A new study published in ACS Materials Au reports a novel way to convert industrial lignin waste into porous, bio-based materials capable of removing both chemical pollutants and bacteria from water.
Study: Upcycling Lignin into Porous Hybrid Beads and Sponges for Efficient Removal of Organic and Biological Contaminants from Water. Image Credit: Manee_Meena/Shutterstock.com
By combining lignin with chitosan using three different cross-linking strategies, the researchers produced sponges and beads that efficiently adsorb organic dyes and bacterial contaminants under laboratory conditions.
The work highlights how waste lignin, produced in vast quantities by the pulp and paper industry, can be repurposed into functional materials for water treatment, while also revealing how material structure and chemistry influence performance.
Lignin is one of the world’s most abundant natural polymers, with an estimated 50 to 70 billion tons produced annually. Yet less than 2 % is used for value-added applications; most is burned for energy.
The material's complex chemical structure has limited broader use, despite its abundance of functional groups and inherent antimicrobial properties.
Wastewater streams often contain a mix of toxic dyes and microbial contaminants, and existing treatment technologies can be costly, energy-intensive, or difficult to recycle. Adsorption-based materials offer a simpler alternative, but many conventional adsorbents lack biodegradability or mechanical stability.
Here, lignin could prove useful.
Get all the details: Grab your PDF here!
Three Routes to Porous Lignin-Chitosan Materials
To address these challenges, the researchers combined kraft lignin with chitosan, a cationic biopolymer derived from chitin, using three complementary fabrication strategies:
- Carbodiimide (EDC/NHS) coupling, which produced highly porous sponge-like materials
- Inverse-suspension polymerization with glutaraldehyde, yielding spherical, mechanically robust beads
- Ionic gelation with alginate and calcium ions, forming large, highly swollen beads through dual cross-linking
By tuning reaction conditions such as temperature, cross-linker concentration, and polymer ratios, the team controlled pore size, surface charge, and structural stability.
Across all material types, cross-linking with chitosan reversed lignin’s surface charge from −37 mV to +51 mV. This positive charge enhanced attraction to anionic pollutants, including the model dye methyl orange.
Microscopy revealed interconnected pores averaging about 25 μm in the sponges and roughly 39 μm on the surface of the beads - just large enough to facilitate mass transfer of both dye molecules and bacterial cells.
Spectroscopic analyses confirmed successful bond formation between lignin and chitosan, while thermal analysis showed stability up to around 273 °C.
Notably, higher cross-linking density in glutaraldehyde-based beads reduced thermal stability, a counterintuitive but important design trade-off highlighted by the authors.
Removing Dyes and Bacteria
In batch adsorption tests, the lignin-chitosan sponge removed nearly all methyl orange within 24 hours under mildly acidic conditions.
The authors attribute this performance to a combination of electrostatic attraction, hydrogen bonding, and π-π interactions between the aromatic dye molecules and the lignin backbone.
The same sponge material also achieved a roughly 4-log (≈99.99 %) reduction in Escherichia coli. Imaging and colony-count assays suggest that bacterial removal is primarily driven by adsorption and contact-mediated effects, rather than the release of biocidal agents.
Different Strengths Between Sponges and Beads
Material geometry played a key role.
Sponge-like structures exhibited faster adsorption kinetics due to their open, interconnected pore networks. Bead-based materials provided greater mechanical stability and easier handling, features particularly relevant to packed-bed or flow-through systems.
Alginate-containing beads exhibited extreme water uptake, swelling by more than 2000-3000 %, reflecting dense, double cross-linked polymer networks.
However, the authors do note that alginate’s negative charge could limit adsorption efficiency in some applications.
Not Yet a Finished Technology, But a Successful Platform
Rather than presenting a ready-made water filter, the study emphasizes structure-property relationships and design trade-offs. Each fabrication method has its limitations, including the use of solvents, process complexity, and cost considerations.
Still, the work demonstrates how lignin, often treated as a low-value byproduct, can be engineered into multifunctional, bio-based adsorbents capable of addressing both chemical and biological water contaminants.
The authors position their approach as a materials platform for future development, rather than an immediate industrial solution. Scaling, long-term durability, and real-world wastewater testing are still open questions.
For researchers in sustainable materials and water treatment, the study provides a detailed methodology for converting industrial biopolymer waste into high-performance adsorption materials - while making it clear that performance depends as much on structure as on chemistry.
Journal Reference
Breitkreuz, N., et al. (2025). Upcycling Lignin into Porous Hybrid Beads and Sponges for Efficient Removal of Organic and Biological Contaminants from Water. ACS Materials Au. DOI: 10.1021/acsmaterialsau.5c00147
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.