A reusable filtration material made from engineered wood and polymer coating captures harmful organic compounds and microbes without chemical additives.
(Nanowerk Spotlight) Access to clean drinking water remains uneven across the globe, particularly in regions where infrastructure is underdeveloped or where natural water sources are contaminated with complex organic pollutants. One of the most persistent problems in water treatment is the removal of natural organic matter (NOM), a broad category of carbon-rich compounds formed by the decomposition of plants, animals, and microorganisms.
These compounds, especially their aromatic components like humic acids, are difficult to eliminate with standard purification methods. Worse still, when NOM reacts with chlorine during water disinfection, it can generate toxic by-products such as trihalomethanes and halophenols, which are linked to cancer and other serious health risks.
Efforts to eliminate NOM have led to a range of technologies including coagulation, catalytic degradation, oxidation processes, and porous material adsorption. While effective to varying degrees, most of these techniques depend on chemical additives. These additives are not only costly and difficult to manage in decentralized settings but also leave behind residues that introduce a new layer of pollution. Adsorption, by contrast, offers a chemical-free route, capturing pollutants on solid surfaces. Yet it often requires acidic pretreatment or chemical modification of water to function efficiently—again undercutting its environmental appeal.
Stimuli-responsive materials have been proposed as an alternative. These systems change their behavior based on environmental triggers such as pH, redox state, or ionic strength. But many of these triggers require aggressive chemicals to function. Carbon dioxide (CO₂) offers a safer alternative. It is non-toxic, widely available, and capable of adjusting pH gently and reversibly when dissolved in water. By using CO₂ as a benign activator, researchers are exploring new avenues for pollution capture without introducing harmful residues.
In a study published in Advanced Materials (“CO2‐Responsive Smart Wood Scaffold for Natural Organic Matter Removal without Secondary Pollution”), scientists from the University of Alberta and Tsinghua University report the development of a CO₂-responsive wood-based scaffold that efficiently captures NOM without the need for added chemicals. This material combines naturally abundant wood with a synthetic polymer that responds to CO₂ exposure, resulting in a highly selective, regenerable system for water purification.
The researchers began by chemically treating natural wood to remove lignin and hemicellulose, preserving its cellulose framework and porous architecture. This scaffold was then coated with a specially designed copolymer composed of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and N-(hydroxymethyl)acrylamide (PNMAM). The PDMAEMA component is sensitive to CO₂ and becomes positively charged when exposed to it, while the PNMAM segment helps the polymer adhere to the wood structure and maintain stability.
Design of the CO₂-responsive wood-based adsorbent. a) Schematic diagram of fabricating the CO₂-responsive wood scaffold and CO₂-triggered natural organic matter (NOM) removal mechanism. b) Conceptual diagram of advanced water treatment using the CO₂-responsive wood scaffold to achieve simultaneous NOM abatement and water disinfection. (Image: Reprinted from DOI:10.1002/adma.202505008, CC BY) (click on image to enlarge)
Upon CO₂ exposure, the polymer undergoes protonation, converting the tertiary amine groups into positively charged sites. These positively charged areas interact strongly with the negatively charged aromatic rings found in NOM compounds like humic acids. The result is a sharp increase in adsorption efficiency. When tested against two model humic acids—Suwannee River humic acid and Leonardite humic acid—the material removed over 96% of these compounds in CO₂-rich conditions, but less than 7% in the absence of CO₂. These findings confirm that the material’s performance is directly tied to CO₂ activation, not just pH change or ionic strength.
To understand the mechanism behind this selective adsorption, the researchers used high-resolution mass spectrometry to examine changes in NOM composition after treatment. They found that aromatic-rich fractions were preferentially captured. Further analysis using atomic force microscopy showed that the strength of interaction between the polymer and aromatic molecules increased fourfold under CO₂ stimulation. These interactions were identified as cation–π bonds—non-covalent attractions between the positively charged polymer groups and the electron-rich π systems of aromatic compounds.
The structure of the scaffold contributes significantly to its performance. Its high porosity and multi-stage architecture give it ample surface area and contact time for water flow, which enhances NOM binding. Importantly, the material’s effectiveness was not compromised in challenging conditions. It maintained high performance in waters with high salt concentrations and in the presence of various ions, heavy metals, and surfactants.
It was also tested on water samples from rivers, lakes, ponds, and seawater in Alberta and British Columbia. Across all samples, the treated water showed major reductions in UV absorbance and dissolved organic carbon levels, meeting Canadian standards for drinking water safety.
The CO₂-responsive scaffold also demonstrated antimicrobial activity. When exposed to bacteria such as E. coli, P. aeruginosa, S. aureus, and MRSA, the material significantly reduced microbial counts. This effect is attributed to the cationic polymer coating, which disrupts microbial cell membranes. The treated water consistently met the World Health Organization’s guidelines for microbial safety, including in tests on real river water.
To evaluate safety, the researchers exposed human dermal fibroblast cells to material extracts. The cells showed no significant toxicity, with high viability even at high concentrations. Imaging confirmed that most cells remained alive and healthy, suggesting the material is safe for human use in water treatment contexts.
Beyond purification, the scaffold allows for recovery of the captured NOM. By simply removing CO₂, the material reverts to its uncharged state and releases the adsorbed substances. The researchers tested the released humic acids as fertilizers in a hydroponic system growing garlic. The recovered material improved shoot length, fresh weight, and dry weight compared to controls, pointing to the potential for resource recovery and circular use.
This work presents a strategy for water purification that avoids chemical additives, resists secondary pollution, and offers multifunctional performance in a wide range of environmental conditions. The approach capitalizes on CO₂’s benign properties to activate selective adsorption and microbial inactivation without external inputs.
The platform is based on abundant, renewable wood and can be adapted to other materials rich in hydroxyl groups. Its modularity and scalability make it a strong candidate for broader environmental applications, including the removal of other aromatic contaminants such as pesticides and pharmaceutical residues.
Future research may focus on optimizing the scaffold’s fabrication using greener methods and extending the technology to remove other emerging pollutants. With growing demand for safe, decentralized, and sustainable water treatment, the CO₂-responsive scaffold offers a technically grounded and environmentally conscious solution.
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