Oxygen vacancy-induced hydroxyl dipole reorientation in hydroxyapatite for enhanced piezocatalytic activity

A new method to boost the piezocatalytic activity of hydroxyapatite (HAP) is proposed that oxygen vacancies were introduced to align the orientation of hydroxyl dipoles in parallel. A series of hydroxyapatites with different contents of oxygen vacancy were synthesized by hydrothermal method and high-temperature calcination. Among them, hydroxyapatite with a moderate oxygen-vacancy concentration (OVHAP-2 h) exhibited an excellent piezocatalytic removal efficiency of 98.43% for bisphenol A (BPA) within 12 min, and its degradation kinetic rate constant was almost 4 times that of pristine HAP. This could be ascribed to the introduction of oxygen vacancies which induce the transformation in the orientation of hydroxyl dipoles from disorderly to parallel. Finally, the possible piezocatalytic mechanism of OVHAP is proposed based on the free radical trapping experiments. This work provides a novel strategy for improving the piezocatalytic performance of HAP, and expands its application in environmental remediation by harvesting mechanical energy. Hydroxyapatite with moderate oxygen vacancies is of excellent piezoelectric properties for the unique function of oxygen vacancies inducing the transformation during the alignment of hydroxyl dipoles from disorderly to parallel. • Hydroxyapatites with different oxygen vacancy concentrations were synthesized. • The introduction of oxygen vacancies induced the hydroxyl dipole reorientation in HAP. • Hydroxyapatite with moderate oxygen vacancy concentrations exhibits enhanced piezocatalysis. • The possible piezocatalytic mechanism of OVHAP is proposed.