Photocatalytic valorisation of real-world substrates

There are several key environmental sustainability challenges that the world needs to address over the next thirty years, particularly against the backdrop of achieving global net carbon zero emission this century. In addition to reducing global carbon emissions, the provision of clean “green” energy, reduction of water pollution and production of high value chemicals in a sustainable manner are clear priorities for sustainable economic growth. The photocatalytic valorisation of real-world substrates (waste biomass, plastic pollution and wastewater) is an opportunity to contribute significantly towards tackling water pollution, cutting CO₂ emissions and contributing to sustainably producing value added chemicals and hydrogen from waste materials and water contaminants/pollutants. To date, however, research is critically lagging in terms of the utilization of actual real-world substrates and instead concentrates on much simpler model compounds such as sugars, monomers, dyes and individual pollutants. Lack of progress in this field is further exacerbated by the general lack of scaling up of photocatalytic technology. Nevertheless, there are some pioneers who have explored the photocatalytic valorization of real-world waste materials which have been highlighted in this review. This review considers the application of semiconductor photocatalysis for such applications with a particular focus on valorisation of waste biomass (e.g. cardboard, grass, wood), plastic pollution (e.g. plastic bottles) and wastewater effluents (e.g. from juice processing factories) to produce hydrogen and value-added chemicals. Current engineering aspects are reviewed and discussed. A perspective of the role of photocatalysis in the circular economy is also discussed and an overall perspective and future outlook is presented.