Mild Synthesis of Ag-Decorated TiO ₂ Aerogels for Light-Driven CO ₂ Reduction

Nanoparticle gelation is a powerful method for creating porous, crystalline, and translucent aerogels, but it requires stable, concentrated dispersions. Conventional methods for dispersing TiO₂ often rely on strong acids like HCl, which are corrosive and limit compatibility with acid-sensitive materials. In this work, we introduce a novel approach using trisodium citrate to functionalize TiO₂ nanoparticles, forming a highly dispersed colloid stable from pH 3 to 12. This approach enables TiO₂ nanoparticle gelation under previously inaccessible conditions, including slightly acidic (pH = 4), near-neutral (pH = 6.5), and mildly alkaline (pH = 9). Our synthesis uses a metal alkoxide as precursor, avoiding TiCl₄ and eliminating HCl as byproduct. We demonstrate cogelation of silver (Ag) and TiO₂ nanoparticles at near-neutral pH, overcoming Ag corrosion challenges found in acid-based methods. The resulting Ag/TiO₂ aerogels are catalytically active for CO₂-to-CO reduction, a key step in developing fossil-free chemical processes. Under visible light, these aerogels show significantly enhanced catalytic performance, highlighting their promise for photothermal catalysis. This citrate-based, chloride-free route broadens the range of accessible multicomponent aerogel compositions for diverse applications, particularly in the realm of (photo)-catalysis and optical materials.