Quantitative tailoring of water state of sulfonated corncob for boosting solar interfacial evaporation and salt resistance

Previous researches on carbon-based solar interfacial evaporation (SIE) have mainly focused on improving the solar absorption, neglecting the effect of water state on the SIE performance. This study proposes an easy strategy by combining carbonization and sulfonation using corncob as the carbon source and concentrated sulfuric acid (H2SO4) as the sulfonating agent to obtain sulfonated carbonized corncob (SCC) samples. The intermediate water to free water (IW/FW) ratio in the range of 0.53–0.96 within SCC samples has been tailored, which depends on the amount of hydrophilic sulfonic acid groups grafted on SCC. It is found that the amount of hydrophilic sulfonic acid groups and porous structure should be optimal in SCC for high IW/FW ratio. The optimized sample named as SCC-2-4.5 with a high IW/FW ratio of 0.96 and similar surface area to carbonized corncob exhibits the low enthalpy of water evaporation of 1800 J g−1, achieving the evaporation rate of 3.16 kg m−2 h−1 and evaporation efficiency of 159%. Meanwhile, SCC-2-4.5 realizes an effective separation of Na+ and Cl−, thanks to the electrostatic repulsion caused by its negatively charged sulfonic acid groups. This study provides an effective technique for regulating water state for carbon-based SIE devices on the molecular level.