Influence of surface-functionalized multi-walled carbon nanotubes on CdS nanohybrids for effective photocatalytic hydrogen production

Abstract

Carbon nanotubes (CNTs) have enormous potential for application due to their extreme hydrophobicity. Further, their physico-chemical properties can be modified by surface functionalization. Acid functionalization of CNTs is one of the basic methodology for modification of their electro-chemical properties, resolving the poor dispersion capability, and improving the surface-active sites to enhance the photocatalytic efficiency. However, the role of surface functional groups on CNTs for water-splitting in association with CdS photocatalysts has not yet been sufficiently explored. Hence, in the present study, we report the influence of surface-functionalized CNT-metal nanoparticle (NP) hybrids attached to CdS nanorods for enhanced photocatalytic H2 production. Significant improvement in photocatalytic H2 production was observed for binary composites such as amine (Nf-), sulfonic (Sf-), and ascorbic acid (Af-) functionalized CNTs and CdS nanorods. Furthermore, the secondary functionalized Af-CNTs were incorporated with metal NPs and the photocatalytic activity was significantly improved in ternary metal-Af-CNT/CdS nanohybrids. Among the metal NPs, Pt- incorporated into Af-CNTs and its CdS nanohybrid led to the highest rate of H2 production (120.1 mmol h−1 g−1), corresponding to a 48-fold enhancement relative to that of pure CdS. The enhanced rate of H2 production is attributed to the influence of the surface functional groups on the CNTs. The intimate interfacial contact between CdS, functionalized CNTs and metal NPs leads to enhanced photocatalytic performance, as a contributing factor for improving photogenerated charge separation and transportation. Moreover, the functional groups on CNTs (Pt-Af-CNT/CdS) led to obvious advantages, such as enhanced photoactivity and photostability of CdS for H2 production. The photocatalytic performance of these nanohybrids was found to be highly influenced by the surface states of the CNTs, suggesting the importance of surface treatment of materials for H2 evolution.