A metal-organic framework with rich accessible nitrogen sites for rapid dye adsorption and highly efficient dehydrogenation of formic acid

• Published in: Dalton transactions : an international journal of inorganic chemistry 2022-06, Vol.51 (22), p.8695-874
• Main Authors: Ding, Run-Dong, Li, Dan-Dan, Leng, Feng, Yu, Jie-Hui, Jia, Ming-Jun, Xu, Ji-Qing
• Format: Article
• Language: English
• Subjects: Accessibility; Acids; Adsorption; Catalysts; Catalytic activity; Cationic dyes; Dehydrogenation; Dimethyl acetamide; Dispersion; Formic acid; Hydrogen production; Metal-organic frameworks; Nitrogen; Noble metals; Pyridines
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d2dt00389a

MOFs with adequate free nitrogen sites have potential applications in dye adsorption and formic acid dehydrogenation. Here, we successfully synthesized a novel 3-D MOF 1 ([(CH 3 ) 2 NH 2 ][Cd(L)DMA]·0.5DMA·1.5H 2 O) with a special two-fold interpenetrating framework through a simple solvothermal reaction between CdCl 2 ·1.5H 2 O and a nitrogen-rich triangular tricarboxylate-based linker (H 3 L, 4,4′,4′′- s -triazine-2,4,6-tribenzoic acid). After removing the guest molecules of dimethylacetamide (DMA) and H 2 O, including the coordinated DMA from 1 by vacuum activation at 423 K, a compound named 1′ with a formula of [(CH 3 ) 2 NH 2 ][Cd(L)] and a similar interpenetrating framework structure was obtained. In comparison with compound 1 , the total void volume of 1′ is nearly doubled, and thus may provide higher potential for the adsorption of other guest molecules. Notably, the pyridine N atoms located in the middle of the triangular tricarboxylate-based linker are not involved in the coordination with Cd 2+ , and are all uniformly dispersed throughout the whole framework of the 3-D MOFs. Due to its unique structural features, the 3-D MOF 1 ′ could effectively adsorb the cationic dye MB + for recycling purposes. The rapid adsorption rate (0.7 × 10 −2 g mg −1 min −1 ) and the relatively high capacity (900 mg g −1 ) for MB + demonstrate the potential of 1 ′ in dye adsorption. In addition, 1′ may also be used as an effective support to immobilize PdAu NPs via the double-solvent method. The resultant catalyst Pd 0.8 Au 0.2 /1 ′ exhibits decent catalytic activity for the dehydrogenation of formic acid with a TOF value of 1854 h −1 at 333 K. The existence of a large void volume and accessible pyridine N atoms provide a suitable environment for achieving a high dispersion of PdAu NPs, thereby leading to the formation of a catalytically active and stable supported noble-metal NP catalyst for H 2 generation from formic acid decomposition. The schematic representation of the application of 1′ in dye adsorption and formic dehydrogenation is presented.