| May 26, 2025 |
Researchers developed a green synthesis strategy using ionic liquids to control gold aerogel structure, boosting recyclability and catalytic degradation of pollutants.
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(Nanowerk Spotlight) Metal aerogels (MAs) are a class of novel porous materials entirely constructed from metallic nanostructures. Among them, Au aerogels have attracted particular attention for their high stability, excellent electrical conductivity, unique plasmonic properties, and outstanding catalytic activity. To further unlock their application potential, precise control over their ligament size (dL) is crucial.
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Although significant advances have been made in regulating dL, most synthetic methods suffer from low efficiency, high cost, and poor environmental compatibility. So far, the preparation of surface-clean Au aerogels with a widely tunable dL remains a major challenge.
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Featuring porous structures and abundant catalytically active sites, MAs have recently been explored for environmental remediation. Conventionally, to enhance catalytic performance, MAs are ultrasonically dispersed into aqueous solutions before being introduced into the reaction system. However, this process disrupts their self-supporting structure, limits recyclability, increases processing costs, and may even lead to secondary pollution.
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To address these issues, Professor Ran Du’s team at Beijing Institute of Technology, in collaboration with Researcher Jin-Hu Dou’s group at Peking University, proposed a novel ionic liquid (ILs)-mediated sol-gel strategy for the green synthesis of MAs. By introducing ILs during the sol–gel process, the researchers achieved fine control over dL and systematically revealed the multifunctional roles of ILs—as initiator, ligand, and solvent.
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Furthermore, the team investigated the structure–property relationships of the resulting Au aerogels in catalytic degradation of organic pollutants in water. Notably, this work marks the first introduction of a light field into MA-mediated water treatment systems, confirming the significant enhancement effect of light irradiation. The self-healing nature of the Au hydrogel also greatly improved the recyclability and stability of the material during catalytic reduction.
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| Figure 1. Investigation of ionic liquids-mediated fabrication of gold aerogels. (Image: Courtesy of the researchers)
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The team’s findings are published in(Advanced Functional Materials (“Deciphering the Multi‐Faces of Ionic Liquids: Manipulating Size‐Tailored Gold Aerogels as Recoverable Catalysts for Water Remediation”)
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ILs, composed entirely of cations and anions, possess several advantageous properties such as environmental friendliness, low volatility, strong solvating power, and tunable composition. Based on the structure of methylimidazolium-type ILs, the study demonstrated that ILs function as initiator, ligand, and solvent in the synthesis of Au aerogels. This strategy was also successfully extended to other metals (Ag, Pd, Rh, Ru) and multi-metallic systems including binary, ternary, quaternary, and quinary alloys.
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| Figure 2. Analysis of the ligand and solvent function played by ionic liquids. (Image: Courtesy of the researchers)
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As initiators, ILs can trigger the sol–gel process at concentrations as low as 0.3 μM, overcoming the limitations of conventional initiators that typically require large quantities and higher costs. As ligands, adjusting the alkyl chain length or the ILs concentration enables precise tuning of the aerogel feature size, yielding Au aerogels with sizes ranging from 8.2 to 22.7 nm, and Ag aerogels ranging from 88.3 to 142.7 nm. As solvents, ILs provide a stable environment that helps maintain the porous network of wet gels under various conditions such as air exposure or heating.
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Additionally, the team developed a green and recyclable ILs recovery strategy via salt-induced phase separation. After gel formation, adding sodium carbonate allows efficient phase separation of ILs from the aqueous system, achieving a recovery yield of ~87.5%. The recovered ILs can be directly reused for subsequent aerogel synthesis, demonstrating their potential as recyclable additives for sustainable and customizable aerogel production.
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| Figure 3. Water remediation by gold aerogels. (Image: Courtesy of the researchers)
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In the treatment of wastewater containing highly toxic nitrophenol pollutants, Au aerogels demonstrate remarkable catalytic performance. Using the reduction of 4-nitrophenol by NaBH4 as a model reaction, the study found that the catalytic efficiency of Au aerogels is inversely correlated with dL. The 8.2 nm Au aerogel achieved 90% conversion within 5 min.
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More importantly, the nanostructured network of the aerogel facilitates multiple light absorption and scattering events, generating localized photothermal effects that further enhance catalytic activity. This work represents the first application of light-enhanced catalysis in MA-mediated water treatment, with the apparent rate constant (kapp) increasing by up to 3.7 times under UV illumination.
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It is worth noting that during catalytic testing, ultrasonic dispersion is often employed to improve mass transfer, but this process can cause mechanical damage to the aerogel structure. Beneficially, the Au hydrogel exhibits outstanding self-healing capability, enabling spontaneous reassembly into monolithic structures after reaction, thereby significantly improving its recyclability and long-term usability.
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This work reveals the multifunctional roles of ILs—as initiator, ligand, and solvent—in the synthesis of gold aerogels and successfully extends the strategy to a range of metals and alloys. It establishes a clear structure–property relationship in catalytic water treatment and provides a general, green pathway for the controlled synthesis of high-performance, recyclable metal aerogels, paving the way for their broader application in environmental remediation.
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Source: Original text provided by Beijing Institute of Technology
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