Ag Nanoparticle-Decorated Carbon Nanotube Sponges for Removal of Methylene Blue from Aqueous Solution

We fabricate a hybrid 3D porous composite as an effective adsorbent for the removal of methylene blue (MB) dyes from aqueous solutions. In this hybrid composite, carbon nanotube (CNT) sponge grown by a chemical vapor deposition (CVD) method was utilized as a porous scaffold due to its large surface area. We decorated the surface of CNTs with a polydopamine layer in order to improve the hydrophilicity of CNT sponge (CNTS) and subsequently deposit silver nanoparticles (AgNPs) onto the surface of CNTs. The polydopamine layer acting as a strong binder plays a crucial role in the successful incorporation of AgNPs onto the surface of CNTs. AgNPs in composites act as a catalyst for the chemical degradation of MB dyes. The incorporation of AgNPs in the networks of CNTS provide a simple and efficient approach for recycling the adsorbents through the chemical reduction of MB dyes. Without the needs to disperse CNTs in MB aqueous solutions and subsequently collect the CNTs with adsorbed MB molecules, CNTS based composites as dye absorbents have the advantage of being efficiently recyclable. The presence of a polydopamine layer significantly improved the adsorption capacities in the networks of CNT-based composites due to the dramatic increase of wettability of CNTS in MB aqueous solutions. In addition, under an electric field the adsorption capacities of CNT-based composites are further improved and the adsorption kinetics of MB molecules are enhanced due to an increase of the diffusion rate of cationic MB dye in the networks of CNT-based composites.