New Insight into Organic Nanoparticle Formation to Improve Solar H2

Organic semiconductor nanoparticles are carbon-based materials that can absorb sunlight and drive photocatalytic reactions, making them promising candidates for solar energy and clean fuel technologies. Until now, researchers believed that with one of the most common methods for making these particles—using ultrasonication to mix liquid components—worked by first forming droplets of solvent (in a miniemulsion) that are later evaporated to form a particle dispersion in water. But a new study published in ACS Nano reveals this isn’t the full story. A team at EPFL’s LIMNO lab discovered that during mixing, the semiconductor materials are actually extracted directly from the solvent into water, forming nanoparticles before evaporation even happens. This unexpected shortcut explains why other researchers have found it difficult to control the particle size, which is important for tuning performance. By switching to a gentler mixing method, the researchers found they could slow this process down and better control the size of the nanoparticles. Smaller particles were found to double hydrogen production compared to larger ones. Yet, the particles made via the original, faster route—were even smaller at just 25 nanometers—and performed up to 14 times better. This breakthrough in understanding not only improves our fundamental knowledge of how these particles form but also points to the factors limiting their performance. Ultimately the improved control over the performance of these nanoparticles can lead to greener, more efficient ways to harness sunlight for clean and sustainable fuels.