Direct in situ activation of Ag⁰ nanoparticles in synthesis of Ag/TiO₂ and its photoactivity

Graphical abstract: - Highlights: • Ag⁰ loaded on TiO₂ was prepared by a direct in situ electrochemical method. • 5 wt% Ag–TiO₂ demonstrated the best photocatalytic degradation of 2-CP. • Isomorphous substitution of Ag with Ti occurred to form Ti−O−Ag bonds. • Ag⁰ and oxygen vacancies trapped electrons to enhance e–H⁺ separation. • Substitution of Ag in the TiO₂ structure decreased the number of oxygen vacancies. - Abstract: Metallic Ag nanoparticles (Ag⁰) were successfully activated using a direct in situ electrochemical method before being supported on TiO₂. Catalytic testing showed that 5 wt% Ag–TiO₂ gave the highest photodegradation (94%) of 50 mg L⁻¹ 2-chlorophenol (2-CP) at pH 5 using 0.375 g L⁻¹ catalyst within 6 h, while under similar conditions, 1 wt% and 10 wt% Ag–TiO₂ only gave 75% and 78% degradation, respectively. Characterization results illustrated that the photoactivity was affected by the amount of Ag⁰ and oxygen vacancies which act as an electrons trap to enhance the electron–hole separation. While, the Ag−O−Ti bonds formation reduced the photoactivity. The degradation followed a pseudo-first order Langmuir–Hinshelwood model where adsorption was the controlling step. Study on the effect of scavengers showed that the hole (H⁺) and hydroxyl radical (OH·) play important roles in the photodegradation. The regenerated photocatalyst was still stable after five cycling runs