Time-Dependent Hydrothermal Synthesis of Zn²⁺ - Modified TiO₂ in Acidic Environment: Effects on Photoconductivity

Titanium dioxide nanoparticles were synthesized via hydrothermal treatment of tetrabutyl titanate in sulfuric acid, with controlled reaction times (10 h and 24 h) and zinc sulfate as a modifier. XRD confirmed exclusive formation of the anatase phase, with longer reaction times promoting crystallite growth. SEM and BET analyses revealed that Zn addition suppressed agglomeration, reduced particle size, and altered porosity, while all samples retained mesoporous character. UV–Vis diffuse reflectance spectroscopy showed a band gap near 3.2 eV, unaffected by Zn content or morphology. Photoconductivity studies demonstrated that under vacuum, conductivity increased by several orders of magnitude, particularly for 24 h Zn-modified samples, due to the generation of oxygen vacancies and Ti3+ states that prolong carrier lifetime. In particular, the TS24Z8 sample exhibited a photoconductivity enhancement of five orders of magnitude relative to its dark conductivity, and nearly 30 times higher than that of the commercial P25 benchmark. In contrast, in air, photoconductivity remained low because of strong surface recombination with adsorbed oxygen. These results highlight the key role of hydrothermal duration and zinc modification in tailoring the defect structure and electronic response of TiO2, offering insights for improved photocatalytic and optoelectronic applications.