Remarkable progress has been made in the development of carbonized chitin nanofiber materials for various functional applications, including solar thermal heating, owing to their N- and O-doped carbon structures and sustainable nature. Carbonization is a fascinating process for the functionalization of chitin nanofiber materials. However, conventional carbonization techniques require harmful reagents, high-temperature treatment, and time-consuming processes. Although CO2 laser irradiation has progressed as a facile and second-scale high-speed carbonization process, CO2-laser-carbonized chitin nanofiber materials and their applications have not yet been explored. Herein, we demonstrate the CO2-laser-induced carbonization of chitin nanofiber paper (denoted as chitin nanopaper) and investigate the solar thermal heating performance of the CO2-laser-carbonized chitin nanopaper. While the original chitin nanopaper was inevitably burned out by CO2 laser irradiation, CO2-laser-induced carbonization of the chitin nanopaper was achieved by pretreatment with calcium chloride as a combustion inhibitor. The CO2-laser-carbonized chitin nanopaper exhibits excellent solar thermal heating performance; its equilibrium surface temperature under 1 sun irradiation is 77.7 °C, which is higher than those of the commercial nanocarbon films and the conventionally carbonized bionanofiber papers. This study paves the way for the high-speed fabrication of carbonized chitin nanofiber materials and their application in solar thermal heating toward the effective utilization of solar energy as heat.
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