Revisiting the Environment Effect on Mass Transfer for Heterogenized Pd₆Ru₈ Metal‐Organic Cage Photocatalyst Confined within 3D Matrix

Abstract

Artificial light-driven splitting of water into hydrogen involves multiple links to emulate natural photosynthesis, including light absorption, electron or energy transfer, surface catalysis et al., in which, the mass transportation of sacrificial reagent and reactant is always ignored. Metal-organic cage (MOC) of Pd 6 Ru 8 (MOC-16), assembling multiple photosensitive Ru and catalytic Pd concomitant with directional electron transfer between them, provides an opportunity to explore the environmental effects from the view point of mass transportation without disturbance of other links. Zr-MOF of UiO-66 is used as a matrix to heterogenize MOC-16 and a series of characterizations are carried out to unravel the composition, structure and optical properties. The intact MOC-16 remains with long-term photo-stability and the outstanding photocatalytic activity is obtained by virtue of a long-lived triplet state. Three matrixes of ZIF-8, ZIF-8 derived carbonate CZIF, and UiO-66 are intercompared for mass transfer based on wettability and porous structure. Water molecule directly takes part in the formation of H 2 catalyzed by MOC-16@UiO-66, evidenced by a kinetic isotope effect, in addition to the proton delivery thanks to the hydrophilic nature of UiO-66. The porous structure of UiO-66 is essential for the permeation of sacrificial reagent to serve as twoelectron donor, in sharp contrast as one-electron donor in nonporous CZIF matrix. These results highlight the importance of microenviroment surrounding molecular catalysts in view of the heterogenization of molecular catalysts, meanwhile, providing a prominent guidance on how to choose 3D support to bridge the homogenous and heterogenous system.[a] D.

Impacts of host–guest assembly on the photophysical and photocatalytic properties of heterogenized molecular photosensitizer and catalysts

“…Under these conditions, we developed a universal "bottle-around-a-ship" coordination-assisted self-assembly to integrate molecular guests into MOFs (Fig. 2C), [47][48][49] where the incarcerated molecular complexes coordinate with MOF nodes or organic linkers improperly before the building of the MOFs, concomitantly generating the structural imperfections and defects around these mismatch-sites. The unique superiority of this strategy is to break through the limitations of the structure and dimensions of molecular guests.…”

“…In our previous works, a Ru(bda)L 2 -based water oxidative catalyst, an atomically precise Au 25 (SG) 18 nanocluster, and a PMD of an octahedral metal-organic cage (MOC) of [Pd 6 (RuL 3 ) 8 ] 28+ (MOC-16) comprising multiple photosensitive ruthenium-units and catalytic palladium-units, 50,51 were successfully encapsulated in the MOF scaffolds of ZIF-8 and/or UiO-66 due to their high tolerances to structural defects. 48,49,51 In our ensuing unpublished works, a Re-based molecular catalyst and a couple of Re and Ru molecular complexes have been incorporated into MOF hosts, and the relevant work is underway. The extending of guest molecular types provides an unprecedented opportunity to mimic natural photosynthesis.…”

“…9A). 50,51,71,72 Aer encapsulating this MOC-16 into ZIF-8 and UiO-66 matrixes, 48,49 the heterogenous host-guest assemblies inherited the distinctive feature of efficient and directional electron transfer in the picosecond domain of MOC-16, while, the lifetimes of the 3 MLCT excited-state were significantly elongated to the microsecond scale due to the inhibition of non-radiative vibrational relaxation by the rigid MOFmatrixes (Fig. 9B).…”

Manipulating the Reaction Pathway of CO2 Photoreduction via the Microenvironment of a Re Molecular Catalyst

“…Incorporating molecular complexes into three-dimensional (3D) porous matrix as a host–guest assembly could circumvent the intrinsic vulnerability of molecular complexes, − meanwhile imparting them as an enzyme-like microenvironment substantially different from that corresponding to the homogeneous bulk solution. Thus far, the tunable photophysical processes and the regulated mass transfer have been well-studied in host–guest assembly, such as electron/energy transfer, proton/ion transport, substrate enrichment, etc. ,− Nevertheless, comparatively little work has referred to diverting the reaction pathway with preferable intermediate species, as a challenging engineering to integrate progressive events of photoexcitation, electron transfer, intermediate species stabilization, and mass transfer in artificial photosynthesis.…”

“…The encapsulation of the Re complex into ZIF-8 and UiO-66 was carried out by a general self-assembly strategy developed in our previous works. ,, In detail, the Re complex interacted with the precursor of 2-methylimidazole (2-MIm) (Figure a) or pre-synthesized Zr-oxo clusters (Figure b), prior to building ZIF-8 and UiO-66 scaffolds with Zn­(NO 3 ) 2 and 1,4-benzenedicarboxylate (BDC) linker ligands, respectively. The intermolecular interaction was monitored by infrared (IR) spectra (Figure c) and 1 H nuclear magnetic resonance (NMR) (Figure d) in a homogeneous mixture of the Re complex with the precursors, akin to the synthetic process.…”