Self-Floating Efficient Solar Steam Generators Constructed Using Super-Hydrophilic N,O Dual-Doped Carbon Foams from Waste Polyester

Abstract

Solar evaporation is recognized as a prospective technique to produce freshwater from non-drinkable water using inexhaustible solar energy. However, it remains a challenge to fabricate low-cost solar evaporators with obviously reduced water evaporation enthalpy to achieve high evaporation rates. Herein, N,O dual-doped carbon foam (NCF) is fabricated from the low-temperature carbonization of poly(ethylene terephthalate) (PET) waste by melamine/molten salts at 340 °C. During carbonization, melamine reacts with carboxylic acids of PET degradation products to yield a crosslinking network, and then molten salts catalyze the decarboxylation and dehydration to construct a stable framework. Owing to rich N,O-containing groups, 3D interconnected pores, super-hydrophilicity, and ultra-low thermal conductivity (0.0599 W m−1 K−1), NCF not only achieves high light absorbance (ca. 99%) and solar-to-thermal conversion, but also promotes the formation of water cluster to reduce water evaporation enthalpy by ca. 37%. Consequently, NCF exhibits a high evaporation rate (2.4 kg m−2 h−1), surpassing the-state-of-the-art solar evaporators, and presents good anti-acid/basic abilities, long-term salt-resistance, and self-cleaning ability. Importantly, a large-scale NCF-based outdoor solar desalination device is developed to produce freshwater. The daily freshwater production amount per unit area (6.3 kg) meets the two adults' daily water consumption. The trash-to-treasure strategy will give impetus to the development of low-cost, advanced solar evaporators from waste plastics for addressing the global freshwater shortage.