Current trends in environmental and energy photocatalysis and ISO standardization

In this review, we report on the recent progress in photocatalysis, emerging trends, and ISO standardization for various energy and environmental applications. Photocatalysis can address several critical environmental issues by utilizing inexhaustible solar energy and simple operational requirements. In principle, the construction of an ideal photocatalytic material can enable hydrogen production, synthetic fuels, mitigation of excess environ-mental CO2, N2 reduction to useful NH3, elimination of environmental toxicants, biohazardous waste decon-tamination, and chemical synthesis reactions. Despite decades of intense research, significant challenges remain before a practical implementation of photocatalysis can be realized for primary applications. Current challenges can be overcome by developing highly efficient materials while overcoming the associated costs in comparison to existing technologies available for specific applications. Specifically, the following emerging engineering design principles have been discussed: (i) surface and interfacial engineering, (ii) defects engineering, (iii) metals as cocatalysts and plasmonic materials, and (iv) heterostructured materials. Special attention is also paid to the sustainability aspects of photocatalysis, especially immobilization, recovery of materials, and miniaturized photoreactors. The emergence of novel photocatalytic materials and applications has made it difficult to make a relative performance comparison due to the lack of a commonly implemented evaluation scale. In this regard, currently available and under development ISO standards pertaining to the evaluation of photocatalytic activity are briefly described and discussed from a critical perspective. An in-depth discussion on the current challenges and prospects of photocatalysis is also presented.