Delaminated titanate and peroxotitanate photocatalysts

Delaminated layered titanates are effective, versatile, robust and practical photocatalytic materials for degradation of organic and microbiological contaminants. In prior studies, these have generally been obtained from Cs-titanate lepidocrocite-analogue parent materials. In this study we show that delaminated sodium nonatitanate (SNT) is equally effective as the delaminated Cs-titanate; yet it is cheaper to synthesize and is obtained in about one-third as many processing steps. Two chemical modifications; ligation with peroxide and treatment with phosphate resulted in improved photodegradation of common dyes; bromophenol-blue and methyl-orange. Together these two dyes provided experimental conditions ranging from pH similar to 4.5-9. All layered titanate materials proved to be more effective colloidal suspension photocatalysts than standard TiO2. Although most common characterization techniques could not distinguish significant differences between the different delaminated titanates (from different parent materials, with chemical modifications), band-gap measurement via UV-vis spectroscopy proved informative. Generally the closer the match between the band-gap and the UV-light source, the more effective the catalyst. Finally, these layered titanates were electrostatically adhered to a surface, and photocatalytic activity was retained in this form. Furthermore, in this surface-adsorbed form we could see clear morphological differences between the Cs-titanate and SNT derived materials, as well as measure the height of the adsorbed layers. All observations by Atomic Force Microscopy indicated that the titanates layers that adhere to mica have a thickness of 1-10 layers thick (similar to 1-4 nm). These materials in their surface-fixed forms are very promising for water treatment technologies. (C) 2011 Elsevier B.V. All rights reserved.