Solar Driven Zero-Liquid Discharge of High-Salinity Phenolic Wastewater

Global freshwater scarcity and escalating hypersaline wastewater discharge challenge sustainable development. Solar-driven zero-liquid-discharge (SDZLD) technology addresses this by using localized solar heating to maximize freshwater recovery while minimizing environmental impact and carbon footprint. However, its practical application faces two major hurdles: salt crystallization at the evaporation interface and contamination of condensate by volatile organic compounds (VOCs), notably phenol. Herein, we present a floating photothermal-photocatalytic solar evaporator based on a hydrogel-sponge nanocomposite. The integration of hydrogel with sponge creates a unique biphasic heterogeneous structure, which establishes an inherent salt concentration gradient for long-term and efficient salt rejection (self-cleaning function). Simultaneously, the Schottky heterojunction formed between Ti₃C₂ MXene and BiOClI generates a strong interfacial electric field that drives efficient photocatalytic mineralization of phenol. The device operates stably for over 30 days in high-salinity wastewater (14 wt % NaCl, 10 mg L^-1 phenol), producing freshwater without salt accumulation and with phenol residues below the detection limit. Under 1-sun illumination, it achieves an evaporation rate of 2.4 kg m^-2 h^-1 with an energy efficiency of 87.8%. Life cycle assessment confirms the significant environmental benefits of our SDZLD technology and estimates a treatment cost of approximately 7.75 EUR per ton of wastewater, which is about 50% lower than that of conventional evaporation pond methods. This work provides an innovative SDZLD-centered strategy to alleviate water scarcity, contributing toward UN Sustainable Development Goal 6.1.