Janus nanostructures for heterogeneous photocatalysis

Water treatment, the hydrogen evolution reaction, and carbon capture are examples of the potential applications for solar photocatalysis. This has led to significant effort in the search for suitable heterogeneous catalysts. However, materials developed to-date often suffer from disadvantages such as charge recombination, low quantum efficiency, chemical instability, and poor economy of production/operation. These factors have made it difficult for the technology to develop beyond laboratory demonstrations. A potential solution to the problem lies with the appropriate design of the catalyst itself, particularly with respect to particle morphology. This review aims to highlight recent efforts directed towards the development and application of an anisotropic, bi-phasic heterodimer, or "Janus" catalyst. While the topic is in its relative infancy, it has been shown that a Janus morphology can improve catalyst performance by almost an order of magnitude. Hence, a systematic review has been undertaken to highlight and assess recent advances in this field. The review begins with the fundamentals of heterogeneous photocatalysis and proceeds to classify modern catalysts, including Janus particles. This is followed by a detailed description of the relevant studies involving Janus morphology and their demonstrated photocatalytic applications. Finally, an overview of the current challenges and future prospects is discussed along with a summary of the key highlights. It is observed that a Janus morphology can impart several intriguing advantages such as amplification of electric near-field and efficient charge separation. In order to unlock the full potential of Janus photocatalyst, further research in this direction is warranted.