Nanoscale heterostructures for photoelectrochemical water splitting and photodegradation of pollutants

Rapid depletion of fossil fuels, surging demands for energy and concerns for environment have inspired the exploration of renewable energy sources including solar energy. Efficient utilization of solar energy mainly relies on the discovery of materials with superior electronic and optical properties for effective light-matter interaction. These materials should have suitable band gap energies for visible light absorption and appropriate band edge locations for generation, rapid transfer and suppressed recombination of charge carriers. Heterostructuring of multiple materials with controlled interfaces and spatial configuration is critical to meet these requirements and holds potential for applications such as photoelectrochemical water splitting. This review article focuses on fundamentals of nanoscale heterostructures and four types of charge transfer/separation mechanisms: charge dissipation through conductive path, charge separation through plasmonic nanoparticles, sensitization of wide band gap semiconductors and charge separation through staggered band gap. Other aspects such as large surface area and multifunctionality from heterostructuring are also discussed. Finally, characterization techniques for understanding photocatalytic activity, charge transfer and band gap energy of the nanoscale heterostructures are described.