Abstract:

Objective With low power consumption and environmental friendliness, interfacial solar-driven steam generation technology has been expected to moderate water scarcity from the explosive growth of industry and population. Based on this technology, the multistage desalination devices are prepared for high-efficient freshwater collection.

Method The 3-D carbon fiber array structure was constructed on the copper plate with excellent thermal conductivity by electrostatic flocking technology, and it was used as a photothermal layer to achieve outstanding light absorption. Non woven fabric with excellent hydrophilicity was used as a water transport channel. After the hydrophobic treatment, the copper plate acted as a water collection layer to rapidly obtain lots of freshwater. Based on the above three components, a ten-stage multistage desalination device with an inclined angle was prepared for high-efficient freshwater collection.

Results The photothermal layer, which was fabricated with carbon fiber arrays and copper plate by electrostatic flocking technology, can reach a high temperature of 78.4 ℃ for the top surface and 73.7 ℃ for the bottom surface under one-sun irradiation(Fig. 4). It shows the excellent photothermal effect and heat conduction. And it mainly benefits from the design of a three-dimensional array structure and the excellent photothermal properties of carbon fiber. It is seen that after the optimization of materials and fabric weight, the non-woven viscose fabric with 80 g/m² can reach a wicking height of 18.1 cm within 30 min, and it spreads rapidly to 5 cm in 3 min. It has an excellent ability for water transport and diffusion, and it can continuously supply water for the photothermal layer during solar-vapor generation(Fig. 5, Fig. 7). The optimized copper plate has excellent hydrophobicity after the hydrophobic treatment. The surface of the copper plate has the shape of hierarchical porous petal-like nanostructures. The tightly packed petal-like structures increase the surface roughness of the copper plate and reduce the surface energy, to improve the surface hydrophobicity of the copper plate. At last, its water contact angle can reach 130°. Based on the above three components, firstly, a single-stage device was constructed to optimize the air gap in Fig. 10. And the highest water collection rate of 0.39 kg/(m²·h) was obtained when the air gap was 3 mm. Therefore, with an air gap of 3 mm, a ten-stage multistage desalination device can achieve a water collection rate of 2.05 kg/(m²·h)(Fig. 11). The water collection rate kept unchanged when the number of device stages was further increased.

Conclusion In our work, with low-cost and simple materials, such as copper plate, carbon fiber and non-woven fabric, a ten-stage multistage desalination device was prepared for high-efficient water collection. With excellent water transport performance, the nonwoven fabric can transport water from bulk water to every photothermal layer for evaporation. Due to the good photothermal effect, the photothermal layer can obtain a high temperature. And with outstanding heat conductivity, the photothermal layer efficiently evaporates the water of non-woven fabric to generate steam. Large amounts of steam condense on the copper sheet to form freshwater. Moreover, the hydrophobic copper plate causes the condensed water to form a waterdrop. Thus, it can reduce latent heat loss. Finally, due to the design of the inclined copper plate, the water droplets slide quickly and are collected. Our multistage seawater desalination device can provide a new idea for the design of efficient solar-driven interfacial devices. It is expected to be one of the effective ways to obtain freshwater in remote and backward areas.

Key words: electrostatic flocking, nonwoven fabric, interfacial solar-vapor conversion technology, multi-stage desalination devices, water collection, solar energy