Solvent-Free Green Synthesis of Cu0.5Ti2(PO4)3 and Cu0.5TiO(PO4) NASICON-Type Compounds from Ilmenite Mineral Sand

Abstract

Ilmenite is a naturally available black or steel-gray color mineral, called titanium iron oxide, FeTiO3.
This valuable mineral comprises a significant amount of titanium that can be utilized as a titanium
source to synthesize various materials. This study focused on synthesizing copper titanium phosphate
compounds via an eco-friendly solid-state reaction route. α-titanium bismonohydrogen
orthophosphate monohydrate (α-Ti(HPO4)2.H2O/α-TiP), derived from beach sand ilmenite used as
the starting material for the synthesis. α-TiP was obtained by digesting ilmenite with 85 wt%
phosphoric acid under reflux conditions. The XRD pattern of the obtained white powder confirmed
the formation of α-TiP. The synthesized α-TiP and copper (Ⅱ) acetate were ground with different
molar ratios (1:2, 1:1, and 2:1) until it forms a fine powder following a solvent-free solid grinding
method. These powder mixtures were calcined at 800 °C for 4 hours utilizing a muffle furnace. The
obtained solid solutions developed green and two different shades of yellow color. The samples were
characterized by XRD, Thermogravimetry (DSC/TGA) techniques, and Raman spectroscopy. The
XRD results revealed the formation of solid solutions containing copper titanium phosphate
(Cu0.5Ti2(PO4)3) at 1:1 and 2:1 molar ratios of α-TiP to copper (Ⅱ) acetate while the products obtained
at 1:2 and 1:1 molar ratios confirmed the formation of copper titanium oxyphosphate (Cu0.5TiOPO4).
Moreover, TGA results confirm the development of these mixed metal phosphates which can be
further analyzed for applications in the ceramic industry. Therefore, calcination of the reaction
mixtures by changing the molar ratios produced different colored stable compounds that can
potentially be used as ceramic pigments, coatings, and electrode materials.

Keywords: Copper titanium phosphate, α-titanium bismonohydrogen orthophosphate monohydrate, Solid-state reaction route