Enhanced Total Contactless Photothermal Desalination by Translucent Thin Film Coating of Crystalline Nanocellulose

The innovative approach of harnessing abundant solar energy to facilitate water purification holds great potential for addressing a diverse range of water-related challenges. Utilizing the same method of photothermal desalination is highly promising, sustainable, and cost effective. However, in photothermal desalination, generally, steam is generated at the liquid-air interface. Despite its immense potential, this results in a lower evaporation rate and is prone to salt fouling. Therefore, to address two main challenges, (1) fouling and (2) maximum interfacial temperature (100 °C), here, we report total contactless photothermal desalination by a translucent thin film coating of Crystalline Nanocellulose (CNC). In contactless photothermal desalination, the active photothermal layer remains in no physical contact with the saline water; thus, automatic antifouling and a temperature above the boiling point of water can be achieved for water purification. In this report, we have sustainably extracted CNC from waste sawdust by a sonochemical extraction method using minimal chemicals. Additionally, the sonoextraction method through cavitation helps in the desulfation of CNC. These thermally stable and highly crystalline CNCs are used in making active translucent photothermal active layers for photothermal desalination. CNCs were well characterized by both microscopic and spectroscopic techniques. In the photothermal desalination, the results show an augmented evaporation rate of ∼3.30 kg/m²·h and virtually infinite recyclability for longer usability. Moreover, the integrated setup reported here comprises an independent module with a highly flexible design that mimics the greenhouse effect for a high solar-to-steam output.