This study investigates the molecular structure and physical properties of plant biomass-derived black carbon (biochar) produced at varying charring temperatures (100–700°C) using wood and grass as starting materials. The research employs BET-N₂ surface area, X-ray diffraction (XRD), synchrotron-based near-edge X-ray absorption fine structure (NEXAFS), and Fourier transform infrared (FT-IR) spectroscopy to analyze the physical-chemical transitions of chars. The results reveal four distinct char categories based on their molecular structure and physical state: (i) transition chars with preserved crystalline precursor materials, (ii) amorphous chars with randomly mixed heat-altered molecules and incipient aromatic polycondensates, (iii) composite chars with poorly ordered graphene stacks embedded in amorphous phases, and (iv) turbostratic chars dominated by disordered graphitic crystallites. These categories differ in their environmental persistence and sorption capabilities. The study highlights that as charring temperature increases, chars undergo structural changes, leading to increased surface area and more ordered structures. Wood chars exhibit higher surface areas and greater crystallinity compared to grass chars. NEXAFS and FT-IR analyses show that aromatic and quinonic compounds become more prevalent at 400°C, while condensation reactions begin at 500°C. At 600–700°C, chars become poorly crystalline, with increased long-range order and nanoporous structures. The research also discusses the environmental implications of these structural differences, noting that char persistence and sorption properties depend on their chemical and physical structure. The study emphasizes the importance of understanding the multiphase model of chars for accurate environmental assessments and applications, such as soil amendment. The findings suggest that char properties vary significantly based on biomass type and charring conditions, highlighting the need for further research to refine the classification and understanding of biochar.This study investigates the molecular structure and physical properties of plant biomass-derived black carbon (biochar) produced at varying charring temperatures (100–700°C) using wood and grass as starting materials. The research employs BET-N₂ surface area, X-ray diffraction (XRD), synchrotron-based near-edge X-ray absorption fine structure (NEXAFS), and Fourier transform infrared (FT-IR) spectroscopy to analyze the physical-chemical transitions of chars. The results reveal four distinct char categories based on their molecular structure and physical state: (i) transition chars with preserved crystalline precursor materials, (ii) amorphous chars with randomly mixed heat-altered molecules and incipient aromatic polycondensates, (iii) composite chars with poorly ordered graphene stacks embedded in amorphous phases, and (iv) turbostratic chars dominated by disordered graphitic crystallites. These categories differ in their environmental persistence and sorption capabilities. The study highlights that as charring temperature increases, chars undergo structural changes, leading to increased surface area and more ordered structures. Wood chars exhibit higher surface areas and greater crystallinity compared to grass chars. NEXAFS and FT-IR analyses show that aromatic and quinonic compounds become more prevalent at 400°C, while condensation reactions begin at 500°C. At 600–700°C, chars become poorly crystalline, with increased long-range order and nanoporous structures. The research also discusses the environmental implications of these structural differences, noting that char persistence and sorption properties depend on their chemical and physical structure. The study emphasizes the importance of understanding the multiphase model of chars for accurate environmental assessments and applications, such as soil amendment. The findings suggest that char properties vary significantly based on biomass type and charring conditions, highlighting the need for further research to refine the classification and understanding of biochar.