Key Takeaways & Executive Findings
- •• • Biochar produced via pyrolysis at >400 °C yields high porosity and thermal stability, enabling long-term CO2 sequestration and gas-phase applications; hydrochar from hydrothermal carbonization retains higher oxygen content and surface functional groups (carboxyl, hydroxyl, carbonyl), favoring aqueous-phase reactions and liquid adsorption. • • Comprehensive characterization using BET, SEM, XPS, XRD, and Raman spectroscopy is essential to link structural and chemical attributes to performance, confirming the potential of both materials for diverse environmental and technological challenges. • • Future development requires application-driven material design, integrating advanced analytics such as in situ characterization and machine learning to predict performance based on feedstock and production parameters, accelerating optimization cycles. • • Sustainable and scalable industrial deployment demands overcoming economic and logistical hurdles, developing robust energy-efficient production systems, and securing supply chains for diverse feedstocks, while exploring novel integrated biorefinery concepts and resource recovery (e.g., phosphorus from wastewater).
Abstract
The conversion of biomass into carbon-rich materials, biochar and hydrochar, has emerged as a promising strategy to address pressing environmental challenges while supporting sustainable industrial development. This review provides a comprehensive analysis of recent advances in the characterization and application of these materials, emphasizing their distinct production methods, physicochemical properties, and functional versatility. Biochar, typically obtained by pyrolysis at high temperatures (>400 °C), exhibits high porosity, aromaticity, and thermal stability, making it well-suited for applications such as CO2 capture, electrochemical 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 techniques reveal 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 wastewater treatment, biofuel production, animal feed, and advanced oxidation processes are examined, alongside their relevance to multiple UN Sustainable Development Goals, particularly 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.
1. Introduction
The valorization of waste biomass into carbon-rich materials addresses critical environmental and energy security issues, yet commercial deployment has been hindered by inconsistent material properties and a lack of standardized production protocols. Existing pyrolysis and hydrothermal carbonization routes yield chars with vastly different surface chemistries and porosities, but without systematic characterization linking these features to end-use performance, industrial adoption remains fragmented. This review consolidates recent advances in characterization techniques—such as BET surface area analysis, SEM imaging, XPS, XRD, and Raman spectroscopy—to establish a robust framework for tailoring biochar and hydrochar for specific applications, from CO2 capture to wastewater treatment.
By delineating the distinct production pathways and resulting physicochemical properties, this work provides a critical benchmark for engineers and researchers seeking to optimize material performance. The emphasis on application-driven design and integration of machine learning addresses the bottleneck of trial-and-error development, offering a pathway to scalable, cost-effective production. Furthermore, the alignment with UN Sustainable Development Goals (SDGs 7, 9, 12, 13) underscores the broader socio-economic impact, positioning these materials as pivotal in the transition to a circular bioeconomy.
Loading authentic research manuscript (Pages 1–5)...
Bruna Rijo, Ana Paula Soares Dias (2026). Recent advances in the characterization and applications of biochar and hydrochar. New Carbon Materials. https://doi.org/10.1016/S1872-5805(26)61070-0
Research & Educational Purpose Only: The translations, structured abstracts, analytical annotations, and data reports provided by SinoGreenTechare intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoGreenTech claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What are the key differences in production conditions and resulting physicochemical properties between biochar and hydrochar that dictate their suitability for specific applications?
Biochar is produced via pyrolysis at high temperatures (>400 °C) under limited oxygen, resulting in high porosity, large surface area, high aromaticity, and superior thermal stability, making it ideal for gas-phase applications like CO2 capture and long-term carbon sequestration. Hydrochar, produced by hydrothermal carbonization in aqueous media at moderate temperatures, retains higher oxygen content and abundant surface functional groups (carboxyl, hydroxyl, carbonyl), which enhance its performance in aqueous-phase catalysis and pollutant adsorption.
Which characterization techniques are most critical for linking structural and chemical attributes to the performance of biochar and hydrochar, and what specific parameters do they measure?
Key techniques include BET (surface area and porosity), SEM (morphology), XPS (surface elemental composition and functional groups), XRD (crystalline structure and degree of graphitization), Raman spectroscopy (carbon structure and defects), and Boehm titration (quantification of oxygen-containing functional groups). These methods provide quantitative data essential for optimizing material design for targeted applications.
What are the main bottlenecks for industrial-scale production and deployment of biochar and hydrochar, and what strategies are proposed to overcome them?
Economic and logistical hurdles, including high production costs and inconsistent feedstock supply, impede scalability. Strategies include developing energy-efficient production systems, securing diverse feedstock supply chains, and implementing advanced post-treatment and functionalization methods to enhance material value. Integration of machine learning for performance prediction can also accelerate development cycles and reduce costs.
How do biochar and hydrochar contribute to achieving UN Sustainable Development Goals, and what specific applications are highlighted?
They support SDG 12 (Responsible Consumption) through waste utilization, SDG 13 (Climate Action) via greenhouse gas reduction and carbon sequestration, SDG 7 (Clean Energy) through applications in energy storage and biofuel production, and SDG 9 (Innovation) by enabling novel industrial processes. Specific applications include wastewater treatment, advanced oxidation processes, and soil improvement.
What are the emerging applications of biochar and hydrochar in integrated biorefinery concepts and resource recovery, and what advantages do they offer?
Emerging applications include utilizing all output fractions in biorefineries, recovering valuable resources like phosphorus from wastewater, and developing next-generation energy storage/conversion systems. Their unique surface chemistry and structural stability enable efficient adsorption and catalytic processes, contributing to a circular bioeconomy.
Related Chinese Research & Cross-Citations
Electrospinning of FeNiCo/carbon nanofibers: a new paradigm for lightweight microwave absorbers
The proliferation of electronic devices has intensified electromagnetic radiation pollution, necessitating advanced microwave absorption materials. This study presents the electrospinning fabrication of FeNiCo/carbon nanofiber (FeNiCo/CNF) composites with exceptional microwave absorption properties. The FeNiCo/CNFs achieved a minimum reflection loss (RLmin) of −55.5 dB at 14.24 GHz with an ultrathin matching thickness of only 1.6 mm. Microstructural analysis and electromagnetic parameter testing revealed that the superior absorption stems from the synergistic interaction between the carbon nanofiber network and FeNiCo alloy nanoparticles, which promotes multiple reflections and efficient energy dissipation. The precise control of coercivity and permeability via systematic modulation of magnetic metal composition enabled enhanced impedance matching and optimized magnetic-dielectric synergy. Furthermore, radar cross-section (RCS) simulations confirmed the material's capability to significantly reduce RCS values across a wide angular range, validating its potential for stealth technology applications. This work introduces a cost-effective and sustainable approach for developing ultralight, high-performance microwave absorbers, addressing the limitations of conventional materials such as high density and poor stability.
Electrochemical Exfoliation of Carbon Paper for Binder-Free Cathodes in Zinc-Ion Supercapacitors
Zinc-ion supercapacitors (ZISCs) are promising energy storage devices due to their low cost, high safety, and minimal environmental impact. However, their low energy density and poor cycling performance hinder practical application. This study presents a simple electrochemical exfoliation method to reconstruct the surface of carbon paper, introducing oxygen functional groups that enhance pseudocapacitance. The resulting binder-free electrode (EECP) exhibits a large surface area and rapid charge transfer, leading to a dominant capacitive-type charge storage mechanism with 78.8% capacitive contribution at 10 mV/s. The EECP electrode delivers a maximum specific capacitance of 252.5 F/g at 1 A/g and retains 81.7% of its capacitance after 10,000 cycles. A full ZISC device, assembled with EECP as the cathode, Zn as the anode, and 1 mol L−1 ZnSO4 aqueous electrolyte, achieves a capacitance of 186.22 F/g at 1 A/g, a capacitance retention of 97.01% after 10,000 cycles, and an energy density of 46.6 Wh/kg at a power density of 500.4 W/kg. These results demonstrate that EECP is a promising cathode material for high-rate, next-generation zinc-ion supercapacitors.
Increasing the Strength of Carbon Nanotube Fibers and Their Use as a Polishing Medium
We report a method for increasing the mechanical strength of carbon nanotube (CNT) fibers while enabling the uniform adhesion of cerium oxide (CeO2) abrasive particles to them using polyethyleneimine (PEI). Results show that 5% of PEI increases the tensile strength of CNT fibers by approximately 175%. CeO2 particles were uniformly deposited on the reinforced CNT fibers by electrophoretic deposition. A flexible polishing tool was fabricated by weaving the CeO2-CNT fibers into a non-woven fabric substrate. When used to polish potassium dihydrogen phosphate crystals, the tool reduced the surface roughness from 200 to 7.6 nm within 10 min. This approach has potential use for the development of new precision processing tools.
Engineered mesoporous carbon spheres with tailored pore structures for improved photothermal-chemotherapy
Carbon-based materials have gained significant attention in anticancer treatment due to their exceptional biocompatibility, yet critical challenges persist in establishing definitive correlations between their porous structures and functional performance. We report the use of a silica template to guide pore formation in the design of mesoporous carbon spheres (mC) with tailored pore structures for improved combined photothermal-chemotherapy. The mesopore size of mC was adjusted by kinetic control of resin polymerization and silica hydrolysis. Structural characterization showed that 4.4 nm mesopores enabled an exceptional gemcitabine loading of 228 mg g−1 and a sustained pH/thermal dual-responsive release with >70% drug release under near-infrared (NIR) irradiation. Finite element analysis demonstrated pore size-dependent heat transfer dynamics, with the improved mC achieving a superior photothermal conversion efficiency of 62% by a combination of N-doping and defect engineering. In vitro evaluations confirmed outstanding biocompatibility with >95% cell viability at 200 μg mL−1 and potent tumor suppression in pancreatic and biliary cancer models with an ~5% cell viability at 25 μg mL−1 where combined therapy showed a 3.7-fold increased cytotoxicity over monotherapy. The improved structure of mC facilitated cascade therapeutic effects with enhanced tumor permeability derived from NIR-triggered hyperthermia and prolonged therapeutic exposure due to pH-responsive drug release. This pore engineering strategy establishes a structure-function process for next-generation theranostic platforms, addressing the critical limitations of conventional pancreatic and biliary cancer therapies through spatiotemporal control of multimodal treatment.
Comparative Studies on Nanocarbon-Modified Carbon Paper Electrodes for Enhanced Electrocatalytic Performance in Vanadium Redox Flow Batteries
Vanadium redox flow batteries (VRFBs) are a promising technology for large-scale energy storage due to their scalability, safety, long cycling life, and decoupled power and energy capacities. However, the slow redox kinetics of vanadium species on conventional carbon electrodes limits their performance. This study investigates the deposition of carbon black (CB), carbon nanotubes (CNTs), and electrochemically exfoliated graphene (Exf-Gr) onto thermally-activated carbon paper (ACP) via spray coating to enhance electrode electrocatalytic activity. Modified electrodes were characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and surface area analysis. Electrochemical properties were evaluated by cyclic voltammetry, electrochemical impedance spectroscopy, and single-cell VRFB testing. Among the modified electrodes, Exf-Gr/ACP exhibited the best performance, achieving a 2.9-fold reduction in charge transfer resistance compared to pristine ACP and delivering 2.5 times the discharge capacity in single-cell tests. This improvement is attributed to Exf-Gr's high surface area, favorable catalytic activity, and excellent dispersion on the ACP substrate. Surface modification with electrochemically exfoliated graphene is a highly effective strategy for improving electrode performance in VRFB systems, with significant implications for large-scale energy storage.
Carbon nanotube-based materials as capacitive deionization electrodes
Capacitive deionization (CDI) is an emerging desalination technology that removes dissolved salts from brackish water via ion electrosorption at electrically charged electrode interfaces. It has gained recognition as a sustainable and cost-effective alternative to conventional methods such as reverse osmosis, electrodialysis, and thermal distillation, which often suffer from high energy consumption and environmental impact. Among electrode materials, carbon nanotubes (CNTs) are particularly attractive due to their high specific surface area, superior electrical conductivity, and excellent electrochemical stability. This review comprehensively analyzes recent advances in performance optimization strategies for CNT-based CDI electrodes, including material engineering and structural design. Key strategies include hybridization with activated carbon, graphene, metal oxides, and metal-organic frameworks (MOFs), as well as surface functionalization and three-dimensional architecture construction. These approaches enhance salt adsorption capacity, charge efficiency, and cycling stability. For instance, dispersing CNTs in activated carbon electrodes improves conductivity and ion transport, while MOF-derived nitrogen-doped carbon/CNT heterostructures exhibit high desalination performance. The review also evaluates the pivotal role of CNT-based electrodes in driving technological progress in CDI and discusses persistent challenges such as electrode fouling, scalability, and cost-effectiveness. Promising research directions, including flow-electrode systems and selective ion removal, are highlighted to overcome current limitations. Overall, CNT-based materials hold significant promise for advancing CDI as a viable water purification technology.