Phase-Driven Hydrothermal Synthesis of TiO₂: Influence of Supernatant and Precipitate Fractions on Photocatalytic Dye Degradation

Semiconductor photocatalysis has attracted increasing attention as a sustainable strategy for the degradation of organic pollutants in wastewater due to its ability to mineralize contaminants under light irradiation. Among semiconductor photocatalysts, TiO₂ stands out because of its chemical stability, low cost and high photocatalytic activity. In this work, TiO₂ nanoparticles were synthesized through the decomposition of ammonium titanyl peroxide (PTA) followed by hydrothermal treatment at 200 °C for 4 h under alkaline conditions (pH 12). After synthesis, the supernatant and precipitate phases were separated, recovered and evaluated independently, while commercial TiO₂ was used as a reference material. The photocatalytic performance was investigated through the degradation of methylene blue and rhodamine B under UV irradiation (254 nm) at 25 °C. Dye concentrations were monitored by UV-Vis spectrophotometry, and degradation efficiencies were determined using the Beer–Lambert law. The TiO₂ obtained from the supernatant phase exhibited the highest photocatalytic activity, achieving degradation efficiencies of 66.7% for methylene blue and 67.1% for rhodamine B. These values exceeded those obtained with commercial TiO₂ (65.9% and 60.8%, respectively) and were significantly higher than those achieved with the precipitate phase (49.5% and 11.6%). The enhanced performance of the supernatant-derived TiO₂ is attributed to the hydrothermal synthesis conditions, which likely promoted the formation of particles with higher surface area and a greater ability to generate reactive oxygen species. Ongoing structural and morphological characterization studies, including X-ray diffraction and scanning electron microscopy, will provide further insight into the relationship between synthesis, microstructure and photocatalytic activity. These findings demonstrate that phase separation during hydrothermal synthesis is a simple and effective strategy for obtaining highly active TiO₂ photocatalysts for environmental remediation.