The works presented in this thesis discuss the red-shift enhanced photocatalysis of TiO2-coated carbon nanotubes by atomic layer deposition. The controllable thickness and uniform TiO¬2 layer is characterized, and the thermal treated composites lead to carbon diffusion into oxygen lattices which results in the efficient photocatalysis at visible light. The recyclable composite filters are also fabricated by atomic layer deposition. The filters are recyclable after the organic degradation without any wastage. The greater photocatalysis of composite filter is attributed to the high specific surface area resulting from the high aspect ratio of CNTs and the interactions between TiO2/CNTs interface. Chapter 1 introduces the background of carbon nanotube and titanium dioxide, including the structure, physical properties and photocatalysis of TiO2/CNTs composites. Chapter 2 describes the experimental setups and characterization techniques employed in this thesis. Chapter 3 discusses the photocatalysis of TiO2/MWCNTs composites including the degradation rate of organic substances and the recyclable composite filter. Chapter 4 concludes the experimental results.