Synthesis of Na-, Fe-, and Co-promoted TiO2/multiwalled carbon nanotube composites and their use as a photocatalyst

Abstract

The use of multiwalled carbon nanotubes (CNTs) in sol-gel synthesized titanium dioxide (TiO$_{2})$ photocatalysts as templates was systematically studied. CNTs have high oxidative thermal stability and the controlled removal of CNTs can be achieved at lower temperatures under air flow by the use of Na, Fe, and Co as a catalyst. These catalysts helped to reduce the oxidation temperature of CNTs; thus anatase phase was achieved without significant sintering. The use of a promoter, heat treatment, and various heat treatment atmospheres was effective in specific surface area, crystallinity, and photocatalytic activity against methylene blue (MB) degradation. While the specific surface area of bare TiO$_{2}$ was 22 m$^{2}$/g, after templating surface areas as high as 191 m$^{2}$/g were obtained. For the photocatalytic characterization, with bare TiO$_{2}$, the rate constant for MB decomposition was 0.81 h$^{-1}$, and for CNT-TiO$_{2}$ it was 1.31 h$^{-1}$. Moreover, after Na promotion, the rate constant increased to 1.85 h$^{-1}$. The results showed that CNTs can be used as a template to tailor and improve the textural properties. Moreover, as a novel material, the Na promotion in CNT-TiO$_{2}$ samples showed the best photocatalytic activity by enhancing the interaction between TiO$_{2}$ and CNT surfaces.