Large-Scale Nanofiber Manufacturing| Biomass Nanofiber-Assembled Superhydrophobic Aerogelswith Simultaneously Enhanced Mechanical Strength andShape Recovery

National University of Singapore’s Zhai Wei: Bottom-Up Assembled Biomass Nanofiber Aerogels Enable Efficient Water Treatment
In June 2024, a major oil spill occurred near Singapore’s Sentosa Island, releasing over 400 tons of fuel into the sea. Similarly, pollution crises have frequently erupted in recent years. Existing remediation materials, such as biomass aerogels, offer advantages like low density and high porosity but face bottlenecks like hydrophilic-induced structural collapse, poor mechanical properties, and limited functionality, failing to meet practical needs.

To address this, Dr. Zhai Wei from the National University of Singapore led the Advanced Biomimetic Engineering Materials team to develop an aerogel using natural polysaccharides (chitosan, CS, and sodium alginate, SA) via ultrasound-assisted nanofiber assembly, directional freeze-casting, and silane modification. The resulting material combines superhydrophobicity, high strength, and elasticity, providing a sustainable solution for water treatment.

Published in Small Structures as “Biomass Nanofiber-Assembled Superhydrophobic Aerogels with Simultaneously Enhanced Mechanical Strength and Shape Recovery,” the paper’s co-first authors are Dr. Dong Xinyu and Dr. Liu Quyang, with Dr. Zhai Wei as the corresponding author.

Key Innovations:

1. Nanofiber Assembly: Ultrasound-driven electrostatic crosslinking of CS/SA forms 60–100 nm nanofibers with enhanced strength and abundant active surface sites.

2. Biomimetic Honeycomb Design: Directional freeze-casting creates anisotropic honeycomb channels, improving vertical compressive strength (0.0098 g/cm³ density) and lateral elasticity.

3. Silane Modification: Trimethoxymethylsilane (MTMS) reinforces nanofiber networks, enabling superhydrophobicity (151° contact angle), 90× oil absorption, and reusability.

   

[Fig. 1] Aerogel preparation & performance overview

Through a three-step method of ultrasonic assembly, silane modification, and freeze-casting, multifunctional, ultralight aerogels were successfully prepared. With a density as low as 0.0098 g/cm³, the aerogel can stand on a feather. It exhibits a superhydrophobic surface (151° contact angle) and recovers 95% of its shape after 80% compression.

[Fig. 2] Nanofiber assembly for structural reinforcement

The ultrasonic field-driven self-assembly transforms the CS/SA solution into a nanofiber suspension, which forms a porous fiber network after freezing. As fiber concentration increases, the aerogel’s density and compressive strength gradually improve.

[Fig. 3] Microstructure control via directional freeze-casting

Directional freeze-casting creates long-range ordered honeycomb channels, demonstrating mechanical anisotropy. The vertical yield strength is twice that of the horizontal direction. Pore structure is controlled by freeze-casting temperature—lower temperatures accelerate ice crystal growth. For example, at liquid nitrogen temperature (−196°C), pore size shrinks to 47 μm, enhancing mechanical stability.

[Fig. 4-5] Silane-modified morphology & performance enhancement

EDX elemental mapping confirms uniform silicon (Si) distribution in the modified aerogel, proving successful MTMS grafting. SEM comparison shows that unmodified CSNF aerogels have loose, sheet-like cell walls, while CSNF-Si aerogels form a dense, interconnected fiber network due to Si-O-Si crosslinking and hydrogen bonding with polysaccharides.When MTMS dosage increases from 0 to 1000 μL, vertical compressive strength jumps from 6.6 kPa to 19.3 kPa, reaching 130.5 kPa at 80% strain. This is because hydrolyzed MTMS generates silanol groups (−Si−OH), forming covalent bonds with CS/SA’s −OH/−NH₂ while self-condensing into a Si-O-Si network, reinforcing the fibers.

[Fig. 6] Ultrahigh elasticity mechanism

Silane-modified aerogels (CSNF-Si) simultaneously enhance strength and elasticity by reinforcing fiber crosslinking points and strengthening the skeletal network. After 80% compression, recovery reaches 95%, with only slight bending observed in the honeycomb walls. Cyclic compression tests show 94.1% resilience at 60% strain, far exceeding unmodified samples.

[Fig. 7] Superhydrophobicity & high-efficiency oil absorption

CSNF-Si aerogels are superhydrophobic and oleophilic, selectively absorbing floating oil or underwater chloroform (up to 90× its weight). Even after 20 reuse cycles, capacity remains above 90%.

Summary:

This work employs molecular-nano-micro multiscale design, using natural chitosan and sodium alginate, combined with ultrasound-assisted nanofiber assembly, directional freeze-casting, and silane modification, to develop a biomass aerogel with superior pollutant removal, ultrahigh elasticity, and superhydrophobicity. The material overcomes traditional aerogel limitations (hydrophilicity, structural collapse, poor mechanics) through fiber reinforcement, biomimetic honeycomb structuring, and silane-enhanced networks, enabling reusability with a solvent-free, eco-friendly process. This technology offers an efficient, sustainable solution for marine oil spills and industrial wastewater treatment.

Paper link: https://doi.org/10.1002/sstr.202500009