No abstract

Heterogeneous electrocatalysis provides better control of the chemical surroundings of the catalyst's active site for improved performance, offers the possibility of overcoming drawbacks of deactivation caused by aggregation or dimerization in homogeneous condition, and permits the use of benign aqueous solutions. Employing metal−organic frameworks (MOFs) or covalent−organic frameworks (COFs) to support the active molecular catalyst of porphyrin for electrochemical conversion of CO 2 to CO is a promising strategy. We have rationally introduced a 3D highly stable porphyrin-based MOF of PCN-222(Fe) into heterogeneous catalysis through the simple dipcoating method. The composite catalyst PCN-222(Fe)/C (mass ratio = 1:2) exhibited high catalytic performance for electrochemical conversion of CO 2 to CO with 494 mV overpotential (where j = 1.2 mA cm −2 ) and maximum 91% FE CO in a CO 2 -saturated 0.5 M KHCO 3 aqueous solution, achieving a TOF of 0.336 site −1 s −1 . The catalyst was found to retain its crystallinity and stability after 10 h of electrolysis at −0.60 V versus RHE (average FE CO 80.4%; RHE, reversible hydrogen electrode), which generates 334 μmol of CO with the TOF of 0.012 s −1 (0.286 site −1 s −1 ). These results indicate that the PCN-222(Fe)/C has a substantial catalytic effect on the electrochemical reduction of CO 2 due to the combination of the intrinsic activity of the porphyrin molecule, and the promising CO 2 adsorption ability endowed by the conserved porosity, as well as the high conductivity of carbon black.

No abstract

Visible‐light driven photoconversion of CO2 into energy carriers is highly important to the natural carbon balance and sustainable development. Demonstrated here is the adenine‐dependent CO2 photoreduction performance in green biomimetic metal–organic frameworks. Photocatalytic results indicate that AD‐MOF‐2 exhibited a very high HCOOH production rate of 443.2 μmol g−1 h−1 in pure aqueous solution, and is more than two times higher than that of AD‐MOF‐1 (179.0 μmol g−1h−1) in acetonitrile solution. Significantly, experimental and theoretical evidence reveal that the CO2 photoreduction reaction mainly takes place at the aromatic nitrogen atom of adenine molecules through a unique o‐amino‐assisted activation rather than at the metal center. This work not only serves as an important case study for the development of green biomimetic photocatalysts used for artificial photosynthesis, but also proposes a new catalytic strategy for efficient CO2 photoconversion.

No abstract

A reaction model for the conversion of methane to C1-oxygenates (methanol and formaldehyde) with NO x (x = 1, 2) has been proposed theoretically using the ab initio molecular orbital method. The geometric and electronic structures for all the present molecules have been calculated by means of the MP2 (frozen core)/6-311++G(2d,p) level of theory. On the basis of the optimized structures, the single point calculations of the energies are carried out at the CCSD(T) level with the same basis sets. Through the theoretical analysis of the simplified CH4−NO x system instead of the experimental CH4−O2−NO system, we found the possible reaction path leading to C1-oxygenates within all the barriers of less than 40 kcal/mol via CH3O at 800 K. NO2 has a higher activity for the hydrogen abstraction from methane than NO and O2, though the calculated rate constants at 800 K indicate that this reaction is the rate-determining step in the conversion of methane to C1-oxygenates. It is also found that increasing the concentration of NO promotes the yield of formaldehyde with the decreasing formation of methanol, which is consistent with recent experimental results in the CH4−O2−NO system.

A chemically stable and thermally stable luminescent Cd­(II)-based metal–organic framework (MOF), [Cd3(DBPT)2­(H2O)4]­·5H2O (1), featuring an open Lewis basic triazolyl active site in the host, was successfully assembled by using the multifunctional ligand of 3-(3,5-dicarboxylphenyl)-5-(4-carboxylphenyl)-1-H-1,2,4-triazole (H3DBPT) to bridge hexanuclear {Cd6} clusters. The host material exhibits ligand-based photoluminescence and solvent-dependent fluorescent intensities, which could selectively detect nitroaromatic compounds (NACs) of 2,4,6-trinitrophenol (TNP) and 4-nitroaniline (4-NA). The most striking property of 1 is the remarkable sensitivity and selectivity toward TNP and 4-NA even in the presence of other NACs of nitrobenzene (NB), which can be attributed to a photoinduced electron transfer mechanism and resonance energy transfer mechanism. Their photoluminescence quenching could be detected at very low concentrations of 1.14 and 0.70 ppm, respectively, and the maximum quenching efficiencies were found to be 98% and 95%, respectively, at 0.08 mM. Significantly, compound 1 also exhibits excellent sensing performance toward nitroimidazole-based drug molecules of ornidazole (ONZ), metronidazoles (MNZ), dimetridazole (DMZ), and 2-methyl-5-nitroimidazole (2-M-5-MZ), which represents one of the rare MOFs-based fluorescent sensors for simultaneous selective detecting drug molecules and NACs. Their photoluminescence quenching efficiencies increase drastically with the analyte amount even in the low concentration range (<0.15 mM) and reach nearly complete quenching (>95%). The remarkable chemical stability and the unusual sensing performance make this Cd-based MOF a promising multiresponsive sensory material for chemical sensing of NACs and nitroimidazole-based drugs.

No abstract