Chun-gong Li,Qi Dang,Qinqin Yang,Dong Chen,Hongliang Zhu,Jiachen Chen,Runjin Liu,Xiang Wang
In order to investigate the pore properties and effect of storage time on the microstructure of CO2-dried aerogels, chitosan aerogel beads were obtained from chitosan hydrogels with an initial concentration in the range of 1.5–3.0 wt% through SCCO2 drying and freeze-drying (as a comparison). The SCCO2-dried chitosan aerogels showed a three-dimensional network structure, and had higher BET surface area (200 m2 g−1) and higher crystallinity (0.62/XRD, 0.80/ATR-FTIR) than the freeze-dried aerogels. The stability of the microstructure of the SCCO2-dried chitosan aerogel beads during 10 months was studied. The BET surface area of the aerogel beads at each concentration declined by 30.5% at 2 months, 56.7% at 6 months and 67.2% at 10 months. Accelerated aging tests of the chitosan aerogel beads were carried out to study the effect of humidity on the chitosan aerogel beads. The average diameter of the chitosan aerogel decreased from 2.3 mm to 0.9 mm when stored at 65 °C with 90% relative humidity (RH). In contrast, there was no obvious change during storage at 65 °C with 20% RH. The amount of adsorbed water increased from 4% to 12% at 65 °C with 90% RH for 96 h, and the bound water content of the aerogel beads gradually increased. This study demonstrates that SCCO2-dried chitosan aerogel beads could be better at maintaining their mesoporous structure, and the adsorption of water from the surrounding air had a significant effect on the microstructure and shrinkage of the chitosan aerogel beads.
Hydrophobic microcrystalline cellulose (MCC) aerogel is synthesized using microcrystalline cellulose and NaOH/urea solution as precursors through the sol–gel route and alkylation hydrophobic coagulation bath. Especially, the effects of different drying modes and content of MCC on the physical chemistry properties are investigated. The results show that samples using nano-self-assembly method combined supercritical CO 2 drying possess loose and uniform porous three-dimensional network structure. The specific surface areas before and after modification are 180.28 m 2 /g and 154.37 m 2 /g with average pore sizes at 22.58 nm and 25.71 nm. The hydrophobic angle is up to 154.3°, the maximum adsorption efficiency can reach 12 g/g, which is also of reusability after 5 adsorption tests. This hydrophobic MCC aerogel has excellent adsorption performance, and simple, rapid, effective oil contamination treatment which is of use in oil adsorption.
The objective of this research was to develop new hydrophobic silica aerogel microspheres (HSAMs) with water glass and hexmethyldisilazane for oil adsorption. The effects of the hexmethyldisilazane concentration and drying method on the structure and organic liquid adsorption capacity were investigated. The hexmethyldisilazane concentration of the modification solution did not influence the microstructure and pore structure in a noteworthy manner, which depended more on the drying method. Vacuum drying led to more volume shrinkage of the silica gel microsphere (SGM) than supercritical CO2 drying, thus resulting in a larger apparent density, lower pore volume, narrower pore size distribution, and more compact network. Owing to the large pore volume and pore size, the HSAMs synthesized via supercritical CO2 drying had a larger organic liquid adsorption capacity. The adsorption capacities of the HSAMs with pore volumes of 4.04–6.44 cm3/g for colza oil, vacuum pump oil, and hexane are up to 18.3, 18.9, and 11.8 g/g, respectively, higher than for their state-of-the-art counterparts. The new sorbent preparation method is facile, cost-effective, safe, and ecofriendly, and the resulting HSAMs are exceptional in capacity, stability, and regenerability.
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