Large scale synthesis of Janus nanotubes and derivative nanosheets by selective etching

• A facile approach to large scale synthesis of Janus nanotubes by selective etching is demonstrated.
• The composition of the Janus nanotubes can be further extended by a favorable growth of other functional materials.
• The application of the Janus nanotubes in magnetic separation and as solid dispersants is demonstrated.
• The Janus nanotube can be extended to derivative nanosheet after being further crushed.
• The method can be scaled up and economical.

One-dimensional Janus nanotubes have been successfully synthesized in large quantity by selective etching of the interior Al2O3 from hydrophobically modified halloysite nanotube with the exterior surface preserved. By simply tuning the etching time, the colloid shape evolves from nanotubes to partially collapsed nanotubes and porous nanorods. The microstructure and chemical composition of the etched hydrophobically modified halloysite are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), FT-IR spectrophotometer and nitrogen adsorption–desorption. The results indicate the interior Al2O3 can be controlled etched. Labeling experiments demonstrate the hydrophilic nanoparticles are predominantly located onto the coarse region of the etched nanotubes. Selective etching of hydrophobically modified halloysite creates Janus nanotubes with a hydrophobic exterior surface and a hydrophilic interior surface. An enhanced capacity for emulsification of the Janus nanotubes toward immiscible mixture is shown. Furthermore, by a favorable growth of other functional materials, composition of the Janus nanotubes can be further extended, enabling different applications from magnetic separation to water purification, drug immobilization and controlled release. After crushing the Janus nanotubes, derivative nanosheets are derived. The method can be scaled up and economical compared with other method, which is the key to further exploit practical application.

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