A team of researchers from City University of Hong Kong, Hong Kong Polytechnic University, and Newcastle University has developed a large-scale, 3D printed, self-floating evaporator that significantly advances solar-driven interfacial desalination, according to results published in Nature Communications. Built from a concave-shaped AlSi10Mg alloy using additive manufacturing, the system reaches nearly 100% photothermal evaporation efficiency, achieving an evaporation rate of 2.23 kg/m²/h and a freshwater collection rate of 1.23 kg/m²/h under one sun. Its floating modular design provides durable, scalable performance while addressing major limitations in fouling, salt accumulation, and energy input.
The core evaporator was fabricated using a 3D metal printer at 370 W and a print speed of 1300 mm/s. It features a polypyrrole-decorated photothermal top layer, an oxidized aluminum alloy (A-O) transition layer, and a PTFE-sealed bottom surface with superhydrophobic properties. Sequential chemical oxidation, electrodeposition, and partial surface sealing were used to assemble the layered structure. Additional components include a replaceable 2D water-intake layer, a lattice-like resin support with low thermal conductivity, and a floating freshwater collector embedded with copper fins. These elements form a modular, maintenance-friendly system suitable for portable and remote operation.
Materials and structural properties were analyzed using scanning electron microscopy (Sigma 500), energy dispersive X-ray spectrometry (Shimadzu EDX-720), and X-ray diffraction (D2 PHASER XE-T). Solar absorption was measured with a Hitachi UH4150 UV-Vis-NIR spectrophotometer and a VERTEX 70 v FTIR spectrometer. Thermal conductivity testing used the Hot Disk TPS 2500S system. Laboratory solar simulation was carried out using a CEL-PE300L-3 PerkinElmer 300W source. FLIR E8xt thermal imaging and KEYSIGHT DAQ970A systems were used to map temperature profiles, and contact angles were measured using a DataPhysics tester. Droplet behavior was captured with a pc0.dimax HS4 high-speed camera. Outdoor conditions during field tests were recorded using a YGY-CJY4 data acquisition unit. Thermal and vapor transport simulations were performed in COMSOL Multiphysics version 5.6.
The concave evaporator structure demonstrated enhanced optical trapping and surface absorption. When decorated with polypyrrole nanoparticles, it reached an average solar absorption of 98.1%. Heat transfer efficiency was confirmed through FLIR thermal mapping and finite element simulations, showing consistent bottom-surface evaporation across all tested conditions. Stability tests conducted over 17 days revealed sustained performance with evaporation rates of 2.23 kg/m²/h, maintained by simply renewing the water-intake layer. Contact angle measurements exceeded 135°, confirming superhydrophobicity. Electrochemical corrosion tests in 3.5 wt% NaCl solution showed a corrosion potential of −0.59 V for sealed oxidized layers, significantly improving over untreated aluminum.
Field trials at Wu Kai Sha Pebbles Beach, Hong Kong, evaluated a full-scale setup integrating a fixed cover and freshwater collector. Embedded copper fins improved thermal convection and enhanced condensation, resulting in a freshwater collection rate of 1.23 kg/m²/h. No external power was required. Cooling was achieved passively through heat exchange with ambient seawater.
The evaporator’s decoupled architecture ensures that water is absorbed only through the bottom, keeping the top absorber layer dry and preventing salt crystallization. PTFE nanoparticle sealing further blocks ion penetration, while chemical oxidation stabilizes the outer aluminum surface. Performance in brine (25 wt% NaCl) remained stable over a 13-day period. ICP-OES testing confirmed that post-desalination concentrations of Na⁺, K⁺, Ca²⁺, and Mg²⁺ all fell within World Health Organization guidelines for drinking water, with sodium levels dropping from 10,800 mg/L to 5.0 mg/L.
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Featured image showcase 3D hierarchical floating setup for photothermal interfacial evaporation. Image via Nature Communications.
