A Self-Floating Solar Evaporator Based on Carbon Black/Polydimethylsiloxane for Highly Efficient and Stable Desalination.

Abstract

The global shortage of freshwater resources is intensifying, prompting the development of solar-driven interfacial evaporation as a promising solution. However, the scalability of existing evaporators remains limited due to high costs, complex fabrication, insufficient stability, and poor salt tolerance. Traditional polymer-based Janus membranes also exhibit low mechanical strength and inadequate weather resistance. While some carbon-based or composite evaporators have demonstrated high performance, their large-scale application is hindered by expensive materials and intricate manufacturing processes. To address these limitations, this study utilizes low-cost commercial melamine foam (MF) as a substrate. Through sol-gel synthesis and spray coating, a Janus-structured CB-PDMS/PMF evaporator is fabricated by compositing carbon black (CB) and polydimethylsiloxane (PDMS) onto the MF surface. The design innovatively employs a water-isolation method to precisely control the thickness of the photothermal layer and the flatness of the evaporation interface. The upper hydrophobic photothermal layer (P layer) absorbs and converts light, while the lower hydrophilic water-transport layer (W layer) enables capillary-driven water supply and self-floating capability, thereby minimizing heat loss. Furthermore, a surface-patterned honeycomb structure enhances light absorption via multireflection, and the Marangoni effect is leveraged to suppress salt accumulation, ensuring excellent salt rejection. Experimental results demonstrate that the optimized Eva-4 evaporator achieves a stable evaporation rate of 1.1 kg·m-2·h-1 under 1 kW·m-2 solar irradiation, with a photothermal conversion efficiency of 75%. It exhibits robust cycling stability, neutralizes strongly acidic/alkaline feedwaters, and produces desalinated water that meets WHO drinking standards. Moreover, the evaporator maintains high salt tolerance across varying salinities. This work provides a cost-effective, scalable approach based on simple fabrication techniques, advancing the application of solar-driven interfacial evaporation for large-scale desalination and wastewater remediation.