Plasmon-powered chemistry with visible-light active copper nanoparticles

In the quest for affordable materials for performing visible-light driven chemistry, we report here intriguing optical and photothermal properties of plasmonic copper nanoparticles (CuNPs). Precise tuning of reaction conditions and surface functionalization yield stable and monodisperse CuNPs, with a strong localized surface plasmon absorption at ∼580 nm. The molar extinction coefficient is estimated to be ∼7.7 × 10⁷ M^-1 cm^-1 at 580 nm, which signifies their suitability for various light-harnessing studies. The characteristic wine-red colour and crystallography studies confirm the presence of mainly Cu(0) atoms in CuNPs, which showed excellent long-term colloidal and compositional stability under ambient conditions (at least 50 days). The as-synthesized oleylamine-capped CuNPs are ligand-exchanged with charged thiolate ligands of both polarities to form stable dispersions in water, with complete retention of their plasmonic properties and structural integrity (for ∼2 days and ∼6 h under inert and ambient conditions, respectively). Photothermal-conversion efficiency of CuNPs is estimated to be ∼80%, raising the surrounding temperature to ∼170 °C within ∼30 s of irradiation with a 1 W 532 nm diode laser, which is 'hot' enough to perform useful solar-vapor generation and high-temperature crystal-to-crystal phase transformation. Our work projects plasmonic CuNPs as an affordable and effective alternative to conventional metal NPs to harness light-matter interactions for future plasmon-powered chemistry.