Visible-Light Photoreduction of CO₂ in a Metal–Organic Framework: Boosting Electron–Hole Separation via Electron Trap States

Abstract

It is highly desirable to convert CO2 to valuable fuels or chemicals by means of solar energy, which requires CO2 enrichment around photocatalysts from the atmosphere. Here we demonstrate that a porphyrin-involved metal-organic framework (MOF), PCN-222, can selectively capture and further photoreduce CO2 with high efficiency under visible-light irradiation. Mechanistic information gleaned from ultrafast transient absorption spectroscopy (combined with time-resolved photoluminescence spectroscopy) has elucidated the relationship between the photocatalytic activity and the electron-hole separation efficiency. The presence of a deep electron trap state in PCN-222 effectively inhibits the detrimental, radiative electron-hole recombination. As a direct result, PCN-222 significantly enhances photocatalytic conversion of CO2 into formate anion compared to the corresponding porphyrin ligand itself. This work provides important insights into the design of MOF-based materials for CO2 capture and photoreduction.

Probing the ultrafast dynamics in nanomaterial complex systems by femtosecond transient absorption spectroscopy

“…The PL lifetime of H 2 TCPP is determined to be 11.32 ± 0.03 ns. Similar to the TA case, two lifetimes with sizable components were also observed for the PL of PCN-222: τ 1 = 0.38 ± 0.02 ns (46%) and τ 2 = 1.63 ± 0.03 ns (54%), or 1.07 ± 0.03 ns on average (not shown here) [26] .…”

Effects of ligand functionalization on the photocatalytic properties of titanium-based MOF: A density functional theory study

“…10 However, because of the large optical band gap (3.6 eV), 10 MIL-125 is only active under UV irradiation. Therefore, it is necessary to modify the organic ligands or 5,16 After introducing the amine group, the band gap of MIL-125 is obviously reduced to about 2.6 eV, 12,18,19 and similar decreasing of the band gap by amine-functionalization is also observed for zirconium-based MOF (NH 2 -Uio-66). 11 A recent investigation indicates that the number of amine group also has obviously influence on the photocatalytic performances of NH 2 -MIL-125.…”

“…Especially, many investigations have demonstrated that MOF materials are promising catalysts in photocatalysis. 5,6,[9][10][11][12][13][14][15][16] As one of the most popular MOF, 1,[5][6][7] the titanium-based MIL-125 can catalyze the oxidation of alcohols to aldehydes under the UV irradiation, indicating that MIL-125 is an active photocatalyst. 10 However, because of the large optical band gap (3.6 eV), 10 MIL-125 is only active under UV irradiation.…”

Climate engineering by mimicking natural dust climate control: the iron salt aerosol method

“…In suitable conditions, UV and visible light can reduce a variety of metal ions in different environments (Monico et al, 2015;Oster and Oster, 1959;Thakur et al, 2015). Photoreduced metal compounds may further act as effective chemical reductants (Ola and Maroto-Valer, 2015;Xu et al, 2015), and the oxidized compounds such as hydroxyl radicals or chlorine atoms can further act as effective oxidants. Zamaraev et al (1994) proposed the decomposition of reducing atmospheric components such as CH 4 by the photolytically induced oxidation power of the oxides of iron, titanium and some other metal oxide containing mineral dust components.…”