Exploration of photo-catalytic activity of nano-hydroxyapatite based on the crystallographic parameters: Estimation of crystallite size using X-ray diffraction data

Nano-hydroxyapatite was synthesized from CaCO3 and waste eggshells reacting with ortho-phosphoric acid, and titanium was doped to enhance the photocatalytic activity. The sample was characterized by X-ray diffraction technique, and different crystallographic parameters were explored focusing on crystallite size, microstrain, crystallinity index, lattice parameter, degree of crystallinity, microstrain, volume fraction of beta-TCP, percentage of HAp, percentage of beta-TCP, dislocation density, volume of unit cell, etc. To justify nano-crystallite size different models and equations such as the Williamson-Hall plot, linear straight -line model, Monshi-Scherrer model, Sahadat-Scherrer model, etc were employed. The effects of photocatalytic activity of synthesized hydroxyapatites were evaluated by varying the dye concentration, pH, interaction time, catalyst dose, and light source (halogen and sunlight). The photocatalytic activity was evaluated by degrading Congo Red dye and a relation was built between crystallographic parameters and catalysis. An easy degradation mechanism was also proposed for the Congo red dye using hydroxyapatite.