Synthesis of different types of nano-hydroxyapatites for efficient photocatalytic degradation of textile dye (Congo red): a crystallographic characterization

Abstract

The textile industry, a vital economic force in developing nations, faces significant challenges including the release of undesired dye effluents, posing potential health and environmental risks which need to be minimized with the aid of sustainable materials. This study focuses on the photocatalytic potential of hydroxyapatite together with different dopants like titanium-di-oxide (TiO₂) and zinc oxide (ZnO). Here, we synthesized hydroxyapatite (HAp) using different calcium sources (calcium hydroxide, calcium carbonate) and phosphorous sources (phosphoric acid, diammonium hydrogen phosphate) precursors through a wet chemical precipitation technique. Pure and doped HAp were characterized via different technologies, which consist of X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), as well as UV-vis spectroscopy. The effectiveness of the synthesized photocatalyst was evaluated by its interactivity with synthetic azo dyes (Congo red). The photodegradation of Ca(OH)₂_HAp, CaCO₃_HAp, ZnO-doped HAp as well as TiO₂-doped HAp, were obtained as 89%, 91%, 86%, and 91%, respectively. Furthermore, at neutral pH, TiO₂-doped HAp shows the highest degradation (86%), whereas ZnO-doped HAp possesses the lowest degradation (73%). Additionally, various XRD models (Monshi–Scherrer's, Williamson–Hall, and Halder–Wagner methods) were employed to study crystallite dimension.