Nanosilver-Coated Organic Porous Films: Integrating Photothermal Evaporation and Hydrogen Generation through the Breath Figure Method

Water scarcity is now a major problem and more regions are hitting the limits of what their freshwater systems can handle. Industrial growth and urban expansion do not help, and the traditional desalination methods—reverse osmosis or multi-stage flash—still demand too much power to be practical on a large scale. They do work but at a cost that poorer regions simply can’t sustain. That’s why solar-driven interfacial evaporation (SDIE) has attracted a lot of attention lately because it takes advantage of sunlight directly at the air–water boundary and generate vapor where it’s needed most. It heats only a thin surface layer rather than the whole water body, the energy efficiency is far higher than with conventional thermal systems. But the reality is, SDIE isn’t ready for broad deployment. Two problems keep coming up. One is the need for affordable photothermal materials that absorb sunlight across a wide spectrum and keep performing after months of use. The other is managing salt accumulation without clogging the structure that feeds the water upward. Silver nanoparticles have strong plasmonic properties that make them almost ideal light absorbers, but they oxidize easily and their absorption band is narrow. And the porous supports that hold these nanoparticles—usually made through sol–gel or template-etching methods—require complicated, sometimes toxic chemistry. Therefore, the technology sits in an awkward spot: brilliant in theory, but still waiting for a material system that’s simple, durable, and truly scalable. To this account, new research paper published in Industrial & Engineering Chemistry Research and conduced by Ruiyun Cai, Jian Jiang, Rui Jiao, Professor Hanxue Sun Zhaoqi Zhu, Jiyan Li and Professor An Li from the Lanzhou University of Technology, the researchers developed two synergistic models: a breath-figure-engineered photothermal evaporation model, describing heat and mass transfer through hierarchical porous membranes, and a plasmon-enhanced photocatalytic model explaining hot-electron generation and hydrogen evolution under illumination.

The team began their fabrication process with the preparation of a PMMA solution in dichloromethane containing a surfactant, didodecyldimethylammonium bromide (DDABr). When this solution was drop-cast onto glass substrates under controlled humidity, condensation droplets from ambient air templated a regular honeycomb network as the solvent evaporated. The resulting film exhibited low-tortuosity vertical channels and uniform pores, forming an ideal scaffold for nanoparticle loading. Monodisperse AgNPs, approximately 25 nm in diameter, were synthesized separately through a polyol reduction of silver nitrate in ethylene glycol. Poly(vinyl alcohol) was used as both a stabilizer and antioxidant, ensuring long-term nanoparticle stability. The AgNP dispersion was then spin-coated onto the PMMA membrane to yield the final PMMA/AgNP composite layer. The authors performed scanning electron microscopy which showed successful formation of uniformly distributed silver nanoparticles embedded within the polymer matrix, while atomic force microscopy confirmed a modest reduction in surface roughness due to nanoparticle infiltration. X-ray diffraction patterns exhibited sharp reflections indexed to metallic silver, and verified the crystalline state of the nanoparticles. Moreover, conducting mercury intrusion porosimetry demonstrated that, although average pore diameters decreased from 2.1 µm to 0.7 µm after AgNP modification, the overall porosity rose to about 63%, reflecting the optimized hierarchical pore structure. Furthermore, mechanical testing showed that AgNP incorporation had negligible influence on tensile strength or flexibility, on the other hand thermogravimetric analysis indicated improved thermal stability. Additionally, the team conducted optical characterization which highlighted the strong broadband absorption of the PMMA/AgNP film (> 87% across 250–2500 nm) enhanced by multiple internal reflections within the porous matrix. The authors Under simulated sunlight (1 kW m⁻²), infrared thermography recorded a rapid surface temperature rise from 22 °C to 46 °C within five minutes, outperforming pristine PMMA. During interfacial evaporation tests, the composite achieved an evaporation rate of 1.76 kg m⁻² h⁻¹ and a photothermal conversion efficiency approaching 96%. Even in brine concentrations up to 15% NaCl, performance remained nearly unchanged, demonstrating excellent salt tolerance through ion-gradient-driven back-diffusion. Moreover, the evaporator retained over 90% of its efficiency after ten operational cycles. Beyond desalination, the film displayed remarkable photocatalytic behavior. In a three-electrode setup using a Na₂SO₄ electrolyte, illumination increased the photocurrent by 26% compared with dark conditions, confirming plasmon-enhanced charge generation. Hydrogen evolution rates reached 48.4 mmol m⁻² h⁻¹, supported by electrochemical impedance measurements showing significantly reduced charge-transfer resistance. The system thus transformed absorbed solar energy into both thermal and chemical outputs with impressive stability.

In conclusion, the work of Professor An Li and colleagues developed novel frameworks that can elucidate the dual functions of their PMMA/AgNPs platform (efficient solar evaporation and simultaneous hydrogen production) and the merged these models within a single, scalable material system managed to link desalination and renewable energy conversion. This is an important advancement in the design of multifunctional solar evaporators that unite desalination and hydrogen production and the team achieved a level of material integration rarely seen in interfacial evaporation research by combining the breath figure method with plasmonic nanostructures. The BF approach, which relies solely on humidity-induced self-assembly, eliminates the need for complex template removal or chemical etching, providing an environmentally benign and scalable fabrication pathway. This simplicity could make the technique attractive for large-area membrane manufacturing, especially in regions with limited infrastructure or resources. The PMMA/AgNPs evaporator is novel because it absorbs sunlight across nearly the full spectrum and converts it into heat with remarkable efficiency, but still maintains strong capillary water flow through its porous network. The structure itself is key—its vertical pores help draw water continuously while the surrounding polymer matrix traps heat just long enough to sustain rapid evaporation. Balancing these two behaviors is not trivial, but the authors’ results are impressive: superb evaporation rate and thermal efficiency, and no significant salt crystallization even after extended operation. The film also withstood repeated cycling in brine without visible degradation, which says a lot about its mechanical integrity and chemical stability under stress. What makes this material especially interesting is that its plasmonic layer drive evaporation and also supports hydrogen generation. The same localized surface plasmon resonance that heats the interface promotes charge separation for photoelectrochemical water splitting. In practical terms, that means the new device can desalinate during the day while simultaneously producing hydrogen, effectively recycling sunlight into both clean water and stored chemical energy.