Tailoring the properties of immobilized titanium dioxide/carbon nanotube composites for photocatalytic water treatment

Abstract

Sol–gel (SG) and hydration–dehydration (HD) methods were used to prepare titanium dioxide/multi-walled carbon nanotube (TiO2/CNT) composites with different carbon contents using functionalized (CNTf) and pristine carbon nanotubes (CNT). Composite materials were mainly constituted by anatase crystallites of 8.0–9.0nm. Surface area of the composite materials varied between 70 and 141m2g−1, with the higher values for the materials produced by SG using functionalized CNT. The composite materials were immobilized on glass slides and tested in the photodegradation of methylene blue (MB). Composite photocatalysts produced by SG method showed higher efficiency for MB degradation than those prepared by HD. The best photocatalytic efficiency was obtained for the material produced by SG method with the highest loading of functionalized CNT. A 62% MB removal was achieved for that catalyst contrasting with 46% obtained with bare TiO2. In addition, it was proved that the introduction of oxygen surface groups in CNT is crucial to prepare TiO2/CNT composites with high photoactivity, promoting the dispersion of TiO2 particles and inducing the CNT action as a photosensitizer. The films with higher efficiency for MB abatement were tested in the photocatalytic degradation of four para-substituted phenols: 4-aminophenol (AP), 4-methoxyphenol (MP), 4-chlorophenol (CP) and 4-nitrophenol (NP). A relationship between the Hammett constant of each para-substituted phenol compound and its degradability by photocatalysis was obtained. A beneficial effect of the introduction of CNT in the matrix of TiO2 was mainly observed for the degradation of AP and MP.