Role of Post-Hydrothermal Treatment on the Microstructures and Photocatalytic Activity of TiO2-Based Nanotubes

Abstract

The present study demonstrates the thermal stability and photocatalytic activity of TiO2-based nanotubes with respect to post-hydrothermal treatment. Titanate nanotubes were synthesized by adapting an alkali hydrothermal method from TiO2 sol using NaOH as a catalyst. The effect of post-hydrothermal heating on the properties—such as structure, morphology, textural properties, and activity—of as-synthesized one-dimensional titania nanostructure is investigated in detail. The characterizations are carried out using SEM, EDX, TEM, XRD, and a BET surface area analyzer. When heated in the presence of water in an autoclave, the protonated titanate phase of the nanotubes converts to anatase phase. Meanwhile, the tubular morphology is gradually lost as the post-hydrothermal heating duration increases. The photocatalytic activity was assessed utilizing the photo-oxidation of an amaranth dye. It is discerned that the as-prepared nanotubes are photocatalytically inactive but become active after post-hydrothermal processing. The activity trend follows the formation of the active phase—the titanate phase crystallizes into a photocatalytically-active anatase phase during post-hydrothermal heating. The effect of experimental parameters, such as reaction pH, dye concentration, and amount of catalyst, on the dye removal is studied. The findings also highlight that the role of holes/OH• is more prominent as compared to conduction band electron/O2−• for the removal of the dye. In addition, the photocatalyst exhibited excellent stability and reusability.

An Overview of Hydrothermally Synthesized Titanate Nanotubes: The Factors Affecting Preparation and Their Promising Pharmaceutical Applications

“…According to the previously mentioned results, it is widely accepted that increasing the duration of heat treatment would improve crystallization, but at the same time it would negatively affect the surface area and therefore highly influence the related surface applications such as photocatalytic activity. From this point of view, if photocatalytic activity is the main target of the TNTs production, a compromise between surface area and crystallinity should be obtained to achieve their desired synergistic effect [45].…”

Mechanistic Understanding in Manipulating Energetics of TiO2 for Photocatalysis

“…Numerous semiconductor photocatalysts, such as TiO 2 , ZnO, ZnS, CdS, CdSe, and WO 3 , have been studied for their photocatalytic activities. − Of these semiconductors, TiO 2 is the most widely used semiconductor photocatalyst because of its stability, low toxicity, low cost, and excellent optoelectronic properties. , In addition, its morphologies are tunable with different shapes and sizes including nanoporous thin films, spheres, nanotubes, nanorods, nanobelts, nanowires, and nanohollows for numerous photocatalytic reactions. − Crystallinity, higher number of reactive sites, exposed facets, and the porous structure of these morphologies can influence the photocatalytic activity of TiO 2 . , It is expected that TiO 2 nanomaterials with high surface area and high crystallinity show greater photocatalytic activity, as the high surface area delivers additional active sites and high crystallinity could decrease the recombination of photoexcited charge carriers . For instance, rod-shaped TiO 2 nanoparticles (NPs) provide large surface area, reactive tips, and free movement of photogenerated electrons along the length of the rod and, as a result, a low recombination rate. , …”

ZnO nanostructure synthesis for the photocatalytic degradation of azo dye methyl orange from aqueous solutions utilizing activated carbon

“…As a result, ZnO has several uses in various scientific projects [13]. ZnO has been produced using a variety of techniques, including the soft chemical method [14], the sol-gel method [15], the vapor-phase growth [16], the vapor-liquid-solid process [17], electrophoretic deposition [18], thermal evaporation [19], homogeneous precipitation [20], chemical vapor deposition [21], chemical bath deposition [22], etc. In the aforementioned inve s tigations, ZnO nanoparticles were only occasionally generated through the activated carbon layer and by an auxiliary matrix approach, as recommended by Park et al [23].…”