Improvement in Sunlight-Irradiated Photocatalytic Activity and Stability of Ca10(PO4)6(OH)2/g-C3N4 for Dye Mixture Degradation

In this work, heterostructures formed by carbon nitride (CN) and hydroxyapatite (HAp) were successfully synthesized by the microwave-assisted hydrothermal method, varying the addition of CN in mass percentages (25-50%). Structural and spectroscopic analyses showed the formation of the CN/HAp heterostructure free from impurities with the presence of both phases, and morphological analyses showed the HAp nanorods together with the CN nanosheets. The obtained heterostructures enabled absorption in the visible region, with a band gap reduction from 5.43 eV (HAp) to 3.07 eV. The photocatalytic activity of the nanoparticles was evaluated under sunlight irradiation on the degradation of organic methylene blue (MB) and methyl orange (MO) dyes, and a mixture (MIX) of both. The heterostructure with 50% CN had degradation efficiency of up to 99% of MB and up to 81% of MO after 20 min. The reusability of the photocatalysts was tested in three cycles and showed improved photocatalytic activity of the heterostructure, maintaining its structural stability in the photodegradation of the dyes by at least 75%. Tests with inhibitors indicated that superoxide (O-2(-)) and hole (h(+)) are the active radicals, indicating that the obtained heterostructure is type I.