Green synthesis of boron and nitrogen co-doped TiO₂ with rich B-N motifs as Lewis acid-base couples for the effective artificial CO₂ photoreduction under simulated sunlight

[Graphical abstract presents]

Boron and nitrogen co-doped Titanium dioxide (TiO₂) nanosheets (BNT) with high surface area of 136.5 m² g⁻¹ were synthesized using ammonia borane as the green and triple-functional regent, which avoids the harmful and explosive reducing regents commonly used to create surface defects on TiO₂. The decomposition of ammonia borane could incorporate reactive Lewis acid-base (B, N) pairs, together with the as-generated H₂ to create mesoporous structure and rich oxygen vacancies in pristine TiO₂. The BNTs prepared from various ammonia borane loading are evaluated in photoreduction of carbon dioxide (CO₂) with steam under simulated sunlight, achieving about 3.5 times higher carbon monoxide (CO) production than pristine TiO₂ under the same conditions. Steady state and transient optical measurements indicated BNT with reduced band gap, rich defect states and elevated conduction band position could enhance the light harvesting efficiency and promote the charge transfer at the catalyst/CO₂ interface. Density functional theory simulation and in situ FTIR suggest that the Lewis acid-base (B, N) pairs on BNT may very substantially increase the activation of inert CO₂ which facilitates their photoreduction with the hydrogen from the water splitting at the surface defects on TiO₂. Finally, a reaction mechanism of Lewis acid-base assisted CO₂ photoreduction leading to substantially improved performance is proposed.