and the bulk xerogel exhibited a mesoporous structure with a surface area of 180xa0m2xa0g−1. Sc2O3 porous xerogel optical coatings were produced on fused silica substrates by dip coating. As shown by UV transmission experiments, these films exhibited a high transparency in the wavelength range 200–1000xa0nm, and refractive indices up to 1.84 at 350xa0nm when calcined at 773xa0K.

Synergy in macrocycle/SiO2 sol–gel nano-composites

Sol–gel (SG) processing of tetraethylorthosilicate is shown to produce porous SiO2 nano-composites and coatings that contain a variety of adsorbed-impregnated and encapsulated macrocycles. Their texture, cation uptake and spectroscopic properties have been probed. Consideration has been given to whether this technology can be combined to form a sensitive sensor for ions in aqueous solution. The synergy and interaction between the guest and host in these nano-composites will have to be fully explored if this technology is to achieve its full potential in medical and environmental fields.

Surface reactivity and bulk properties of ZrO2. Part 1.—Thermochemistry of ZrO2, Y2O3–ZrO2 and K–ZrO2 aerogels in O2 and H2

Pure and doped zirconia aerogels have been characterized in order to understand their thermochemistry in oxidative and reductive atmospheres. Thermal analysis (TG–DTA) indicates that the aerogels underwent crystallization at lower temperatures in reductive atmospheres than in oxidative ones. K-doped ZrO2 crystallized at much higher temperatures than pure and Y-doped ZrO2 in both atmospheres. Residual gas analysis combined with IR spectroscopy (FTIR) during oxidation-reduction revealed that the surface residuals (i.e. ethanol, acetate and water, etc.) remaining in the samples after supercritical drying were oxidatively decomposed in the oxidative atmosphere and hydrogenatively decomposed in the reductive atmosphere. Both Y- and K-doped ZrO2 were reactive to hydrogen and oxygen at high temperatures, but probably by different mechanisms. Charged molecular oxygen was present on the surface of K-doped ZrO2 at temperatures > 673 K. As a result, K-doped ZrO2 has been shown to be more active towards hydrogen than Y-doped ZrO2 at relatively low temperature. The importance of this reactivity is considered.

In situ investigation of Pt100−xAux and Pt100−ySny nanoalloys

Dispersed sols of 1–10 nm sized Pt100−xAux and Pt100−ySny nanoalloys have been prepared separately at various x and y above and below the miscibility limit in the bulk metals. Pt100−xAux was derived from trisodium citrate reduction of aqueous solutions of H2PtCl6 and HAuCl4. Pt100−y–Sny was produced by (i) complexing Sn2+ with glucose at 323 K at pH > 7, (ii) neutralising this with H2PtCl6 addition and (iii) reducing the bimetallic precursor with glucose on raising the temperature to 373 K. For Pt100−xAux (where both metals were zero-valent) as x increased the average size of nanoalloy particles increased. These particles adsorbed onto graphite, where the extent of hydrogen chemisorption at 298 K decreased by 67% at 9 at% Au. Pt/SnO2nanoparticles (<3 nm in size) were adsorbed onto alumina. The Pt interacted with and catalysed the reduction of SnO2, with some Pt100−ySny nanoalloy formation at about 673 K which even in the bulk occurs over a wider range of compositions than Pt–Au) and enhanced H2 chemisorption at 17–33 at% Sn. Nevertheless some Sn must remain in a positive oxidation state on the alumina surface. The ratio of rates of 2MP/3MP formation from MCP and n-hexane may be informative in chemically fingerprinting (and revealing fundamental differences in) these nanoalloy surfaces. The reasons for this are seen in terms of the surface structures on these two types of nanoalloy particles (i.e. the availability of contiguous asymmetric pairs of active surface atoms *, which, as expected, is found to pass through a maximum or decrease beyond specific values of x and y).

The challenges of characterising nanoparticulate catalysts: general discussion

Rosa Arrigo, Kassim Badmus, Francesca Baletto, Maurits Boeije, Michael Bowker, Katharina Brinkert, Aram Bugaev, Valerii Bukhtiyarov, Michele Carosso, Richard Catlow, Revana Chanerika, Philip R. Davies, Wilke Dononelli, Hans-Joachim Freund, Cynthia Friend, Simone Gallarati, Bruce Gates, Alexander Genest, Emma K. Gibson, Justin Hargreaves, Stig Helveg, Haoliang Huang, Graham Hutchings, Nicola Irvine, Roy Johnston, Stanley Lai, Carlo Lamberti, Joseph Macginley, David Marchant, Toru Murayama, Rene Nome, Yaroslav Odarchenko, Jonathan Quinson, Scott Rogers, Andrea Russell, Said Said, Paul Sermon, Parag Shah, Sabrina Simoncelli, Katerina Soulantica, Federico Spolaore, Bob Tooze, Laura Torrente-Murciano, Annette Trunschke, David Willock and Jiaguang Zhang

Application of new nanoparticle structures as catalysts: general discussion

Baletto, Francesca, Boeije, Maurits, Bordet, Alexis, Brinkert, Katharina, Catlow, C. Richard A., Davies, Josh, Dononelli, Wilke, Freund, Hans-Joachim, Friend, Cynthia, Gates, Bruce, Genest, Alexander, Guan, Shaoliang, Hardacre, Christopher, Hargreaves, Justin, Huang, Haoliang, Hutchings, Graham J., Johnston, Roy, Lai, Stanley, Lamberti, Carlo, Marbaix, Julien, Miranda, Caetano Rodrigues, Nome, Rene, Peron, Jennifer, Quinson, Jonathan, Richards, Nia, Roesch, Notker, Russell, Andrea, Said, Said, Selvam, Parasuraman, Sermon, Paul, Shozi, Mzamo, Skylaris, Chris-Kriton, Spolaore, Federico, Walkerdine, James, Whiston, Keith and Willock, David 2018. Application of new nanoparticle structures as catalysts: general discussion. Faraday Discussions 208 , pp. 575-593. 10.1039/C8FD90016G file