Ilmenite Ore-derived Lepidocrocite-type of High Purity Titanate Nanotubes for Methylene Blue Photodegradation

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Abstract
The synthesis of high-purity lepidocrocite-type titanate nanotubes from natural ilmenite minerals remains challenging due to the presence of iron impurities and the limited understanding of their structural stability during thermal treatment. This study presents a controlled purification and hydrothermal synthesis route for producing high-purity lepidocrocite-type titanate nanotubes from ilmenite-derived titanium dioxide (TiO₂) nanoparticles. Titanium oxosulfate (TiOSO₄) leachate obtained from the sulfate process was prepared via ethylenediaminetetraacetic acid (EDTA)-assisted purification, yielding TiO₂ nanoparticles with a purity of 99%, which were subsequently converted into titanate nanotubes by hydrothermal treatment. Structural characterization confirmed that the nanotubes retained their multilayered lepidocrocite-type titanate (H₂Ti₃O₇) structure after calcination up to 300°C while exhibiting improved crystallinity and a well-defined tubular morphology. The optimized sample (PF300) exhibited the highest specific surface area (256.9 m²g⁻¹) and pore volume (0.54 cm³g⁻¹), together with a direct band gap of 3.29 eV. Photocatalytic performance was evaluated through the degradation of methylene blue (MB), achieving removal efficiencies of 98% and 96% under ultraviolet and visible light irradiation, respectively. The outstanding performance originated from the synergistic effect of adsorption and photocatalysis, with preserved tubular morphology, a layered lepidocrocite structure, a high specific surface area, favorable optical properties, and efficient charge separation. These findings demonstrate that EDTA-assisted purification combined with controlled thermal treatment provides an effective strategy for producing high-performance lepidocrocite-type titanate nanotubes from natural ilmenite, with promising potential for solar energy-harvesting applications.