| Summary: | In the present study, TiO<sub>2</sub>-montmorillonite (MMT) composites were synthesized hydrothermally under variable conditions, including the TiO<sub>2</sub>/MMT mass ratio, reaction pH, reaction temperature, and dwelling time. These samples were determined by X-ray photoelectron spectrometry (XPS), ultraviolet–visible spectroscopy% (UV-Vis DRS), electrochemical impedance spectroscopy (EIS), transient photocurrent responses, photoluminescence (PL) spectra, electron paramagnetic resonance (EPR), and N<sub>2</sub> adsorption–desorption isotherms. The photocatalytic activity was evaluated as the ability to promote the visible-light-driven degradation of 30 mg/L of aqueous methylene blue, which was maximized for the composite with a TiO<sub>2</sub> mass ratio of 30 wt% prepared at a pH of 6, a reaction temperature of 160 °C, and a dwelling time of 24 h (denoted as 30%-TM), which achieved a methylene blue removal efficiency of 95.6%, which was 4.9 times higher than that of pure TiO<sub>2</sub>. The unit cell volume and crystallite size of 30%-TM were 92.43 Å<sup>3</sup> and 9.28 nm, respectively, with a relatively uniform distribution of TiO<sub>2</sub> particles on the MMT’s surface. In addition, 30%-TM had a large specific surface area, a strong light absorption capacity, and a high Ti<sup>3+</sup> content among the studied catalysts. Thus, the present study provides a basis for the synthesis of composites with controlled structures.
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