Figures (6)  Tables (4)

    • Figure 1. 

      The "precursor engineering" paradigm of biomass torrefaction: a transformation pathway from feedstock to functional materials.

    • Figure 2. 

      The mechanisms of chemical and structural evolution in biomass components during torrefaction.

    • Figure 3. 

      The role of torrefaction-derived porous carbon in enhancing supercapacitor electrochemical performance.

    • Figure 4. 

      The application performance of torrefaction-derived carbon materials in aquatic environmental remediation.

    • Figure 5. 

      The schematic illustration of biomedical applications for torrefaction-derived carbon quantum dots (CQDs).

    • Figure 6. 

      The design strategies and applications of multifunctional composites based on torrefied biomass.

    • Parameter Typical range Impact on solid product properties
      Temperature Light (200–235 °C) 1. Initial deoxygenation and aromatization; significant decrease in atomic O/C ratio.
      2. Selective degradation of hemicelluloses; initial pore formation.
      3. Preliminary improvement in grindability; enhanced hydrophobicity.
      Mild (235–275 °C) 1. Intensified deoxygenation and aromatization; further reduction in atomic O/C ratio and increase in HHV.
      2. Cellulose begins to react; enhanced stability of the carbon skeleton.
      3. Markedly improved grindability, yielding finer, more uniform powder.
      Severe (275–300 °C) 1. Deep deoxygenation and aromatization; formation of a highly cross-linked, stable carbon structure; atomic O/C ratio reaches its lowest.
      2. Energy density (HHV) peaks, properties closer to coal.
      3. Optimal mechanical stability, suitable for subsequent aggressive activation.
      Residence time 0–60 min Mass yield: Lower at longer times/higher temperatures.
      Reaction pathways: Short, intense treatments promote rapid devolatilization.
      Volatile composition: Affects the balance of condensable vs non-condensable gases.
      Atmosphere Inert: N2, Ar
      Reactive: CO2, steam, air      		 Carbon content: CO2 can enhance decarboxylation, slightly increasing carbon content.
      Reaction kinetics: Steam can act as a soft oxidant and sweeping gas, influencing reaction pathways and by-product composition.
      Process direction: Prevents combustion; guides process toward controlled carbonization rather than gasification.

      Table 1. 

      Key torrefaction process parameters and their influence on product characteristics and application potential

    • Biomass feedstock Torrefaction conditions (°C) Activation conditions Specific surface area (m²/g) Specific capacitance (F/g) Ref.
      Basswood 260 KOH 579 434 [90]
      Wooden chopsticks 300 KOH 62 74.77 [91]
      Sterculia foetida 250 KOH 713 387 [92]
      Food waste 260 KOH 734.4 189.7 [93]
      Corncob 300 KOH 1,722 382.6 [94]
      Syzygium oleana 250 KOH 1,218 188 [95]
      Sugarcane bagasse 300 KOH 791.2 314 [96]

      Table 2. 

      The performance of torrefaction-derived porous carbons as supercapacitor electrodes

    • Target pollutant Material type and modification Performance metric Primary mechanism(s) Ref.
      Methylene blue Torrefied rice husk Adsorption capacity: 322–628 mg/g Pore filling (hierarchical porosity)
      π-π interactions with graphitic domains
      Electrostatic attraction with negatively charged surface      		 [97]
      Lead (Pb2+) Torrefied coconut shell Adsorption capacity: 201.19 mg/g Ion exchange with H+ from -COOH and -OH groups
      Surface complexation forming stable (COO)2 Pb precipitates      		 [98]
      Tetracycline Torrefied rice husk Adsorption capacity: 68.97 mg/g Pore filling (hierarchical porosity)
      π-π interactions with graphitic domains
      Electrostatic attraction with negatively charged surface      		 [99]

      Table 3. 

      The application of torrefaction-derived carbon materials in environmental remediation

    • Composite type Primary synthesis strategies Key synergistic properties Representative applications
      Magnetic carbon 1. Pre-/post-torrefaction impregnation with metal salts (e.g., Fe3+, Co2+) followed by thermal reduction.
      2. Co-precipitation of magnetic nanoparticles (e.g., Fe3O4) onto carbon surface.      		 1. High adsorption/catalytic capacity of carbon matrix.
      2. Carbon matrix prevents nanoparticle agglomeration, enhances electron transfer, and stabilizes nanoparticles against leaching.      		 1. Magnetically recoverable adsorbents/catalysts for wastewater treatment.
      2. Magnetically guided drug delivery and magnetic hyperthermia for cancer therapy.
      3. Resource recovery (e.g., precious metals from e-waste).
      Carbon/TiO2 hybrids 1. Sol-gel method using precursors.
      2. In-situ growth/deposition of TiO2 from solution.
      3. Chemical vapor infiltration (CVI).      		 1. Pollutant pre-concentration by carbon adsorbent
      2. Carbon acts as an electron shuttle, suppressing charge carrier recombination in TiO2.
      3. Carbon can act as a photosensitizer, extending light absorption into the visible range.      		 1. Highly efficient photocatalytic degradation of pollutants in air and water.
      2. Photocatalytic water splitting for H2 production.
      3. CO2 photoreduction to solar fuels.
      Carbon/SiO2 composites Sol-gel synthesis using silica precursors (e.g., TEOS), followed by ambient (xerogel) or supercritical (aerogel) drying. 1. Nanocomposite reinforcement: Carbon scaffold imparts mechanical robustness to brittle silica.
      2. Thermal superinsulation: Synergy between silica's nanoporosity and carbon's role as an infrared opacifier results in ultra-low thermal conductivity.
      3. Unique electrothermal properties: Combination of thermal insulation and electrical conductivity.      		 1. Next-generation thermal superinsulators for buildings, pipelines, and aerospace.
      2. Lightweight, insulating substrates for electronics.
      3. Electrothermal insulation and self-sensing structures.
      3D-printable conductive
      inks      		 1. Dispersion of fine torrefied carbon powder into a polymeric binder matrix (e.g., PDMS for flexibility, PVDF for stability, PLA for biodegradability).
      2. Additives (surfactants, rheology modifiers) for optimal printability.      		 1. Structural design freedom from 3D printing.
      2. Shear-thinning rheology for extrusion-based printing and shape retention after deposition.
      3. Multi-functionality: Can combine conductivity with flexibility, biodegradability, or high surface area.      		 1. Custom-shaped, interdigitated micro-supercapacitors and battery electrodes.
      2. Wearable and flexible strain sensors (electronic skin).
      3. High-surface-area biosensors and conductive scaffolds for tissue engineering.

      Table 4. 

      Multifunctional composite systems based on torrefied biomass and their synergistic characteristics