Selective Photocatalytic Reduction of CO₂ to CO Mediated by Silver Single Atoms Anchored on Tubular Carbon Nitride

Abstract

Artificial photosynthesis is a promising strategy for converting carbon dioxide (CO 2 ) and water (H 2 O) into fuels and value-added chemical products. However, photocatalysts usually suffered from low activity and product selectivity due to the sluggish dynamic transfer of photoexcited charge carriers. Herein, we describe anchoring of Ag single atoms on hollow porous polygonal C 3 N 4 nanotubes (PCN) to form the photocatalyst Ag 1 @PCN with AgÀ N 3 coordination for CO 2 photoreduction using H 2 O as the reductant. The assynthesized Ag 1 @PCN exhibits a high CO production rate of 0.32 μmol h À 1 (mass of catalyst: 2 mg), a high selectivity (> 94 %), and an excellent stability in the long term. Experiments and density functional theory (DFT) reveal that the strong metal-support interactions (AgÀ N 3 ) favor *CO 2 adsorption, *COOH generation and desorption, and accelerate dynamic transfer of photoexcited charge carriers between C 3 N 4 and Ag single atoms, thereby accounting for the enhanced CO 2 photoreduction activity with a high CO selectivity. This work provides a deep insight into the important role of strong metal-support interactions in enhancing the photoactivity and CO selectivity of CO 2 photoreduction.

Hydroxyl-Bonded Ru on Metallic TiN Surface Catalyzing CO2 Reduction with H2O by Infrared Light

“…During the stability tests, the total generation of CO/H 2 reaches 36.13 μmol, which delivers a turnover frequency (TOF) of 1.98 h −1 , comparable to other up-to-date CO 2 reduction catalysts. 11,39 Also, no detectable changes occur in the crystal, chemical, and surface structures of the used catalyst (Figure S25). These observations underline the high stability and fine reusability of the HO-Ru/TiN photocatalyst.…”

“…13,34,41−43 Besides, the distinctive signal of COOH* species, a key intermediate involved in CO 2to-CO conversion, emerges at 1547 cm −1 , 3,6 which will transform into the adsorbed CO molecules (CO*, 2073 cm −1 , Figure S30) after releasing a H 2 O molecule upon accepting proton and electron. 5,11,23 Formation of these carbon-containing species indicates efficient CO 2 activation and conversion of the photocatalyst. Meanwhile, HO-Ru/TiN also displays two distinct and broad negative peaks at 1620 and 3450 cm −1 , corresponding to the bending and stretching vibrations of H 2 O, which integrated with the detection of OH* (3742 cm −1 ) and OOH* (1280 cm −1 ) species, suggesting the adsorption/activation and conversion of H 2 O molecules.…”

“…The DRIFTS spectra collected in the dark reveal efficient CO 2 capture by the HO-Ru/TiN catalyst (Figure S29). After photoirradiation (Figure a), the signals assigned to activated CO 2 molecule (CO 2 *, 1715 cm –1 ), chelating bridged carbonate (c-CO 3 2– , 1745 cm –1 ), monodentate carbonate (m-CO 3 2– , 1516 and 1461 cm –1 ), bidentate carbonate (b-CO 3 2– , 1345 cm –1 ) and bicarbonate (HCO 3 – , 1180 cm –1 ) appear and further intensify along with irradiation time. ,,− Besides, the distinctive signal of COOH* species, a key intermediate involved in CO 2 -to-CO conversion, emerges at 1547 cm –1 , , which will transform into the adsorbed CO molecules (CO*, 2073 cm –1 , Figure S30) after releasing a H 2 O molecule upon accepting proton and electron. ,, Formation of these carbon-containing species indicates efficient CO 2 activation and conversion of the photocatalyst. Meanwhile, HO-Ru/TiN also displays two distinct and broad negative peaks at 1620 and 3450 cm –1 , corresponding to the bending and stretching vibrations of H 2 O, which integrated with the detection of OH* (3742 cm –1 ) and OOH* (1280 cm –1 ) species, suggesting the adsorption/activation and conversion of H 2 O molecules. ,,, In comparison, the above phenomena occur rather modestly on bare TiN (Figure b), highlighting the efficient activation of CO 2 together with H 2 O by the Lewis pair sites.…”

“…Decorating electron-capturing species, such as noble metal nanoparticles, on pristine catalysts is a reliable approach to promote the separation of light-induced charges to reinforce photocatalytic CO 2 reduction . Of note, it is more attractive when such catalytic-active species are dispersed atomically with well-defined and regulatable electronic structures, , which may provide a perfect catalyst platform to unveil the site-performance correlation. Indeed, exciting single-atom-mediated CO 2 reduction progress has been made by the semiconductor photocatalysts, but the parallel study on the metallic alternatives is still much less achieved.…”

Metal-Based Ionic Liquid Induced Strategy for Loading Single Atoms and the Coordination Mode Effect on CO2 Photoreduction

“…Further increasing the content of Co atoms reduces the CO 2 reduction performance, probably because too many Co atoms lead to a shorter average interatomic distance, which reduces the intrinsic activity of Co atoms. 43 The total CO production is up to 871 μmol g −1 with a small amount of ethane (around 11 μmol g −1 , Figure S18) in 25 h on Co sur -Bi 24 O 31 Br 10 -0.05 (Figure 3c). In order to evaluate the stability of Co sur -Bi 24 O 31 Br 10 -0.05, the XRD, XPS spectra, and HAADF-STEM (Figures 4f, 4g S22).…”