Fabrication of CN-HAp heterostructures from eggshells with improved photocatalytic performance in degrading of mixing dyes under sunlight

In this work, hydroxyapatite (HAp) and g-C3N4 (CN) heterostructures were synthesized by the microwave-assisted hydrothermal method (MAHM). The calcium precursor for HAp synthesis was obtained from white eggshells. The influence of increasing the CN mass percentage (60–95%) in the heterostructure was investigated through structural characterizations via XRD, morphological characterizations through FESEM, and optical properties by UV–Vis and PL. The XRD results indicated hydroxyapatite formation from the eggshells and the heterostructures showed high crystallinity. The morphological and optical characterizations indicate the interface region between the phases, leading to a decrease in the intensity of the photoluminescence (PL) of the heterostructures, as well as a widening of the wavelength absorption band in relation to the spectrum of emission from the CN evidencing the decrease in the recombination of the photogenerated charges. The photocatalytic performance of heterostructures was first studied in the degradation of crystal violet (CV) and methyl orange (MO) dyes under UV light irradiation, in which heterostructures containing 80% and 95% CN had better performance over a period of 120 min. The best heterostructures were tested in the degradation of CV, MO, and a mixture (MIX) of both dyes under sunlight irradiation. The results under solar irradiation showed that the heterostructures with 80% and 95% CN degraded the CV dye in more than 99%, the MO dye in more than 80% and the MIX in more than 80% in 120 min. Therefore, obtaining environmentally friendly and economically sustainable CN-HAp heterostructures is another interesting option for use in photocatalysis.