Capillary flow-driven efficient nanomaterials for seawater desalination: Review of classifications, challenges, and future perspectives

Solar energy is a sustainable energy source with many applications. Desalination of ocean/wastewater with solar energy has attracted considerable interest worldwide. However, solar desalination is a slow process with poor efficiency. In order to improve performance, highly efficient photothermal absorbers have been introduced. The main objective of the present work is to investigate capillary flow driven high broadband (full solar spectrum) absorptivity nanostructured absorbers for sea/wastewater treatment. The recent development in porous and self-floatable nanomaterial-enriched absorbers have improved the evaporation process through high broadband solar absorptivity (>95%) and porosity (>99%). One motivation of the research is to link the researchers of traditional absorbers to research on advanced materials, so the results of low-efficiency capillary materials are compared with the highly efficient materials. The ions in the seawater, including Na+, Mg2+, K+, Ca2+ and other contaminants before and after desalination, are investigated. Further, the effectiveness, best applicable material, challenges and future projections are described. The advanced nanostructured photothermal absorbers have the potential of being the most suitable candidates to be used in solar desalination systems. More improvements are needed in the absorbers stabilities, salt-blocking, scalability, lack of toxicity and affordability for commercialization.