Sol–gel synthesis and characterization of calcium-deficient hydroxyapatite photocatalysts suitable for hydrogen production: influence of the drip rate in the photocatalytic activity

In the present work, the sol–gel synthesis of calcium-deficient hydroxyapatite samples is reported, under four different drip rates, to investigate their effects on their photocatalytic activity in the water splitting reaction, under UV irradiation. The results of the structural and chemical composition characterizations show that the increase in the drip rate has a negative effect on the stoichiometry, inducing significant deficiencies in the calcium and oxygen content. Likewise, the values of the band gap and valence band energies were determined, showing a correlation between them, and the deficiencies of Ca, O and OH induced by the drip rate. Finally, the photocatalytic production of hydrogen in the presence of the synthesized samples was evaluated, showing in all cases production rates much higher than that obtained by using Degussa P25 as a photocatalyst, under the same conditions.