Synthesis of hierarchical hollow sodium titanate microspheres and their application for selective removal of organic dyes

Titanate-based materials are attractive inorganic adsorbents for wastewater treatment. In this study, hierarchical hollow sodium titanate microspheres (HHSTMs) were successfully synthesized via a template-assisted method. Silica microspheres were selected as hard templates, with a uniformly smooth TiO₂ shell first grown onto the surface of the SiO₂ cores. Then, through an alkaline hydrothermal process, the silica core was removed and the TiO₂ shell gradually converted into a sodium titanate shell with a preserved morphology. The as-synthesized HHSTMs are constructed from twined nanobelts, with a high surface area of 308 m² g⁻¹. A typical organic dye, methylene blue, was employed to investigate the adsorption properties of the HHSTMs. The adsorption process matched well with the Langmuir isothermal model, with the maximum adsorption capacity of methylene blue reaching 443 mg g⁻¹. Moreover, the resulting HHSTMs can be used to selectively capture of methylene blue from a cationic-anionic dye binary system due to their negatively charged surface. All adsorption processes were very fast and could complete in ten minutes.