Fabrication of photostable ternary CdS/MoS2/MWCNTs hybrid photocatalysts with enhanced H2 generation activity

Abstract

This article reports the synthesis and photocatalytic H2-generation of pristine and CdS-based hybrid photocatalysts. Acid-treated-multi-walled carbon nanotubes (a-MWCNTs) and colloids of the exfoliated two-dimensional MoS2 nanosheets were used for the preparation of binary CdS/a-MWCNTs and ternary CdS/MoS2/a-MWCNTs nanocomposites. Controlled exfoliation of as-synthesized bulk marigold flower-like MoS2 to few-layer MoS2 nanosheets shows a strong absorption and photoluminescence, indicating an indirect to direct bandgap transition. The visible-light photocatalytic H2-evolution performance of the ternary nanocomposites was superior to that of the binary and pure photocatalysts. Transient photocurrent results revealed that the ternary nanocomposite exhibits a maximum photocurrent density of 11.12mA/cm2, which is 12 times higher than that of pristine CdS. This enhanced H2-generation performance and photocurrent response is attributed to the CdS/MoS2 heterojunction, which increases charge-separation efficiency of the composite. Furthermore, the presence of a-MWCNTs, as a co-catalyst/support, accounts for this excellent performance involving electron transfer from photoexcited CdS to MoS2 edges through a-MWCNTs; this transfer results in enhanced charge separation. This enhanced charge-separation efficiency and photostability was demonstrated using a suitable mechanism, which was evident from photocurrent measurements and photoluminescence data. In such ternary hybrids, metal co-catalysts showed H2-evolution activity with the following order: Pd>Ni>Au>Ag>Cu. This work further highlights the role of MoS2/CNTs p-n junction embedded in CdS which serves as a promising heterojunction that promoted hydrogen production.