The appeal of nanocellulose begins with its feedstock. Unlike synthetic ion-exchange resins or petroleum-derived adsorbents, cellulose can be extracted from wood, cotton, agricultural residues, and even bacterial fermentation, making it renewable, inexpensive, and biodegradable. At the nanoscale, cellulose takes two dominant forms that behave very differently in water. Cellulose nanocrystals, or CNCs, are rigid rod-like crystals typically prepared by acid hydrolysis, while cellulose nanofibrils, or CNFs, are long, flexible filaments obtained through mechanical disintegration, often combined with chemical pretreatments such as TEMPO-mediated oxidation, carboxymethylation, or deep eutectic solvent processing. Both forms carry an abundance of surface hydroxyl groups, which serve as chemical handles for grafting functional ligands, and both can be tuned to carry carboxyl, amino, thiol, or other charged groups that bind metal ions with high affinity.

Conventional adsorbents, the review notes, generally suffer from limited adsorption capacity, poor recyclability, and unsustainable raw material sources. Activated carbons, clays, and chitosan derivatives have all been tried against heavy metals with varying degrees of success, but the practical record shows recurring failures at scale: adsorbents saturate quickly, regenerate incompletely, and shed fines into treated water. Hydrogels sidestep several of these problems. As swollen three-dimensional networks, they offer internal pore space where metal ions can diffuse and be captured, and their soft, water-rich structure provides an ideal matrix for embedding functional nanomaterials, from carbon dots to metal-organic frameworks to nanoparticles of zero-valent iron. Crucially, hydrogels can be cast into beads, sheets, sponges, or monoliths that are easy to handle, pack into columns, and retrieve from treated water without filtration losses.

One of the review’s most valuable contributions is its mechanistic distinction between the two families of nanocellulose hydrogels. CNC-based hydrogels achieve synergistic adsorption through the functional groups arrayed on their crystal surfaces and through the composite networks formed when nanocrystals reinforce polymer matrices such as polyacrylamide or sodium alginate. Within these networks, metal ions are captured primarily by complexation and ion exchange, mechanisms that can be quantified and optimized by adjusting the surface charge density, aspect ratio, and crosslinking chemistry of the nanocrystals. In contrast, CNF-based hydrogels exploit their continuous fiber networks: the long fibrils create interconnected channels that promote mass transport deep into the gel, while the fibril surfaces bind ions electrostatically and trap them within the pore network. This combination of electrostatic attraction and pore entrapment gives CNF gels their characteristic high uptake and rapid kinetics, particularly for cations such as Cu(II) and Pb(II).

Performance, the review shows, hinges on chemistry. Carboxymethylated cellulose nanofibrils can remove copper ions efficiently because their deprotonated carboxylate groups exchange sodium or hydrogen for dissolved metal cations. Polyethylenimine grafted onto nanocellulose through microwave-assisted synthesis has demonstrated ultra-high adsorption capacity for lead and phosphate, an amine-rich surface that chelates cations while simultaneously binding anions. For the oxyanion chromium(VI), the chemistry flips: positively charged sites are needed, so researchers have grafted poly(acryloyl hydrazide) onto cellulose nanocrystals or used poly(m-aminobenzene sulfonate)-functionalized nanofibrils, achieving excellent adsorption capacities. Thiol-modified cellulose sponges capture mercury ions through soft-soft sulfur-metal interactions, while Fe-Cu alloy coatings on nanocrystals combine lead removal with antibacterial function, a dual capability relevant to real waters that carry both chemical and microbial hazards.

Several studies highlighted in the review push the technology toward intelligence, not just capacity. Fluorescent carbon dots incorporated into cellulose nanofibril and chitosan hydrogels allow simultaneous sensing and scavenging, so the same material that removes Cu(II) and Cr(VI) signals its progress optically, enabling operators to monitor saturation in real time. Stimuli-responsive designs add another layer: pH-responsive nanocellulose/alginate/metal-organic framework hydrogels can regulate ion uptake with changes in acidity, opening possibilities for triggered regeneration or controlled release. Mechanical durability, long the Achilles’ heel of hydrogel adsorbents, has been addressed through double-network architectures, ion-induced crosslinking with cations such as zinc, and physically crosslinked, self-healing composites of polyacrylamide and cellulose nanofibers that survive repeated deformation during column operation.

Cost and sustainability, the review emphasizes, are as decisive as performance. Low-cost production routes using agricultural waste feedstocks, including rice husk, banana rachis, sugarcane bagasse, barley straw, ramie fibers, garlic and agave waste, and licorice residue, demonstrate that nanocellulose adsorbents can be sourced from materials that would otherwise be burned or landfilled. Ball milling, mechanochemical processing, deep eutectic solvents, formic acid and choline chloride pretreatments, and Fenton-based oxidation have all been deployed to liberate nanocellulose from these matrices with reduced energy and chemical inputs compared with traditional sulfuric acid hydrolysis and intensive homogenization. Studies that tracked the economics of dicarboxylic nanocellulose for copper removal report competitive costs against commercial alternatives, suggesting that sustainability here need not come at a premium.

Real-world validation is beginning to appear. Nanocellulose/alginate composite beads modified in situ have been tested for purifying mining effluents, one of the harshest chemical environments any adsorbent can face, and porous sodium alginate/cellulose nanofiber microspheres have been evaluated in wastewater matrices rather than clean laboratory solutions. Rice husk-derived nanocellulose scaffolds have shown highly efficient removal of heavy metal ions from contaminated water, and nitro-oxidized nanofibrils from banana rachis have delivered both effective lead removal and strong structural films. Yet the review is blunt about the remaining gaps. Scalable, low-cost preparation remains an obstacle: many laboratory protocols rely on exotic reagents, long reaction times, or energy-intensive homogenization that would be difficult to reproduce at a treatment plant. Antifouling performance in complex water matrices is another unresolved challenge, since organic matter, oils, and microbial biofilms compete for surface area and can poison binding sites far faster than heavy metals arrive.

The authors close by sketching a roadmap for engineering translation. Future development, they argue, should prioritize functional designs that combine adsorption with detection and self-reporting, architectures that resist fouling in chemically complex effluents, and manufacturing processes validated on waste-derived feedstocks at industrially relevant scales. If those goals are met, nanocellulose hydrogels could shift heavy metal remediation away from energy-hungry precipitation and membrane processes and toward a quieter, greener model: materials grown from plants, deployed as soft three-dimensional networks, and returned harmlessly to the biosphere when spent. For a world in which four decades of sediment records show heavy metal contamination resurging even in highly regulated coastal waters, the prospect of a renewable adsorbent that captures lead from water and can be built from rice husks is more than a laboratory curiosity. It is a plausible piece of the global water security puzzle, and the detailed mechanistic understanding assembled in this review brings the field measurably closer to the day when that piece can be put into service.

Subject of Research: Nanocellulose-based hydrogels for heavy metal removal from contaminated water

Article Title: Review: nanocellulose-based hydrogels for heavy metal removal from water

Article References: Zuo, R., Wu, S., Sun, D., & Liu, Y. (2026). Review: nanocellulose-based hydrogels for heavy metal removal from water. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13763-z

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13763-z

Keywords: nanocellulose, hydrogels, cellulose nanocrystals, cellulose nanofibrils, heavy metal removal, water treatment, adsorption, agricultural waste, green adsorbents, wastewater remediation, stimuli-responsive materials, pollution