Preparation of halloysite-derived mesoporous silica nanotube with enlarged specific surface area for enhanced dye adsorption

The enlargement of specific surface area of halloysite-derived nanotubes could benefit the performance and applications of halloysite mineral. In this work, we propose and demonstrate a novel approach to prepare halloysite-derived mesoporous silica nanotubes with substantial specific surface area. The specific surface area up to 608 m(2)/g is achieved from the natural halloysite (Hal) via a simple process of calcination, alkali-treating and acid-etching. The amorphous Si-O-Al network of the calcined Hal is alkali-treated, becoming an amorphous hydroxyl-enriched sodium aluminum silicate phase. The Al-O and Na-O compositions are selectively acid etched to in-situ develop mesopores within the residual silica framework, producing the hydroxyl-enriched mesoporous silica nanotubes. The alkali-treatment is crucial to determine the morphology and porosity of the final nanotubes. The optimized mesoporous silica nanotubes behave favorable monolayer adsorption with capacity of 618 mg/g for methylene blue, allowing a promising adsorbent in the future. (C) 2016 Elsevier B.V. All rights reserved.