【Frontiers in HaiChuan Chemical Technology】The Institute of Physics and Chemistry, Chinese Academy of Sciences has made a series of advances in the field of biomass aerogels
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The Institute of Physics and Chemistry has made a series of advances in the field of biomass aerogels. A gel is a three-dimensional porous material formed by the aggregation of colloidal particles or polymer chains, featuring abundant nanoscale pores, and boasts advantages such as a high specific surface area and high porosity. Since its inception, it has become a \"star material\" in both academia and the industry. Over the past decade, with the growing acceptance of the concept of sustainable development, biopolymer aerogels have become a focus of research in materials science due to their high-density functional groups and high biocompatibility. Among the various biomass polymer materials, chitosan is the second most abundant polymer in nature after cellulose. More importantly, its molecular structure contains a large number of amino groups, which endow it with certain unique properties: good water solubility. The amino groups can be protonated to NH3+ in aqueous acidic solvents, facilitating their dissolution; this makes it possible to develop various approaches for designing and constructing micro- and nano-structures using bottom-up molecular methods ； Amino groups possess high chemical reactivity and biomedical functions ； Amino groups can serve as a nitrogen source for N-doped carbon materials. Thanks to these properties, the microsphere research group at the Oil and Gas Development and Energy-Saving/Environmental Protection New Materials Research Center of the Institute of Physics and Chemistry has carried out research on chitosan aerogels in areas such as heat insulation, electromagnetic wave absorption, seawater desalination, and gas adsorption over the past few years. In the field of thermal insulation, the research team prepared an anisotropic chitosan aerogel that is lightweight, large in size, elastic, and possesses excellent thermal management properties, through unidirectional freeze casting and silanization modification. Theoretical calculations were used to analyze the influence of the microstructure on mechanical and thermal properties, as well as the anisotropic heat transfer behavior. Anisotropic chitosan aerogels exhibit a honeycomb-like porous and layered structure, granting them advanced thermal management properties; their radial thermal conductivity is low (30.4 mW m-1 K-1) whereas their axial thermal conductivity is twice as high (60.1 mW m-1 K-1). The calculation results show that the thermal management capability of anisotropic chitosan aerogels is superior to that of isotropic materials (with thermal conductivities of 10 and 22 mW m-1 K-1, respectively). This provides a reference for further designing biopolymer aerogels for ultra-insulation applications. (ACS Sustainable Chemistry & Engineering. 2021, 9, 28, 9348-9357)
To meet the needs of more complex applications, the research team added hollow glass microspheres in different proportions to chitosan aerogel, taking full advantage of the synergistic effect between the chemical cross-linking of chitosan aerogel to form a network structure and the accumulation of hollow glass microspheres to create a skeletal structure. This approach enabled the creation of biomass aerogel/hollow glass microsphere composites with low density, high porosity, low thermal conductivity, good mechanical properties, and excellent flame-retardant characteristics. Compared to traditional adhesives that cannot form a network structure, hollow glass microspheres are typically filled to their maximum volume; otherwise, they distribute unevenly within the adhesive, resulting in reduced performance of the composite material. Unlike traditional adhesives, chitosan aerogels with a porous network structure can not only reduce the thermal conductivity due to their high porosity, but also adjust the filling volume of hollow glass microspheres through chemical cross-linking to achieve a uniform distribution. On the other hand, when the filling ratio of hollow glass microspheres is increased to over 40%, it not only enhances the flame-retardant effect but also allows the evenly distributed hollow glass microspheres to aggregate to form a skeletal structure, thereby improving the mechanical properties of the composite material. Through the synergy between the two, it is possible to regulate the properties of composite materials in terms of density, thermal conductivity, mechanical strength, and flame retardancy. (International Journal of Biological Macromolecules. 2024, 256, 2, 128329) In the field of seawater desalination, the research team designed a sustainable evaporator based on chitosan aerogels, which combines light absorption, heat management, water transport, and salt resistance. A solar interfacial evaporator with a chitosan aerogel-carbon nanotube (CA-CNT) bilayer structure was prepared by a simple deposition method. The hydrophilic CA substrate features low thermal conductivity and a vertically arranged pore structure, which helps to improve the evaporation efficiency, water transport capacity, and salt resistance of the evaporator. The upper-layer CNTs exhibited an excellent solar light absorption rate of 95.04%. At a solar intensity of 1 kW m-2, the evaporation rate of the evaporator is 1.55 kg m-2 h-1. Its practical applicability was tested under natural outdoor lighting conditions, with a fresh water yield of 7.15 kg m-2 d-1, which is sufficient to meet the daily water needs of three adults. Furthermore, this evaporator also exhibits good capacity for purifying wastewater containing heavy metals and dyes. This work provides a simple strategy for obtaining fresh water from seawater and wastewater. (Chemical Engineering Journal Advances. 2022, 10, 15, 100260)
To further improve the evaporation performance and salt tolerance of the evaporator, the research team prepared chitosan/carbon nanotube aerogels with radial pores using a one-pot in-situ strategy and radial freezing method, and employed dust-free paper rods as channels for one-dimensional upward water transport, thereby constructing a novel 3D-structured solar interfacial evaporator (R-CSC). Its unique water transport pathway enhances the radial transport of the salt solution at the top of the evaporator, allowing salts to deposit selectively at the top edge, thereby achieving zero liquid discharge and salt recovery. Experiments and thermodynamic calculations have shown that increasing the height of the evaporator can effectively improve evaporation performance. For an R-CSC evaporator with a diameter of 1.7 cm, when the evaporator height is increased to 3 cm, the solar evaporation rate reaches 2.93 kg m-2 h-1, and the solar evaporation efficiency is 97.86 %. In addition, the effect of relative humidity on the evaporation performance of 3D evaporators was also systematically studied. On this basis, further research was conducted on the effects of material properties, aqueous solutions, and operating environments on the salt deposition behavior in evaporators, which can guide researchers in making rational designs based on specific conditions to achieve directional salt deposition at the edges. (Chemical Engineering Journal. 2025, 515, 1, 163411)
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