Creating a highly dispersed ZnO is one strategy to improve the photocatalytic activity of this material. However, pure ZnO always presents in an agglomerate state. The current study aimed to improve the dispersibility by adding SiO2 particle through ultrasonication. The amount of SiO2 particle is crucial to maintain a good dispersibility. The impact of silica ratio and ultrasonication time on particle morphology and photocatalytic performance were studied to obtain a nanocomposite with a good dispersibility. Composites were prepared with silica mass ratios ranging from 0.25% to 1.15% and exposed to ultrasonication for 10–240 min. Characterization methods, including x-ray diffraction (XRD), Fourier transform infrared (FTIR), dynamic light scattering (DLS), and transmission electron microscopy (TEM), revealed that a 0.25% silica ratio resulted in smaller, uniformly distributed particles. Longer ultrasonication enhanced cavitation effects, improving particle dispersion and reducing agglomeration. Photocatalytic tests showed composites with lower silica ratios and optimized ultrasonication achieved 96.5% methylene blue (MB) degradation within 60 min of sunlight exposure (k = 0.0200 min−1), linked to increased surface area and ZnO dispersion. Photoluminescence (PL) analysis confirmed that 0.25% silica produced the highest PL intensity, correlating with superior photocatalytic activity. This study emphasizes the importance of optimizing silica ratio and ultrasonication time for designing efficient photocatalytic materials. © 2025 Canadian Society for Chemical Engineering.