Bamboo-based carbon composites with hollow magnetic nanostructures achieve high electromagnetic shielding through absorption, combining low weight, structural integrity, and thermal performance for advanced electronic applications.
(Nanowerk Spotlight) The electromagnetic spectrum has become increasingly congested as wireless signals from digital devices accumulate across overlapping frequency bands. As consumer electronics, wireless networks, and connected infrastructure expand into every corner of daily life, devices increasingly operate in dense signal environments that produce interference and radiative leakage. Smartphones, electric vehicles, home automation systems, and industrial robotics all generate electromagnetic fields that can disrupt nearby components or expose users to radiative emissions. At high frequencies, this interference can degrade signal integrity, destabilize precision equipment, and prompt safety concerns in medical and residential contexts.
The traditional solution — surrounding devices in metal enclosures — works, but at a cost. These materials are heavy, rigid, and environmentally taxing to produce. In applications where weight, flexibility, and sustainability matter, metal shielding becomes a liability. To address this, researchers have explored lightweight polymer-based alternatives and carbon-based nanomaterials, including carbon nanotubes, graphene, and MXenes. These offer electrical conductivity and wave attenuation without the burden of metal. But they are expensive to manufacture and often require synthetic precursors or complex processing. Worse, many of them reflect electromagnetic energy instead of absorbing it, increasing the risk of secondary interference rather than solving it.
One promising direction is to combine electrical and magnetic components within porous carbon frameworks derived from biological materials. This approach takes advantage of the intrinsic structure of plant matter, which offers mechanical strength, low density, and hierarchical porosity ideal for wave scattering and energy dissipation. Most efforts to date have focused on wood as the starting material, but its slow growth rate and relatively high density limit its scalability. A faster-growing alternative with similar structural characteristics is bamboo, which has attracted growing interest as a base for bio-derived shielding materials.
Still, a recurring limitation remains. Biomass-derived materials tend to rely heavily on electrical conduction for shielding and suffer from poor impedance matching with free space. As a result, much of the incident energy is reflected rather than absorbed. To solve this, researchers have begun embedding magnetic nanoparticles in carbonized biomass, aiming to add magnetic loss mechanisms to the existing conductive ones. The challenge is doing so without adding weight, sacrificing porosity, or compromising structural integrity during high-temperature processing.
The result is a thin, mechanically robust, and electrically conductive material that achieves high electromagnetic shielding through absorption rather than reflection. The authors use a combination of chemical templating and structural engineering to produce a material that is simultaneously magnetic, conductive, and architecturally suited to trapping electromagnetic waves. The process is designed for scalability and relies on low-cost, renewable inputs.
To produce the composite, the researchers chemically treated bamboo to remove lignin and introduce carboxyl groups into the cellulose scaffold. These functional groups allowed cobalt ions to bind to the surface, where they reacted with ferricyanide ions to form uniform crystals of a cobalt–iron Prussian blue analog, a type of metal–organic framework (MOF).
The authors then etched these crystals using tannic acid, which selectively dissolved the internal core of each nanocube while preserving the shell. This step created hollow nanostructures capable of supporting multiple internal reflections. The final material was obtained by compressing and carbonizing the entire structure at high temperature under nitrogen.
The resulting composite, referred to as HCoFe@CN/BC-900, was only 0.14 millimeters thick and had a density of 0.278 grams per cubic centimeter. Despite its low mass, it achieved an electromagnetic shielding effectiveness of 50.1 decibels across the 8.2 to 12.4 gigahertz range. This means it blocked more than 99.999 percent of incident radiation. The reflection component was limited to 6.57 decibels, indicating that most of the energy was absorbed rather than reflected.
Schematic illustration of as-prepared HCoFe@CN/BC composites. (Image: Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
This performance results from several coordinated mechanisms. The bamboo-derived carbon framework forms a continuous network that conducts electrons, allowing incoming radiation to dissipate as heat. The embedded cobalt–iron particles provide magnetic loss pathways through natural resonance and eddy currents. The hollow interiors of the nanocages increase internal surface area and create multiple points of scattering and reflection, giving electromagnetic waves more opportunities to be absorbed. In addition, interfacial polarization at the boundary between metal and carbon promotes local charge buildup, which enhances dielectric loss.
Microscopy confirmed that the hollow structures remained intact after carbonization. Spectroscopic analysis showed that the carbon matrix had a high degree of graphitization and good electrical conductivity. X-ray diffraction and electron microscopy identified the presence of cobalt–iron alloy particles. Electrical conductivity reached 51.3 siemens per centimeter, while magnetic measurements showed strong ferromagnetic behavior. The specific surface area of the composite was 172.1 square meters per gram, with a pore volume of 0.055 cubic centimeters per gram.
The shielding performance was further evaluated using a metric that normalizes shielding effectiveness by both thickness and density. This specific shielding efficiency, or SSE/t, reached 12,872.6 decibels·square centimeters per gram. This places the material ahead of most previously reported biomass-derived composites and many synthetic ones. The authors attribute this to the combined effects of electrical conduction, magnetic loss, internal scattering, and interfacial polarization — all of which contribute to enhanced wave attenuation without requiring bulky material.
In addition to its electromagnetic properties, the composite exhibited strong thermal performance. When a low voltage of 2 volts was applied, the surface temperature rose to 118 degrees Celsius within 15 seconds. The temperature response was linear with voltage squared, in line with Joule’s law. The material maintained stable performance over repeated heating and cooling cycles, indicating reliable electrothermal conversion. This dual functionality opens the possibility of using the composite not only for shielding but also for active heat management in smart home applications.
The team demonstrated the material’s capabilities in practical scenarios. When placed between a Tesla coil and a wireless charging device, the composite blocked transmission entirely. In a model simulating an infant crib exposed to electromagnetic fields, the material prevented induced current from reaching a test object. Simulation data showed that the specific absorption rate dropped to nearly zero with the composite in place. These results highlight the material’s ability to block both electric and magnetic components of the field, protecting nearby equipment or people from exposure.
The study also emphasized the simplicity and scalability of the process. Unlike many shielding materials that rely on intricate nanofabrication or exotic inputs, this composite begins with a fast-growing plant and uses standard chemical treatments. The hollow nanostructures are produced through mild etching, and the entire system is processed through compression and heat treatment. This gives the material a lower environmental footprint and positions it well for integration into flexible, large-area applications such as interior coatings, thermal films, or wearable devices.
By combining hollow magnetic nanostructures with a porous carbon framework derived from bamboo, the authors have achieved a material that meets multiple performance goals simultaneously. It is thin, light, conductive, and magnetically responsive. It absorbs rather than reflects electromagnetic energy. It can be manufactured from renewable feedstock using a streamlined process. And it performs well under electrical load, making it suitable for integrated thermal management.
The results suggest a viable route toward scalable, sustainable shielding materials for next-generation electronic systems. The design principles demonstrated here — coupling structural hierarchy with electrical and magnetic functionality in a low-density matrix — may apply to a wider class of bio-derived composites aimed at electromagnetic and thermal control in complex environments.
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