Bioinspired Hollow Fibers With Efficient Transport Channels for Wide Humidity Atmospheric Water Harvesting

Original Authors: Yaxuan Wang, Jiarui Zhang, Ting Xu, Xuan Wang, Meng Zhang, Junjie Qi, Han Zhang, Kun Liu, Liyu Zhu, Lin Dai, Chuanling Si

Original paper is accessible at: https://doi.org/10.1002/adfm.74928

The real challenge in AWH materials: performance vs portability

Atmospheric water harvesting (AWH) has emerged as a promising solution to global water scarcity, especially given that the atmosphere contains nearly 12,900 km³ of water vapor. However, despite rapid advances in sorbent materials such as MOFs, silica gels, and salt-based composites, a persistent limitation remains:

👉 Most materials cannot simultaneously achieve:

• High water uptake across wide humidity ranges

• Fast adsorption/desorption kinetics

• Mechanical flexibility and portability

This trade-off has limited real-world deployment, particularly for wearable or decentralized water systems.

Bioinspiration: learning from cotton fibers

This study introduces a new design paradigm inspired by natural cotton fibers, which contain internal hollow channels that enable:

• Efficient capillary-driven moisture transport

• Rapid water uptake and release

• Internal storage space for moisture

Based on this concept, the authors developed hollow hybrid fibers using:

• sulfonated cellulose nanofibers (s-CNF) → hydrophilicity

• sodium alginate (SA) → structural network

• carbon nanotubes (CNTs) → photothermal conversion

• LiCl → strong hygroscopic adsorption

The result is a cotton-like hollow architecture with efficient transport pathways and enhanced sorption performance.

Why hollow structure matters

The hollow fiber design fundamentally changes both adsorption and desorption mechanisms:

During adsorption:

• Provides more active sites for water binding

• Reduces vapor transport resistance

• Enables dual-surface interaction (inner + outer walls)

During desorption:

• Confines photothermal heat (from CNTs)

• Increases evaporation surface area

• Enables faster vapor diffusion through internal channels

👉 Compared to solid fibers, hollow fibers show:

• ~2× higher desorption rates

• Significantly faster moisture transport

Water uptake performance across humidity ranges

One of the strongest contributions of this work is consistent performance across extreme humidity conditions.

For the optimized fiber (CSC15):

• 0.41 g/g at 11% RH

• 2.22 g/g at 57% RH

• 5.00 g/g at 95% RH 

This demonstrates:

👉 Strong performance in BOTH:

• Low humidity (chemisorption dominated)

• High humidity (capillary condensation dominated)

Compared to many state-of-the-art materials, these fibers outperform across both regimes.

Adsorption kinetics: fast and efficient

The hybrid fibers exhibit very fast adsorption behavior:

• Initial adsorption rate up to 1.92 kg/(kg·h) within the first hour

• Faster than both:

  • Pure LiCl (~1.6 kg/(kg·h))

  • Base fiber (~1.0 kg/(kg·h))

This is due to:

• Uniform LiCl distribution (no agglomeration)

• Hollow transport pathways

• Hydrophilic polymer network

Desorption performance: photothermal advantage

Using CNTs, the fibers achieve efficient solar-driven desorption:

• Light absorption > 94% (300–780 nm)

• Temperature rises to ~55°C within 5 minutes

• Desorption rate up to:

  • 4.52 kg/(kg·h) (hollow fibers)

  • vs ~2.08 kg/(kg·h) for solid fibers

Additionally:

• ~89–96% of water released within 180 minutes

• Stable over 10 adsorption–desorption cycles

System-level performance: from material to device

The fibers can be woven into flexible textiles, enabling practical AWH systems.

Outdoor performance:

• Water uptake: ~4.0 g/g per cycle

• Water production rate:

  • ~2.8–3.0 g/g/day (single cycle)

  • ~4.55 g/g/day (dual-cycle operation) 

Efficiency:

• Evaporation efficiency: ~76–82%

• Collection efficiency: ~68–76%

👉 This demonstrates real-world viability—not just lab performance.

Water quality: safe for use

Collected water was analyzed and found to meet WHO drinking water standards, with ion concentrations such as:

• Li⁺: ~0.51 mg/L

• Ca²⁺: ~5.4 mg/L

• Cl⁻: ~3.1 mg/L

This confirms that the system is not only efficient but also practically usable.

Key insights (Important)

1. Hollow structure is a game changer for mass and heat transfer

2. Material + architecture integration drives performance

3. Wide humidity operation (11–95% RH) is achievable

4. Photothermal CNTs enable low-energy desorption

5. Wearable, flexible AWH systems are now feasible

6. Performance is competitive with (or better than) many MOF/aerogel systems

Takeaway

This work moves AWH forward in a critical direction:

👉 From high-performance materials➡️ to practical, wearable, and scalable systems

By combining bioinspired design + advanced materials + system integration, it demonstrates a pathway toward:

💧 portable, solar-driven water harvesting across diverse climates