Co‐Hydrothermal Carbonization of Cotton Stalks and MnO2 for Direct Solar Steam Generation with High Efficiency

Biomass‐based photothermal materials for solar steam power generation have been a recent research hotspot. However, despite the many research advances that have been made, many challenges remain. For example, high temperature carbonization leads to the loss of hydrophilicity, the surface coating is easy to peel off, hydrothermal carbonization (HTC) does not guarantee the photothermal performance, and hydrothermal carbonization fluid (HTC‐F) is difficult to handle. Herein, a new material (H‐CS/MnO 2 ) is prepared by co‐hydrothermal carbonization of cotton stalks (CS) and MnO 2 , and a stable and effective evaporation system is designed. While both ensure super hydrophilicity, the stable loading of MnO 2 leads to an excellent photothermal performance. Experimental results show that H‐CS/MnO 2 reaches 93.46% evaporation efficiency and the evaporation rate can reach 2.43 kg m −2 h −1 under 1 sun. Moreover, by means of recycling, not only the treatment of HTC solution is solved, but also the carbon dots are continuously enriched and exhibit certain photothermal effects during the recycling process. In addition, H‐CS/MnO 2 exhibited excellent salt resistance and corrosion resistance. The obtained condensate heavy ion concentration removal rate reached more than 99.9%. Therefore, the H‐CS/MnO 2 fabricated herein has the possibility of practical application in the future.