Facile Synthesis of Titanium Phosphates from Ilmenite Mineral Sand: Potential White Pigments for Cosmetic Applications.

Ilmenite mineral sand was used to synthesize titanium bismonohydrogen orthophosphate monohydrate, Ti(HPO4)2·H2O, and titanium phosphate, TiP2O7, two white pigments suitable in cosmetic applications. Ti(HPO4)2·H2O was obtained after digesting ilmenite in 85% phosphoric acid at 150 °C for 5 hours. On standing, unreacted ilmenite and white Ti(HPO4)2·H2O solid separated into two layers and Ti(HPO4)2·H2O was calcined at 900 °C to obtain the crystalline TiP2O7. Chemical and morphological characteristics were investigated using X-ray diffraction, transmission electron microscopy, scanning electron microscopy coupled with energy dispersive X-ray analysis, Fourier-transform infrared, and X-ray photoelectron spectroscopic techniques. The water retention (WR) capacities were measured at a relative humidity of 57% and indicate that Ti(HPO4)2·H2O and TiP2O7 have increased WR ability when compared with the pigment grade (PG) TiO2. The optical properties of Ti(HPO4)2·H2O, TiP2O7, and PG-TiO2 were compared using Ultraviolet-visible diffuse reflectance spectroscopy. The relative photoactivity of Ti(HPO4)2·H2O and TiP2O7 was determined using a chemical method based on the photobleaching behavior of a stable radical, 1,1-diphenyl 2-picrylhydrazyl. The photoactivities of Ti(HPO4)2·H2O and TiP2O7 are lower than that of PG-TiO2.