TiO 2 anatase nanotubes for the purification of uranium,arsenic and lead containing water: an X-ray Photoelectron Spectr
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TiO2 anatase nanotubes for the purification of uranium,arsenic and lead containing water: an X-ray Photoelectron Spectroscopy study Marco Bonato1, K. Vala Ragnarsdottir2,3 and Geoffrey C. Allen1 1 Interface Analysis Centre, University of Bristol, Bristol, BS8 8BS, U.K. 2 Department of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, U.K. 3 Institute of Earth Science, School of Engineering and Natural Sciences, University of Iceland, Hjardarhagi 6, Reykjavik 107, Iceland ABSTRACT TiO2 anatase nanotubes synthesised via anodic oxidation were used as adsorbent for the uptake of U and Pb from aqueous solution and the photoremoval of As(III). An X-ray photoelectron spectroscopy study of the sorbent medium surface revealed a high adsorption of U and Pb at pH 8. The adsorption of the uranyl ion was enhanced in an anoxy (N2) atmosphere, because this prevents the formation of very stable carbonyl complexes. As(III) was adsorbed on TiO2 but in the presence of O2 and UV light was oxidized to As(V). XPS analysis revealed that in the pH range 3-9 As(V) was always the major species detected at the surface of the titania photocatalyst. INTRODUCTION Titanium dioxide is one of the most important photocatalytic materials for ground water purification and heterogeneous photocatalysis. It offers an attractive low temperature, low cost, catalytic technique, for the decomposition and removal of organic pollutants in both the liquid and gaseous phase in the presence of UV light [1]. This surface reactivity makes it an excellent adsorbent material for the potential uptake of inorganic pollutants such as uranium, lead and arsenic from ground waters. In the case of arsenite (As(III), AsO33-), it is possible to couple the adsorbent capability of titania with its photocatalytic properties. As(III) is easily adsorbed and oxidized on the surface of the titania to the arsenate ion, As(V) – AsO43-, which is less noxious than the trivalent ion and easier to eliminate using coagulation methods [2,3]. In this communication we report a study of the adsorbtion of the metals uranium, lead and arsenic on TiO2 using X-ray photoelectron spectroscopy. The amount of metal adsorbed was quantified by measurements of surface coverage expressed in atomic percent. TiO2 anatase nanotubes have recently been given special scientific attention for their increased surface area, enhanced photocatalytic effect and simplicity of synthesis. The nanotubes used in this experimental work were synthesised via anodic oxidation of titanium in a fluorine bearing solution[4,5]. EXPERIMENTS AND METHODS Synthesis and characterization of the TiO2 anatase nanotube. A titanium foil (1x1 cm) was mechanically polished under ambient laboratory conditions with increasingly fine grades of silicon carbide paper to 4000 grade (~2 µm). Preparation of the anatase nanotubes on the titanium metal surface was achieved by anodic oxidation at room
temperature (21 ºC), carried out for 20 min. at a constant 20 V, in 0.5 wt% HF aqueous solution with a platinum counter elec
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