Carbon nanotubes (CNTs) are promising nanomaterials that have the potential to revolutionize water and waste treatment practices in the future. The direct use of unbounded CNTs, however, poses health risks to humans and ecosystems because they are difficult to separate from treated water. Here, we report the design and synthesis of carbon nanotube ponytails (CNPs) by integrating CNTs into micrometer-sized particles, which greatly improves the effectiveness of post-treatment separation using gravitational sedimentation, magnetic attraction, and membrane filtration. We further demonstrate that CNPs can effectively perform major treatment tasks, including adsorption, disinfection, and catalysis. Using model contaminants, such as methylene blue, Escherichia coli, and p-nitrophenol, we show that all the surfaces of individual CNTs in CNPs are accessible during water treatment. Hierarchical structures containing CNPs can be employed in a multitude of nano-material engineering applications, such as water and waste treatment.
 This invention was made with government support under Grant No. CBET-1033848 awarded by the National Science Foundation and Grant No. CFP-12-3923 awarded by the Department of Energy. The government has certain rights in the invention.