Abstract
In this study, agricultural waste luffa vines (LVs) were used to develop solar evaporators by surface carbonization and KOH treatment combined with freeze-drying method. Scanning electron microscopy (SEM), solar absorption, solar thermal management and salt dissolution tests showed that the water vapor generation rate of a single column of LV-based solar evaporator after surface carbonization was as high as 3.26 kg m−2 h−1 under 1 sun, and its evaporation efficiency (118%) even exceeded the theoretical valve. After 36 h of continuous use, there was almost no salt deposition. Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle, thermal conductivity, evaporation enthalpy, and low field nuclear magnetic resonance (LF-NMR) analyses indicated that the high evaporation efficiency of LV-based solar evaporators after surface carbonization was mainly due to high water transport capacity, low water evaporation enthalpy, and high light absorption rate (91%) of LV. The excellent salt-deposition resistance benefitted from the natural multilayered gradient porous structures of LV, forming spontaneous salt backflowing systems. The desalinization rate of LV-based solar evaporators exceeded 99.9%, which was even higher than those of many membrane elements and thermal desalination systems. They also had excellent removal effects on dyes and oily wastewater. After 30 d of continuous soaking, the compressive strength of 2–cm LVs was still 9.4 MPa. KOH-freeze-drying treatment further improved the salt-deposition resistance of LV-based solar evaporators, but reduced their evaporation efficiency and mechanical performance. This work suggests that LVs with carbonized surface have significant potential for development of environmentally friendly biomass solar evaporators with efficient evaporation, excellent resistance to salt deposition, and good durability.
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