A plant-inspired aerogel uses solar evaporation to extract heavy metals from soil at 1.5 meters depth, far beyond any living root system’s reach.
(Nanowerk Spotlight) Heavy metals like lead, copper, and cadmium dissolve in rainwater and migrate steadily downward through soil, settling into dense, oxygen-poor layers where conventional cleanup methods struggle to operate. The deeper these ions travel, the more difficult and expensive they become to remove.
Heavy metal contamination covers vast stretches of agricultural and industrial land. Excavating and washing thousands of hectares is not feasible. Chemical treatments applied in place risk secondary pollution and degrade soil structure over time. Even newer approaches using nanomaterial-based soil remediation focus primarily on shallow layers. The scale and depth of the problem demand something that works passively, in place, and at low cost.
Plants fit that description. Through transpiration, they pull water upward from soil to leaf using nothing but solar energy, carrying dissolved metals with it. Certain species absorb toxic ions effectively enough to reduce soil contamination over a growing season. But roots rarely reach beyond one meter, and growth takes months.
The deeper pollution migrates, the less any plant can do. Previous artificial systems that mimic transpiration have treated only surface soil, lacking the internal architecture to extend their reach further down.
A study published in Advanced Materials (“Bioinspired Artificial Plant for Deep Soil Heavy Metal Remediation”) from a team at Zhejiang University constructed a monolithic artificial plant from a bioinspired aligned porous aerogel made of chitosan and modified activated carbon nanoparticles. In seven-day tests it achieved effective remediation at 1.5 meters depth, surpassing the reach of conventional phytoremediation.
Preparation, structures and fundamental characteristics of bioinspired aligned porous chitosan/modified activated carbon(mCNPs) aerogel (BAMCs): a) Ice-templating fabrication process of BAMCs. The pre-crosslinked dispersion with all components was immersed into the cold source at a speed of 0.8 mm·min−1, and freeze-dried after 24 hours post-crosslinking. b) Optical image of BAMC. c,d) Scanning electron microscope (SEM) images of BAMC in different magnification. The sample was prepared in −90°C with average pore of width ∼30 µm, marked as BAMC-30 µm. e) SEM images of random structured mCNPs/chitosan aerogel via isotropic freezing (RMC). f) Infrared image showing different water absorbing behavior of BAMC and RMC. g) The height of water absorption front vs time correspond to infrared images (f). (Image: Reproduced with permission from Wiley-VCH Verlag) (click on image to enlarge)
The key question was how to build a material with the directional water transport of a plant stem but without the biological limitations. The team used a technique called ice-templating. They dispersed chitosan and acid-treated carbon nanoparticles in water with a glutaraldehyde crosslinker, then lowered the mixture into a cryogenic bath at a controlled speed. The vertical temperature gradient forced ice crystals to grow upward from the bottom, pushing the dissolved solids into compacted walls. Freeze-drying removed the ice, leaving behind a cylinder of vertically aligned channels.
By varying the freezing temperature, the team tuned channel width from 15 to 80 µm. The best performance came at an intermediate width of roughly 30 µm. At that size, capillary forces supplied water fast enough to sustain rapid solar-driven evaporation at the surface without drying out the channels below.
These aligned channels solve the central transport problem. In randomly structured porous materials, water and dissolved ions follow tortuous, indirect paths that slow movement to a crawl. The vertical channels cut a direct route from bottom to top. In comparative tests, the aligned material wicked water at twice the speed of its randomly porous counterpart, and copper ions moved through it eight times faster.
Sunlight powers the driving force. The carbon nanoparticles embedded in the channel walls absorb solar radiation and convert it to heat at the material’s upper surface. That heat drives continuous water evaporation, which creates an upward suction through the aligned channels, pulling contaminated pore water from the surrounding soil. Under one-sun illumination, the 30 µm aerogel reached an evaporation rate of 3.36 kg·m⁻²·h⁻¹, among the highest values reported for solar-driven evaporators.
Once ions enter the material, chemistry takes over. Hydroxyl, amine, and carboxyl groups on the chitosan and carbon nanoparticle surfaces selectively bind heavy metal ions while largely ignoring common soil minerals like calcium, magnesium, and potassium. Under two-sun irradiation over seven days, the material captured 139.2 mg of copper per gram, about 1.35 times more than in the dark. That gap confirmed that solar-driven convection, not passive diffusion alone, controls remediation performance.
The relationship between evaporation rate and adsorption followed a three-stage pattern. At low evaporation rates, ion movement depended on diffusion, and adsorption stayed flat. Once evaporation crossed a threshold, convective flow took over and adsorption rose sharply. Beyond a saturation point, further increases in evaporation added little benefit. Across all conditions, the aligned aerogel outperformed both randomly structured and commercial alternatives.
The critical test was depth. The team assembled elongated aerogel columns and inserted them into 1.5-meter containers of contaminated soil under one-sun irradiation. To boost evaporation without increasing light intensity, they attached carbon nanoparticle-coated filter papers to the top of the material, mimicking leaves. A 3 cm paper nearly quadrupled the evaporation rate.
Ion removal followed a two-stage depth profile. Above a critical depth, both convection and adsorption drove heavy metal extraction. Below that line, water flow from the soil became negligible and only passive adsorption operated. Faster evaporation pushed the critical depth deeper. The aligned aerogel achieved the greatest critical depth of any material tested, confirming its advantage for reaching contamination below one meter.
In four-week tests using real contaminated soil, the artificial plant reduced copper from 94.6 to 26.9 mg·kg⁻¹. Chromium, cadmium, lead, and zinc concentrations all dropped by 40 to 70 percent. The evaporation rate held steady throughout, and the material showed no structural degradation. Sandy soils yielded the strongest results, consistent with their looser texture allowing faster convective flow.
Each aerogel unit treats a lateral radius of about 10 mm from its surface, a range that scales with diameter. Arrays of these artificial plants could cover contaminated sites, operating on solar energy alone without excavation, chemical inputs, or external power. The material’s composition can also be tuned for different target pollutants by modifying the adsorption chemistry. Where real plants take months and reach less than a meter, this system reached 1.5 meters in a week.
For authors and communications departmentsclick to open
Lay summary
Prefilled posts
Nanowerk Newsletter
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
