A simple and novel synthetic route to prepare anatase TiO2 nanopowders from natural ilmenite via the H3PO4/NH3 process

Abstract

A simple and novel technique for the preparation of anatase TiO2 nanopowders using natural ilmenite (FeTiO3) as the starting material is reported. Digesting ilmenite with concentrated H3PO4 under refluxing conditions yields a white α-titanium bismonohydrogen orthophosphate monohydrate (TOP), Ti(HPO4)2·H2O, which can be easily isolated via gravity separation from unreacted ilmenite. The addition of ammonia to the separated TOP followed by calcination at 500°C completes the preparation of anatase TiO2. Calcination at temperatures above 800°C converts the anatase form of TiO2 to the stable rutile phase. The removal of iron from ilmenite during the commercial production of synthetic TiO2 is problematic and environmentally unfriendly. In the present study, the removal of iron was found to be markedly simple due to the high solubility of iron phosphate species in concentrated H3PO4 with the precipitation of TOP. The titanium content of the prepared samples on metal basis with silica and phosphorous as major impurities was over 90%. Prepared TiO2 samples were characterized using X-ray fluorescence, Fourier-transform infrared spectroscopy, Raman spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, and X-ray diffraction analyses. The photocatalytic potentials of the commercial and as-prepared TiO2 samples were assessed by the photodegradation of rhodamine B dye.