Interplay between the morphology, crystal facets and silver modifications of titanium dioxide nanomaterials in the context of photocatalysis

Abstract

Titanium dioxide (TiO₂) having the morphology of nanofibers (TNFs), nanorods (TNRs), and nanograss (TNGs) nanostructures were prepared. Synthetic procedures had a great impact on the obtained morphology and phase. Nanomaterials were prepared under neutral conditions in the presence of ethylene glycol for TNFs, while those obtained under strongly basic conditions during the recrystallization process of the TiO₂ powder exhibited the morphology of TNRs. Both materials, TNFs and TNRs, exhibited the anatase phase. In contrast, under strongly acidic conditions in the presence of toluene, TNGs were formed that crystallized in the rutile phase. Specific exposed planes are directly related to the crystal morphology. XRD measurements revealed that in the case of anatase nanomaterials (TNFs, TNRs), the {101} facet was exposed, while in rutile nanomaterials (TNGs 1 and 2), the {110} facet was exposed. The interplay between the morphology, the most stable facets, and modification with silver had a great impact on the photocatalytic properties. Anatase nanomaterials, especially those with low crystallinity (TNFs), exhibited the highest photoactivity towards rhodamine B (RhB) decomposition, while highly crystalline rutile crystals did not exhibit good photocatalytic performance, neither in UV nor in simulated solar light (SSL). However, the photoactive performance could be enhanced for most materials by modification of their surface with metallic silver and the creation of a Schottky barrier. The mechanisms of photocatalytic decomposition were revealed using hole scavengers, hydroxyl radicals and superoxide anion radicals. Finally, the antibacterial activity of the nanostructures was assessed using bacterial cultures of Staphylococcus aureus and Proteus mirabilis. The maximum zones of inhibition (ZOI) recorded for TNGs 1 Ag was 7.1 ± 012 mm against P. mirabilis and 7.2 ± 0.04 mm against S. aureus. Meanwhile, TNGs 2 Ag showed the maximum ZOI of 9.1 ± 0.09 mm against P. mirabili.