(536h) Continuous-Flow Microwave Synthesis of Titania Nanotubes for Moisture Harvesting

Titania nanotubes are potential materials in multiple applications due to their high specific surface area, excellent photocatalytic activity, ion-exchangeable ability and superhydrophilic property. Synthetic methods of titania nanotubes have been extensively investigated, which include assisted-template method, sol-gel process, electrochemical oxidation, hydrothermal method and microwave-assisted synthesis. In this study, we report a highly efficient method for continuous synthesis of titania nanotubes. Titania nanotubes were synthesized by using anatase TiO₂ as precursor in concentrated NaOH at different heating temperature of 100 ^oC ~ 130 ^oC, under different pressure of 2 ~ 4 bar, and for different residence time of 15 min and 30 min via microwave-assisted flow synthesis method. The as-synthesized materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and micro-Raman. The optimum synthesis temperature, pressure and residence time were found to be 120 °C, 4 bar and 15 min, respectively.

Further, the titania nanotubes were modified to provide moisture harvesting property. The moisture harvesting materials were obtained by nano-confinement of low water activity (LWA) materials within the interlayer spaces of superhydrophilic titania nanotubes. The LWA material, consisting of cyclodextrin molecules covalently linked to the titania surface, attracts water vapor from atmosphere, and then the water accumulates on the superhydrophilic titania surface draining to form droplets on the tip of the nanotubes. The modified titania nanotubes could be a promising resource to supplement the ever-increasing water need.