The search for a simple, scalable, and eco-friendly method for synthesizing micro-sized photocatalysts is an urgent task. Plasma technologies are highly effective and have wide possibilities for targeted synthesis of novel materials. The mass-average temperature of plasma treatment is higher than the stability temperature of anatase and brookite, the most photoactive polymorphs of titanium dioxide. In this work, by optimizing the plasma treatment conditions and selecting source materials, a method for synthesizing micro-sized photocatalyst based on heterocomposite TiO₂/ZnO particles with high anatase content is proposed. The synthesis method involves treating a powder mixture of titanium and zinc by low-temperature argon plasma under atmospheric conditions. The relationship between the structural-phase composition, morphology, and photocatalytic properties of the microparticles was investigated. A model for the synthesis of composite microparticles containing anatase, rutile, and heterostructural contact with zinc oxide is proposed. The photocatalytic degradation of methylene blue and metronidazole was studied to evaluate both sensitized and true photocatalytic processes. The metronidazole degradation confirmed the intrinsic photocatalytic activity of the synthesized composites. Additionally, the features of photocatalysis under UV and solar irradiation were studied, and a photocatalysis mechanism is proposed. The synthesized micro-sized heterocomposite photocatalyst based on TiO₂/ZnO contained anatase (36%), rutile (60), and brookite (4%) and showed a photocatalytic activity during the methylene blue degradation process under UV irradiation (high-pressure mercury lamp, 250 W): 99% in 30 min.