Formation and Characterization of TiO₂ - BiVO₄ Heteroaggregates Produced in a Planetary Ball Mill

This dissertation investigates the formation and photocatalytic performance of TiO₂–BiVO₄ heteroaggregates produced by planetary ball milling. The main objective is to understand how processing parameters and composition influence the spatial distribution of phases and the resulting photocatalytic activity. Heteroaggregates were synthesized under different milling conditions (1, 5, and 10 minutes milling time with different milling balls, 32 and 42 balls) and composition ratios (1:2, 1:1, and 2:1). Structural characterization was performed using X-ray diffraction (XRD), while Raman spectroscopy was used to obtain spatially resolved composition maps. Photocatalytic activity was evaluated through methylene blue degradation experiments monitored by time resolved Raman mapping. Local reaction rate constants were extracted and processed using filtering, baseline correction, and kinetic modeling. A statistical density mapping approach was introduced to analyze the distribution of activity as a function of local composition. The results show that moderate milling conditions (5 minutes, 42 balls) produce the most efficient heteroaggregates, while excessive milling reduces activity due to structural densification. The 1:2 composition ratio exhibits the highest and most consistent photocatalytic performance. The study demonstrates that photocatalytic efficiency depends on both processing conditions and local composition. Limitations include experimental variability and partial data loss in some Raman measurements.