Hydrothermal‐Calcination Synthesis of TiO ₂ Microcrystals With Highly Reactive Facets for Enhanced Photocatalytic Degradation of Rhodamine B

A series of TX‐TiO 2 samples derived from an H 2 Ti 3 O 7 precursor were synthesized over a wide temperature range (180°C–1050°C) using NH 4 F as a morphology‐controlling agent. The products exhibited a clear phase and facet evolution: phase‐pure anatase (T180‐TiO 2 to T750‐TiO 2 ) with exposed {101}, {010}, and [111]‐oriented facets; mixed‐phase anatase/rutile (T800‐TiO 2 to T900‐TiO 2 ) with exposed {010}/{101} and {110} facets; and phase‐pure rutile (T950‐TiO 2 to T1050‐TiO 2 ) with near‐rodlike and irregular morphologies lacking well‐defined dominant facets. The systematic evolution provided an ideal model for establishing a quantitative structure‐activity relationship between facet exposure and photocatalytic performance. The samples were systematically characterized by powder x‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high‐resolution TEM (HRTEM), nitrogen adsorption, x‐ray photoelectron spectroscopy (XPS), and UV–vis–NIR spectroscopy. Photocatalytic evaluation revealed that T700‐TiO 2 with exposed {010} facets exhibited the highest degradation rate (94.0%) and apparent rate constant (0.0217 min −1 ), outperforming other TX‐TiO 2 samples and commercial CM‐TiO 2 . Even after normalizing by specific surface area, T700‐TiO 2 maintained the highest intrinsic activity (6.14×10 −4 min −1 ·g·m −2 ), confirming its superior intrinsic reactivity. The outstanding photocatalytic activity of T700‐TiO 2 is attributed to the synergistic effects of its exposed {010} facets, high crystallinity, and pure anatase structure.