Inspired by the water cycle process in nature, using sunlight to drive water evaporation to obtain clean fresh water has attracted widespread attention from researchers. Under natural evaporation conditions, the utilization rate of sunlight is low and the actual evaporation is slower. Researchers are trying to apply photothermal film materials with good light absorption and photothermal conversion capabilities into solar-driven evaporation systems to improve evaporation efficiency.
Previous research has shown that a rough surface with controllable microstructure can effectively reduce the diffuse reflectance of light, achieve effective absorption of sunlight in the entire wavelength range, and is conducive to efficient water evaporation. However, the construction method of surface microstructure is relatively complex and often requires special equipment or means to complete, which increases the difficulty and cost of membrane material preparation.
Accordingly, the membrane separation and catalysis team led by Jiang Heqing, a researcher at the Qingdao Institute of Bioenergy and Processes, Chinese Academy of Sciences, proposed to use a composite strategy of nanomaterials of different dimensions to control the surface microstructure of the photothermal film, thereby improving the light capture efficiency. Obtain ideal photothermal evaporation efficiency.
By combining two-dimensional graphene and one-dimensional carbon nanotubes, the researchers achieved perturbation of the ordered structure of a single component and increased the surface roughness of the photothermal film. Through the optimization of this surface microstructure, the diffuse reflection in the solar spectrum range can be reduced to less than 4.7%, and the film surface temperature under light can reach 77°C. The disordered accumulation increases the porosity within the membrane, which is beneficial to the transmission and diffusion of water molecules within the membrane. Compared with natural evaporation, the evaporation process efficiency based on this nanocomposite photothermal film is increased by 190%, and the sunlight utilization rate exceeds 80%.
Schematic diagram of preparation of nanocomposite photothermal film based on two-dimensional graphene and one-dimensional carbon nanotubes
In practical applications, the nanocomposite photothermal film proposed in this study can not only maintain stable performance in simulated water samples containing acids, alkali and organic pollutants, but also accelerate water evaporation in seawater with different salinity contents, showing Excellent fresh water production capacity. Moreover, the preparation process of this type of photothermal composite membrane is simple and can be constructed on different porous substrates. The research results are expected to promote the preparation of clean fresh water driven by sunlight.It can be used to achieve efficient, green and sustainable seawater desalination and fresh water protection under emergency conditions. Relevant research results were published in Journal of Materials Chemistry A.
Online photothermal evaporation test system (a) and solar-driven evaporation promotion performance test of photothermal film materials (b-d)
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