可控电纺核-壳温敏荧光纳米材料及其用于Pickering乳液和油/水分离的研究

The nanoparticles and nanofibers coated by PNIPAM to form core/shell structure can switch hydrophilicity to hydrophobicity on surface caused by the rise of temperature. The core-shell nanoparticles and nanofibers have been successfully applied in Pickering emulsions and oil/water separation, respectively. Up to now, the core-shell nanoparticles and nanofibers are usually prepared via controllable living free radical polymerization such as ATRP, RAFT and SET-LRP which are not suitable for production in large scale. Meanwhile, cellulose has not been used for develop core-shell nanomaterials prepared via electrospinning, yet. NaOH/urea aqueous solution at -12℃ has been regarded as efficient green solvent of cellulose. Aimed at preparing core-shell nanoparticles and nanofibers which both are composed of cellulose coated by PNIPAM via electrospinning, this proposal based on the cellulose dissolution in NaOH and urea aqueous solution at -12℃, will firstly apply coaxial electrospinning to prepare core-shell nanoparticles, and apply coaxial and conventional electrospinning in cellulose/PNIPAM mixed solution to prepare core-shell nanofibers, responsively. The resultant core-shell nanoparticles and nanofibers will be used as thermo-responsive Pickering emulsifiers and oil/water separation materials, respectively. Moreover, quantum dots will be strategically introduced into the shell of Pickering emulsifiers and functional mechanism of thermo-responsive Pickering emulsifiers can be explained by the optical properties of quantum dots influenced by temperature variations in association with the motion process of quantum dots in the emulsion.

以PNIPAM为壳层材料的核-壳型纳米球与核-壳型纳米纤维具备通过改变温度切换材料表面亲/疏水性的功能，分别在Pickering乳液和油水分离中发挥了重要作用。目前，制备以PNIPAM为壳层的核-壳型纳米材料主要通过ATRP、RAFT、SET-LRP等可控活性自由基聚合，难度大且不利于大规模生产。低温NaOH/尿素水溶液被认为是绿色高效的纤维素溶剂，然而尚未作为静电纺丝体系制备核-壳型纤维素纳米材料。本项目将基于-12℃纤维素/NaOH/尿素水溶液体系，拟通过静电纺丝分别制备以PNIPAM为壳层、纤维素为核层的核-壳型纳米球和核-壳型纳米纤维。首先，通过同轴电纺制备核-壳型纳米球；其次，通过同轴电纺和混合溶液电纺分别制备核-壳型纳米纤维；所制备的材料将分别作为温敏型Pickering乳化剂和油水分离材料。此外，通过同轴电纺将量子点固定在温敏型Pickering乳化剂中以研究其乳化机理。

将聚N-异丙基丙烯酰胺（PNIPAM）作为壳层材料的核-壳型纳米微球作为Pickering乳化剂，能够通过控制温度切换乳液乳化/破乳，从而实现工业生产的连续性。通过传统化学方法制备核-壳型微球不仅实验条件要求苛刻，并且所制备的微球材料多为凝胶状，不便于运输及使用。同轴静电喷雾技术能够一步制备具有核-壳型精细结构的固态纳米球。本项目系统开展了四个方面的研究：（1）同轴静电喷雾制备核-壳型纳米球；（2）核-壳型纳米球作为Pickering乳化剂；（3）温敏型碳点的制备及其作为Pickering乳化剂；（4）生物碳/纳米纤维气凝胶复合材料的制备及其油/水分离。研究结果表明以醋酸纤维素和PNIPAM分别作为核层和壳层聚合物，采用同轴静电喷雾成功制备了单分散的核-壳型纳米球，其表面呈现明显的温敏性；将核-壳型纳米球作为Pickering乳化剂，在25 ℃时能够分别乳化正庚烷/水和甲苯/水体系，形成稳定的水包油型乳液，并且通过升高温度（35~45 ℃）能够实现完全破乳。核-壳型纳米球乳化正庚烷/水的最低浓度为3.5 mg/mL，其液滴表面的纳米球覆盖率较低，随着纳米球浓度增加，液滴平均直径不断减小；当纳米球浓度达到15.3 mg/mL时，液滴发生团簇；随着纳米球浓度进一步增大，液滴表面的纳米球由单层包覆变成多层包覆，使得乳液更加稳定。以葡萄糖/咪唑型离子液体为原料成功制备了水溶性的荧光碳点，在25 ℃时此碳点能够乳化水/正己烷体系；通过碳点表面接枝PNIPAM成功制备了温敏型碳点，作为Pickering乳化剂能够通过控制温度实现水/甲苯体系的乳化和破乳。以柚子皮为原料制备了多孔生物碳，并与电纺PVDF、SiO2纳米纤维相结合制备了纳米纤维气凝胶复合材料，此复合材料具有较大的比表面积和较强的吸油能力和乳液分离效率，对三氯甲烷的最大吸附量达到85.31 g/g，对甲苯/水乳液的分离效率超过99 %。