The Fabrication And Characterization Of UV/Visible Light Responsive TiO₂-Based Materials For Adsorption And Catalysis

Adsorption and catalysis are important water treatment technologies in the field of environmental engineering. The development of environment functional materials has become a hot spot in this field. However, in the regeneration and recycling of used adsorbents or catalysts, either chemical or energy input is needed. Besides, secondary pollution and deactivation of materials are usually inevitable, and eventually lead to deterioration of the removal capacity for pollutants and the increase of processing cost. Therefore, the preparation of environmental functional materials with high removal efficiencies, improved recycling performances and prolonged lifetimes is of great significance in the treatment of wastewater.Herein we prepared a type of TiO2 xerogel with the sol-gel method. The resultant xerogel could be used as an adsorbent for the remediation of azo dye contaminated water. As compared to the conventional adsorbents, the TiO2 xerogel showed a high adsorption capacity to Acid Orange 7 in acidic solutions (769 mg g-1). The point more interesting is that the xerogel possesses a photo-responsive "on-off" behavior: adsorbed azo dyes under UV irradiation and released them back to aqueous solutions after switching off the UV light.This process is target-selective and repeatable. Such a host-guest like interaction is attributable to the reversible changes of surface functional groups under UV irradiation and in the dark, which alters the particle size and surface wettability of the TiO2 xerogel. Valuable resources could be potentially recycled from waste effluents when the xerogel is properly assembled. Since the work condition for dye-sensitized solar cells (DSSCs) are continuous solar irradiation, this concept might be useful for the anchoring of dyes in DSSCs for a higher energy conversion efficiency.The exhausted xerogel was calcined at high temperature. The obtained TiO2 nanoparticles showed good visible light response. It could be used as a photocatalyst for the degradation of Acid Orange 7. In this adsorption-calcination process, non-metal doping is achieved by adsorption of azo dyes before calcination. As compared with the directly prepared TiO2 photocatalyst from fresh xerogel, the TiO2 nanoparticles from exhausted xerogel showed a much higher photocatalytic activity upon visible light irradiation. In this way, the titanium-based materials are endowed with improved performances as well as a prolonged lifetime.The underlying mechanisms behind this strategy warrant a further study.