Leaf-inspired hierarchical porous CdS/Au/N-TiO2 heterostructures for visible light photocatalytic hydrogen evolution

Photosynthesis has been for many years a fascinating source of inspiration for the development of model systems able to achieve efficient solar-to-chemical transduction. In the hot field of artificial photosynthesis, considerable progress has been made toward converting solar energy into the carbon-free fuel "hydrogen" through photocatalytic water splitting. Here, we report a promising photocatalytic system with both desirable morphology and suitable band-gap configuration for efficient visible light water splitting. Such photocatalyst is realized by the inspiration from leafs morphology and photosynthesis basic mechanism - Z scheme reaction. The unique architectures - hierarchical macro/mesoporous morphology of natural leaves are retained in the man-made systems to enhance overall light harvesting and to offer more absorption and reaction sites for the catalytic reactions. The photocatalytic modules - CdS(shell)/Au(core)/N-TiO2 heterostructures are served as a prototype here to demonstrate this concept, in which N-TiO2 and CdS serve as PS II and PS I, respectively, while Au acts as the electron transfer mediator, contributing to the enhancement of electron hole separation and interfacial charge transfer. The CdS(shell)/Au(core)/N-TiO2 heterostructures are obtained via a two-step photodeposition method. The particle sizes of Au cores, the contents and thicknesses of CdS shells are controlled by varying the synthetic parameters (e.g. irradiation time) to obtain an optimized activity. The H-2 evolution rates of optimized CdS/Au/N-TiO2 heterostructures are about 2.6 times of N-TiO2 under UV/visible light, and about 270 times of Au/N-TiO2 under visible light irradiation. The systems have high visible light harvesting, high hydrogen evolution rate and long electron-hole lifetimes compared with non-incorporated systems. The design of this system is based on both biological morphology and mechanism paradigms, which would provide a proof of concept for the bio-inspired design of artificial photosynthetic system for enhanced photocatalytic performance. (C) 2013 Elsevier B.V. All rights reserved.