Pd(/FeO)-on-ZIFs: nanoparticle deposition on (nano-)MOFs from ionic liquids

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2022-06, Vol.1 (22), p.11955-1197
• Main Authors: Koikolainen, Olga, Sondermann, Linda, Roitsch, Stefan, Simon, Ilka, Dietrich, Dennis, Gvilava, Vasily, Barthel, Juri, Thomas, Jörg, Janiak, Christoph, Boldog, Ishtvan
• Format: Article
• Language: English
• Subjects: Aminophenol; Catalysts; Catalytic activity; Composite materials; Crystals; Deposition; Ferromagnetism; Ionic liquids; Ions; Iron oxides; Metal-organic frameworks; Nanoparticles; Nitrophenol; Palladium; Palladium chloride; Photomicrographs; Stability; Substrates; Topology; Zeolites
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d2ta00883a

Well-defined spherical Pd-NPs (∼6-12 nm size, 4-17% wt content) were efficiently deposited on nano- or micro- (∼100-2500 nm) crystals of zeolite imidazolate frameworks (ZIFs) from different ionic liquids (ILs, typically 1-butyl-3-methylimidazolium bistriflimidate, [BMIm]NTf 2 ) at 180-230 °C under microwave (MW) heating for 1-10 min. The firm, nearly exclusive on-surface deposition, proven by systematic analysis of TEM micrographs, is achieved via size-exclusion of the IL-solvated PdCl 2 precursor. The one-pot high-quality NP deposition from partially stabilizing IL media leads to particularly well-defined metal nanoparticles-on-metal-organic frameworks, MNP-on-MOF(NP)s . They are contraposed to MNP@MOFs or non-specified MNP/MOFs, and are viewed as an extension of MNPs from ionic liquids, securing MNP-agglomeration protection after removal of the IL and reversible redispersion, and offering the functionality of the porous support. Pd-on-ZIF-8-NP (R = Me substituent of the azole ligand) demonstrated the highest stability and morphological quality, while the ZIF-90 analogues with the same sod topology (R = COOH, CHO, CH 2 CH 2 NH 2 ) or the triazolate MAF-66 (R = NH 2 ) with dia topology showed lesser stability (particularly for R = COOH and CHO). Ferromagnetic Pd/Fe 3 O 4 - and Fe 3 O 4 /Pd-on-ZIF-8-NP, ZIF-90-NH 2 (-NP), and MAF-66 composites with nanoparticulated Fe 3 O 4 (5-13 nm size, 5-22% wt content) demonstrate the feasibility of sequential NP deposition of varied nature. The Pd-on-ZIF composites demonstrated high catalytic activity in the reduction of 4-nitrophenol to 4-aminophenol by NaBH 4 in water (TOF 0.38-4.10 vs. 0.088 s −1 for 10% wt Pd/C; amino-functionalization and the presence of Fe 3 O 4 are a major and a minor factor, respectively). The reduction of the same substrate with H 2 in apolar media was much slower for the composite catalysts compared to Pd/C (10% wt ) due to possible poisoning by the residual IL. Selected ionic liquids are efficient media for deposition of Pd nanoparticles on nano- or micro- (100-2500 nm) crystals of different zeolitic imidazolate frameworks at 180-230 °C (MW, 1-10 min).