Constructing Functional Radiation-Resistant Thorium Clusters for Catalytic Redox Reactions.

When catalytic reactions are interfered with by radiation sources, thorium clusters are promising as potential catalysts due to their superior radiation resistance. However, there is currently very little research on the design synthesis and catalytic application of radiation-stable thorium clusters. In this work, we have elaborately engineered and fabricated three high-nuclear thorium cluster catalysts denoted as Th12L3-MA12, Th12L3-MA6-BF6, and Th12L3-Fcc12, which did not undergo any significant alterations in their molecular structures and compositions after irradiation with 690 kGy γ-rays. We systematically investigated the photocatalytic/thermocatalytic properties of these radiation-resistant thorium clusters for the first time and found that γ-rays could not alter their catalytic activities. In addition, it was found that ligand engineering could modulate the catalytic activity of thorium clusters, thus expanding the range of catalytic applications of thorium clusters, including reduction reactions (nitroarene reduction) and some oxidation reactions (N-heterocyclic oxidative dehydrogenation and diphenylmethane oxidation). Meanwhile, all of these organic transformation reactions achieved a >80% conversion and nearly 100% product selectivity. Radiation experiments combined with DFT calculations showed that the synergistic catalysis of thorium-oxo core and ligands led to the generation of specific active species (H+, O2•-, or tBuO/tBuOO•) and activation of substrate molecules, thus achieving superior catalytic performance. This work is not only the first to develop radiation-resistant thorium cluster catalysts to perform efficient redox reactions but also provides design ideas for the construction of high-nuclearity thorium clusters under mild conditions.

Modulated Connection Modes of Redox Units in Molecular Junction Covalent Organic Frameworks for Artificial Photosynthetic Overall Reaction.

The precise tuning of components, spatial orientations, or connection modes for redox units is vital for gaining deep insight into efficient artificial photosynthetic overall reaction, yet it is still hard achieve for heterojunction photocatalysts. Here, we have developed a series of redox molecular junction covalent organic frameworks (COFs) (M-TTCOF-Zn, M = Bi, Tri, and Tetra) for artificial photosynthetic overall reaction. The covalent connection between TAPP-Zn and multidentate TTF endows various connection modes between water photo-oxidation (multidentate TTF) and CO2 photoreduction (TAPP-Zn) centers that can serve as desired platforms to study the possible interactions between redox centers. Notably, Bi-TTCOF-Zn exhibits a high CO production rate of 11.56 µmol g-1 h-1 (selectivity, ∼100%), which is more than 2 and 6 times higher than those of Tri-TTCOF-Zn and Tetra-TTCOF-Zn, respectively. As revealed by theoretical calculations, Bi-TTCOF-Zn facilitates a more uniform distribution of energy-level orbitals, faster charge transfer, and stronger *OH adsorption/stabilization ability than those of Tri-TTCOF-Zn and Tetra-TTCOF-Zn.

Interpenetrating 3D Covalent Organic Framework for Selective Stilbene Photoisomerization and Photocyclization.

The selective photoisomerization or photocyclization of stilbene to achieve value upgrade is of great significance in industry applications, yet it remains a challenge to accomplish both of them through a one-pot photocatalysis strategy under mild conditions. Here, a sevenfold interpenetrating 3D covalent organic framework (TPDT-COF) has been synthesized through covalent coupling between N,N,N,N-tetrakis(4-aminophenyl)-1,4-benzenediamine (light absorption and free radical generation) and 5,5'-(2,1,3-benzothiadiazole-4,7-diyl)bis[2-thiophenecarboxaldehyde] (catalytic center). The thus-obtained sevenfold interpenetrating structure presents a functional pore channel with a tunable photocatalytic ability and specific pore confinement effect that can be applied for selective stilbene photoisomerization and photocyclization. Noteworthily, it enables photogeneration of cis-stilbene or phenanthrene with >99% selectivity by simply changing the gas atmosphere under mild conditions (Ar, SeleCis. > 99%, SelePhen. < 1% and O2, SeleCis. < 1%, and SelePhen. > 99%). Theoretical calculations prove that different gas atmospheres possess varying influences on the energy barriers of reaction intermediates, and the pore confinement effect plays a synergistically catalytic role, thus inducing different product generation. This study might facilitate the exploration of porous crystalline materials in selective photoisomerization and photocyclization.

Achieving High Photo/Thermocatalytic Product Selectivity and Conversion via Thorium Clusters with Switchable Functional Ligands.

Structural exploration and functional application of thorium clusters are still very rare on account of their difficult synthesis caused by the susceptible hydrolysis of thorium element. In this work, we elaborately designed and constructed four stable thorium clusters modified with different functionalized capping ligands, Th6-MA, Th6-BEN, Th6-C8A, and Th6-Fcc, which possessed nearly the same hexanuclear thorium-oxo core but different capabilities in light absorption and charge separation. Consequently, for the first time, these new thorium clusters were treated as model catalysts to systematically investigate the light-induced oxidative coupling reaction of benzylamine and thermodriven oxidation of aniline, achieving >90% product selectivity and approximately 100% conversion, respectively. Concurrently, we found that thorium clusters modified by switchable functional ligands can effectively modulate the selectivity and conversion of catalytic reaction products. Moreover, catalytic characterization and density functional theory calculations consistently indicated that these thorium clusters can activate O2/H2O2 to generate active intermediates O2·-/HOO· and then improved the conversion of amines efficiently. Significantly, this work represents the first report of stable thorium clusters applied to photo/thermotriggered catalytic reactions and puts forward a new design avenue for the construction of more efficient thorium cluster catalysts.

Confining and Highly Dispersing Single Polyoxometalate Clusters in Covalent Organic Frameworks by Covalent Linkages for CO2 Photoreduction.

Single clusters have attracted extensive research interest in the field of catalysis. However, achieving a highly uniform dispersion of a single-cluster catalyst is challenging. In this work, for the first time, we present a versatile strategy for uniformly dispersed polyoxometalates (POMs) in covalent organic frameworks (COFs) through confining POM cluster into the regular nanopores of COF by a covalent linkage. These COF-POM composites combine the properties of light absorption, electron transfer, and suitable catalytic active sites; as a result, they exhibit outstanding catalytic activity in artificial photosynthesis: that is, CO2 photoreduction with H2O as the electron donor. Among them, TCOF-MnMo6 achieved the highest CO yield (37.25 µmol g-1 h-1 with ca. 100% selectivity) in a gas-solid reaction system. Furthermore, a mechanism study based on density functional theory (DFT) calculations demonstrated that the photoinduced electron transfer (PET) process occurs from the COF to the POM, and then CO2 reduction and H2O oxidation occur on the POM and COF, respectively. This work developed a method for a uniform dispersion of POM single clusters into a COF, which also shows the potential of using COF-POM functional materials in the field of photocatalysis.

Controllable Synthesis of COFs-Based Multicomponent Nanocomposites from Core-Shell to Yolk-Shell and Hollow-Sphere Structure for Artificial Photosynthesis.

The precise tuning and multi-dimensional processing of covalent organic frameworks (COFs)-based materials into multicomponent superstructures with appropriate diversity are essential to maximize their advantages in catalytic reactions. However, up to now, it remains an ongoing challenge for the precise design of COFs-based multicomponent nanocomposites with diverse architectures. Herein, a metal organic framework (MOF)-sacrificed in situ acid-etching (MSISAE) strategy that enables continuous synthesis of core-shell, yolk-shell, and hollow-sphere COFs-based nanocomposites through tuning of core decomposition (NH2 -MIL-125 into TiO2 ) rate is developed. More importantly, due to the multiple active sites, fast transfer of carriers, increased light utilization ability, et al, one of the obtained samples, NH2 -MIL-125/TiO2 @COF-366-Ni-OH-HAc (yolk-shell) with special three components, exhibits high photocatalytic CO2 -to-CO conversion efficiency in the gas-solid mode. The MSISAE strategy developed in this work achieves the precise morphology design and control of multicomponent hybrid composites based on COFs, which may pave a new way in devealoping porous crystalline materials with powerful superstructures for multifunctional catalytic reactions.