Nanoparticles enwrapped with nanotubes: A unique architecture of CdS/titanate nanotubes for efficient photocatalytic hydrogen production from water

CdS/titanate nanotubes (CdS/TNTs) photocatalysts with a unique morphology were successfully synthesized via a simple one-step hydrothermal method. Compared with traditional CdS@TNTs composite photocatalysts prepared by the common two-step method, CdS/TNTs exhibited much higher activity for photocatalytic hydrogen evolution under visible light irradiation. Transmission electron microscopy (TEM) revealed that the CdS nanoparticle was intimately enwrapped by the surrounding TNTs. This unique architecture resulted in the appropriate dispersion of CdS nanoparticles and the intimate multipoint contacts between the CdS nanoparticle and TNTs, which led to significant enhancement of charge separation in CdS/TNTs. Accordingly, the photoactivity was improved. Meanwhile, X-ray powder diffraction (XRD) demonstrated that the highly crystalline hexagonal CdS was obtained in CdS/TNTs, which was also essential for the enhanced photocatalytic performance. The unique morphology and photocatalytic activity of CdS/TNTs were influenced by the Cd/Ti molar ratio with an optimal value of 0.05. Under this condition, the CdS amount was only 6 wt% of the total photocatalyst, which was important from an environmental point of view. The influence of loaded Pt on the activity of CdS/TNTs had also been investigated. The hydrogen production rate of 2.0 wt% Pt-loaded CdS/TNTs reached 353.4 μmol h^-1, with the apparent quantum yield of 25.5% at 420 nm. This study provides a potential way to synthesize highly efficient composite photocatalysts with a novel architecture.