Titanate Nanotubes Coated with Ag Nanoparticles: Efects of Annealing Temperature on Crystalline Structure, Morphology, and Photocatalytic Activity

Silver nanoparticles (AgNPs) were initially incorporated into titanate nanotubes (Ag-TNTs) synthesized through a hydrothermal process, employing a photoreduction technique. The Ag/TNT samples were annealed between 70 and 350 ºC to optimize
the properties and functionalities of the composite material. The Ag/TNTs were characterized using X-ray difraction (XRD),
high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared spectroscopy (FT-IR), UV–Visible spectroscopy (UV–Vis), and UV–Visible difuse refectance spectroscopy (UV–Vis DRS). XRD analysis revealed the
formation of silver titanate through the exchange of extra-framework Na+ ions in TNTs with Ag+ ions. New peaks at 28.3°
and 48.2° appeared in the XRD pattern of Ag/TNTs-350, indicating a partial transformation of the nanotabular TNTs to
anatase nanotubes due to the temperature change. The interaction observed between the Ag and TNT particles is believed
to be linked to a distinct medium band at 1384 cm−1. This band possibly indicates that silver ions may interact with oxygen
or nitrogen-containing groups on the surface of the TNT particles. HRTEM analysis revealed that the inclusion of AgNPs
did not signifcantly alter the original nanotube morphology of TNTs, except in the Ag/TNTs-350 sample, which exhibited
structural faws and uneven walls. The bandgap reduction from 2.7 eV in TNTs-100 to 2.2 eV in Ag/TNTs-350 underscores
the impact of AgNPs and annealing on modulating electronic properties and improving photocatalytic performance. The
photocatalytic activity of Ag/TNTs-70-350 nanostructures was evaluated based on the degradation of MB dye in an aqueous
solution under natural sunlight. The interaction of Ag-TNTs with titanate/titania crucially infuences visible light activity,
with degradation rates consistently increasing as annealing temperatures rise. The computational analysis revealed that the
HOMO–LUMO gap and singlet–singlet excited state energies of the amorphous clusters closely resembled those of crystalline Ag/TNTs, indicating their potential for efcient dye removal