Fe-Based MOFs for Photocatalytic CO₂ Reduction: Role of Coordination Unsaturated Sites and Dual Excitation Pathways

Abstract

The utilization of solar energy for the conversion of CO2 into valuable organic products is one of the best solutions to solve the problems of global warming and energy shortage. The development of photocatalysts capable of reducing CO2 under visible light, especially those containing earth-abundant metals, is significant. Herein we report that a series of earth-abundant Fe-containing MOFs (MIL-101­(Fe), MIL-53­(Fe), MIL-88B­(Fe)) show photocatalytic activity for CO2 reduction to give formate under visible light irradiation. The direct excitation of the Fe–O clusters in these MOFs induces the electron transfer from O2– to Fe3+ to form Fe2+, which is responsible for the photocatalytic CO2 reduction. Among the three investigated Fe-based MOFs, MIL-101­(Fe) showed the best activity due to the existence of the coordination unsaturated Fe sites in its structure. All three amine-functionalized Fe-containing MOFs (NH2-MIL-101­(Fe), NH2-MIL-53­(Fe) and NH2-MIL-88B­(Fe)) showed enhanced photocatalytic activity in comparison to the unfunctionalized MOF, due to the existence of dual excitation pathways: i.e., excitation of an NH2 functionality followed by an electron transfer to the Fe center in addition to the direct excitation of Fe–O clusters.

Efficient approach for simultaneous CO and H2 production via photoreduction of CO2 with water over copper nanoparticles loaded TiO2

“…293 µmolg -1 h -1 was observed. The formation of formic acid during photocatalytic reduction of CO 2 has been reported in literature [41][42][43][44] as well as the photocatalytic splitting of formic acid to H 2 and CO 2 has also been explored [45][46]. Here the photocatalytic splitting of formic acid was performed to confirm that hydrogen generation proceeds as a result of photocatalytic splitting of formic acid/formates formed during the CO 2 reduction and which is also a concomitant to CO 2 reduction to CO (SI Fig.…”

Design and fabrication of semiconductor photocatalyst for photocatalytic reduction of CO2 to solar fuel

“…Interestingly, MOFs are also a class of potential semiconductors [257], which could be also directly applied in the photocatalytic CO 2 reduction as photocatalysts [258][259][260][261]. For example, Fu et al [259] reported that a photoactive Ti-containing metal-organic framework, NH 2 -MIL-125(Ti), exhibited a good photocatalytic activity for reduction of CO 2 to formate anion under visible light irradiation.…”

Understanding metal–organic frameworks for photocatalytic solar fuel production

“…The resemblance between MOFs and bulk transition metal oxides encouraged more than a decade ago the first examples of photocatalytic MOFs. [11][12][13][14][15] Since then, frameworks based on Ti, [16][17][18] Zr, [19][20][21][22][23][24] Fe, 25,26 etc. have been reported for different artificial photosynthetic reactions (i.e.…”