Photocatalytic, recyclable CdS nanoparticle-carbon nanotube hybrid sponges

Semiconducting nanoparticles with lower bandgap (e.g., CdS) are alternative photocatalysts to TiO2, since they have a potentially wider range light of absorption and improved catalytic efficiency. However, they must be securely anchored on a porous substrate for practical applications. Here, we report a hybrid porous photocatalyst fabricated by grafting 4-6 nm diameter CdS nanoparticles uniformly throughout the entire macroporous structure of a three-dimensional carbon nanotube (CNT) sponge. The unique feature of our structure is that only the CdS nanoparticles grafted on the outside surface are active in photocatalysis, while other nanoparticles are stored inside the sponge in the fresh state for use when the catalyst is recycled. Our CdS-CNT hybrid sponges show high efficiency in removing organic contaminants from water. Spectroscopic measurements show that the hybrid sponges are multifunctional, simultaneously performing organic molecular adsorption (using the inter-CNT spacing), and photocatalytic decomposition (by the CdS nanoparticles grafted on the surface), both of which contribute to water purification. Furthermore, the surface part of the sponges can be stripped off to expose inner nanoparticles for use when the catalyst is recycled, without performance degradation.