Enhanced Photocatalytic Efficiency of a Least Active Ag-TiO₂ by Amine Adsorption

An Ag-TiO₂ photocatalyst with 3.5 atom % silver content, synthesized by a single step sol-gel method, possessed silver nanoparticles (AgNPs; 1-5 nm) on the TiO₂ surface, but owing to the nonplasmonic nature of AgNPs and the wide band gap of TiO₂, this material exhibited poor activity in a photocatalytic degradation reaction. However, this least active Ag-TiO₂ catalyst showed a sudden increase in activity during a photocatalytic amine self-coupling reaction showing the highest activity, which was interpreted as amine (reactant) adsorption-driven activity enhancement. We found that amine adsorption occurred over AgNPs converting into plasmonic AgNPs as well as on the TiO₂ surface reducing the band gap and therefore facilitated the visible light excitation and the electron-transfer process efficiently, resulting into overall enhancement in the photocatalytic activity. Thus, a very efficient, stable, and visible light active photocatalyst (amine-adsorbed Ag-TiO₂) was developed by simply adsorbing an amine in the least active Ag-TiO₂ photocatalyst.