Chemistry, Physics & Earth Sciences
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Browsing Chemistry, Physics & Earth Sciences by Author "Al Qahtani, Hassan"
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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.
ItemChemically-Synthesised, Atomically-Precise Gold Clusters Deposited and Activated on Titania(Royal Society of Chemistry, 2013-01-17) Anderson, David P ; Alvino, Jason F ; Gentleman, Alexander ; Al Qahtani, Hassan ; Thomsen, Lars ; Polson, Matthew I J ; Metha, Gregory F ; Golovko, Vladimir B ; Andersson, GuntherSynchrotron XPS was used to investigate a series of chemically-synthesised, atomically-precise gold clusters Aun(PPh3)y (n = 8, 9, 11 and 101, with y depending on cluster size) immobilized on titania nanoparticles. The gold clusters were washed with toluene at 100 °C or calcined at 200 °C to remove the organic ligand. From the position of the Au 4f7/2 peak it is concluded that cluster size is not altered through the deposition. From the analysis of the phosphorous spectra, it can be concluded that the applied heat treatment removes the organic ligands. Washing and calcination leads to partial oxidation and partial agglomeration of the clusters. Oxidation of the clusters is most likely due to the interaction of the cluster core with the oxygen of the titania surface after removal of ligands. The position of the Au 4f7/2 peak indicates that the size of the agglomerated clusters is still smaller than that of Au101.
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.