Synthesis of Fe- or Ag-doped TiO 2 –MWCNT nanocomposite thin films and their visible-light-induced catalysis of dye degradation and antibacterial activity

Thin films of TiO2, TiO2-multiwalled carbon nanotubes (TiO2–MWCNT), Fe-doped TiO2–MWCNT (Fe–TiO2–MWCNT), and Ag-doped TiO2–MWCNT (Ag–TiO2–MWCNT) supported on glass substrates were successfully prepared by sol–gel drop coating method. MWCNTs were treated by H2SO4 and HNO3 to oxidize graphitic carbon. The composites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, Fourier-transform infrared (FTIR) spectroscopy, and ultraviolet–visible (UV-Vis) absorption spectroscopy to confirm their structure and optical properties. XRD patterns of all prepared films exhibited (101), (004), (200), (105), (211), (204), (116), (220), (215), and (224) planes of anatase-phase TiO2. A pronounced broad peak at ~3400 cm−1 in the FTIR spectrum of the MWCNT confirmed oxidation of some carbon atoms on the surface of MWCNTs by HNO3 and H2SO4. The photocatalytic and antibacterial activities of the prepared materials were tested under visible-light irradiation based on degradation of methylene blue (MB) dye in aqueous solution and reduction in the viable count of Escherichia coli, respectively. Fe or Ag was doped into the TiO2-MWCNT composites, lowering the bandgap and thereby enabling enhanced photocatalytic activity in the visible-light region. Based on the MB photodegradation results, the photocatalytic efficiency of the Fe–TiO2–MWCNT and Ag–TiO2–MWCNT composites could be due to the following mechanism: (1) adsorption and photoinduced electron absorption by MWCNT, and (2) electron trapping by Fe or Ag within the TiO2 matrix, in addition to the usual photocatalytic activity of TiO2. Moreover, as-synthesized Ag–TiO2–MWCNT composite films showed outstanding antimicrobial activity.