超疏水纤维素复合气凝胶的制备及其油水分离

纤维素气凝胶因具有强亲水性和低油水选择性,且目前纤维素气凝胶表面的疏水化处理过程较冗长,限制了其在油水分离领域的应用。为了解决上述问题,笔者以硫酸水解微晶纤维素制备得到的纳米纤维素(CNC)为原料,利用甲基三甲氧基硅烷(MTMS)在水相中对其进行硅烷化改性,通过冷冻干燥得到了硅烷化纤维素复合气凝胶。结果表明:所制备的纤维素复合气凝胶具有轻质、多孔特性,随着MTMS添加量的增加,密度逐渐升高(≤0.012 0 g/cm^3),孔隙率略有下降; MTMS的加入对纤维素复合气凝胶的微观形貌影响不大,其骨架结构以二维片层形貌为主,聚甲基硅氧烷均匀地包覆在纤维素片层表面; MTMS的加入使纤维素复合气凝胶的热稳定性明显提高,且未改变纤维素气凝胶的晶型结构,但导致其结晶度逐渐下降。纤维素复合气凝胶的表面接触角随着MTMS添加量的增加而升高,最高达到153.7°,表现出优异的超亲油/超疏水性能。作为吸油材料,超疏水纤维素复合气凝胶不仅可以吸附多种油类和有机溶剂(吸附容量达到52～121 g/g),而且表现出很好的循环使用性能。

Fabrication of superhydrophobic cellulose composite aerogels for oil/water separation

Due to the hydrophilicity and low oil/water absorption selectivity, the unmodified cellulose-based aerogels are limited for the oil/water separation application. Furthermore, the surface hydrophobic modification process of cellulose aerogels is time-consuming, which limits the large-scale production of aerogel-based absorption materials. In order to solve these problems, the authors fabricated superhydrophobic cellulose composite aerogels by freeze-drying the suspensions of cellulose nanocrystals (CNC), a natural nanomaterial isolated by sulfuric acid hydrolysis of microcrystalline cellulose, in the presence of methyltrimethoxysilane (MTMS) with various concentrations. The modified cellulose composite aerogels displayed ultralight property and porous structure with the density ranging from 0.0052g/cm^3 to 0.0120g/cm^3 and the porosity ranging from 99.66% to 99.30%. The SEM images showed that the addition of MTMS had little effect on the morphology of the cellulose composite aerogels with 2D-sheet-like skeleton structure. The polymethylsiloxane formed a thin layer on the cellulosic substrate and did not change the porous structure of the cellulose aerogel. Compared with the unmodified cellulose aerogel, the modified cellulose composite aerogels remained the cellulose Ⅰ structure, while the crystallinity of the composite aerogel decreased with the increase of MTMS usage. Meanwhile, the thermal stability of the cellulose composite aerogel was enhanced with the increase of MTMS usage. The surface contact angle of the modified cellulose composite aerogels increased with the increase of MTMS usage. The highest surface contact angle was up to 153.7°. The modified cellulose composite aerogel could float on the water surface and displayed good oil/water absorption selectivity because of its excellent superhydrophobic/superoleophilic properties. As the oil absorption material, the superhydrophobic cellulose composite aerogel not only efficiently absorbed a wide range of oils and organic solvents with absorption capacities in the range of 52-121 g/g, but also exhibited remarkable recyclability.