SiO₂/TiO₂/Ag multilayered microspheres: Preparation, characterization, and enhanced infrared radiation property

Graphical abstract: - Highlights: • Novel SiO₂/TiO₂/Ag core–shell multilayer microspheres with tunable TiO₂ and Ag layers were prepared. • Complete Ag shell was fabricated by Ag-seeds growth process. • The SiO₂/TiO₂/Ag core–shell composites exhibited the good infrared emissivity value than SiO₂ and SiO₂/TiO₂ substrates. - Abstract: SiO₂/TiO₂/Ag core–shell multilayered microspheres were successfully synthesized by the combination of anatase of TiO₂ modification on the surfaces of SiO₂ spheres and subsequent Ag nanoparticles deposition and Ag shell growth with face-centered cubic (fcc) Ag. The composites were characterized by TEM, FT-IR, UV–vis, Raman spectroscopy and XRD, respectively. The infrared emissivity values during 8–14 μm wavelengths of the composites were measured. The results revealed that TiO₂ thin layers with the thickness of ∼10 nm were coated onto the SiO₂ spheres of ∼220 nm in diameter. The thickness of the TiO₂ layers was controlled by varying the amount of TBOT precursor. Homogeneous Ag nanoparticles of ∼20 nm in size were successfully deposited by ultrasound on the surfaces of SiO₂/TiO₂ composites, followed by complete covering of Ag shell. The infrared emissivity value of the SiO₂/TiO₂ composites was decreased than that of pure SiO₂. Moreover, the introduction of the Ag brought the remarkably lower infrared emissivity value of the SiO₂/TiO₂/Ag multilayered microspheres with the lowest value down to 0.424. Strong chemical effects in the interface of SiO₂/TiO₂ core–shell composites and high reflection performance of the metal Ag are two decisive factors for the improved infrared radiation performance of the SiO₂/TiO₂/Ag multilayered microspheres