An aerogel is a solid-like material produced by drying a gel and removing its solvent, resulting in a substance that appears solid on the outside but contains numerous pores filled with air, giving it extremely low density. In March 2013, scientists at Zhejiang University developed an ultra-light material known as "carbon-based aerogel," which has a density of just 0.16 mg/cm³—only one-sixth that of air—and is currently the lightest material in the world. 
Material Introduction 
An aerogel is a solid-like material formed by drying a gel and removing its solvent, resulting in a structure that appears solid on the outside but contains numerous pores filled with air, giving it an extremely low density. A research team led by Professor Gao Chao from the Department of Polymer Science and Engineering at Zhejiang University successfully created a new record for the "lightest material" by freeze-drying a water solution containing two nanomaterials—graphene and carbon nanotubes—at low temperatures, thereby removing water while preserving the structural framework. The previous record holder was a material called "graphene aerogel," developed by German scientists at the end of 2012, with a density of 0.18 milligrams per cubic centimeter. This breakthrough was published online on February 18, 2013, in the journal Advanced Materials and featured prominently with an illustration in the "Research Highlights" section of Nature magazine. 1


Features Introduction 
"The structure of 'all-carbon aerogel' resembles that of a 'carbon sponge,' so even if you place an aerogel the size of a coffee cup on a blade of dogtail grass, the delicate grass hairs won't bend," said Gao Chao. 
Although it appears "extremely fragile," the "all-carbon aerogel" demonstrates remarkable structural resilience, quickly recovering after being compressed to 20% of its original volume thousands of times. Moreover, the "all-carbon aerogel" is one of the most effective materials for oil absorption. Conventional oil-absorbing products typically absorb only about ten times their own weight in organic solvents, whereas the "all-carbon aerogel" can absorb up to 900 times its own mass. 1


Our country has successfully developed 
On March 19, Professor Gao Chao from the Department of Polymer Science and Engineering at Zhejiang University presented a solid-state material made of "all-carbon aerogel." 
Scientists at Zhejiang University have developed an ultra-light material known as "all-carbon aerogel," with a density of just 0.16 milligrams per cubic centimeter—making it the lightest material ever created. Aerogels are formed by drying gels in a semi-solid state and removing their solvents, resulting in solid-looking materials filled with numerous pores saturated with air, which gives them extremely low density. Professor Gao Chao's research group from the Department of Polymer Science and Engineering at Zhejiang University successfully froze-dried a water solution containing graphene and carbon nanotubes under low-temperature conditions, eliminating water while preserving the structural framework, thereby setting a new record for the world's lightest material. The previous record holder was a material called "graphene aerogel," developed by German scientists at the end of 2012, with a density of 0.18 milligrams per cubic centimeter. According to reports, the "all-carbon aerogel" is also one of the most effective oil-absorbing materials available. Conventional oil-absorbing products typically absorb only about ten times their own weight in organic solvents, whereas the all-carbon aerogel can absorb up to 900 times its own mass. 
Aerogels are the lightest known material, recognized by Guinness World Records. They earned their name due to their numerous internal pores filled with air. In 1931, American scientists first created aerogels using silica, nicknamed "frozen smoke." In 2011, researchers from HRL Laboratories in the U.S., the University of California, Irvine, and the California Institute of Technology collaborated to produce an aerogel made of nickel, with a density of just 0.9 milligrams per cubic centimeter—setting a record as the world's lightest material at the time. When placed on a dandelion flower, the soft绒毛 showed almost no deformation—a photograph that was selected as one of Nature magazine’s top ten images of the year and left Gao Chao deeply impressed: could he develop a material capable of challenging this limit? 
China's graphite reserves are extremely abundant, accounting for two-thirds of the world's total. Scientists have long been exploring ways to utilize graphite more efficiently. "Transforming graphite into graphene—a single-layer sheet structure composed of carbon atoms—can increase its value by thousands of times." After five or six years of research, Gao Chao's team has successfully developed one-dimensional graphene fibers and two-dimensional graphene films. This time, they aim to create three-dimensional porous graphene materials to break this record. 1


Easy to make 
Shape and size can be freely adjusted, enabling large-scale manufacturing. 
In the laboratory, reporters saw carbon sponges of various sizes—some as large as tennis balls, others as small as wine bottle stoppers. Under an electron microscope, carbon nanotubes and graphene jointly support countless pores. 
"Just like large-scale spatial structures such as sports stadiums, which use steel bars as supports and high-strength membranes as walls, the materials are both lightweight and strong overall," said Sun Haiyan, a doctoral student in the research group. "Here, carbon nanotubes serve as the framework, while graphene acts as the wall." 
Among the reported achievements, the "carbon sponge" developed by Professor Gao Chao's research group still holds the record for being the lightest material—reaching a density of 0.16 milligrams per cubic centimeter, lower than that of helium. The related paper was published online in Advanced Materials on February 18. However, the team has little interest in applying for a Guinness World Record, as "lightness is not its most significant innovation," Gao explained. Instead, its value lies in its simple preparation method and the outstanding properties demonstrated by the material. 
Scientists explained that the fundamental principle of aerogel preparation involves removing the solvent from a gel while preserving its intact framework. In previous methods, researchers primarily used the sol-gel process and template-directed approaches. The former allows for batch synthesis but lacks controllability; the latter produces ordered structures but relies on the precise structure and size of templates, making large-scale production difficult. The group led by Gao Chao took an alternative route and developed a novel template-free freeze-drying method: by freeze-drying an aqueous solution containing graphene and carbon nanotubes at low temperatures, they obtained "carbon sponges" with freely adjustable shapes. This approach simplifies the manufacturing process and enables large-scale production and application of this ultra-light material. 
"No templates are needed; it only depends on the container. The size of the container determines the size that can be produced, which can reach thousands of cubic centimeters or even larger," said Gao Chao. 1


Superior performance 
High elasticity and strong adsorption, with broad application prospects 
The title of the Nature magazine review is "Solid Carbon: Elastic and Lightweight," highlighting the surprising performance of this novel material. 
The "carbon sponge" is highly elastic, capable of returning to its original shape even after being compressed by 80%. It exhibits ultra-fast and ultra-high adsorption capacity for organic solvents, making it the most oil-absorbent material reported to date. Conventional oil-absorbing products typically absorb only about ten times their own weight in liquid, whereas the carbon sponge can absorb approximately 250 times its weight, with a maximum capacity reaching up to 900 times its weight—and it absorbs only oil, not water. This "feast-eating" material absorbs organic substances at an astonishing speed: each gram of the carbon sponge can absorb 68.8 grams of organic matter per second. Researchers suggest this makes it ideal for handling oil spills at sea: "We could simply scatter them on the ocean surface to rapidly absorb spilled oil. Thanks to their elasticity, the absorbed oil can be squeezed out for recovery and reuse, and the carbon sponges themselves can be reused." 
Currently, the laboratory is conducting further applied research on the adsorption properties of this material. Researchers say that "carbon sponge" could also become an ideal phase-change energy storage insulation material, a catalyst support, an acoustic absorber, and a high-performance composite material. However, like a newborn baby, this emerging material is still in its early stages, and scientists find it difficult to accurately predict its application areas and future prospects. It will depend on the imagination of society and industry to bring this new material out of the lab and realize its practical value. 1


Material Applications 
All-carbon aerogels are expected to play a significant role in addressing environmental pollution, such as oil spill cleanup at sea, water purification, and even air purification. Traditional methods of aerogel production often fail to enable mass manufacturing, but the research team's newly developed "low-temperature freeze-drying method" makes the production process much more convenient, paving the way for large-scale fabrication and application of this ultra-light material. 
Nature magazine has featured this research in its "Research Highlights" section, accompanied by a prominent illustration and commentary. The "all-carbon aerogel" is expected to play a significant role in addressing environmental pollution, including oil spill cleanup at sea, water purification, and even air purification. 
In 2013, the laboratory was conducting further applied research on the adsorption properties of this material. Besides pollution control, "all-carbon aerogel" could also become an ideal material for energy storage and thermal insulation, catalytic supports, and sound absorption. 1


Contributors to this entry: 
Cheng Peng - Associate Professor - Southwest University  
Source: Science Popularization China