CO 2 -laser-induced carbonization of calcium chloride-treated chitin nanopaper for applications in solar thermal heating.

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 CO 2 laser irradiation has progressed as a facile and second-scale high-speed carbonization process, CO 2 -laser-carbonized chitin nanofiber materials and their applications have not yet been explored. Herein, we demonstrate the CO 2 -laser-induced carbonization of chitin nanofiber paper (denoted as chitin nanopaper) and investigate the solar thermal heating performance of the CO 2 -laser-carbonized chitin nanopaper. While the original chitin nanopaper was inevitably burned out by CO 2 laser irradiation, CO 2 -laser-induced carbonization of the chitin nanopaper was achieved by pretreatment with calcium chloride as a combustion inhibitor. The CO 2 -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.