Porous sulfated titanium dioxide from sol-gel associated to emulsion as pores templates

Titanium dioxide has attracted great interest due to the diversity of its properties essentially hold up by structural aspects that consist of Ti octahedra (TiO6) arranged in different ways. The rutile phase is... [ view full abstract ]

Titanium dioxide has attracted great interest due to the diversity of its properties essentially hold up by structural aspects that consist of Ti octahedra (TiO₆) arranged in different ways. The rutile phase is thermodynamically stable at temperatures close to the ambient whereas the anatase one turns into rutile at temperatures between 600 and 700 °C. The sulfation of TiO₂ is an alternative to stabilize the anatase phase, the surface area upon high-temperature calcination treatment as well as to promote the porous structure. The process proposed in this work aims to combine the formation of porous titanium dioxide and its sulfation in a single step by sol-gel process combined with emulsion templates; to shape the porous structure surfactants and oil were added under stirring in order to generate a macro-mesoporous structure from emulsion templates, producing ceramic foams after drying and thermal treatment. According to XRD structural characterization the addition of sulfate species leads to a stabilization of the anatase phase, since single-phase materials with anatase as only phase were observed even at 700 °C for sulfated materials, while for non-sulfated TiO₂ calcined at 700°C, the rutile phase was observed as a second phase. FTIR spectra show bands around 1050-1250 cm^-1 assigned to links of SO₄^2- groups in the sulfated TiO₂ samples, which N₂ adsorption-desorption isotherms are typical of macro-mesoporous materials. The surface area of the non-sulfated TiO₂ foam, equal to 50 m²/g, increases to 62 and to 80 m²/g as the Ti⁴⁺:SO₄^2- ratio increases from 0.1 to 1. The ability to control the macro- mesoporous structure on different length scales enables this material as candidate for supercapacitor as it offers the combination of the nanoscale dimension with a high defined geometry and surface area.