A Novel Nonchemical Approach to the Expansion of Halloysite Nanotubes and Their Uses in Chitosan Composite Hydrogels for Broad-Spectrum Dye Adsorption Capacity

A novel method based on cryoscopic expansion of halloysite nanotubes via frozen water molecules entrapped in their lumens and subsequent lyophilization was described. Detailed analyses confirmed that the inner and outer diameters as well as the surface area of the nanotubes could be efficiently increased without disturbing the inherent tubular structure. The benefits of cryo-expanded nanotubes for the enhancement of chitosan hydrogel performances were discussed. The composite hydrogels, depending on their compositions and morphologies, exhibited significantly enhanced swelling and mechanical properties compared with neat chitosan hydrogel. This effect was even more pronounced in the hydrogels containing cryo-expanded halloysite nanotubes. Although neat chitosan is a selectively good adsorbent for anionic dyes, in the presence of a small amount of cryo-expanded halloysite, the resultant composite hydrogel can establish a relatively high adsorption capacity for anionic and cationic dyes as a broad-spectrum dye adsorbent. (C) 2015 Society of Plastics Engineers