Stable synthesis mechanism and photocatalytic properties of TiO2 nanocrystals with different morphologies derived from potassium titanate nanowires

Abstract

This study explored key factors influencing TiO₂ morphology using potassium titanate nanowires (KTNWs) as precursors. The pH of the hydrothermal solution was identified as critical in controlling TiO₂ morphology. Different washing methods for precursors synthesized under alkaline conditions lead to varying pH environments in the subsequent hydrothermal solutions, thereby influencing the growth direction of TiO₂ nuclei. Even a very slight pH change could cause a huge difference in the morphology of TiO₂, by adjusting precursor washing methods, rod-like, cuboidal, and octahedral bipyramidal TiO₂ nanocrystals were synthesized, the octahedral bipyramidal TiO₂ exhibiting the smallest particle size. Acid treatment could stabilize the octahedral bipyramidal morphology of the TiO₂ nanocrystal, and reduced particle size by nearly 86% than that of rod-like TiO₂-R nanocrystal. Acid treated sample TiO₂-R-H7 achieved the best photocatalytic activity, which was nearly 3 times than that of original TiO₂. Adjusting (NH₄)₂CO₃ morphology-controlling agent concentrations further regulated {001} facet exposure ratio to improve the photocatalytic activity, the TiO₂-R-0.14 synthesized at 0.14 mmol per L (NH₄)₂CO₃ showing about 2.6 times than that of original TiO₂. However, excessive (NH₄)₂CO₃ concentrations would reduce the photocatalytic activity due to increased particle size and fewer oxygen vacancies. This study provides insights into the growth mechanisms of TiO₂ morphologies and highlights acid treatment as a strategy to reduce particle size and enhance photocatalytic activity, offering guidance for designing high-performance TiO₂ based photocatalyst.