Nano vs. bulk: surfactant-controlled photophysical and morphological features of luminescent lanthanide MOFs

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2023-10, Vol.11 (41), p.22478-22491
• Main Authors: Maxeiner, Moritz, Wittig, Lea, Sedykh, Alexander E., Kasper, Thomas, Müller-Buschbaum, Klaus
• Format: Article
• Language: English
• Subjects: Differential thermal analysis; Downsizing; Lanthanides; Luminescence; Metal-organic frameworks; Morphology; Particle size; Particle size distribution; Photoluminescence; Photons; Size distribution; Surfactants; Synthesis
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/D3TA05219B

A surfactant-assisted bottom-up synthesis route provides access to nanoscale metal–organic frameworks (nMOFs) that exploit size-dependent property advantages. This includes an increased surface-to-volume ratio, improved dispersibility and superior morphological properties by a narrow size distribution compared to the bulk analogues. Photophysical properties such as photoluminescence are also influenced by particle size, surfactant components and post-synthetic modification. The series of the related organic linkers (H 2 bdc, H 2 bpdc and H 2 bpydc) together with trivalent lanthanides (Ln 3+ = Eu 3+ , Tb 3+ ) in synthesis and post-synthetic modification together with surface-active agents (CTAB, PVP) were used to assemble luminescent nMOFs for three archetype MOFs: nLn 3+ -bdc, nDUT-5:Ln 3+ and nMOF-253:Ln 3+ . Both, dispersibility and morphology benefit from the CTAB- and PVP-controlled bottom-up particle downsizing down to 35 nm. DLS confirms homogeneous, narrow particle size distributions down to ±5 nm, which is 21-times smaller than the bulk analogues. Moreover, excellent luminescence QYs of up to 78.1(3)% were determined for the Ln 3+ -containing nMOFs. Successful post-synthetic modification with trivalent lanthanide ions of nMOFs was accomplished showing an improved photoluminescence sensitization effect compared to the bulk MOFs and exhibiting increased Ln 3+ -to-linker emission intensity ratios. The amount and photophysical properties of surfactants encapsulating the nMOFs were further quantified by DTA/TG-MS and UV-Vis-DRS. Finally, this work aims to elaborate thoroughly on the previously mentioned properties of nMOFs by comparison with their bulk analogues. Since surfactants play a key role in this synthesis route, the pros and cons of this approach were also assessed concerning several nMOF features.