Multi-channel electron transfer induced by polyvanadate in metal-organic framework for boosted peroxymonosulfate activation
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SUBMITTER: Lan M
PROVIDER: S-EPMC11341957 | biostudies-literature | 2024 Jan
REPOSITORIES: biostudies-literature
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Project description:The molecule-substrate interaction plays a key role in charge injection organic-based devices. Charge transfer at molecule-metal interfaces strongly affects the overall physical and magnetic properties of the system, and ultimately the device performance. Here, we report theoretical and experimental evidence of a pronounced charge transfer involving nickel tetraphenyl porphyrin molecules adsorbed on Cu(100). The exceptional charge transfer leads to filling of the higher unoccupied orbitals up to LUMO+3. As a consequence of this strong interaction with the substrate, the porphyrin's macrocycle sits very close to the surface, forcing the phenyl ligands to bend upwards. Due to this adsorption configuration, scanning tunneling microscopy cannot reliably probe the states related to the macrocycle. We demonstrate that photoemission tomography can instead access the Ni-TPP macrocycle electronic states and determine the reordering and filling of the LUMOs upon adsorption, thereby confirming the remarkable charge transfer predicted by density functional theory calculations.Charge transfer at molecule-metal interfaces affects the overall physical and magnetic properties of organic-based devices, and ultimately their performance. Here, the authors report evidence of a pronounced charge transfer involving nickel tetraphenyl porphyrin molecules adsorbed on copper.
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Project description:Methane (CH4), which is the main component of natural gas, is an abundant and widely available carbon resource. However, CH4 has a low energy density of only 36 kJ L-1 under ambient conditions, which is significantly lower than that of gasoline (ca. 34 MJ L-1). The activation and catalytic conversion of CH4 into value-added chemicals [e.g., methanol (CH3OH), which has an energy density of ca. 17 MJ L-1], can effectively lift its energy density. However, this conversion is highly challenging due to the inert nature of CH4, characterized by its strong C-H bonds and high stability. Consequently, the development of efficient materials that can optimize the binding and activation pathway of CH4 with control of product selectivity has attracted considerable recent interest. Metal-organic framework (MOF) materials have emerged as particularly attractive candidates for the development of efficient sorbents and heterogeneous catalysts due to their high porosity, low density, high surface area and structural versatility. These properties enable MOFs to act as effective platforms for the adsorption, binding and catalytic conversion of CH4 into valuable chemicals. Recent reports have highlighted MOFs as promising materials for these applications, leading to new insights into the structure-activity relationships that govern their performance in various systems. In this Account, we present analysis of state-of-the-art MOF-based sorbents and catalysts, particularly focusing on materials that incorporate well-defined active sites within confined space. The precise control of these active sites and their surrounding microenvironment is crucial as it directly influences the efficiency of CH4 activation and the selectivity of the resulting chemical products. Our discussion covers key reactions involving CH4, including its activation, selective oxidation of CH4 to CH3OH, dry reforming of CH4, nonoxidative coupling of CH4, and borylation of CH4. We analyze the role of active sites and their microenvironment in the binding and activation of CH4 using a wide range of experimental and computational studies, including neutron diffraction, inelastic neutron scattering, and electron paramagnetic resonance, solid-state nuclear magnetic resonance, infrared and X-ray absorption spectroscopies coupled to density functional theory calculations. In particular, neutron scattering has notable advantages in elucidating host-guest interactions and the mechanisms of the conversion and catalysis of CH4 and CD4. In addition to exploring current advances, the limitations and future direction of research in this area are also discussed. Key challenges include improvements in the stability, scalability, and performance of MOFs under practical conditions, as well as achieving higher selectivity and yields of targeted products. The ongoing development of MOFs and related materials holds great promise for the efficient and sustainable utilization of CH4, transforming it from a low-density energy source into a versatile precursor for a wide range of value-added chemicals. This Account summarizes the design and development of functional MOF and related materials for the adsorption and conversion of CH4.
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Project description:A spontaneous entrapment of electron-donating small guest molecules, including tetrathiafulvalene (TTF) and N,N,N',N'-tetramethyl-1,3-propanediamine (TMPDA), was realized in a structurally flexible metal-organic framework, {Mn7(2,7-AQDC)6(2,6-AQDC)(DMA)6}∞ (AQDC = anthraquinone dicarboxylates, DMA = N,N-dimethylacetamide), with electron-accepting anthraquinone groups, generating two MOF guest charge transfer complexes: {Mn7(2,7-AQDC)6(2,6-AQDC)(DMA)6(TTF)5} and {Mn7(2,7-AQDC)6(2,6-AQDC)(DMA)4(H2O)2(TMPDA)7}. Using a mild impregnation procedure, single crystals of the target complexes were obtained via a crystal-to-crystal conversion, and the crystals were suitable for structural analysis. Single crystal X-ray analysis demonstrated the different arrangements of these intercalated donor molecules: some donor molecules interacted with the anthraquinone groups and formed infinite D-A-A-D stacks, some appeared beside the anthraquinone groups but only formed donor-acceptor pairs, and the remainder of the molecules simply filled the space. The charge transfer between the guests and the framework was spectroscopically confirmed, and the radical densities on the organic species were estimated using magnetic susceptibility measurements. Compared with a solid-state mixture of anthraquinone and donor molecules, the evenly distributed donor molecules in the micropores of the MOF resulted in a "solid solution" state and significantly promoted the degree of charge transfer between donors and acceptors. Such an encapsulation process may be adopted as a new strategy for post-modification of the electronic and magnetic properties of MOFs, as well as for generating new semiconducting charge-transfer complexes.
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