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• Carbon doped TiO 2 /kaolinite composite was rationally designed and assembled. • The composite's reaction rate constant is about 25 times higher than that of pure TiO 2. • TiIII defects and localized occupied states are responsible for performance enhancement. • Kaolinite induced carrier effect plays important role in catalytic activity enhancement. • The composite material might be a promising candidate for degrading trace amounts of pollutants. In this work, kaolinite supported monodispersed TiO 2 with carbon regulation was prepared through rational design and different dimensions' assembly, leading to generation of TiIII species in carbon doped TiO 2 /kaolinite (C-TiO 2 /kaolinite) composite. The C-TiO 2 /kaolinite composite exhibited improved degradation performance towards ciprofloxacin under visible light, with a reaction rate constant of 0.00597 min−1, which is about 3.24 and 24.88 times higher than that of 2.0C-T (2.0% carbon-doped TiO 2) and pure TiO 2 , respectively. Based on various materials characterization methods and DFT calculations, it was indicated that the electronic structure was correlated with the changes in light absorption, charge carrier lifetime, and reactive oxygen species (ROS). The enhanced visible light responding ability could be attributed to the synergistic effect between natural kaolinite and nanosized TiO 2 , the formation of localized occupied states in the gap, and the formation of TiIII defects consisted of surface oxygen vacancies. All of them effectively increase the separation efficiency, migration velocity, and lifetime of the photoinduced charge carriers under visible-light irradiation. Overall, our study provides a promising candidate for effective degradation of trace amounts of pharmaceutical and personal care products and other highly toxic contaminants with the assistance of solar light. [ABSTRACT FROM AUTHOR]