Enhancing the photocatalytic properties of TiO2 by coupling with carbon nanotubes and supporting gold

The photodegradation of methylene blue in aqueous solutions is studied using various photocatalysts, including neat TiO2, CNT-TiO2, Au-TiO2, and Au-CNT-TiO2 composites MB. Materials were synthesized and extensively characterized by XRD, TEM, DRFIT spectroscopy, N-2 adsorption-desorption isotherms, as well as diffuse reflectance UV-vis spectroscopy. By using CNT-TiO2 composite as catalysts, it was found that CNT act as adsorbent and photosensitizer to improve the photoactivity of neat TiO2. Among the CNT-TiO2 composites with different CNT weight ratio (0.2-20%), the 2%CNT-TiO2 shows the best photoactivity. When CNT content is larger than 2%, the surplus CNT may absorb and scatter light photons. Combined with the decrease of TiO2 amount in composite, the photoactivity is reduced. To further improve the photoactivity of 2%CNT-TiO2, different Au loads varying from 0.25% to 1% were introduced by the deposition-precipitation method. The 0.25%Au-2%CNT-TiO2 composite had the highest photoactivity. The increase in activity was explained by the surface plasmon resonance of Au that makes the composite to absorb more photons than the 2%CNT-TiO2, thus overcoming the disadvantages of surplus CNT addition. On the other hand, 0.25%Au-2%CNT-TiO2 composite also presents higher activity than 0.25%Au-TiO2 due to higher adsorption capacity provided by CNT introduction. The addition of CNT and Au simultaneously has a much stronger synergic role than when each of them is introduced individually. (C) 2012 Elsevier B.V. All rights reserved.