Reversible photochromic effect in the TiO2—polymer hybrid system

Abstract

The photochromism of poly methyl methacrylate–TiO2 composites have been investigated in this research. Amorphous titanium oxide was synthesized by sol–gel using titanium isopropoxide. The titanium solution was mixed with a dissolved polymer. The composite shows photo-response under UV radiation by changing, generally, to a dark brown tonality. This effect was reversible in different time ranges according to the intensity and exposure time. The mechanism for this photochromic change was proposed as a reduction of TiOOH domains to Ti3+ and not directly from amorphous TiO2, which provide electron-hole pairs after absorbing UV. The backscattered electrons image shows the clusters or domains of titanium compounds as white dots, ranging from 0.1 to 1 μm. The electron spin resonance spectroscopy signals indicated a titanium valence change from Ti(IV) to Ti(III). The X-ray photoelectron spectroscopy peaks positions for Ti 2p1/2 and Ti 2p3/2 were assigned as Ti4+. The values were obtained for Ti 2p3/2 and the identified species were Ti4+ and Ti3+, that correspond to TiO2, Ti2O3, and Ti(OOH). Few and small crystalline domains were identified by Transmission Electron Microscope as orthorhombic TiO2.’