Scalable biodegradable Janus solar evaporator derived from wastepaper and tea residue for sustainable seawater desalination and wastewater purification

Abstract

Solar-driven interfacial evaporation (SDIE) offers a promising route for clean water production with reduced dependency on traditional energy sources, yet the development of sustainable and scalable solar evaporators remains a key challenge. Herein, a biodegradable and scalable Janus solar evaporator fabricated from recycled wastepaper and tea residue is proposed, promoting eco-friendly clean water production while valorizing waste materials. The incorporation of 2D Ti3C2 (MXene) and 1D multi-walled carbon nanotubes (MWCNT) forms a 3D macroscopic photothermal architecture, with enhanced light trapping and synergistic heat localization, significantly boosting evaporation performance. The evaporator achieves a high evaporation rate of 1.52 kg m−2h−1 with a solar-to-vapor conversion efficiency of 90.79% under one sun illumination. It exhibits durable salt-rejection capability via an inherent salt-blocking mechanism, ensuring long-term desalination stability. Furthermore, it effectively purifies simulated industrial wastewater without compromising its evaporation performance. An outdoor prototype system demonstrates freshwater production of ≈6.8 L m−2 day−1 under average solar irradiance of 0.54 kW m−2, underscoring its potential for scalable and sustainable solar water treatment.