Chitosan as a Platform for PFAS Removal: Building Sustainable Solutions from Natural Polymers

Everyday products containing PFAS: from non-stick cookware to waterproof textiles, these 'forever chemicals' pervade modern life and contaminate water sources globally

Per- and polyfluoroalkyl substances (PFAS), known as "forever chemicals," represent one of the most pressing environmental contamination challenges facing modern society. These synthetic compounds, characterised by exceptionally stable carbon-fluorine bonds, resist natural degradation for over a millennium and now contaminate up to 90% of drinking water sources in the United States (PFAS Free UK, 2025; Yale Sustainability, 2025). Exposure to PFAS has been causatively linked to kidney and testicular cancer, liver toxicity, immune system suppression, thyroid dysfunction, and reproductive disorders (Fenton et al., 2020; EPA, 2024). This critical environmental challenge necessitates innovative, sustainable, and scalable remediation technologies. Among emerging solutions, chitosan has demonstrated exceptional promise as a versatile platform for PFAS adsorption, particularly when strategically modified to enhance performance.

The PFAS Challenge and Chitosan's Unique Properties

PFAS comprise over 14,000 synthetic chemicals featuring chains of carbon atoms bonded to fluorine atoms, creating one of the strongest bonds in organic chemistry. This molecular stability, whilst technologically valuable for applications including firefighting foams, non-stick cookware, and water-resistant textiles, renders PFAS virtually indestructible in natural environments (Yale Sustainability, 2025). Long-chain PFAS such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) accumulate in hepatic and renal tissues with half-lives ranging from 2.3 to 5.4 years in humans, facilitating chronic toxicity (Fenton et al., 2020). Standard wastewater treatment plants achieve only partial PFAS removal, underscoring an urgent need for advanced treatment technologies capable of capturing the full spectrum of PFAS congeners.

Chemical structure of Chitin and Chitosan

Chitosan emerges as an exceptionally promising candidate for PFAS remediation, distinguished by a unique combination of properties that enable effective pollutant capture. Derived through partial deacetylation of chitin—the second most abundant natural polysaccharide—chitosan comprises repeating units of D-glucosamine and N-acetyl-D-glucosamine. Unlike cellulose and other polysaccharides, chitosan possesses cationic character in acidic to neutral pH conditions, arising from protonation of amino groups to form -NH₃⁺ moieties. This positive charge density establishes the foundation for electrostatic interactions with anionic PFAS molecules.

The molecular architecture of chitosan provides multiple synergistic mechanisms for PFAS adsorption. Primary among these is electrostatic attraction between protonated amino groups and the anionic carboxylate or sulfonate head groups characteristic of perfluoroalkyl carboxylic acids and perfluoroalkyl sulfonic acids (Zhang et al., 2011; Saawarn et al., 2025). Beyond electrostatic forces, chitosan's abundant hydroxyl groups facilitate hydrogen bonding with PFAS functional groups, whilst hydrophobic interactions between fluorocarbon tails and chitosan's polymer backbone contribute significantly to long-chain PFAS adsorption (Saawarn et al., 2025; Zhang et al., 2011).

Experimental investigations have demonstrated substantial PFAS removal capabilities. Zhang et al. (2011) reported that crosslinked chitosan beads achieved a maximum sorption capacity of 5.5 mmol/g for PFOS, substantially exceeding conventional granular activated carbon. Similarly, Saawarn et al. (2025) demonstrated that chitosan-modified magnetic biochar attained approximately 94% PFOA removal efficiency under optimised conditions, with a maximum adsorption capacity of 517 mg/g according to Langmuir isotherm modelling.

Strategic Modifications Unlock Enhanced Performance

Whilst native chitosan exhibits considerable PFAS adsorption capacity, strategic chemical modifications dramatically enhance stability, selectivity, kinetics, and capacity across diverse water chemistries.

Crosslinking for Stability: A fundamental challenge in applying chitosan lies in its solubility in acidic environments. Crosslinking addresses this by forming covalent bonds between chitosan chains, creating a three-dimensional network that resists dissolution (Cagnetta et al., 2024; Saheed et al., 2021). Cagnetta et al. (2024) developed mechanochemically crosslinked chitosan using high-energy ball milling, achieving superior stability in highly acidic solutions (pH 3). Remarkably, chitosan crosslinked with dextran sulfate achieved a maximum adsorption capacity of 1,559 mg/g at pH 3, whilst simultaneously removing 98.75% of Cr(VI) and 87.40-95.87% of three PFAS compounds from simulated chromium electroplating wastewater (Cagnetta et al., 2024).

Chemical structure of trimethyl chitosan showing quaternary ammonium groups that provide permanent positive charge for pH-independent PFAS capture

Quaternary Ammonium Functionalisation: The introduction of quaternary ammonium moieties enhances chitosan's electrostatic interaction capacity and broadens its effective pH range. Unlike primary amines requiring protonation, quaternary ammonium groups maintain permanent positive charge independent of solution pH (Zhang et al., 2024). Zhang et al. (2024) synthesised a chitosan-coated fluorinated covalent organic framework (COF@CS) that achieved a maximum PFOA capacity of 2.8 mmol/g at pH 5, with adsorption rates of 6.2 mmol/g·h⁻¹. The material demonstrated remarkable chemical stability and excellent reusability over five regeneration cycles using 70% ethanol/1 wt% NaCl solution (Zhang et al., 2024).

Composite Materials: The integration of chitosan with complementary materials creates adsorbents that exploit synergistic interactions. Pervez et al. (2024) modified graphene oxide with cetyltrimethylammonium chloride to create composites achieving nearly 100% removal of 11 PFAS compounds, with equilibrium reached within 5 minutes—orders of magnitude faster than granular activated carbon. The adsorption proved insensitive to solution pH, ionic strength, and natural organic matter, maintaining 100% PFAS removal efficiency when treating actual river water samples (Pervez et al., 2024).

Similarly, Mahpishanian et al. (2024) developed magnetic amine-functionalised graphene oxide achieving removal rates exceeding 95% for long-chain PFAS and 85% for short-chain PFBS within 30 minutes. The magnetic functionality enabled facile separation from treated water using external magnetic fields, addressing a key limitation of conventional powder adsorbents (Mahpishanian et al., 2024).

Mechanistic Understanding and Adsorption Processes

Electrostatic attraction between positively charged chitosan surfaces and negatively charged PFAS groups constitutes the primary binding mechanism, particularly for short-chain PFAS lacking extensive hydrophobic character (Pezoulas et al., 2025; Zhang et al., 2024). Density functional theory calculations revealed that introducing cationic ammonium moieties caused PFAS binding energy to increase fourfold compared to neutral adsorbents (Pezoulas et al., 2025).

For long-chain PFAS, hydrophobic interactions between extended perfluoroalkyl tails and hydrophobic regions of chitosan contribute substantially to adsorption, with binding affinity increasing proportionally with chain length (Zhang et al., 2011). Fluorophilic interactions—specific affinity between fluorinated adsorbent surfaces and fluorocarbon tails—represent a selective binding modality that preferentially captures PFAS over competing organic anions (Pezoulas et al., 2025). Hydrogen bonding between chitosan's hydroxyl and amino groups and PFAS functional groups provides supplementary stabilisation (Saawarn et al., 2025).

Sustainability and Circular Economy: The Entoplast Advantage

The environmental sustainability of chitosan-based PFAS remediation depends fundamentally on production methods. Traditional chitosan manufacture relies on crustacean shells, a supply chain fraught with sustainability challenges including overfishing, habitat destruction, and resource-intensive chemical extraction (Schäfer et al., 2025).

Black Soldier Fly (Hermetia illucens): Nature's sustainable powerhouse for circular economy chitosan production

Entoplast Ltd has pioneered sustainable chitosan production leveraging the black soldier fly (Hermetia illucens, BSF) as a superior alternative feedstock. Black soldier fly larvae efficiently convert diverse organic waste streams into biomass rich in protein and chitin (Siddiqui et al., 2022; Entoplast, 2024). This insect-based production pathway embodies circular economy principles by transforming waste liabilities into high-value biopolymer products.

Life cycle assessments reveal dramatic sustainability advantages: BSF production generates approximately 70% lower greenhouse gas emissions, requires minimal land and water inputs, and produces no fishing-related environmental damage (Schäfer et al., 2025).

Comprehensive characterisation studies confirm that BSF-derived chitosan exhibits physicochemical properties comparable or superior to commercial crustacean-derived products, displaying equivalent biocompatibility, antimicrobial activity, and biodegradability, whilst offering enhanced mechanical strength in certain formulations (Schäfer et al., 2025; Triunfo et al., 2022).

Conclusion: Partnering for Sustainable PFAS Solutions

The convergence of escalating PFAS contamination and environmental consciousness demands solutions combining exceptional technical performance with genuine sustainability. Chitosan-based adsorbents fulfil this mandate, leveraging cationic charge density, amphiphilic character, and chemical versatility to capture the full spectrum of PFAS congeners. Chemical modifications including crosslinking, quaternary ammonium functionalisation, and composite formation with graphene oxide or magnetic nanoparticles unlock enhanced removal kinetics, capacity, and selectivity rivalling conventional technologies.

Successful regeneration and reusability demonstrated across multiple studies validate the economic feasibility of chitosan-based systems (Zhang et al., 2024; Pezoulas et al., 2025). When coupled with sustainable sourcing from black soldier fly biomass through circular economy pathways and green extraction methodologies, chitosan emerges as a transformative platform for PFAS remediation.

For researchers, environmental engineers, water utilities, and investors seeking effective, scalable, and sustainable solutions to the PFAS crisis, chitosan-based technologies merit accelerated deployment. We invite you to partner with Entoplast in advancing sustainable water treatment. Whether developing innovative adsorbent formulations, implementing pilot treatment systems, or seeking reliable sources of premium chitin and chitosan, our team possesses the expertise, materials, and commitment to support your success. Contact us at hello@entoplast.com to explore collaborative opportunities and discover how our sustainable biopolymers can empower your PFAS remediation initiatives.