Recent advances in the characterization and applications of biochar and hydrochar

The conversion of biomass into carbon-rich materials, biochar and hydrochar, has emerged as a promising strategy to solve pressing environmental challenges while supporting sustainable industrial development. A comprehensive analysis of recent advances in the characterization and application of these materials, is provided, emphasizing their distinct production methods, physicochemical properties, and functional versatility. Biochar, typically obtained by pyrolysis at high temperatures, has a high porosity, aromaticity, and thermal stability, making it well-suited for applications such as CO2 capture, electro-chemical energy storage, catalysis, and soil improvement. In contrast, hydrochar, produced by hydrothermal carbonization in aqueous media at moderate temperatures, retains a higher number of surface functional groups and heteroatoms, offering advantages in aqueous-phase catalysis, pollutant adsorption, and bioremediation. The critical role of physicochemical characterization in optimizing material performance is outlined, and analytical techniques including liquid nitrogen adsorption, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, infrared spectroscopy, Boehm titration, and thermogravimetric analysis are discussed. These show how physical-chemical characteristics such as surface area, functional group chemistry, and degree of graphitization, govern the materials’ suitability for specific applications. Emerging uses in waste water treatment, biofuel production, animal feed, and advanced oxidation processes are examined, alongside their relevance to multiple UN Sustainable Development Goals, particularly in climate action, clean energy, and responsible production. The materials are versatile and can be produced on a large scale. Their performance can be fine-tuned using different production and post-treatment processes, making them key enablers in the transition to a circular, carbon-conscious economy.