Chemistry, Physics & Earth Sciences
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Browsing Chemistry, Physics & Earth Sciences by Author "Adnan, Rohul H"
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ItemChemically Synthesised Atomically Precise Gold Clusters Deposited and Activated on Titania. Part II(Royal Society of Chemistry, 2013-07-24) Anderson, David P ; Adnan, Rohul H ; Alvino, Jason F ; Shipper, Oliver ; Donoeva, Baira ; Ruzicka, Jan-Yves ; Al Qahtani, Hassan ; Cowie, Bruce ; Aitken, Jade B ; Golovko, Vladimir B ; Metha, Gregory F ; Andersson, GuntherSynchrotron XPS was used to investigate a series of chemically synthesised, atomically precise gold clusters Aun(PPh3)y (n = 8, 9 and 101, y depending on the cluster size) immobilized on anatase (titania) nanoparticles. Effects of post-deposition treatments were investigated by comparison of untreated samples with analogues that have been heat treated at 200 °C in O2, or in O2 followed by H2 atmosphere. XPS data shows that the phosphine ligands are oxidised upon heat treatment in O2. From the position of the Au 4f7/2 peak it can be concluded that the clusters partially agglomerate immediately upon deposition. Heating in oxygen, and subsequently in hydrogen, leads to further agglomeration of the gold clusters. It is found that the pre-treatment plays a crucial role in the removal of ligands and agglomeration of the clusters.
ItemFactors influencing the catalytic oxidation of benzyl alcohol using supported phosphine-capped gold nanoparticles(Royal Society of Chemistry, 2014-11-20) Adnan, Rohul H ; Andersson, Gunther ; Polson, M I J ; Metha, G F ; Golovko, V BTwo phosphine-stabilised gold clusters, Au101(PPh3)21Cl5 and Au9(PPh3)8(NO3)3, were deposited and activated on anatase TiO2 and fumed SiO2. These catalysts showed an almost complete oxidation of benzyl alcohol (>90%) within 3 hours at 80 °C and 3 bar O2 in methanol with a high substrate-to-metal molar ratio of 5800 and turn-over frequency of 0.65 s−1. Factors influencing catalytic activity were investigated, including metal–support interaction, effects of heat treatments, chemical composition of gold clusters, the size of gold nanoparticles and catalytic conditions. It was found that the anions present in gold clusters play a role in determining the catalytic activity in this reaction, with NO3− diminishing the catalytic activity. High catalytic activity was attributed to the formation of large gold nanoparticles (>2 nm) that coincides with partial removal of ligands which occurs during heat treatment and catalysis. Selectivity towards the formation of methyl benzoate can be tuned by selection of the reaction temperature. The catalysts were characterised using transmission electron microscopy, UV-vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy.
ItemFar-infrared absorption spectra of synthetically-prepared, ligated metal clusters with Au6, Au8, Au9 and Au6Pd metal cores(Royal Society of Chemistry, 2013-09-11) Alvino, Jason F ; Bennett, Trystan ; Anderson, David ; Donoeva, Baira ; Ovoshchnikov, Danii ; Adnan, Rohul H ; Appadoo, Dominique ; Golovko, Vladimir B ; Andersson, Gunther ; Metha, Gregory FThe far infra-red absorption spectra of a series of chemically synthesised, atomically precise phosphine-stabilised gold cluster compounds have been recorded using synchrotron light for the first time. Far-IR spectra of the Au6(Ph2P(CH2)3PPh2)4(NO3)2, Au8(PPh3)8(NO3)2, Au9(PPh3)8(NO3)3, and Pd(PPh3)Au6(PPh3)6(NO3)2 clusters reveal a complex series of peaks between 80 and 475 cm−1, for which all significant peaks can be unambiguously assigned by comparison with Density Functional Theory (DFT) geometry optimisations and frequency calculation. Strong absorptions in all spectra near 420 cm−1 are assigned to the P–Ph3 stretching vibrations. Distinct peaks within the spectrum of each specific cluster are assigned to the cluster core vibrations: 80.4 and 84.1 cm−1 (Au6) 165.1 and 166.4 cm−1 (Au8), 170.1 and 185.2 cm−1 (Au9), and 158.9, 195.2, and 206.7 cm−1 (Au6Pd). The positions of these peaks are similar to those observed to occur for the neutral Au7 cluster in the gas phase (Science, 2008, 321, 674–676). Au–P stretching vibrations only occur for Au6 near 420 cm−1, although they appear near 180 cm−1 for Au6Pd and involve gold core vibrations.
ItemGrouping and aggregation of ligand protected Au9 clusters on TiO2 nanosheets(Royal Society of Chemistry, 2016-11-10) Al Qahtani, Hassan ; Higuchi, R ; Sasaki, T ; Alvino, J F ; Metha, G F ; Golovko, V B ; Adnan, Rohul H ; Andersson, Gunther ; Nakayama, TAtomically precise chemically synthesised Au clusters, in the form of [Au9(PPh3)8](NO3)3, were deposited onto titania nanosheets after UV pre-treatment of the substrate and examined with scanning tunneling microscopy (STM), atomic force microscopy (AFM) and synchrotron X-ray photoelectron spectroscopy (XPS) before and after heat treatment. The STM, AFM and XPS results complement each other. AFM was performed to determine the height of the deposited species and their dispersion on titania nanosheets. STM shows groups of clusters that at least partially consist of individual clusters both before and after annealing. STM cannot exclude the existence of individual clusters on the titania nanosheets outside the groups. XPS shows that before annealing the Au clusters are attached to the titania surface as individual clusters thus as clusters with non-agglomerated cluster cores. After annealing, both individual and agglomerated clusters are found on the surface. The combination of AFM, STM and XPS shows that the groups formed by the clusters consist of individual and agglomerated clusters.