The photodegradation of methylene blue in aqueous solutions is studied using various photocatalysts, including neat TiO(2), CNT-TiO(2), Au-TiO(2), and Au-CNT-TiO(2) 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-TiO(2) composite as catalysts, it was found that CNT act as adsorbent and photosensitizer to improve the photoactivity of neat TiO(2). Among the CNT-TiO(2) composites with different CNT weight ratio (0.2-20%), the 2%CNT-TiO(2) 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 TiO(2) amount in composite, the photoactivity is reduced. To further improve the photoactivity of 2%CNT-TiO(2), different Au loads varying from 0.25% to 1% were introduced by the deposition-precipitation method. The 0.25%Au-2%CNT-TiO(2) 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-TiO(2), thus overcoming the disadvantages of surplus CNT addition. On the other hand, 0.25%Au-2%CNT-TiO(2) composite also presents higher activity than 0.25%Au-TiO(2) 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.
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