Photocatalytic activity of vinylidene fluoride-containing copolymers/anatase titanium oxide/silica nanocomposites

Abstract

A series of three fluorinated copolymers (FP) based on vinylidene fluoride (VDF) were involved in the preparation of original FP/anatase titanium oxide (an-TiO2), and FP/silica/an-TiO2 nanocomposites. These FP copolymers were prepared by conventional free radical copolymerization of VDF with various functional fluorinated comonomers such as F2CCFCO2Me, FCHCFCO2H, and F2CCFC3H6OCOCH3 in good yields (>60%) and had number average molecular weights of ca. 50,000gmol−1. Anatase titanium oxide in the FP/an-TiO2 nanocomposites underwent an effective modification into rutile polymorphism after calcination at 1000°C. Although the parent an-TiO2 nanoparticles changed completely into rutile nanoparticles after calcination at 1000°C, an-TiO2 embedded in the FPs/silica/an-TiO2 nanocomposites retained their structures without any phase transformation into rutile, due to locking the TiO species at the interface of TiO2 domains by the TiOSi units, whose lattice can be formed by the interaction of silica with an-TiO2 nanoparticles. Even after such a thermal treatment, these nanocomposites displayed a higher photocatalytic activity for the discoloration of methylene blue as well as those of the corresponding nanocomposites before calcination, although the original an-TiO2 nanoparticles could not exhibit a photocatalytic ability after calcination. Among these nanocomposites based on VDF-containing copolymers, poly(VDF-co-CF2CFCO2CH3)/SiO2/an-TiO2 before and after calcination displayed better photocatalytic properties than those of the other FP nanocomposites. More interestingly, this FP/silica/an-TiO2 nanocomposite even after calcination at 1000°C was able to preserve the same photocatalytic activity as that before calcination. In addition, these FP/TiO2 and FP/SiO2/TiO2 composites exhibited high thermal stability up to 800°C with a loss weight of 2% (or ca. 14% for the acidic FP) only.