Microwave-Assisted\nHydrothermal Synthesis of Photocatalytic\nTruncated-Bipyramidal TiO<sub>2</sub>/Ti<sub>3</sub>CN Heterostructures\nDerived from Ti<sub>3</sub>CN MXene

TiO<sub>2</sub>/MXene heterostructure has garnered significant\ninterest as a photocatalyst due to its large surface area and efficient\ncharge carrier separation at the interface. However, current synthesis\nmethods produce TiO<sub>2</sub> without clear crystal faceting and\noften require complicated postprocessing step, limiting its practical\napplications. We demonstrate a facile and controlled microwave-assisted\nhydrothermal synthesis for transforming multilayered Ti<sub>3</sub>CN MXene to a truncated-bipyramidal TiO<sub>2</sub>/Ti<sub>3</sub>CN heterostructure. The resulting TiO<sub>2</sub> nanocrystals at\nthe Ti<sub>3</sub>CN surface exhibited crystalline anatase truncated\nbipyramids, exposing {001} and {101} facets. We further tailored an\nindirect optical band gap of the TiO<sub>2</sub>/Ti<sub>3</sub>CN\nheterostructure in the range of 3.17–3.23 eV by varying the\nhydrothermal synthesis time from 15 min to 5 h at a fixed temperature\nof 160 °C. Efficient charge separation allowed us to decompose\n97% of methylene blue (MB) within 30 min of ultraviolet (UV) light\nirradiation, ∼3.9-fold faster than the benchmark P25, higher\nthan any other TiO<sub>2</sub>/MXene heterostructures. With simulated\nwhite light, we achieved over 60% efficiency of the dye decomposition\nwithin 2 h of irradiation, which resulted in 1.5-fold faster kinetics\nthan P25. We also observed a similar excellent performance of Ti<sub>3</sub>CN-derived TiO<sub>2</sub> in decomposing various persistent\nsynthetic dyes, including commercial textile dye, methyl orange, and\nrhodamine B. In conclusion, our study provides a strategy for utilizing\nMXene chemical reactivity to produce highly crystalline optically\nactive TiO<sub>2</sub>/Ti<sub>3</sub>CN heterostructure. The developed\nheterostructure can serve as an efficient photocatalyst for the degradation\nof organic pollutants.