A Janus porous carbon nanotubes/poly (vinyl alcohol) composite evaporator for efficient solar-driven interfacial water evaporation

Wastewater treatment technology using evaporation at the water interface is a rapidly growing research focus in the field of solar evaporation for clean water production. And the technology has far-reaching significance for solving the increasingly global freshwater shortage problem. Herein, a multi-walled carbon nanotube/polyvinyl alcohol porous composite evaporator with high conversion efficiency, broad solar absorption, and Janus structure was prepared via a simple freeze-drying technique. In the evaporator, the anisotropic wettability of hydrophobic PDMS and hydrophilic PVA porous composite makes it a good evaporator with a high salt rejection rate of 99.86%. And the evaporator can float on the water-air interface greatly reduces the heat loss to the water and improves the light-to-heat conversion efficiency. Under 1 sun illumination (1 KW m−2), the evaporator displayed a relatively high evaporation rate of 1.34 kg m−2 h−1 and the photothermal conversion efficiency reached 85.71%. In addition, the organic matter and heavy metal ions of the lake water and the wastewater were greatly reduced after purification treatment, with the removal rate reaching 93.14% and 96.81%, respectively. Moreover, the reusability test and outdoor experiment were carried out to demonstrate its photothermal performance in practical application. In total, the solar-driven water evaporator has excellent photothermal conversion capability and durable properties and the results make it have great application potential in using solar energy evaporation to purify wastewater.