How is Nanocellulose Used in Water Purification?

Industrialization, urbanization, and population growth have led to a decline in water quality, leaving 1.8 billion people without enough water and 4 billion facing water shortages for at least one month each year.

Although technologies like reverse osmosis and ion exchange are used to remove contaminants, they are expensive and inefficient.

As a solution, nanocellulose—a renewable, biodegradable material—has become a promising, affordable alternative for water filtration, providing better contaminant removal and offering hope for addressing the global water crisis.¹

Image Credit: Alena Matrosova/Shutterstock.com

What is Nanocellulose?

Cellulose is the most abundant carbohydrate on Earth, with an estimated annual production of 10¹⁰ tons. It is a natural macromolecule made of glucose units linked by β-1,4-glycosidic bonds, forming linear homo-polysaccharide chains. It is sourced from renewable materials such as plants, wood, algae, and microorganisms and maintains its structural integrity through hydroxyl groups that form intra- and inter-molecular hydrogen bonds.²

Nanocellulose, a nanoscale derivative of cellulose, is produced by breaking these hydrogen bonds through mechanical, chemical, or enzymatic processes. It is biodegradable, with fibers that are 200–5000 times longer than wide, a crystallinity of 60–80 %, and a modulus of 70–130 GPa, depending on the extraction process and biomass source.¹

Nanocellulose can be classified into three types based on its structure and source: cellulose nanofibers (CNF), cellulose nanocrystals (CNC), and bacterial nanocellulose (BNC).

CNCs are created by acid hydrolysis of cellulose-rich sources, removing the non-crystalline areas and producing rod-like structures with widths of 4–20 nm and lengths of 100–500 nm. CNFs are made by mechanical processing, sometimes with chemical or enzymatic treatments to reduce energy use. This results in fibers with both crystalline and non-crystalline regions, diameters of 4–100 nm, and lengths up to 1 μm.

BNC is synthesized through bacterial fermentation, where microorganisms convert saccharide-based media into pure cellulose fibrils with 20–100 nm diameters and lengths extending several micrometers. Unlike CNCs and CNFs, it is free from lignin and hemicellulose, making it the purest form of nanocellulose.

These structural and compositional differences influence their applications in biomedical engineering, composites, and nanotechnology.^3,4

Nanocellulose bioprinting at TU GrazPlay

Mechanism of Nanocellulose in Water Purification

Adsorption

Nanocellulose is highly effective at adsorbing various water contaminants, including heavy metal ions like Pb²⁺, Cd²⁺, As³⁺, Cu²⁺, Hg²⁺, and Cr⁶⁺, and organic pollutants such as dyes, pesticides, and pharmaceuticals. These pollutants, which come from industrial activities like metal plating, fertilizer manufacturing, and textile dyeing, are harmful to both humans and aquatic ecosystems because they don’t break down easily and can accumulate in organisms.

Nanocellulose-based adsorbents remove these contaminants through two processes: physisorption (using van der Waals forces) and chemisorption (involving covalent or ionic bonds). The hydroxyl (-OH) and carboxyl (-COO-) groups on nanocellulose interact with metal ions through electrostatic attraction and ion exchange.³

Modifying nanocellulose with functional groups like ammonium, sulfonate, and phosphate improves its ability to adsorb contaminants by introducing anionic groups that strongly bind to heavy metal ions.

For example, a study on TEMPO-oxidized cellulose nanofibers with negatively charged carboxylate groups showed strong binding to positively charged metal ions. At low concentrations, Cu(II) bonded only with carboxylate groups, while at higher concentrations, it also interacted with protonated carboxylate groups, increasing the adsorption capacity.⁵

Another study found that cellulose nanocrystals, modified with acrylic acid through hydrothermal methods, effectively removed Cu(II), Cd(II), and Pb(II) from wastewater. The adsorption followed pseudo-second-order kinetics and matched the Freundlich isotherm model, suggesting multilayer adsorption via electrostatic bonding with sulfonate and carboxylate groups.⁶

Filtration

Nanocellulose-based membranes are favored for water remediation due to their high adsorption capacity, biodegradability, mechanical stability, phase-change-free operation, reduced energy consumption, and high separation efficiency, particularly in nanofiltration (NF) and reverse osmosis (RO) applications.

These membranes, fabricated via sequential vacuum filtration, remove water contaminants through physical sieving and chemical bonding, facilitating charge-mediated interactions and size-based exclusion.

A study published in Environmental Science & Technology demonstrated that incorporating 0.02 wt% CNCs into a polyamide layer increased membrane permeability by 60 % while maintaining high divalent salt rejection (Na₂SO₄: 98.7 %; MgSO₄: 98.8 %).⁸

In another study, Dabaghian et al. developed carbon nanofiber/cellulosic membranes for forward osmosis desalination, utilizing amine- and carboxyl-functionalized carbon nanofibers. These membranes achieved an enhanced water flux of 15 L/m² h, demonstrating their effectiveness in seawater desalination.⁹

More recently, Xu et al. developed muli-functional membrane technology by embedding cellulose nanocrystals and silver nanoparticles into a polyamide layer, achieving high water permeability (25.4 L/m²·h·bar) and 99.1 % Na₂SO₄ rejection. These membranes exhibited strong antibacterial properties with a 99.4 % reduction in Escherichia coli viability, while Ag⁺ leaching tests confirmed nanoparticle stability for long-term efficacy.¹⁰

Coagulation and Flocculation

Coagulation and flocculation are cost-effective solid-liquid separation methods that rely on charge interactions between colloidal particles and coagulants or flocculants. Coagulation uses simple electrolytes to compress the electrostatic double layer, while flocculation involves long-chain polyelectrolytes.

With rising concerns over synthetic polymers and metal-based coagulants, natural alternatives like nanocellulose-based materials have gained interest due to their biodegradability and biocompatibility, as all charged nanocellulose materials are effective as coagulants and flocculants.

A study published in the Industrial & Engineering Chemistry Research developed dicarboxyl cellulose (DCC) from Phyllostachys heterocycla (bamboo pulp cellulose) using the Schiff base route. The researchers dissolved bamboo pulp cellulose in a NaOH-urea solution, oxidized it to dialdehyde cellulose using NaIO₄, and then reacted the dialdehyde cellulose with residual urea and NaOH to synthesize dicarboxyl cellulose. This one-step process simplified the traditional two-step synthesis method and reduced the environmental impact associated with cellulose solvents.

The resulting dicarboxyl cellulose showed excellent coagulation-flocculation properties, with CaCl₂ enhancing floc formation and simplifying post-treatment, making it a cost-effective solution for wastewater treatment.^1,11

Advantages of Nanocellulose in Water Purification

Nanocellulose is a renewable, cost-effective alternative to petroleum-based materials and inorganic filtration membranes in water treatment. Its surface can be modified to improve pollutant adsorption, and its fibrous structure, high strength, and biocompatibility make it an effective material for wastewater treatment.

Studies show that BNC integrates well with biological tissues, causing minimal inflammation. Composites made from CNC or CNF with chitosan or poly(vinyl alcohol) are also highly biocompatible, making them safe for filtration.

Additionally, nanocellulose has strong thermal stability, with degradation temperatures between 200 and 300 °C, depending on the synthesis method. This stability helps it maintain its integrity under the high temperatures and pressures typical in water treatment.^1,2

Challenges of Nanocellulose in Water Purification

Dependence on Natural Resources

Nanocellulose production depends on natural biomass sources, which raises concerns about the sustainability of harvesting these resources. While using waste biomass as a feedstock can help reduce environmental impact, challenges remain in ensuring that production is both environmentally sustainable and efficient.

High Production Costs

Even though nanocellulose production facilities exist in countries like the USA, Canada, Sweden, and Japan, the high costs of producing CNF and CNC still make it difficult for nanocellulose to be widely adopted for water purification.

Complex Characterization of Nanocellulose in Dispersion

It is hard to characterize the structure and properties of nanocellulose in wet or dispersed states due to its varying colloidal behavior and rapid Brownian motion. This complicates the optimization of nanocellulose for stable and effective filtration, particularly for water purification.

Limited Research on Structure-Property Relationships

While we know well the structure-property relationships for cellulose, there is limited research on nanocellulose materials due to their high production costs. Further research is needed to optimize nanocellulose’s mechanical strength, hierarchical structure, and overall performance for better water purification.^1,2,7

What Does the Future Hold for Nanocellulose in Water Purification?

Despite these challenges, ongoing research offers significant potential to improve industrial wastewater treatment. By combining nanocellulose with materials like graphene oxide (GO), its mechanical strength, surface area, and adsorption abilities can be enhanced, enabling cost-effective and scalable production of filtration systems

As research into scalable production methods continues, nanocellulose-based filtration systems are set for widespread commercialization, with applications in various fields like wastewater treatment and water purification.^12,13

To explore more about these areas and other advanced technologies in water management, check out the following resources:

References and Further Reading

1. Das, R., Lindstrom, T., Sharma, P. R., Chi, K., & Hsiao, B. S. (2022). Nanocellulose for sustainable water purification. Chemical Reviews, 122(9), 8936-9031. https://doi.org/10.1021/acs.chemrev.1c00683
2. Iqbal, D., Zhao, Y., Zhao, R., Russell, S. J., & Ning, X. (2021). A Review on Nanocellulose and Superhydrophobic Features for Advanced Water Treatment. Polymers, 14(12), 2343. https://doi.org/10.3390/polym14122343
3. Patil, T. V., Patel, D. K., Dutta, S. D., Ganguly, K., Santra, T. S., & Lim, K. (2022). Nanocellulose, a versatile platform: From the delivery of active molecules to tissue engineering applications. Bioactive Materials, 9, 566-589. https://doi.org/10.1016/j.bioactmat.2021.07.006
4. Mautner, A. (2020). Nanocellulose water treatment membranes and filters: A review. Polymer International, 69(9), 741-751. https://doi.org/10.1002/pi.5993
5. Liu, P., Garrido, B., Oksman, K., & Mathew, A. P. (2016). Adsorption isotherms and mechanisms of Cu (II) sorption onto TEMPO-mediated oxidized cellulose nanofibers. RSC advances, 6(109), 107759-107767. https://doi.org/10.1039/C6RA22397D
6. Liu, S., Low, Z., Hegab, H. M., Xie, Z., Ou, R., Yang, G., Simon, G. P., Zhang, X., Zhang, L., & Wang, H. (2019). Enhancement of desalination performance of thin-film nanocomposite membrane by cellulose nanofibers. Journal of Membrane Science, 592, 117363. https://doi.org/10.1016/j.memsci.2019.117363
7. Zubair, M., Arshad, M., & Ullah, A. (2020). Nanocellulose: A sustainable and renewable material for water and wastewater treatment. Natural Polymers-Based Green Adsorbents for Water Treatment, 93-109. https://doi.org/10.1016/B978-0-12-820541-9.00009-0
8. Bai, L., Liu, Y., Bossa, N., Ding, A., Ren, N., Li, G., … & Wiesner, M. R. (2018). Incorporation of cellulose nanocrystals (CNCs) into the polyamide layer of thin-film composite (TFC) nanofiltration membranes for enhanced separation performance and antifouling properties. Environmental science & technology, 52(19), 11178-11187. https://doi.org/10.1021/acs.est.8b04102
9. Dabaghian, Z., Rahimpour, A., & Jahanshahi, M. (2016). Highly porous cellulosic nanocomposite membranes with enhanced performance for forward osmosis desalination. Desalination, 381, 117-125. https://doi.org/10.1016/j.desal.2015.12.006
10. Xu, C., Chen, W., Gao, H., Xie, X., & Chen, Y. (2020). Cellulose nanocrystal/silver (CNC/Ag) thin-film nanocomposite nanofiltration membranes with multifunctional properties. Environmental Science: Nano, 7(3), 803-816. https://doi.org/10.1039/C9EN01367A
11. Zhu, H., Zhang, Y., Yang, X., Liu, H., Zhang, X., & Yao, J. (2015). An eco-friendly one-step synthesis of dicarboxyl cellulose for potential application in flocculation. Industrial & Engineering Chemistry Research, 54(10), 2825-2829. https://doi.org/10.1021/ie503020n
12. Valencia, L., Monti, S., Kumar, S., Zhu, C., Liu, P., Yu, S., & Mathew, A. P. (2019). Nanocellulose/graphene oxide layered membranes: elucidating their behaviour during filtration of water and metal ions in real time. Nanoscale, 11(46), 22413-22422. https://doi.org/10.1039/C9NR07116D
13. Mokhena, T.C., Mochane, M.J., Mtibe, A. et al. Recent advances on nanocellulose-graphene oxide composites: a review. Cellulose 31, 7207–7249 (2024). https://doi.org/10.1007/s10570-024-06055-9

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