Photocatalytic Activity of Titanium Dioxide Nanotubes Following Long-Term Aging

Anodic titanium dioxide (TiO2) nanotubes were found to be active photocatalysts. These photocatalysts possess a high surface area, even when supported, rendering them potential candidates for water treatment. In this work, photocatalytic surfaces were produced by anodizing commercially pure Ti plates using two different electrolyte compositions and correspondingly diverse process parameters. Changes in the physical and chemical stability as well as photocatalytic activity were studied over a fifty-two-week aging process. During this period, the nanotubular surfaces were exposed to flowing synthetic greywater, solar irradiation, and the natural environment. The physical and phase stability of the materials anodized using the organic electrolyte were found to be outstanding and no degradation or change in crystalline structure was observed. On the other hand, materials anodized in the aqueous electrolyte proved to suffer from light-induced phase transition from anatase to rutile. Surfaces synthesized in the organic electrolyte were more resistant to fouling and showed a better tendency to recover photocatalytic activity upon cleaning. In conclusion, the nanotubes produced in the organic electrolyte proved to be stable, rendering them potentially suitable for real-life applications.

Synthesis of Aromatic and Aliphatic N-Heterocyclic Salts and Their Application as Organic Electrolyte Supporters in Electrochemical Capacitor

Aromatic and aliphatic N-heterocyclic chemical salts were synthesized by counter-anion-exchange reactions after substitution reactions in order to apply them as organic electrolyte supporters in an electrochemical capacitor (super capacitor). The aromatic N-heterocyclic salts were N-methylpyridinium tetrafluoroborate ([MPy]+[BF4]−), N-methylpyridinium hexafluorophosphate ([MPy]+[PF6]−), 1,3-dibuthylimidazolium tetrafluoroborate ([DI]+[BF4]−), 1,3-dibuthylimidazolium hexafluorophosphate ([DI]+[PF6]−), 1-buthyl-4-methyl-1,2,4-triazolium tetrafluoroborate ([BMTA]+[BF4]−), and 1-buthyl-4-methyl-1,2,4-triazolium hexafluorophosphate ([BMTA]+[PF6]−). The aliphatic N-heterocyclic salts were N,N-dimethylpiperilidium tetrafluoroborate ([DMP]+[BF4]−), N,N-dimethylpiperilidium hexafluorophosphate ([DMPy]+[PF6]−), N,N-dimethylpyrrolidium tetrafluoroborate ([DMPy]+[BF4]−) and N,N-dimethylpyrrolidium hexafluorophosphate ([DMPy]+[PF6]−), 1-ethyltriethamine tetrafluoroborate ([E-TEDA]+[BF4]−), and 1-ethyltriethamine hexafluorophosphate ([E-TEDA]+[PF6]−), respectively. We confirmed the successful synthesis of the aromatic and aliphatic N-heterocyclic chemical salts by 1H-NMR, FT-IR, and GC/MS analysis before conducting the counter-anion-exchange reactions. Then, we determined the electrochemical potential of vanadium acetylacetonate (V(acac)3) under acetonitrile in the presence of the N-heterocyclic chemical salts as energy-storage chemicals. By cyclic voltammetry, the maximum voltages with the N-heterocyclic chemical salts in acetonitrile reached 2.2 V under a fixed current value. Charge-discharge experiments were performed in the electrochemical capacitor with an anion-exchange membrane using a non-aqueous electrolyte prepared with a synthesized N-heterocyclic salt in acetonitrile.