J. Cosmet. Sci., 70, 149–159 (May/June 2019) 149 Facile Synthesis of Titanium Phosphates from Ilmenite Mineral Sand: Potential White Pigments for Cosmetic Applications LALINDA PALLIYAGURU, M. USHAN S. KULATHUNGA, K. G. UPUL R. KUMARASINGHE, CHAMPA D. JAYAWEERA, and PRADEEP M. JAYAWEERA* , Department of Chemistry, University of Sri Jayewardenepura, Nugegoda, Sri Lanka (L.P., M.U.S.K., K.G.U.R.K., C.D.J., P.M.J.) Accepted for publication June 8, 2019. Synopsis 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 refl ectance 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. INTRODUCT ION Pigment-g rade (PG) titanium dioxide (TiO2) has a number of applications in the cosmetic industry (1–3). Skin care products that use PG-TiO2 have several disadvantages, e.g., certain degree of photocatalytic breakdown of sebum which provides lubrication and protection to the skin from infections (4,5). In addition, it has been reported that nanoscale TiO2 could penetrate into the body through the skin, causing health risks (6,7). Mixing of silicon dioxide (SiO2) with PG-TiO2 has been recently investigated in view of mini- mizing the sebum breakdown and absorption through the skin (6). Application of SiO2-TiO2 composite in cosmetics has been severely hampered by the hardness of the composite Address all correspondence to P. M. Jayaweera at pradeep@sjp.ac.lk .

JOURNAL OF COSMETIC SCIENCE 150 compared with PG-TiO2. This opens up an opportunity for a new substitute to replace the PG-TiO2 or TiO2-SiO2 in the cosmetic industry. Titanium phosphates (TPs) are gentle white powders and weakly photoactive (8,9). Therefore, TPs are potential candidates for replacing PG-TiO2 or TiO2-SiO2. Usually, TPs are synthesized using titanium com- pounds, such as titanium chloride and sulfate (10–13). The decomposition of sphene, CaTiOSiO4, by H3PO4 has also been successfully used to synthesize TPs (14). The direc t use of a natural material to synthesize TPs has environmental and economic advantages. The common natural titanium-rich minerals used in the TiO2 manufacturing process are rutile, ilmenite, and leucoxene (15). Ilmenite (FeTiO3) is currently the most common feedstock because many rutile deposits are becoming depleted through com- mercial use (16,17). The prese nt investigation reveals a simple, low-cost method to synthesize titanium bis- monohydrogen orthophosphate monohydrate (TOP) and TP with the chemical formulae of Ti(HPO4)2·H2O and TiP2O7 respectively, using a natural starting material of ilmenite mineral sand. The optical properties, the water retention (WR) capacities, and the pho- toactivities of the synthesized TPs were compared with PG-TiO2 to assess the suitability of these materials for the cosmetic industry. EXPERIMENT AL SECTION In a typic al experiment, TOP, i.e., Ti(HPO4)2·H2O was synthesized by digesting 100 g of ilmenite (Lanka Mineral Sands Limited, Rajagiriya, Sri Lanka) and 400 mL of 85% H3PO4 (Daejung Chemicals, Siheung-si, South Korea) for 5 h with vigorous stirring at 150 °C. The reaction mixture was allowed to cool and settle down at room temperature. Dense unreacted ilmenite (gray black color) settled down to the bottom of the vessel rapidly, whereas less dense solid TOP (white color) slowly settled as two very distinct solid layers (Figure 1). Leachate was carefully decanted and the solid TOP layer was sepa- rated out from the unreacted ilmenite and thoroughly washed with distilled water several times to remove any trace acid. TOP was dried at 80 °C and stored in a desiccator for further use. The resulted TOP was converted to TP by calcining (box-type resistance furnace SX-2.5-10, Zhejiang Top Cloud-Agri Technology Co. Ltd, Zhejiang, China) at 900 °C for 4 h. X-ray diffrac tion (XRD) patterns of ilmenite and the synthesized TPs were analyzed us- ing XRD instrument (Rigaku Ultima-IV, Rigaku, Tokyo, Japan) equipped with Cu Kα source and scintillation detector. The morphology of the powder materials were investi- gated by the high-resolution transmission electron microscopy (HR-TEM ZEISS Libra 200 Cs-TEM, Carl Zeiss AG, Oberkochen, Germany) at an accelerating voltage of 200 kV. An energy-dispersive X-ray (EDX) analysis coupled with (scanning electron microscopy, Zeiss EVO 18, Carl Zeiss AG) microscope was also used to obtain the elemental identi- fi cation of the samples. X-ray photoelec tron spectroscopic (XPS) analyses were carried out with Axis Ultra DLD spectrometer (Kratos, Kratos Analytical Ltd, Manchester, UK) using a monochromatic Al Kα source. Instrument base pressure was 8 × 10-10 Torr. The XPS spectra were collected using an analysis area of ~300 × 700 μm. The pass energy of 160 and 20 eV were used for wide and narrow spectra, respectively. The charge neutralizer system was used for all analyses. Curve fi tting of raw data was performed using XPS Peak Fit software Version 4.1