Tailored Linker Defects in UiO-67 with High Ligand-to-Metal Charge Transfer toward Efficient Photoreduction of CO₂

Abstract

Defect engineering can be used as a potential tool to activate metal−organic frameworks by regulating the pore structure, electronic properties, and catalytic activity. Herein, linker defects were effectively controlled by adjusting the amount of formic acid, and UiO-67 with different CO 2 reduction capabilities was obtained. Among them, UiO-67-200 had the highest ability to selectively reduce CO 2 to CO (12.29 μmol g −1 h −1 ). On the one hand, the results based on timeresolved photoluminescence decay curves and photochemical experiments revealed that UiO-67-200 had the highest charge separation efficiency. On the other hand, the linker defects affected the band structure of UiO-67 by changing the lowest unoccupied molecular orbital (LUMO) based on the density functional theory and UV−vis spectra. Hence, the proper linker defects enhanced the ligand-to-metal charge transfer process by promoting the transfer of electrons between the highest occupied molecular orbital and LUMO. Additionally, in situ Fourier transform infrared spectra and 13 CO 2 labeling experiments also indicated that COOH* was an important intermediate for CO formation and that CO originated from the photoreduction of CO 2 .

Controlling the Adsorption and Release of Ocular Drugs in Metal–Organic Frameworks: Effect of Polar Functional Groups

“…Finally, the O 1s spectra are rather similar for the three MOFs evaluated with three well-defined contributions, a main one at 531.6 eV and two shoulders at 529.8 and 533.4 eV. These contributions correspond to OH, ZrO, and OCO, respectively . Similarly to Zr 3d, the main oxygen peak in the functionalized samples is shifted to higher binding energies (531.8 eV), thus reflecting the presence of defects.…”

“…At this point, it is interesting to highlight that whereas the nonfunctionalized UiO-66 loses more than 60% of its weight at 800 °C, functionalized derivatives lose less than 55% of the original weight. The higher residual weight at 800 °C in the functionalized MOFs could be another indication of the structural defects (missing linkers) anticipated by the XRD measurements. ,, From the TG analysis, a higher number of defects can be inferred for samples UiO-66-NH 2 (after removing humidity), although UiO-66-NO 2 has a larger structural instability.…”

“…At this point, it is important to highlight that both Zr contributions exhibit a slight shift to higher binding energies (185.1 and 182.7 eV) upon functionalization with NH 2 . This shift reflects the electron deficiency state of the ZrO clusters due to the high concentration of missing linker defects . The N 1s spectrum shows different contributions depending on the functionalization performed.…”

Construction of a ZnIn2S4/Au/CdS Tandem Heterojunction for Highly Efficient CO2 Photoreduction

“…Photocatalytic reduction of CO 2 is a sustainable technology that simulates the photosynthesis of green plants and converts CO 2 into valuable compounds. − The photocatalytic reduction technology has the advantage of being green and nonpolluting and has simple reaction conditions. In addition, the photoreduction of CO 2 is essentially an oxidation–reduction reaction process under the action of photogenerated carriers. − In the past few years, more and more semiconductors have been reported to be used for the photocatalytic reduction for CO 2 , such as TiO 2 , CuIn 5 S 8 , UiO-66, and g-C 3 N 4 . − Among them, ZnIn 2 S 4 as an eco-friendly photocatalyst with a typical layer structure has the advantages of an adjustable band gap, excellent photochemical stability, and low cost, so it is widely used in photocatalytic water hydrogen production, pollution degradation, CO 2 reduction reaction, etc. − Moreover, importantly, three-dimensional (3D) flower spherical ZnIn 2 S 4 has a suitable band structure that can not only make efficient use of visible light but also can convert CO 2 into valuable gaseous fuels; the excellent structure and specific surface area can provide more attachment sites for other semiconductors. , However, due to the rapid recombination of photogenerated carriers in the ZnIn 2 S 4 single-component semiconductor, a very small percentage of photogenerated electrons migrate to active sites to participate in the photocatalytic reduction reaction, resulting in a very low photocatalytic efficiency. , …”

Zirconium-Based MOFs and Their Biodegradable Polymer Composites for Controlled and Sustainable Delivery of Herbicides

“…In general, MCPA-modulated MOFs exhibited lower pore volumes and BET surface areas. This can be attributed to either the number of defects introduced into the structure when MCPA was used as a modulator and/or the loading of the herbicide into the pores. − PS-MCPA@UiO-67 exhibited the lowest amount of N 2 adsorption, indicating that the sample has little to no porosity, which is further indicated by the structural changes and loss of crystallinity observed in the PXRD.…”