Metal functionalization of two-dimensional nanomaterials for electrochemical carbon dioxide reduction

With the mechanical exfoliation of graphene in 2004, researchers around the world have devoted significant efforts to the study of two-dimensional (2D) nanomaterials. Nowadays, 2D nanomaterials are being developed into a large family with varieties of structures and derivatives. Due to their fascinating electronic, chemical, and physical properties, 2D nanomaterials are becoming an important type of catalyst for the electrochemical carbon dioxide reduction reaction (CO₂RR). Here, we review the recent progress in electrochemical CO₂RR using 2D nanomaterial-based catalysts. First, we briefly describe the reaction mechanism of electrochemical CO₂ reduction to single-carbon (C₁) and multi-carbon (C₂₊) products. Then, we discuss the strategies and principles for applying metal materials to functionalize 2D nanomaterials, such as graphene-based materials, metal-organic frameworks (MOFs), and transition metal dichalcogenides (TMDs), as well as applications of resultant materials in the electrocatalytic CO₂RR. Finally, we summarize the present research advances and highlight the current challenges and future opportunities of using metal-functionalized 2D nanomaterials in the electrochemical CO₂RR.

A Photoluminescent Cd(II) Coordination Polymer with Potential Active Sites Exhibiting Multiresponsive Fluorescence Sensing for Trace Amounts of NACs and Fe3+ and Al3+ Ions

The elaborately designed π-electron-rich fluorescent ligand 1,4-bis(1-carboxymethylene-4-imidazolyl)benzene (H₂L), possessing bifunctional groups including the carboxylate groups (building units) and 4-imidazoyl groups (N-donor potential active sites) has been employed to construct fluorescent coordination polymers. A luminescent sensor, namely [Cd(L)(phen)₂]·5H₂O (1), was obtained, which has a one-dimensional structure. The fluorescent material shows a blue emission maximum at 457 nm with a luminescence lifetime of 488 ns and a quantum yield (QY) of 4.56%. Significantly, 1 serves as a promising multiresponsive luminescent sensor to detect trace nitroaromatic compounds (NACs) with the limits of detection (LOD) of 7.21 × 10^-8, 1.85 × 10^-5, and 1.15 × 10^-5 mol/L for 2-nitrophenol (2-NP), 3-nitrophenol (3-NP), and 4-nitrophenol (4-NP), respectively. Furthermore, CP 1 exhibits fluorescent turn-off and turn-on sensing behavior for Fe³⁺ and Al³⁺ metal ions with trace amounts of 1.05 × 10^-7 and 1.13 × 10^-7 mol/L, respectively. Experimental methods and theoretical calculations were employed to elucidate the sensing mechanism in detail.

Series of Cadmium(II) Coordination Polymers Based on a Versatile Multi-N-Donor Tecton or Mixed Carboxylate Ligands: Synthesis, Structure, and Selectively Sensing Property

Five Cd(II) metal-organic frameworks (MOFs), [Cd(HL)₂] (1), [Cd(HL)₂(H₂O)₂] (2), [Cd₃(HL)₂(obda)₂] (3), [Cd₂(HL)₂(ohmbda)(DMA)(H₂O)] (4), and [Cd₂(HL)(btc)(H₂O)₂]·3H₂O (5), were prepared by reactions of Cd(NO₃)₂·4H₂O with 1-(1H-imidazol-4-yl)-4-(4H-tetrazol-5-yl)benzene (H₂L) or mixed carboxylate ancillary ligands of 1,2-benzenedicarboxylic acid (H₂obda), 5-hydroxy-1,3-benzenedicarboxylic acid (H₂ohmbda), and 1,3,5-benzenetricarboxylic acid (H₃btc), respectively. Their structures have been characterized by single-crystal X-ray diffraction, elemental analysis, infrared spectroscopy (IR), thermogravimetric analysis, and powder X-ray diffraction. Compounds 1 and 2 are supramolecular isomeric frameworks without consideration of the solvent molecules. Complex 1 exhibits a binodal (3, 5)-connected two-dimensional (2D) layer structure with the point (Schläfli) symbol of (5²·6)(5⁵·6⁴·7), while complex 2 shows a 2D + 2D → 3D (three-dimensional) framework. Complex 3 is a (3, 5, 6)-connected tetranodal 3D net with the point (Schläfli) symbol of (4·8²)₂(4⁵·6·8⁴)₂(4⁵·6⁵)₂(4⁸·6⁶·8). Compound 4 is a (3, 3, 8)-connected trinodal 3D net with the point (Schläfli) symbol based on a binuclear [Cd₂N₂O] subunit, while 5 is a 2-nodal (3, 4)-connected 2D V₂O₅-type network based on [Cd₂N₂(COO)₂] SBU. The studies of molecular sensing properties show that the luminescent MOFs can be employed as fluorescent sensors for the detection of Fe³⁺ and nitro compounds. Compound 1 and 3 exhibit quenching responses for Fe³⁺ in dimethylformamide solution with detection limits of 2.3 × 10^-6 and 8.6 × 10^-7 M, respectively. Meanwhile, compound 5 can sense 4-nitrophenol with a detection limit as low as 5.75 × 10^-7 M.

Syntheses, structures, and magnetic properties of mixed-ligand complexes based on 3,6-bis(benzimidazol-1-yl)pyridazine

Six new metal-organic coordination polymers (CPs) [Ni(L)(2,5-TDC)(H2O)] n (1), [Ni(L)(1,3-BDC)(H2O)] n (2), [Ni(L)(1,4-BDC)(H2O)] n (3), [Mn(L)(2,5-TDC)(H2O)] n (4), [Mn(L)(2,6-PYDC)(H2O)] n (5) and [Mn(L)(1,4-NDC)] n (6) were achieved by reactions of the corresponding metal salt with mixed organic ligands (L = 3,6-bis(benzimidazol-1-yl)pyridazine, 2,5-H2TDC = thiophene-2,5-dicarboxylic acid, 1,3-H2BDC = isophthalic acid, 1,4-H2BDC = terephthalic acid, 2,6-H2PYDC = pyridine-2,6-dicarboxylic acid, 1,4-H2NDC = naphthalene-1,4-dicarboxylic acid) under solvothermal condition. CPs 1-6 were characterized by single-crystal X-ray diffraction, IR, TG, XRD and elemental analyses. Their structures range from the intricate 3D CPs 1, 3, 4 and 6 to the 2D coordination polymer 2 and the infinite 1D chain 5. The CPs 1-4 and 6 underlying networks were classified from the topological viewpoint, disclosing the distinct sql (in 1), pcu (in 3 and 6), new topology (in 2), and dia (in 4) topological nets. Moreover, analysis of thermal stability shows that they had good thermal stability. Finally, magnetic properties of CPs 1-6 have been studied, the results showed that complex 2 had ferromagnetic coupling and complexes 1, 3-6 were antiferromagnetic.

New complexes constructed from in situ nitration of (1H-tetrazol-5-yl)phenol: synthesis, structures and properties

New complexes based on three precursors via in situ nitration have been prepared. Moreover, the solid state UV-vis spectra and band gap energy of those complexes were investigated, and the luminescent properties (1–3, 7 and 8) and magnetic properties (3–6 and 9) were also discussed.