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.

Automated summary

The study developed a carbon nanotube/polyvinyl alcohol porous composite evaporator with high efficiency, broad solar absorption, and Janus structure, which can effectively reject salt and reduce heat loss. The evaporator demonstrated a high evaporation rate and photothermal conversion efficiency in experiments, with a high removal rate for organic matter and heavy metal ions in lake water and wastewater.