Hot carrier photocatalysis using bimetallic Au@Pt hemispherical core–shell nanoislands

We report the fabrication of core–shell Au@Pt nanoislands grown on glass substrates using a facile and reproducible combination of magnetron sputtering and thermal annealing. Au@Pt NPs exhibit a lattice strain of ~ 0.2% and a slightly positively charged Au core due to electron transfer from Au to Pt during equilibration. The localized surface plasmon resonance peak of Au redshifts incrementally from 2.13 to 2.0 eV and broadens in a controllable manner with the addition of ultrathin Pt shells (1–3 nm). This has been linked to the hemispherical morphology of the nanoislands and the high index glass substrate with subsequent resonance peak broadening as a consequence of the high annealing temperatures utilized. The quality factor of the LSPR resonance decreased gradually from ~ 13 to ~ 3 as bare Au nanoislands were coated with 3 nm of Pt. The Au@Pt nanoislands demonstrated superior methylene blue degradation performance (up to efficiencies of 31%) due to the hot hole injection from the bimetallic nanoparticle into the dye molecule despite the absence of any semiconducting photocatalytic support. Raman thermometry studies involving Stokes and anti-Stokes spectra helped shed light on the hot electron dynamics of the composite system and validated hot carrier injection from Au to Pt.