Mass Measurements Reveal Preferential Sorption of Mixed Solvent Components in Porous Nanoparticles

Abstract

The interplay of physical and chemical properties at the nanometer scale provides porous nanoparticles with unique sorption and interaction capabilities. These properties have aroused great interest toward this class of materials for application ranging from chemical and biological sensing to separation and drug delivery. However, so far the preferential uptake of different components of mixed solvents by porous nanoparticles is not measured due to a lack of methods capable of detecting the resulting change in physical properties. Here, a new method, nanomechanical mass correlation spectroscopy, is used to reveal an unexpected dependence of the effective mass density of porous metal-organic framework (MOF) nanoparticles on the chemistry of the solvent system and on the chemical functionalization of the MOF's internal surface. Interestingly, the pore size of the nanoparticles is much too large for the exclusion of small solvent molecules by steric hindrance. The variation of effective density of the nanoparticles with the solvent composition indicates that a complex solvent environment can form within or around the nanoparticles, which may substantially differ from the solvent composition.

Nanoparticle Characterization: What to Measure?

“…The crystalline structure of the particles is clearly visible; c) SEM micrographs of the same particles as in (b), after coating with a thin layer of carbon to avoid sample ionization. b,c) Reproduced under the terms of the Creative Commons Attribution‐NonCommercial license . Copyright 2018, The Authors.…”

“…By allowing multiple particles to flow simultaneously through the embedded channel and by employing an autocorrelation analysis of the time‐domain mass signal, the resolution of these devices could be extended to the characterization of nanometer‐sized polymer particles . This technique, called Nanomechanical Mass Correlation Spectroscopy, was used to investigate the complex partitioning of binary solvent mixtures within the framework of mesoporous metal‐organic framework (MOF) nanoparticles with different surface functionalization ( Figure ) . The particles exhibited different effective densities in solution as a function of pore functionalization and solvent composition, indicating that the local microenvironment within the pore structure of porous nanoparticles might not reflect the bulk solvent composition.…”

“…An autocorrelation analysis of the time‐domain signal is used to enhance the particle contribution with respect to the uncorrelated noise background; b,c) MIL‐101(Cr) porous nanoparticles were suspended in binary mixtures of different polarities to investigate the dependence of the particle density to the composition of the solvent mixtures. (a–c) Reproduced under the terms of the Creative Commons Attribution‐NonCommercial license . Copyright 2018, The Authors.…”

The Chemistry of Reticular Framework Nanoparticles: MOF, ZIF, and COF Materials

“…Recently a new methodology, termed nanomechanical mass correlation spectroscopy, has been introduced to measure the interaction between liquids and nanoparticles, in particular MOF nanoparticles. [247] In this technique a micromechanical resonator [248] with embedded fluidic channels is employed to directly measure the buoyant mass of nanoparticles in solution. [249] The resonator acts as mass/frequency transducer.…”

Circumventing Wear and Tear of Adaptive Porous Materials

“…For this purpose, the best available analyses are gas pycnometry, [44,45] mercury porosimetry, [46] and mass correlation spectroscopy. [47,48] So far, we have outlined a comprehensive albeit not necessarily complete list of analytical techniques and stressed the importance of their complementarity in gathering different types of information. However, another important aspect to be considered is the representativeness of the acquired data.…”