Let your light shine: the photocatalytic reduction of carbon dioxide to the formate anion under visible light irradiation is for the first time realized over a photoactive Ti-containing metal-organic framework, NH(2)-MIL-125(Ti), which is fabricated by a facile substitution of ligands in the UV-responsive MIL-125(Ti) material.

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.

Metal-organic framework (MOF) NH2 -Uio-66(Zr) exhibits photocatalytic activity for CO2 reduction in the presence of triethanolamine as sacrificial agent under visible-light irradiation. Photoinduced electron transfer from the excited 2-aminoterephthalate (ATA) to Zr oxo clusters in NH2 -Uio-66(Zr) was for the first time revealed by photoluminescence studies. Generation of Zr(III) and its involvement in photocatalytic CO2 reduction was confirmed by ESR analysis. Moreover, NH2 -Uio-66(Zr) with mixed ATA and 2,5-diaminoterephthalate (DTA) ligands was prepared and shown to exhibit higher performance for photocatalytic CO2 reduction due to its enhanced light adsorption and increased adsorption of CO2 . This study provides a better understanding of photocatalytic CO2 reduction over MOF-based photocatalysts and also demonstrates the great potential of using MOFs as highly stable, molecularly tunable, and recyclable photocatalysts in CO2 reduction.

Nanomaterials-based biomimetic catalysts with multiple functions are necessary to address challenges in artificial enzymes mimicking physiological processes. Here we report a metal-free nanozyme of modified graphitic carbon nitride and demonstrate its bifunctional enzyme-mimicking roles. With oxidase mimicking, hydrogen peroxide is generated from the coupled photocatalysis of glucose oxidation and dioxygen reduction under visible-light irradiation with a near 100% apparent quantum efficiency. Then, the in situ generated hydrogen peroxide serves for the subsequent peroxidase-mimicking reaction that oxidises a chromogenic substrate on the same catalysts in dark to complete the bifunctional oxidase-peroxidase for biomimetic detection of glucose. The bifunctional cascade catalysis is successfully demonstrated in microfluidics for the real-time colorimetric detection of glucose with a low detection limit of 0.8 μM within 30 s. The artificial nanozymes with physiological functions provide the feasible strategies for mimicking the natural enzymes and realizing the biomedical diagnostics with a smart and miniature device.

Ti-substituted NH2-Uio-66(Zr/Ti) prepared by using a post-synthetic exchange (PSE) method showed enhanced photocatalytic performance for both CO2 reduction and hydrogen evolution under visible light. Density functional theory (DFT) calculations and electron spin resonance (ESR) results reveal that the introduced Ti substituent acts as a mediator to facilitate electron transfer, which results in enhanced performance.