Studies of the location of precious metals in nanocrystalline titanium dioxide using XRD and XANES

Abstract

. 64.70.Nd, 81.16.Be Au, Ag, Pt and Pd doped TiO 2 nanocrystals were prepared using sol-gel routes. X-ray Near Edge Structure (XANES) was used to study the location of these precious metal dopants in nanocrystalline TiO 2 . The effects of these dopants on the phase transformation and grain growth were investigated using X-ray diffraction (XRD). Two dopant concentrations i.e. 1 and 5% were studied and similar results were found. Silver and Palladium initially form oxides but annealing at high temperatures converts them to metals. Gold and and silver do not affect the anatase -rutile transformation temperature whereas palladium and platinum do. 1 Introduction Titanium dioxide, TiO 2 , is a very important technological material which is currently being investigated for advanced functional and environmental applications, such as photocatalysis, photovoltaic cells and solid state gas sensing [1,2]. TiO 2 has a large band gap energy and due to this, it absorbs only the ultraviolet (UV) part of solar radiation leading to low conversion efficiency. Various approaches have been employed to extend the absorption edge of TiO2 from the UV into the visible region. In photovoltaic cells, TiO2 is sensitized with dyes to extend its photosensitivity to longer wavelengths. Alternatively, the light sensitivity of TiO 2 can be shifted into the visible region by narrowing the band gap [3,4]. This is generally done by doping TiO 2 with certain elements [5].In the nanocrystalline state, TiO 2 , like other oxides, can dissolve higher concentrations of impurities than its bulk counterparts as they have an increased density of grain boundaries where considerable amounts of dopants can segregate. This dopant segregation has been found in some cases to improve the catalytic activity and electrical properties. In previous computational work [6] we have studied the influence of the dopants (i.e. Pt, Pd, Ag, and Au) on the optical and structural properties of single crystalline anatase TiO 2 using the local spin density approximation (LSDA) within the density functional theory. The results show that doping TiO 2 with these precious metals enhances absorption in the visible range (i.e. above 400 nm) with Ag showing the most enhanced absorption. This offers the possibility of considerable improvement in photovotaic cells.Experimental information is essential for the verification and ultimate improvement of the simulations and EXAFS experiments are unique in providing this kind of information . For example, the EXAFS can determine the oxidation state of the dopant, the detailed local environment of the dopant (nature of the neighbours, bond distances to neighbours, degree of disorder, etc.) and segregation of the dopant.In this contribution we report the XANES and XRD studies of precious metal doped nano-TiO 2.

Superior self‐cleaning features on wool fabric using TiO2/Ag nanocomposite optimized by response surface methodology

“…One of the ingredients of the impregnating bath was Ag/TiO 2 , as a result of which peaks of Ag appeared around 2θ = 38°. These results are consistent with the previous findings 31, 39. Also, through the full width at half maximum of peaks (FWHM), the crystal sizes can be compared 39.…”

“…31,39 Also, through the full width at half maximum of peaks (FWHM), the crystal sizes can be compared. 39 Higher FWHM shows the small crystals, whereas lower FWHM indicates bigger crystals. 31 Based on eq.…”

“…From practical point of view, nano Ag particles are effective in enhancing the antimicrobial properties of TiO 2 13. The process of preparing the TiO 2 /Ag nanocomposite in an ultrasound bath and under UV rays is proposed as follows 37–39…”

“…13 The process of preparing the TiO 2 /Ag nanocomposite in an ultrasound bath and under UV rays is proposed as follows. [37][38][39] The discoloring mechanism of methylene blue (MB), with the chemical formula C 16 N 3 SCl, in the presence of TiO 2 /Ag nanocomposite and under UV rays has been reported by Mills and Wang. 40 The effects of TiO 2 /Ag nanocomposite described on the wool fabrics.…”

Effects of Ag/Cu metal co-doping on the structural properties of nanocrystalline TiO<inf>2</inf>

“…This indicates that Ag and Cu). For the singly doped samples, the metals start to appear at 900°C although they overlap with the rutile peaks.The absence of metal peaks at lower temperatures could be because they are initially present as oxides and convert to metals at high temperatures as was previously shown by XANES studies[6] on Ag-Ti02.The lattice parameters (Table 1) suggest that the Ti02 lattice is not deformed by doping. The grain sizes of doped powders are smaller than that of the undoped sample and this is consistent with observations from other studies where the reduction mechanism was also discussed at length[7],[8].…”