In order to systematically understand the hydrothermal carbonization reactions and kinetics of glucose at 180 °C, the structures of intermediate and final chemical products were identified, the conversion paths were clarified, and the conversion rates and yields were calculated. By comparing the hydrothermal reaction paths and kinetics of 5-hydroxymethylfurfural (HMF), fructose, and glucose, it is proven that HMF is the most important intermediate and the sole precursor of hydrothermal carbon. The degradation of glucose, fructose, and HMF follows the first-order reaction, and the formation of hydrothermal carbon linearly depends on the conversion of HMF. Approximately 28% of HMF is converted from fructose and ∼72% is from glucose. Also, the hydrothermal reaction time-dependent morphologies and structures of the resulting hydrothermal carbon are compared, and their structures before and after heat treatment are characterized.

Utilization of carbon materials for harvesting solar energy is a green, feasible, sustainable, and promising way to manufacture freshwater from sewage and seawater. However, sunlight absorption efficiency, light to thermal conversion efficiency, and expensive cost are still limitations for large‐scale solar steam generation. Here, a solar steam evaporator which is fabricated by carbonized willow catkins films and activated by different metal chlorides under nitrogen at 800 °C is demonstrated. Under the light irradiation intensity of one sun (1000 W m−2), water evaporation rate of the prepared evaporator is up to ≈2.17 kg m−2 h−1, and the surface temperatures reach up to 50 and 91.7 °C under water‐saturated and dry situations, respectively, indicating good steam generation ability and heat localization performance of the fabricated evaporator. The SEM, BET, DSC, and ICP‐MS results show that such a high water evaporation rate of the prepared carbon materials is due to the typical tubular micro‐structure, which decreases water enthalpy of evaporation and the water evaporation in the form of molecular clusters. This method of carbonized and activated willow catkins films provides a sustainable way for efficiently harvesting solar energy to produce fresh water from seawater and sewage.

The fiber spinning methods determine the formation of the physical structures of polyacrylonitrile (PAN) fibers which further affect stabilization reactions and the mechanical performances of the resultant carbon fibers. In this study, PAN fibers were prepared by both dry-jet gel spinning (g-PAN) and dry-jet wet spinning (w-PAN), and their stabilization behaviors were compared. While the stabilized w-PAN fibers show sheath-core structures, the stabilized g-PAN fibers exhibit relatively uniform stabilized structures along the radial direction. Additionally, the stabilization reactions of g-PAN fibers occur faster than that of w-PAN fibers, and the cyclization, oxidation, and crosslinking reaction activation energies of g-PAN fibers are lower than that of w-PAN fibers, respectively. Moreover, the carbon yield of g-PAN is higher than that of w-PAN fibers. We believe that above changes are possibly ascribed to the formation of different PAN sheath structures and oriented chain structures during dry-jet wet spinning and dry-jet gel spinning. It is concluded that gel spinning could significantly reduce the sheath-core difference of PAN fibers and the stabilized fibers as compared with wet spinning, which leads to a faster stabilization and more uniform stabilized structures.