A Covalent Organic Framework Bearing Single Ni Sites as a Synergistic Photocatalyst for Selective Photoreduction of CO₂ to CO

Abstract

Photocatalytic reduction of CO2 into energy-rich carbon compounds has attracted increasing attention. However, it is still a challenge to selectively and effectively convert CO2 to a desirable reaction product. Herein, we report a design of a synergistic photocatalyst for selective reduction of CO2 to CO by using a covalent organic framework bearing single Ni sites (Ni-TpBpy), in which electrons transfer from photosensitizer to Ni sites for CO production by the activated CO2 reduction under visible-light irradiation. Ni-TpBpy exhibits an excellent activity, giving a 4057 μmol g–1 of CO in a 5 h reaction with a 96% selectivity over H2 evolution. More importantly, when the CO2 partial pressure was reduced to 0.1 atm, 76% selectivity for CO production is still obtained. Theoretical calculations and experimental results suggest that the promising catalytic activity and selectivity are ascribed to synergistic effects of single Ni catalytic sites and TpBpy, in which the TpBpy not only serves as a host for CO2 molecules and Ni catalytic sites but also facilitates the activation of CO2 and inhibits the competitive H2 evolution.

Developing Luminescent Ratiometric Thermometers Based on a Covalent Organic Framework (COF)

“…(TpBpy-Dy_acac), confirming as uccessful grafting of the COF with lanthanide complexes.Asimilar decrease in surface area was also observed in TpBpy compounds modified with other metal ions. [36,37] TheFTIR spectrum of TpBpy shows the presence of minor traces of Bpy by the presence of the N À Hs tretching band ( % 3300 cm À1 )a nd the absence of the C = Os tretching band (1637 cm À1 ), which excludes the presence of Tp ( Figure S2). Additionally,s trong peaks corresponding to stretching vibrations of the keto form were observed at 1608 (C=O) and 1579 cm À1 (C=C).…”

A stable covalent organic framework for photocatalytic carbon dioxide reduction

“…This shows that the material has very good stability compared to other previous reports. 29,30 When the run was extended to a total of 50 hours a further loss of crystallinity is observed ( Fig. S43 and S44 †) along a loss of activity, highlighting that stability is still one of the important challenges in the eld.…”

“…For example, a rhenium modied 2D imine triazine-COF produced around 750 mmol g À1 h À1 CO with 98% selectivity, 29 and a b-ketoenamine-linked COF modi-ed with nickel, plus the use of an additional dye, gave a CO production rate of 811 mmol g À1 h À1 CO with 96% selectivity. 30 These comparisons should be made with caution, though, since photocatalytic rates also depend strongly on the precise experimental set-up that is used. 41 Control experiments were carried out to conrm that the source of the CO generated is indeed a photocatalytic process (Table S2 †).…”

“…26,27 These materials also have potential for direct photocatalytic CO 2 reduction: for example, an azine-based COF, N 3 -COF, was shown to exhibit gas phase photocatalytic CO 2 reduction. 28 Likewise, a 2D imine triazine-COF loaded with rhenium 29 and a b-ketoenamine-linked COF decorated with both nickel and a light-absorbing dye 30 were studied for the same reaction. All of these COFs have limited effective conjugation lengths in the 2D plane of the framework because they are based on imine, azine, or b-ketoenamine-linkers.…”

Covalent Organic Frameworks for the Capture, Fixation, or Reduction of CO2

“…A comprehensive study of photocatalytic CO 2 reduction at the single Ni sites of a COF was recently undertaken by Zhong et al (2019). The synthesized material, so named Ni-TpBpy is a ketoenamine linked COF resultant from the solvothermal condensation of 1,3,5-triformylphloroglucinol and 5,5 ′ -diamino-2,2 ′ -bipyridin.…”