Extremely black carbon nanotube materials with three-dimensional networks for highly efficient solar-driven vapor generation

Abstract

Porous CNT sponge (CNTS) and aligned CNT array (CNTA) were used as light absorbers to generate water vapor by harvesting solar energy. To improve the wettability of water on superhydrophobic CNTs and enhance water transport in porous CNT materials, CNTs were decorated with a hydrophilic silk fibroin (SF) protein coating. Water rapidly infiltrates the porous SF-modified CNT materials. Importantly, strong water–SF interactions via the hydrogen bonding between SF protein molecules and CNT sidewalls resulted in a reduction in the vaporization enthalpy of water in the SF-modified CNT materials, which facilitated vapor generation. Additionally, the SF-modified CNT light absorbers exhibit excellent vapor generation performance over a wide pH range of 2 to 12 and good stability. The SF-modified CNT materials thus have the advantage of being potentially applicable to the purification of wastewater and desalination of brackish water with high or low pH values. SF-CNTA light absorbers with vertically aligned CNTs, which are of great benefit in water transport and vapor escape, achieved a water evaporation rate of 3.2 kg m⁻² h⁻¹ under one sun irradiation with an energy transfer efficiency of 94%. After a desalination treatment, the concentrations of primary ions in seawater are greatly decreased and meet the requirements for drinking water.