Titanium-Loaded Photocatalytsts for Removal of Organic Dyes From Wastewater Using Visible Light Irradiation

Heterogeneous photocatalytic oxidation (HPO) processes employing catalysts such as TiO₂, ZnO, etc., using UV light has shown promising results for the degradation of persistent organic pollutants, and their conversion to more biologically degradable and less toxic substances. However, a large number of organic contaminants cannot be fully degraded by such methods. In order to meet increasingly more stringent environmental regulations and laws, more efficient processes for the removal of organic pollutants are needed. Among the most promising and advanced methods being investigated, photocatalysis at semiconductors and at TiO₂, in particular, receives a considerable attention as reflected by the recent large body of research published in this field. Titanium dioxide, however, can be easily degraded when subjected to the relatively harsh UV irradiation. Moreover, use of UV irradiation is not attractive in a large industrial scale water treatment processes because of its potential harmful effects on humans. Both of the problems cited above could be resolved if UV irradiation could be replaced by a harmless visible light irradiation.

Titanium dioxide nanoparticles successfully anchored into 3-D mesoporous material (TUD-1) using a sol-gel preparation strategy were prepared and tested as photocatalysts, employing only visible light (λ = 447 nm), for the treatment of wastewaters containing azo dyes. Samples of different Si/Ti ratio, ∞, 100, 75, 50 and 25 and 10 w/w were prepared and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet spectroscopy (UV), and nitrogen adsorption at 77K. The newly developed Ti-TUD-1 photocatalysts showed excellent activity towards the removal of the tested Azo dyes solutions. Up to 98% of azodyes were successfully removed from the contaminated wastewater. Moreover, the catalysts showed remarkable stability under the relatively mild irradiation conditions used. Repeated photodegradation tests demonstrated remarkable reproducibility and showed no decrease in photocatalytic activity after 5 cycles.