Generalized Synthesis of Highly‐Dispersed, Ultrafine Transition Metal Nanoparticles on Silica Spheres for Enhanced Optical Absorption

Robust synthesis of ultrafine metal nanoparticles (ufMNPs) below 5 nm with clean surfaces and strong optical absorption in the visible spectral range is challenging due to their instability originating from large surface-to-volume ratios. This work reports a general strategy involving two sequential steps: i) loading metal precursor ions onto the surface of silica nanospheres (SiO_x NSs) by forming a uniform coating of metal oxyhydroxide [MO_y(OH)_z] through preferred surface acid-base reactions and ii) thermally reducing MO_y(OH)_z in forming gas at elevated temperatures to form ufMNPs evenly dispersed on the surface of SiO_x NSs. The capability of this synthesis strategy is verified by loading ufMNPs of various transition metals and bimetallic combinations onto the SiO_x NSs. The ufMNPs exhibit strong optical absorption enhanced by the optical scattering resonances in the SiO_x NSs, which generate intense electric fields near the surface of the SiO_x NSs. The SiO_x NSs also support stabilizing the ufMNPs, which do not need additional organic capping reagents. The successful synthesis of SiO_x-NS-supported ufMNPs with clean surfaces and enhanced optical absorption is promising for exploring the photocatalytic properties of ufMNPs.