UV–vis spectra were carried out in the supernatant of both vitamins@P25TiO2NPs samples after centrifugation to measure the amount of unbound vitamin. Standard curves at 375 nm and 255 nm were done for vitamin B2 and C, respectively, using a Synergy BioTeK multi-mode microplate reader.
Barium sulfide is produced by carbothermic reduction of barium sulfate. Zinc sulfate is obtained from a variety of zinc products, often waste, by treatment with sulfuric acid.