Enhanced solar steam generation using CNTs-HEC/PVDF porous composite membrane
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摘要: 太阳能界面水蒸发技术在解决目前人类所面临的能源和淡水资源短缺方面具有广阔的应用前景。水输运是太阳能水蒸发过程中十分重要的一环。理想状态下的水输运是输送适量的水来维持太阳能蒸发层高效、稳定的水蒸发。而蒸发层所拥有的多孔结构所产生的毛细管作用力决定了其水输运的能力。因此，蒸发层内部的孔隙结构非常重要。本文以聚偏氟乙烯(PVDF)为基体，借助碳纳米管(CNTs)的优异光吸收能力，通过羟乙基纤维素(HEC)掺杂并与戊二醛进行交联制备了可用于太阳能界面水蒸发的CNTs-HEC/PVDF多孔复合膜。CNTs-HEC/PVDF复合膜的多孔结构形成的微通道提高了水输运和蒸汽逸出能力，从而增强了太阳能界面水蒸发性能。在1 kW·m−2的太阳光照射下，其水蒸发速率达到1.81 kg·m−2·h−1，相应的光热转化效率为95%。相关实验结果还展现出该复合膜具有优异的循环使用性能、化学稳定性和高效的污水净化能力。Abstract: Solar interface water evaporation technology has a broad application prospect in solving the shortage of energy and fresh water resources that mankind is currently facing. Water transport was a very important step in the solar steam generation process. The ideal water transport was to transport the right amount of water to maintain efficient and stable water evaporation from the solar evaporation layer. The capillary force generated by the porous structure of the evaporation layer determined its ability when transporting water. Therefore, the pore structure inside the evaporation layer was very important. In this paper, a porous carbon nanotubes-hydroxyethyl cellulose/polyvinylidene fluoride (CNTs-HEC/PVDF) composite membrane for solar interfacial water evaporation was produced, which was doped with HEC and cross-linking with glutaraldehyde on a PVDF depended on the excellent light absorption capacity of CNTs. The solar interfacial water evaporation performance was improved as the microchannels formed by the porous structure of CNTs-HEC/PVDF composite membranes enhanced water transport and vapor escape. The water evaporation rate reaches 1.81 kg·m−2·h−1 under 1 kW·m−2 of solar irradiation, and the corresponding photothermal conversion efficiency is 95%. The relevant experimental results also show that the composite membrane has excellent recycling performance, chemical stability and efficient sewage purification ability.
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图 1 不含羟乙基纤维素(HEC)的碳纳米管/聚偏氟乙烯(CNTs/PVDF)样品图像(a)及其SEM图像((b), (c))；含有HEC的CNTs-HEC/PVDF样品图像(d)及其SEM图像((e), (f))
Figure 1. Photographs of carbon nanotubes/polyvinylidene fluoride (CNTs/PVDF) sample without hydroxyethyl cellulose (HEC) (a) and SEM images ((b), (c)); Photographs of CNTs-HEC/PVDF with HEC (d) and SEM images ((e), (f))
图 2 CNTs/PVDF ((a), (b))和CNTs-HEC/PVDF ((c), (d))的水接触角；(e)不同复合膜的紫外-可见-近红外吸收光谱
AM 1.5G—Air mass 1.5 global
Figure 2. Water contact angle of CNTs/PVDF ((a), (b)) and CNTs-HEC/PVDF ((c), (d)); (e) UV-Vis-NIR absorption spectra of different membranes
图 3 去离子水、CNTs/PVDF复合膜和CNTs-HEC/PVDF多孔复合膜界面的蒸发性能：(a)质量变化；(b)光热转换效率(左)和水蒸发率(右)；(c)本体水温变化；(d)表面温度
Figure 3. Evaporation performance at the interface of pure water, CNTs/PVDF composite membrane and CNTs-HEC/PVDF porous composite membrane: (a) Mass change; (b) Photothermal conversion efficiency (Left) and water evaporation rate (Right); (c) Bulk water temperature change; (d) Surface temperature
图 4 不同 CNTs浓度复合膜对太阳能水蒸发性能的影响：(a)质量变化；(b)光热转换效率；(c)蒸发率(左)和平均表面温度(右)；(d) 整体水温变化
Figure 4. Effects of different CNTs concentration composite membranes on solar water evaporation performance: (a) Mass change; (b) Photothermal conversion efficiency; (c) Evaporation rate (Left) and average surface temperature (Right); (d) Bulk water temperature change
图 5 不同HEC浓度复合膜对太阳能水蒸发性能的影响：(a)质量变化；(b) 光热转换效率；(c) 蒸发率(左)和平均表面温度(右)；(d) 整体水温变化
Figure 5. Effects of different HEC concentration composite membranes on solar water evaporation performance: (a) Mass change; (b) Photothermal conversion efficiency; (c) Evaporation rate (Left) and average surface temperature (Right); (d) Bulk water temperature change
图 6 甲基橙(MO)溶液(a)和罗丹明B (RhB)溶液(b)经CNTs-HEC/PVDF多孔复合膜处理前后的吸收光图谱和实物图
Figure 6. Absorption spectra and physical pictures of methyl orange (MO) solution (a) and rhodamine B (RhB) solution (b) before and after CNTs-HEC/PVDF porous composite membrane treatment
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