A new review synthesizes a decade of research into one of the most promising materials for water purification, biochar–hydrogel composites, and concludes that their effectiveness is governed by a single, critical factor: the chemistry of their surfaces. The work, led by corresponding author Dr. Dong Hee Kang at Morgan State University, provides a unified framework for understanding how these materials function and a clear roadmap for designing more robust and efficient filters to tackle global water contamination.
Biochar, a carbon-rich material made from pyrolyzed biomass, and hydrogels, water-absorbing polymer networks, are powerful on their own. When combined, they create a synergistic adsorbent with enhanced capabilities. This review analyzes the extensive body of literature to demonstrate that the true power of these composites comes from their surface functional groups—specific chemical moieties like carboxyl, hydroxyl, and amine groups that act as molecular-scale "hooks" to capture contaminants. The hydrogel matrix not only adds its own functional groups but also makes the biochar’s reactive sites more accessible, explaining why the composite consistently outperforms its individual components.
The Blueprint for Adsorption
The analysis clarifies that different functional groups are specialized for different tasks. Composites rich in oxygen-containing groups are excellent at binding heavy metal ions through electrostatic attraction and complexation. Those functionalized with nitrogen- or sulfur-containing groups show a stronger and more selective affinity for certain pollutants, including dyes and pharmaceuticals. This function-specific performance means that composites can be rationally engineered to target specific contaminants simply by controlling the chemical architecture of their surfaces.
From Lab to Reality: The Durability Challenge
While lab results are promising, a major challenge has been translating this performance to real-world wastewater, which contains a complex soup of competing ions and organic matter. The review critically assesses why performance often drops in these conditions and examines the crucial issue of reusability. Effective regeneration is key to economic viability, yet harsh chemical treatments can degrade the functional groups and the composite’s structure over time. The authors identify a pressing need for standardized durability testing and milder regeneration protocols to ensure long-term stability.
"Our analysis moves beyond simply creating new materials and focuses on the 'why'—why these composites work so well," explains Dr. Dong Hee Kang. "The superior performance comes from a cooperative functional-group architecture, where hydrogel-derived sites enhance the intrinsic properties of biochar. This function-guided approach is essential for engineering adsorbents that are not just effective, but also resilient and reusable in complex, real-world conditions."
A Roadmap for Resilient Materials
The review calls for a shift in the field, away from empirical material discovery and toward hypothesis-driven design. Future work must focus on developing composites with robust, covalently-anchored functional groups that can withstand multiple regeneration cycles. It also emphasizes the importance of evaluating materials in realistic water matrices and conducting thorough life-cycle and techno-economic analyses to ensure the solutions are scalable, affordable, and environmentally safe.
By consolidating years of research into a cohesive, function-first framework, this work provides the clear-eyed perspective needed to accelerate the development of biochar-hydrogel technology. It offers a blueprint for scientists and engineers to create the next generation of smart, sustainable, and highly effective materials for securing the world’s water resources.
Corresponding Author:
Dong Hee Kang
Department of Civil and Environmental Engineering, Morgan State University, Baltimore, MD, USA
Original Source:
https://doi.org/10.1007/s44246-026-00260-w
Contributions: Md Nashir Uddin led the conceptualization, methodology development, and original draft preparation; Dr. Mohammad A.H. Badsha and Bashir Talukder contributed to data curation; Yulai Yang, Dr. Samendra Sherchan, and Dr. Mohammad A.H. Badsha supported reviewing and editing; Ms. Abigail Samwini prepared the visualizations; Dr. James G. Hunter was responsible for funding acquisition; and Dr. Dong Hee Kang provided supervision, validation, and critical review and editing of the manuscript. Md Nashir Uddin wrote the original manuscript draft, and all authors critically reviewed and approved the final version.
Carbon Research
Literature review
Not applicable
Enhancing water remediation using biochar-hydrogel composites: the critical role of surface functional groups
28-May-2026
The authors declare that they have no competing financial interests or professional relationships that could have influenced the work reported in this paper.