The general synthesis and control of the coordination environment of single‐atom catalysts (SACs) remains a great challenge. Herein, a general host–guest cooperative protection strategy has been ...developed to construct SACs by introducing polypyrrole (PPy) into a bimetallic metal–organic framework. As an example, the introduction of Mg2+ in MgNi‐MOF‐74 extends the distance between adjacent Ni atoms; the PPy guests serve as N source to stabilize the isolated Ni atoms during pyrolysis. As a result, a series of single‐atom Ni catalysts (named NiSA‐Nx‐C) with different N coordination numbers have been fabricated by controlling the pyrolysis temperature. Significantly, the NiSA‐N2‐C catalyst, with the lowest N coordination number, achieves high CO Faradaic efficiency (98 %) and turnover frequency (1622 h−1), far superior to those of NiSA‐N3‐C and NiSA‐N4‐C, in electrocatalytic CO2 reduction. Theoretical calculations reveal that the low N coordination number of single‐atom Ni sites in NiSA‐N2‐C is favorable to the formation of COOH* intermediate and thus accounts for its superior activity.
A host–guest cooperative protection strategy has been developed for constructing single‐atom catalysts (SACs), extending the range of available precursors from nitrogenous to non‐nitrogenous MOFs. The obtained Ni‐SACs (NiSA‐Nx‐C; x=2, 3, 4) at different pyrolysis temperatures feature varying nitrogen coordination numbers. The best of these catalysts, NiSA‐N2‐C, shows superior activity and selectivity in CO2 electroreduction.
► The synthetic strategies to design DyIII-based single molecule magnets are demonstrated. ► Detailed analysis of mono- and dinuclear systems provides significant insight for modulating the ...relaxation dynamics of Dy-based SMMs. ► The assembly of multinuclear Dy SMMs using various ligands is summarized. ► Favorable structural units could be exploited in the formation of new Dy-based SMMs are highlighted.
The last few years have seen a huge renaissance in the study of the magnetism of lanthanide coordination complexes, especially in the field of single molecule magnets (SMMs) due to the large inherent anisotropy of lanthanide metal ions. It has led to intense activity on the part of synthetic chemists to produce systems suitable for detailed study by physicists and materials scientists, thus synthetic development has been playing a major role in the advancement of this field. In this review, we demonstrate the research developed in the few years in the fascinating and challenging field of Dy-based SMMs with particular focus on how recent studies tend to address the issue of relaxation dynamics in these systems from synthetic point of view. In addition, the assembly of multinuclear Dy SMMs using various ligands is summarized, showing that several typical motifs are favorable structural units which could be exploited in the formation of new Dy-based SMMs and supramolecular architectures.
While catalysis is highly dependent on the electronic structure of the catalyst, the understanding of catalytic performance affected by electron spin regulation remains challenging and rare. Herein, ...we have developed a facile strategy to the manipulation of the cobalt spin state over covalent organic frameworks (COFs), COF-367-Co, by simply changing the oxidation state of Co centered in the porphyrin. Density functional theory (DFT) calculations together with experimental results confirm that CoII and CoIII are embedded in COF-367 with S = 1/2 and 0 spin ground states, respectively. Remarkably, photocatalytic CO2 reduction results indicate that COF-367-CoIII exhibits favorable activity and significantly enhanced selectivity to HCOOH, accordingly much reduced activity and selectivity to CO and CH4, in sharp contrast to COF-367-CoII. The results highlight that the spin-state transition of cobalt greatly regulates photocatalytic performance. Theoretical calculations further disclose that the presence of CoIII in COF-367-Co is preferable to the formation of HCOOH but detrimental to its further conversion, which clearly accounts for its distinctly different photocatalysis over COF-367-CoII. To the best of our knowledge, this is the first report on regulating photocatalysis by spin state manipulation in COFs.
Covalent organic frameworks (COFs), constructed by organic building blocks through strong covalent bonds, featuring well-defined structures, excellent stability and desired semiconductor-like ...behavior, have been employed for extensive potential applications, especially in photocatalysis. In this review, we summarize the different methods for the synthesis of COFs, such as solvothermal synthesis, microwave synthesis, ionothermal synthesis, room temperature solution synthesis, mechanochemical synthesis and interfacial synthesis firstly. Then, the structural features of COFs such as diversity, tailorability, stability and porosity. Whereafter, the advantages and fundamentals of COFs in photocatalysis are introduced. Furthermore, the photocatalytic applications of COF-based materials toward H2 production, CO2 reduction, organic transformation and pollution degradation are discussed. Particularly, diverse strategies for improving photocatalytic performance and the corresponding structure-activity relationships are highlighted. Finally, the challenges and future prospects for the development of efficient COF-based photocatalysts are briefly indicated.
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•An overview of the introduction of different methods for the synthesis of COFs.•The structural features of COFs including diversity, tailorability, stability and porosity.•The advantages and fundamentals of COFs in photocatalysis.•Photocatalytic applications of COF-based materials in the fields of H2 production, CO2 reduction, organic transformation and pollution degradation.•The challenges and opportunities for the development of COF-based photocatalysts.
Covalent organic frameworks (COFs) are a new class of crystalline porous materials obtained from covalently attached organic building units. By virtue of the unique characteristics such as periodic and well-defined structures, low-density, high surface area, excellent stability as well as desired semiconductor-like behavior, COFs have gained tremendous attention for functional applications in many fields, especially in photocatalysis. In this review, we summarize the different methods for the synthesis of COFs, such as solvothermal synthesis, microwave synthesis, ionothermal synthesis, room temperature solution synthesis, mechanochemical synthesis and interfacial synthesis firstly. Then, the structural features of COFs including diversity, tailorability, stability and porosity are provided. Afterwards, the fundamentals and advantages of COFs for photocatalysis are briefly introduced. Following this, the photocatalytic applications of COF-based materials toward H2 production, CO2 reduction, organic transformation and pollution degradation are discussed. Meanwhile, a series of strategies are highlighted to improve photocatalytic performance for the understanding of the structure-property relationship in this part. Finally, the remaining challenges and prospects on further development of efficient COF-based photocatalysts are indicated.
Efficient modulation of single‐molecule magnet (SMM) behavior was realized by deliberate structural modification of the Dy2 cores of Dy2(a′povh)2(OAc)2(DMF)2 (1) and Zn2Dy2(a′povh)2(OAc)6⋅4 H2O (2; ...H2a′povh=N′‐amino(pyrimidin‐2‐yl)methylene‐o‐vanilloyl hydrazine). Compound 1 having fourfold linkage between the two dysprosium ions shows high‐performance SMM behavior with a thermal energy barrier of 322.1 K, whereas only slow relaxation is observed for compound 2 with only twofold connection between the dysprosium ions. This remarkable discrepancy is mainly because of strong axiality in 1 due to one pronounced covalent bond, as revealed by experimental and theoretical investigations. The significant antiferromagnetic interaction derived from bis(μ2‐O) and two acetate bridging groups was found to be crucial in leading to a nonmagnetic ground state in 1, by suppressing zero‐field quantum tunneling of magnetization.
Magnetostructural correlations: Single‐molecule magnet (SMM) behavior was modulated by deliberate structural modification of the Dy2 cores of Dy2(a′povh)2(OAc)2(DMF)2 (1) and Zn2Dy2(a′povh)2(OAc)6⋅4 H2O (2; H2a′povh=N′‐amino(pyrimidin‐2‐yl)methylene‐o‐vanilloyl hydrazine; see figure). Compound 1 shows high‐performance SMM behavior, whereas only slow relaxation is observed for 2.
Dual‐atom catalysts (DACs) have emerged as efficient electrocatalysts for CO2 reduction owing to the synergistic effect between the binary metal sites. However, rationally modulating the electronic ...structure of DACs to optimize the catalytic performance remains a great challenge. Herein, we report the electronic structure modulation of three Ni2 DACs (namely, Ni2−N7, Ni2−N5C2 and Ni2−N3C4) by the regulation of the coordination environments around the dual‐atom Ni2 centres. As a result, Ni2−N3C4 exhibits significantly improved electrocatalytic activity for CO2 reduction, not only better than the corresponding single‐atom Ni catalyst (Ni−N2C2), but also higher than Ni2−N7 and Ni2−N5C2 DACs. Density functional theory (DFT) calculations revealed that the high electrocatalytic activity of Ni2−N3C4 for CO2 reduction could be attributed to the electronic structure modulation to the Ni centre and the resulted proper binding energies to COOH* and CO* intermediates.
Three Ni2 dual‐atom catalysts (DACs) with electronic structures tailored by the regulation of the coordination environment of Ni atoms, have been prepared for electrocatalytic CO2 reduction. The optimal Ni2−N3C4 exhibits the highest performance for the reduction of CO2 to CO, highlighting the significance of the electronic structure for electrocatalytic CO2 reduction in DACs.
A stable porous metal-organic framework (MOF) containing methyl viologen cations exhibits reversible photochromic, thermochromic and fluorescence changes via host-guest interactions, and can be used ...for fast and selective detection of oxygen by naked eye recognition of color change within five seconds.
A dynamic fluorescent metal-organic framework has been constructed using triphenylene-2,6,10-tricarboxylate and Tb(3+) as building blocks, which exhibits guest-responsive structural dynamism and ...selective sensing of nitroaromatic explosives.
Magnetic personality: The incorporation of a bulky auxiliary ligand in β‐diketone‐based dysprosium(III) single‐ion magnets (SIMs) remarkably increases the anisotropic barriers, representing a ...promising route toward the design of higher‐anisotropic‐barrier SIMs (see scheme).
