• Biochar and hydrochar are carbon-rich materials derived from biomass via pyrolysis and hydrothermal carbonization, respectively, with distinct physicochemical properties.
• Biochar exhibits high porosity, aromaticity, and thermal stability, making it suitable for CO2 capture, energy storage, catalysis, and soil improvement.
• Hydrochar retains more surface functional groups and heteroatoms, offering advantages in aqueous-phase catalysis, pollutant adsorption, and bioremediation.
• Comprehensive characterization using techniques like N2 adsorption, SEM, XRD, XPS, Raman, FTIR, Boehm titration, and TGA is essential for optimizing performance in diverse applications.