Photonic Band Gap and Bactericide Performance of Amorphous Sol-Gel Titania: An Alternative to Crystalline TiO2

Abstract

In addition to its traditional application in white pigments, nanocrystalline titania (TiO2) has optoelectronic and photocatalytic properties (strongly dependent on crystallinity, particle size, and surface structure) that grant this naturally occurring oxide new technological applications. Sol-gel is one of the most widely used methods to synthesize TiO2 films and NPs, but the products obtained (mostly oxy-hydrated amorphous phases) require severe heat-treatments to promote crystallization, in which control over size and shape is difficult to achieve. In this work, we obtained new photocatalytic materials based on amorphous titania and measured their electronic band gap. Two case studies are reported that show the enormous potential of amorphous titania as bactericide or photocatalyst. In the first, amorphous sol-gel TiO2 thin films doped with N (TiO2−xNx, x = 0.75) were designed to exhibit a photonic band gap in the visible region. The identification of Ti-O-N and N-Ti-O bindings was achieved by XPS. The photonic band gaps were found to be 3.18 eV for a-TiO2 and 2.99 eV for N-doped a-TiO2. In the second study, amorphous titania and amine-functionalized amorphous titania nanoparticles were synthetized using a novel base-catalysed sol-gel methodology. All the synthesized amorphous TiO2 nanoparticles exhibit bactericide performance (E. coli, ASTME 2149-13).

Synthesis and Characterization of Novel Integral Asymmetric Monophasic Cellulose–Acetate/Silica/Titania and Cellulose–Acetate/Titania Membranes

“…Titania, either amorphous or crystalline, has been shown to possess an outstanding bactericidal performance, even without previous ultra-violet (UV) stimuli [ 25 , 26 ]. Although the mechanistic details of the TiO 2 photocatalyzed reactions remain complex and are not completely understood [ 26 , 27 ], the role of TiO 2 is widely recognized in the formation of reactive oxygen species (ROS) (hydroxyl, superoxide anion radicals, O 2 , O 2 − ).…”

“…Titania, either amorphous or crystalline, has been shown to possess an outstanding bactericidal performance, even without previous ultra-violet (UV) stimuli [ 25 , 26 ]. Although the mechanistic details of the TiO 2 photocatalyzed reactions remain complex and are not completely understood [ 26 , 27 ], the role of TiO 2 is widely recognized in the formation of reactive oxygen species (ROS) (hydroxyl, superoxide anion radicals, O 2 , O 2 − ). When in close proximity to bacteria, these ROS’s damage bacterial cell membranes through lipid peroxidation, enhance membrane fluidity, and cause cell integrity disruption, eventually leading to cell death [ 26 , 27 ] ( Figure 1 c).…”

Effect of Annealing Temperature on Spatial Atomic Layer Deposited Titanium Oxide and Its Application in Perovskite Solar Cells

“…The decrease in the band gap with an increasing annealing temperature implies the structural change of the films. The samples annealed at below 750 °C have band gap values similar to anatase TiO 2 (~3.2–3.25 eV), while the 750 °C-annealed sample shows a reduced band gap similar to rutile TiO 2 [ 48 ].…”

Enhancement of NOx photo-oxidation by Fe- and Cu-doped blue TiO2

“…This can be attributed to the new energy levels created by the introduction of Ti 3+ species, oxygen vacancies, and Fe/Cu ions. Also, the amorphous phase present on the surface of the anatase phase in reduced TiO 2 contains imperfections such as ionic impurities and dangling bond in the crystal surface that causes other electronic states present in the bandgap, shortening the recombination probability (Gonçalves et al 2018). Table 1 shows a comparative table of the efficiencies of Cu-and Fe-doped TiO 2 with other metadoped titania.…”