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TiO2 nanotubes have been co-doped with chromium and tungsten by electrochemical anodization. Tungsten and chromium single doped and pure TiO2 nanotubes have also been synthesized. Many methods have been used to characterize the products obtained. Following doping and co-doping of TiO2, the optical absorption edges are considerably red shifted to the visible region due to the induced impurity states within the band gap. The samples prepared were used as photoanodes for photocathodic protection in order to retard 403 stainless steel corrosion. Chromium and tungsten co-doping was found to enhance the visible photocatalytic activity of the resulting TiO2 nanotubes. Better photoelectrochemical performance and photocathodic protection properties were shown by (Cr-W)-co-doped TiO2, Cr-doped TiO2 and W-doped TiO2 samples compared with the undoped TiO2 nanotubes. The best co-doped TiO2 sample showed a photocurrent density, which was 2.6 times higher than that of the undoped TiO2. Under light illumination, the (Cr-W)-co-doped TiO2 photoelectrode decreased the potential of the coupled 403 stainless steel in a 3.5 wt. % NaCl solution to 400 mV, indicating an effective photocathodic protection. The synergetic effects of co-doping by chromium and tungsten may be responsible for the enhanced visible photocatalytic activity.

Substrate-assisted laser desorption/ionization (SALDI) is a kind of soft ionization method that is most suitable for the analysis of low molecular weight analytes when it is coupled with a time-of-flight mass spectrometer. Unlike the conventional matrix-assisted laser desorption/ionization, there is no interference in the SALDI with matrices for the low mass analyte peaks (m/z < 700). The focus of this work is to develop substrates based on nanomaterials to obtain higher sensitivity, better reproducibility, and easier preparation. The mass spectra of some small molecules (capecitabine, hemin, methadone, noscapine, oxycodone, thebaine, malathion, chlorpyrifos, ethion, permethrin, and phosalone) deposited on the TiO 2 -nanotube (TiO 2 -NTs) plate by the SALDI-TOF-MS technique are reported. The nanotubes are synthesized in different diameter sizes of nanotubes via the anodizing method. The intensity of the analyte peaks and the softness of ionization are optimized by varying the diameter of nanotubes and adding relevant alkali salts to the analytes. In addition, the reproducibility of the signal intensity of analytes is optimized by changing the surface hydrophilicity of the TiO 2 -NT plate.

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