Charge State of Au25(SG)18 Nanoclusters Induced by Interaction with a Metal Organic Framework Support and Its Effect on Catalytic Performance.

We investigated the charge transfer between Au25(SG)18 nanoclusters and metal-organic framework (MOF) supports including Mil-101-Cr, Mil-125-Ti, and ZIF-8 by an X-ray photoemission technique and discussed the influence of resulted charge states of supported Au25(SG)18 nanoclusters on the 4-nitrophenol reduction reaction. Charge transfer from Au25(SG)18 to Mil-101-Cr induces positive charge Auδ+ (0 < δ < 1) while charge transfer from ZIF-8 to Au25(SG)18 generates negative charge Auδ- due to different metal-support interactions. Au25(SG)18 on Mil-125 shows metallic Au0, similar to unsupported Au25(SG)18, due to negligible charge transfer. The resulted charge state of Auδ- inhibits the formation of adsorbed hydride (H-) species because of electrostatic repulsion, while Auδ+ impairs the reductive ability of adsorbed hydride (H-) species due to strong affinity between them. In comparison, metallic Au0 in Au25(SG)18/Mil-125 and unsupported Au25(SG)18 presents the optimum catalytic activity. The current work provides guidelines to design effective metal nanoclusters in heterogeneous catalysis through metal-support interaction exerted by metal-oxo/nitric clusters within MOFs.

A robust photocatalyst of Au25@ZIF-8@TiO2-ReP with dual photoreductive sites to promote photoelectron utilization in H2O splitting to H2 and CO2 reduction to CO.

Sustaining long-term chemical or photochemical stability of a homogeneous molecular catalyst remains a significant challenge. We report a remarkable improvement of the activity and stability of a Au25@ZIF-8@TiO2-ReP catalyst via composition engineering with double redox active sites of Au25 NCs and a Re(i) complex for H2 and CO evolution to promote electron utilization.

Heterogenization of Photochemical Molecular Devices: Embedding a Metal-Organic Cage into a ZIF-8-Derived Matrix To Promote Proton and Electron Transfer.

Application of a molecular catalyst in artificial photosynthesis is confronted with challenges such as rapid deactivation due to photodegradation or detrimental aggregation in harsh conditions. In this work, a metal-organic cage [Pd6(RuL3)8]28+ (MOC-16), characteristic of a photochemical molecular device (PMD) concurrently integrating eight Ru2+ light-harvesting centers and six Pd2+ catalytic centers for efficient homogeneous H2 production, is successfully heterogenized through incorporation into a metal-organic framework (MOF) of ZIF-8 and then transformed into a carbonate matrix of Znx(MeIm)x(CO3)x (CZIF), leading to hybridized MOC-16@CZIF. This MOC@MOF integrated photocatalyst inherits a highly efficient and directional electron transfer in the picosecond domain of MOC-16 and possesses one order increased microsecond magnitude of the triplet excited-state electron in comparison to that of the primitive MOC-16. The carbonate CZIF matrix endows MOC-16@CZIF with water wettability, serving as a proton relay to facilitate proton delivery by virtue of H2O as proton carriers. Electron transfer during the photocatalytic process is also enhanced by infiltration of a sacrificial agent of BIH into the CZIF matrix to promote conductivity, owing to its strong reducing ability to induce free charge carriers. These synergistic effects contribute to the extra high activity for H2 generation, making the turnover frequency of this heterogeneous MOC-16@CZIF photocatalyst maintain a level of ∼0.4 H2·s-1, increased by 50-fold over that of a homogeneous PMD. Meanwhile, it is robust enough to tolerate harsh reaction conditions, presenting an unprecedented heterogenization example of homogeneous PMD with a MOF-derived matrix to mimic catalytic features of a natural photosystem, which may shed light on the design of multifunctional PMD@MOF materials to expand the number of molecular catalysts for practical application in artificial photosynthesis.