Defect Sites in Titanium Dioxide Nanoparticles unde - ACS Publications

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The Effect of Gold Nanoclusters on the Production of Ti Defect Sites in Titanium Dioxide Nanoparticles Under UV and Soft X-ray Radiation Trystan Bennett, Rohul Hayat Adnan, Jason F Alvino, Rantej Kler, Vladimir B. Golovko, Gunther G Andersson, and Gregory Francis Metha J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp5119162 • Publication Date (Web): 18 Mar 2015 Downloaded from http://pubs.acs.org on March 26, 2015

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The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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The Journal of Physical Chemistry

The Effect of Gold Nanoclusters on the Production of Ti3+ Defect Sites in Titanium Dioxide Nanoparticles under Ultraviolet and Soft X-ray Radiation Trystan Bennett1, Rohul H. Adnan2,3, Jason F. Alvino1, Rantej Kler1,4, Vladimir Golovko2†, Gregory F. Metha1†, and Gunther G. Andersson4†

1 2

Department of Chemistry, University of Adelaide, South Australia 5005, AUSTRALIA

The MacDiarmid Institute for Advanced Materials and Nanotechnology, Department of Chemistry, University of Canterbury, Christchurch 8140, NEW ZEALAND 3 4

Chemistry Department, University of Malaya, 50603 Kuala Lumpur, MALAYSIA

Flinders Centre for NanoScale Science and Technology, Flinders University, Adelaide SA 5001, AUSTRALIA

†

Department of Chemistry The University of Adelaide South Australia 5005 Australia Phone: +61 8 8303 5943 Facsimile: +61 8 8303 4358 Email: [email protected] The MacDiarmid Institute for Advanced Materials and Nanotechnology Department of Chemistry University of Canterbury Christchurch 8140 NEW ZEALAND Phone: +64 3 364 2442 Facsimile: +64 3 364 2110 Email: [email protected] Centre for NanoScale Science and Technology, Flinders University, SA 5001 GPO Box 2100 Australia Phone: +61 8 8201 2309 Email: [email protected] ACS Paragon Plus Environment


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Abstract The production rate and saturation point of Ti3+ defect sites on titanium dioxide P-25 and anatase nanoparticles doped with Au101(PPh3)21Cl5 (Au101) metal nanoclusters was investigated under synchrotron X-ray irradiation alone, as well as combined X-ray and UV radiation. The saturation point in the growth of the normalized relative populations of Ti3+ centers on anatase and P-25 titania nanoparticles with and without Au101 nanoclusters present at the surface was found to vary with the type of support. It was influenced by the presence of gold nanoclusters: a higher concentration of Ti3+ centers was generated where gold nanoclusters were deposited onto anatase nanoparticles and irradiated by both X-ray and UV photons, compared with X-ray irradiation alone. Conversely, all samples based on the TiO2 P-25 support displayed reduced levels of Ti3+ center populations at the saturation points under combined X-ray and UV combined radiation, compared to the samples exposed exclusively to X-ray radiation. The initial rate of production of Ti3+ defect sites was found to decrease for combined UV and X-ray irradiation in the case when Au101 was deposited onto anatase. However, the opposite trend in the initial production rate of Ti3+ centers was observed in the case of Au101 deposited onto TiO2 P-25 surface. Keywords: atomically precise metal clusters, titania, titania defects, X-ray photoelectron spectroscopy, photocatalysis

Introduction The stable oxide of titanium, TiO2, has potential for a wide range of industrial applications such as self-cleaning1 or anti-microbial surfaces, to photodegradation of harmful chemicals in wastewater,2 and photocatalytic applications for the production of industrially relevant small molecules such as H2 or CH4.3 Surface modification of titania with metal nanoparticles4-7 and metal oxides8 is another popular research direction. Since the groundbreaking paper in 1979 by Fukushima and Honda highlighting the photocatalytic abilities of titanium dioxide,9 the number of publications concerning titanium dioxide has exploded, surpassing 10,000 in 2012 alone.10 A driving force for this large number of publications has been the desire to understand the mechanisms on which the catalytically driven processes are based.11-12 The remarkable catalytic performance of titanium dioxide has been linked in part to the presence of defect sites within the metal oxide,13 potentially due to their effect on the binding energies of small molecules.14 These defects may take the form of vacancy sites within the bulk of the metal oxide lattice or at the surface, dopant substitutions within the metal oxide lattice, interstitial atoms or dopants, and localized electron or hole trapping, among others.15-16 Within the last decade, efforts have been made to quantify the presence and ratios of these defects with the defect disorder of titania now largely understood primarily for the high temperature (> 1000 K) regime.16-19 However, the migration of structural defects such as vacancies, interstitial sites and dopants has been shown to occur at an appreciable rate only at the temperatures above 400 K.20 Importantly for this study, the defect disorder is poorly understood when there is a clear lack of migratory behavior within the surface layer.

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One of the most often studied titania defects is the Ti3+ center, or Ti3+ defect site, which is formed via the trapping of an excited electron onto a lattice titania site,13 and is distinct from interstitial Ti3+ defects, which arise due to Ti3+ species within the TiO2 lattice. The Ti3+ centers can form on the surface or within the lattice of titanium dioxide thin films, nanoparticles, and bulk materials.21 The formation of Ti3+ center is characterized by the blue-grey coloration of the titania material,13 and spectroscopic techniques such as X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) spectroscopy may be employed to quantify the relative normalized populations of the Ti3+ defect states. These Ti3+ centers have been widely reported to be vital for the catalytic activity of both bare and surface-doped titanium dioxide surfaces.22-26 Due to the ease of production of these Ti3+ centers,14 a wide variety of methods for the fabrication of titania containing Ti3+ centers has been reported in the literature, including synthesis in the presence of surface modifying agents,27 thermal treatments,28-29 treatments under reducing atmospheres,21 bombardment by electrons or γ-rays,30 X-rays, and irradiation under ultraviolet (UV) light.31 The latter study is particularly important, as the high band-gap of titania requiring irradiation with sub400 nm wavelength light for generation of photoexcited electrons necessarily implies that employment of any unmodified titania surfaces in photoexcitation-driven processes will encounter Ti3+ center formation.32 The mechanism of formation of these localized electron defect sites is well described elsewhere;16-17, 33 briefly, in standard Kroger-Vink notation,34

⇄ •• + 2 + 2 + ⇄ ••• + 3 +

(1) (2)

where represents an electron localized onto a titanium atom, referred to as a Ti3+ defect center. Gold nanoclusters deposited onto metal oxide supports, whether produced under UHV via laser ablation,35 or synthesized chemically, are known to exhibit catalytic activity.36 Nanocluster reactivity toward small molecules has been shown to strongly depend on the nanocluster size,37-38 so maintaining the size of nanoclusters deposited onto surfaces is a key challenge. Titanium dioxide surface defects have been shown to affect the nucleation, growth, and stability of gold nanoclusters deposited on a metal oxide surface using UHV techniques,39-41 as well as the photocatalytic properties of these systems.4, 32-34 Given the direct band-gap of rutile, compared with the indirect band-gap of anatase, it would be expected that TiO2 P-25, given its ca. 20 % rutile component, would exhibit a higher Ti3+ center production rate, due to the greater availability of photoexcited electrons, though this would have little or no effect on the final saturation points. Conversely, the unknown nature of interaction between gold nanoclusters and the surface, which may or may not donate electrons into the surface,35, 42 would also be expected to have some effect on both the generation rate and saturation point of these localized under low temperature regime defects. A similar study to the present work has been undertaken on N-doped titanium dioxide nanoparticles, which reported the kinetics of formation of Ti3+ centers.43 Evidence for the interaction between free triphenylphosphine ligands (liberated from the gold nanoclusters) and the titania support has been presented previously, which would have an unknown electronic effect.7 While a difference in the mechanism of formation of photoexcited electrons is not


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expected for irradiation under UV light compared with X-ray photons, some differences between the Ti3+ center formation rates may be expected because the cross section for the interaction of photons with Ti3+ depends on the energy of the photons. Here we present results that shed light on the initial Ti3+ defect formation rate and saturation level of Ti3+ populations following irradiation by UV light (3.26 eV, 380 nm). We also provide information on the effects of irradiation with X-rays (690 eV, 1.80 nm) used to quantify the Ti3+ populations using XPS on the Ti3+ formation (alone and in combination with UV irradiation).

Methods

To investigate the interactions between gold nanoclusters and titania support under UV radiation, a representative ligated, chemically synthesized prepared gold nanocluster Au101(PPh3)21Cl5 (hereafter referred to as Au101) was studied. The gold nanoclusters were deposited onto two different types of titania supports - pure anatase nanoparticles (99.5 %, ca. 70 m2/g, 10-30 nm particles, SkySpring Nanomaterials, USA) and TiO2 P-25 nanoparticles (99.5 %, ca. 50 m2/g, 21 nm avg. particle size, Evonik Industries, USA). Prior to deposition of the gold nanoclusters, the titania nanoparticles were treated with sulfuric acid,44 which we have previously shown to inhibit agglomeration of gold nanoclusters protected by phosphine ligands.5 Post-deposition, the samples either had no posttreatment (“as made”), or were treated at elevated temperature (200 °C) under pure O2 atmosphere at ambient pressure. Full details of the synthesis and surface deposition of the nanoclusters and post-treatment of the samples have been described in detail in our earlier reports.5-6 In total, five samples were analyzed. For ease of discussion, the samples are assigned a code based on their support (A or P for anatase or P-25, respectively) and post-treatment (1 or 2 for none or heat/O2, respectively), with an indicating prefix if Au101 is present.

A1: Pure anatase P1: Pure P-25 Au101-A1: Au101 on anatase, no post-treatment Au101-P1: Au101 on P-25, with no post-treatment Au101-P2: Au101 on P-25, calcined at 200 °C under O2

A suspension of the support-immobilized nanoclusters was made up in dichloromethane at a concentration of ca. 10 mg·mL-1. A single drop of this suspension was deposited onto a clean ca. 10 x 10 mm silicon (Si) wafer and dried in air. This drop-casting procedure was repeated until an even film coverage was achieved. Each sample was then dried under vacuum in the desiccator and fixed by a double-sided copper tape onto a gold-plated holder for XPS analysis. The details for the XPS sample analysis are described elsewhere.5-6 Photoelectron spectra were recorded at the soft X-ray beam-line at the Australian Synchrotron (AS) using a SPECS Phoibos 150 hemispherical electron analyzer with the incident photon energy set to 690 eV. The beam was adjusted to an irradiation spot size of ca. 600 x 600 μm, providing an X-ray photon flux of approximately 1012 photons mm-2·s-1, conditions that do not induce thermal damage to either samples of NaAuCl4, as well as Au9 or Au101 nanocluster on TiO2.5, 45 High resolution XPS spectra of Ti were recorded at a pass energy of 10 eV, yielding an instrumental resolution of 295 meV.



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The ultraviolet light source utilized for irradiation of all samples was a low-power LED source, with a peak emission occurring at 380 nm, and a full-width at half maximum of 5 nm. The output from this source was collimated to a uniform beam with an intensity of ca. 15 mW/cm2, and was directed normally onto the sample within the soft X-ray beam-line end-station, to enable in situ measurements under UV irradiation. The light source was ca. 0.5 m from the sample, with a beamspot diameter of 5 cm. Total irradiation time between the initial incident radiation, and the final scan completion, was ca. 25 minutes. For each sample, eleven scans of the Ti 2p peak were recorded at intervals of 100 seconds (starting at t = 0), with a twelfth Ti 2p peak scan recorded 300 seconds subsequently, after which a scan of each of the Au 4f and C 1s regions was recorded. The samples were then irradiated with UV light, and all scans immediately repeated while under UV irradiation. Thus, while recording the spectra without UV irradiation, the samples have been exposed to X-ray radiation only, while recording the spectra with UV irradiation switched on the samples have been exposed to both UV and X-ray radiation. For each set of measurements (X-ray only and UV/X-ray radiation) a fresh spot on the sample was chosen. Due to the nature of the measurement process, the dose of X-ray and/or UV radiation was increasing over the course of the scans for each spot. The 2p region of titanium in each case displayed two prominent peaks, corresponding to 2p3/2 and 2p1/2 of Ti4+. Additionally, fitting of spectra revealed a second set of minor intensity Ti 2p peaks at slightly lower energies, which correspond to the 2p3/2 and 2p1/2 features of Ti3+.13 A single Au 4f7/2 and 4f5/2 doublet was observed for the Au 4f XPS region, for the Au101-doped samples. The two pure titania samples, P1 and A1, did not display any photoelectron signal at this energy region, as expected. Each of the 24 Ti spectra, the C spectra, and the Au spectra for each sample was fit according to the following procedure. A Shirley background was first applied to remove the electron-scattering background. A pseudo-Voigt function composed of the sum of Gaussian (70%) and Lorentzian (30%) functions was used to fit all peaks and all peak positions were allowed to vary using nonlinear leastsquares minimization. The ratio of 70:30 for the Gaussian and Lorentzian contribution resulted in the best fit. However, in order to investigate the influence of the Gaussian and Lorentzian ratio on the results, all data were also fitted with a 40:60 Gaussian and Lorentzian contribution. A Gaussian contribution less than 40% or more than 70% did not result in acceptable fitting results. Fitting the Ti XP spectra with a ratio of 40:60 Gaussian to Lorentzian contribution results in a lower Ti3+ content. However, the conclusions drawn from the change in ratios between the Ti3+ and the Ti4+ content are not affected because all ratios change in the same way when changing the Gaussian to Lorentzian contribution in the fitting procedure (vide infra). All Ti 2p spectra where fitted with a pair of doublets allowing a variation of the FWHM for the Ti4+ peak. In the first approximation, the FWHM of the Ti3+ doublet was allowed to vary with fitting, and then the average of these was taken and held constant for the final fitting procedure. The offset between the 2p3/2 and 2p1/2 peaks was constrained to be identical for the Ti3+ doublet, and the Ti4+ doublet in fitting. The offset between the 2p3/2 peak of the Ti3+ and Ti4+ doublets was also held constant across all samples, after being determined in an identical way to the Ti3+ FWHM. The final offset between Ti3+ and Ti4+ 2p peaks used for all samples was -1.27 eV, which is in good agreement with the literature reports of this value.46-48 The Au 4f spectra were fitted with a single doublet


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corresponding to the 4f7/2 and 4f5/2 peaks, with the splitting of the doublet held constant at 3.67 eV. The C 1s region was fit with a single peak, which arose due to adventitious carbon. The position of this C 1s peak was used to calibrate all other spectra collected for each sample/irradiation combination, to correct for charging effects, as well as any instrument drift. For the Ti3+:Ti4+ ratio calculations, the error in the fits was calculated via standard error propagation techniques. The error in each individual fit is estimated at ca. 4000 arb. units of intensity, which corresponds to an approximate relative error of 0.01 units in each ratio calculation. The error will be discussed in regard to the significance of the changes because the observed changes in Ti3+ content are small.

Results and Discussion An illustrative example showing the changes in the XP spectra for spectra under purely X-ray radiation, as well as co-irradiated with UV light, is shown in Figure 1. The total Ti intensity remained constant within error during data acquisition across spectra recorded on one spot on a sample. Between the first and twelfth spectra, the primary difference observed is the lower energy shoulder of the main titania peak at ca. 457 eV, due to the increase in the population of Ti3+ species.13 An example of typical fitting is shown in Figure 2, which demonstrates the fitting of the two Ti doublets, as well as the applied Shirley background described above. It can be noticed that the shape of the background slightly changes with the irradiation such that after irradiation the background in the range of the Ti 2p1/2 peak has slightly increased. We have no explanation for the change in background, however this change does not influence the data evaluation significantly. For Figure 1, all spectra are scaled such that the Ti4+ 2p3/2 peak intensities are the same for all spectra, in order to highlight the change in peak intensity arising due to Ti3+ center formation; this does not change the ratio between the Ti3+ and Ti4+ peak intensities. For each fitted spectrum, the areas of the two Ti doublets were calculated. The relative ratio of these areas, taken as Ti3+:Ti4+, was then calculated. The Ti3+:Ti4+ ratio for each spectrum is a measure of the presence of titanium atoms in the Ti3+ state, as a proportion of the total titanium atom population, which arise due to the absorption of both UV and X-ray photons. These 24 ratios for each sample, twelve without UV radiation, and twelve with UV co-irradiation, are shown in Table 1. Note the omission of several spectra for sample A1 under UV co-irradiation, which were not recorded. The first spectrum of Au101-A1 under X-ray radiation has also been omitted, due to charging effects. From our previous reports,5-6 investigations of the P 2p XPS signal from the phosphine groups revealed that for small gold clusters (Au8, Au9 and Au11) deposited onto H2SO4 pretreated titania there is very little removal of the phosphine ligands from the gold cluster core (i.e. the clusters remain intact upon deposition), with no interaction between the titania substrate and the gold atoms due to the presence of these ligands. The same conclusion could not be drawn for Au101 on titania because the P signal could not be separated from the background in these measurements. However, we assume that the Au101 clusters behave similarly to the smaller analogues for which experimental evidence was obtained and there is little to no removal of the ligands from the Au core. As a consequence, due to the lack of interaction between the Au core and the titania, it would



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be expected that sample Au101-P1 would behave in a manner similar to that of the Au-free P1 sample, which had no gold present. Conversely, for sample Au101-P2, our previous reports have shown that there is close to complete removal of the phosphine ligands from the gold core under the O2 calcination treatment which at the same time results in agglomeration of the nanoclusters and enhancement of the interaction between gold particles and the titania substrate. The Au 4f signal position reported for our previous work5 was 83.9 eV for sample Au101-P1, 83.9 eV for Au101-P2, and 83.7 eV for Au101-A1. For the current work, the Au 4f peak positions are 83.6 eV for Au101-P1, 83.7 eV for Au101-P2, and 83.7 eV for Au101-A1, while under UV these shifted slightly to 83.7 eV for Au101-P1, 83.8 eV for Au101-P2, and 83.9 eV for Au101-A1. We are therefore confident that these samples are identical to the samples investigated in previous studies. As can be seen from Table 1, for each set of twelve spectra, the Ti3+:Ti4+ ratio either increases with increasing irradiation time, i.e. the Ti3+:Ti4+ ratios increase down each column, or is constant with increasing irradiation time (within error margins as shown in Table 1). The point where the maximum Ti3+:Ti4+ ratio is achieved ranges from at the first scan, such as for sample Au101-P2 under combined X-ray and UV radiation, to 400 seconds, for sample P1 under X-ray radiation only. The final Ti3+:Ti4+ ratio attained by each sample, under each irradiation type, varied across the samples, ranging from 0.066 ± 0.01 for sample Au101-P2 under combined X-ray and UV irradiation, to 0.097 ± 0.01, attained by sample Au101-A1 under combined X-ray and UV irradiation. The maintenance or increase of the Ti3+:Ti4+ ratio across all these series provides evidence of Ti3+ defect generation under a given type of radiation from which the rate of Ti3+ defect generation could be estimated. Table 1 also presents the ratio of the average of the Ti3+:Ti4+ ratio for the final four scans with UV coirradiation, to the average of the Ti3+:Ti4+ ratio for the final four scans without UV co-irradiation, denoted Ravg. When Ravg is above 1, the proportion of Ti3+:Ti4+ reached under UV co-irradiation is greater than that achieved when the sample is only irradiated with X-ray photons, while an Ravg below 1 indicates the X-ray radiation achieved a higher proportion of Ti3+ than when the sample was co-irradiated with UV light. Ravg ranges from 0.87 ± 0.03 for sample Au101-P2, to 1.21 ± 0.04 for sample Au101-A1. The value of Ravg would be expected in all cases to be greater than 1, given that the samples experience a moderate increase in total photon flux with the addition of the UV source, which is known to generate Ti3+ centers.31 For sample A1, the Ravg of 0.99 ± 0.03 implies no effect to the total Ti3+ proportion with the addition of the UV radiation. With the addition of Au101, however, sample Au101-A1 displayed an Ravg of 1.21 ± 0.04, which suggests the interaction between the gold nanoclusters and the titania surface has the effect of increasing the trapping of electrons onto titanium atoms, increasing the proportion of Ti3+ centers under UV light. A difference between sample A1 and sample P1was also observed, with the latter measured to have an Ravg value of 0.91 ± 0.02, suggesting a difference between supports in their behaviour under UV light. The behavior of sample P1 did not mirror sample A1 with the addition of Au101, with no differences found between sample P1, and samples A101-P1 (Ravg = 0.95 ± 0.04) and A101-P2 (Ravg = 0.87 ± 0.03). For each of the samples, the Ti3+:Ti4+ ratio versus time was plotted and visually inspected, to gauge the relative increase in Ti3+ centers per unit of time under irradiation across samples. The plots of Ti3+:Ti4+ ratios versus time, for each of the five samples are shown in Figure 3. Note the initial rise in Ti3+ proportion observed in many samples (e.g. sample A1 under X-ray radiation only), before the


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sample reaches the saturation point. The point at which a particular sample saturation of Ti3+ centers is achieved is indicative of the rate of generation of Ti3+ defect sites for that sample, with a later saturation point indicative of a slower Ti3+ site production rate. For the case of A1 (Figure 3, top), the sample was observed to reach the saturation point of Ti3+ centers at 200 seconds under X-ray radiation alone, while with the addition of UV radiation, the sample was determined to reach the Ti3+ center saturation point prior to the recording of the first XPS scan. For sample P1, the saturation point under X-ray radiation occurred at 400 seconds (Figure 3, above center), with several scans of increasing Ti3+:Ti4+ ratios preceding the sample reaching the saturation point. For this sample, the point where the sample reached saturation point under X-ray and UV combined radiation was also 400 seconds, indicating minimal effect on the rate of production of Ti3+ centers upon addition of UV radiation. For both irradiations, the production rate of Ti3+ centers for sample A1 is faster than for sample P1. Sample Au101-A1 (Figure 3, center) was determined to reach the Ti3+ saturation point at 200 seconds under X-ray radiation only, and also at 200 seconds when under X-ray and UV combined radiation. Compared to sample A1 the addition of gold nanoclusters (sample Au101-A1) results in lower rates of Ti3+ center generation under combined UV and X-ray radiation, an effect opposite to that observed for Au101 on the P-25 support. Sample Au101-P1 was determined to reach the Ti3+ center saturation point at 300 seconds while under X-ray radiation (Figure 3, below center), which was unchanged with the addition of UV radiation. This similar behavior is expected, given the minimal interaction between gold nanocluster and titania surface expected for this sample.5 Sample Au101-P2 under X-ray radiation alone (Figure 3, bottom) was determined to reach Ti3+ center saturation point at 300 seconds also, suggesting the interaction between the gold nanocluster and the titania surface is negligible under X-ray radiation. With the addition of UV radiation, however, sample Au101-P2 reached Ti3+ saturation point at the first XPS scan, indicative of a large increase in Ti3+ center production rate. The increase in Ti3+ production rate is observed despite the fact that the saturation point of Ti3+ decreases for sample P1. As above, the presence of rutile in P-25 is suggested as the potential cause.

Conclusions The saturation point of Ti3+ centers on anatase and P-25 titania nanoparticles with and without the deposition of Au101 nanoclusters onto the surface was found to vary with support and gold nanocluster effects. For anatase nanoparticles, an equal proportion of titanium atoms were found to occupy the Ti3+ state at saturation under both X-ray + UV radiation, and X-ray irradiation alone. With the addition of gold nanoclusters to this support, the saturation point of Ti3+ centers under X-ray + UV combined radiation was found to increase significantly. Conversely, P-25 support was found to possess a lower saturation point of Ti3+ centers when under X-ray + UV light, compared with X-ray illumination alone, and this behavior was found to remain unchanged by the addition of gold nanoclusters to the support. The rate of production of Ti3+ defects was found to decrease with the addition of UV radiation where Au101 was interacting with the surface of anatase. However, the production rate of Ti3+ centers increased with the addition of UV radiation, where Au101 was interacting with the titania surface in the case of P-25 TiO2.



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When utilizing XPS to investigate the Ti3+ center generation on titania surfaces, care must be taken when attempting to analyze the results, in light of the differing behavior exhibited by anatase nanoparticles compared to the P-25 substrate. Furthermore, the rate of Ti3+ defect site generation can be altered substantially when the surface is doped with gold nanoclusters.

Acknowledgements This research was undertaken on the soft X-ray beamline at the Australian Synchrotron, Victoria, Australia (M7465). Financial support from the Centre for Energy Technologies at the University of Adelaide, the MacDiarmid Institute for Advanced Materials and Nanotechnology, the University of Canterbury, and the University of Malaya is also gratefully acknowledged.


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Figure 1: Overlay of first and last scans without and with UV radiation, for sample P1, and a magnification of the 458 – 456 eV region, inset.



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Figure 2: Overlay of experimental scan with three fitted peaks for the 1300 second scan with X-ray radiation only, for sample A1.


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Table 1: Summary of Ti3+:Ti4+ ratios for each sample, with and without UV radiation.

Without UV1

With UV1

Ravg2 2

Scan (s)

A1

0 100 200 300 400 500 600 700 800 900 1000 1300 0 100 200 300 400 500 600 700 800 900 1000 1300

0.035 0.064 0.072 0.076 0.076 0.076 0.077 0.073 0.078 0.075 0.075 0.071 0.071 0.068 0.074 0.071 0.079

P1

101-A1

101-P1

0.043 0.062 0.061 0.050 0.078 0.069 0.065 0.079 0.074 0.071 0.085 0.079 0.071 0.089 0.078 0.074 0.087 0.080 0.073 0.091 0.086 0.077 0.091 0.083 0.068 0.087 0.087 0.076 0.088 0.085 0.076 0.097 0.081 0.074 0.089 0.053 0.064 0.052 0.053 0.071 0.074 0.071 0.079 0.078 0.074 0.082 0.084 0.079 0.079 0.084 0.082 0.084 0.086 0.080 0.088 0.078 0.073 0.079 0.084 0.089 0.077 0.083 0.088 0.078 0.086 0.082 0.075 0.089 0.088 0.076 0.097 0.087 0.99 ± 0.03 0.91 ± 0.02 1.21 ± 0.04 0.95 ± 0.04 1 The error for all values is ± 0.01 units.

101-P2

0.039 0.056 0.062 0.070 0.071 0.074 0.075 0.077 0.078 0.077 0.073 0.074 0.061 0.060 0.063 0.063 0.067 0.065 0.065 0.063 0.066 0.069 0.062 0.066 0.87 ± 0.03

The ratio of the average of the final four scans of the Ti3+:Ti4+ proportion with UV co-irradiation, to the average of the final four scans of the Ti3+:Ti4+ proportion without UV co-irradiation.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3: Plot of Ti3+:Ti4+ ratio versus time for both pure X-ray radiation, as well as X-ray and UV combined radiation, for sample A1 (top), sample P1 (above center), sample Au101-A1 (center), sample Au101-P1 (below center), and sample Au101-P2 (bottom).


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Table of content graphic (TOC)


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Overlay of first and last scans without and with UV radiation, for sample P1, and a magnification of the 458 – 456 eV region, inset. 122x94mm (300 x 300 DPI)



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Overlay of experimental scan with three fitted peaks for the 1300 second scan with X-ray radiation only, for sample A1. 121x93mm (300 x 300 DPI)


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Plot of Ti3+:Ti4+ ratio versus time for both pure X-ray radiation, as well as X-ray and UV combined radiation, for sample A1 (top), sample P1 (above center), sample Au101-A1 (center), sample Au101-P1 (below center), and sample Au101-P2 (bottom). 214x289mm (300 x 300 DPI)



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190x142mm (300 x 300 DPI)


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Defect Sites in Titanium Dioxide Nanoparticles unde - ACS Publications

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