Low-Temperature Adsorption and Diffusion of Methanol in ZIF-8 Nanoparticle Films

Effect of surface species on the alcohol-acid adsorption from FTS wastewater on graphene: A structure-capacity study

Fischer-Tropsch synthesis (FTS) wastewater retaining low-carbon alcohols and acids are organic pollutants as a limiting factor for FTS industrialization. In this work, the structure-capacity relationships between alcohol-acid adsorption and surface species on graphene were reported, shedding light into their intricate interactions. The graphene oxide (GO) and reduced graphene oxide (rGO) were synthesized via improved Hummers method with flake graphite (G). The physicochemical properties of samples were characterized via SEM, XRD, XPS, FT-IR, and Raman. The alcohol-acid adsorption behaviors and adsorption quantities on G, GO, and rGO were measured via theoretical and experimental method. It was revealed that the presence of COOH, C=O and CO species on graphene occupy the adsorption sites and increase the interactions of water with graphene, which are unfavorable for alcohol-acid adsorption. The equilibrium adsorption quantities of alcohols and acids grow in pace with carbon number. The monolayer adsorption occurs on graphene was verified via model fitting. rGO has the highest FTS modeling wastewater adsorption quantity (110 mg/g) due to the reduction of oxygen species. These novel findings provide a foundation for the alcohol-acid wastewater treatment, as well as the design and development of high-performance carbon-based adsorbent materials.

Adsorption and diffusion of the H2/CO2/CO/MeOH/EtOH mixture into the ZIF-7 using molecular simulation

The adsorption and diffusion of synthesis gas components (methanol, ethanol, H₂, CO_2, and CO molecules) in ZIF-7 by grand canonical Monte Carlo and molecular dynamics simulation were investigated. The initial diffusion coefficient at the beginning of the process depends on the kinetic diameter of the guest molecules. Also, the diffusion coefficient at equilibrium conditions probably depends on the interaction between the guest molecules with the ZIF-7 framework. The radial distribution function results indicate that the distribution of guest molecules in the framework is affected by the interaction between the guest molecules. These results indicate that the CO, CO₂, and H₂ guest molecules are adsorbed on both the Zn metal atom and the organic linker (especially the C₁ atom). In contrast, the organic linker is the most favorable adsorption site for methanol and ethanol guest molecules. In addition, the diffusion coefficient of guest molecules in binary mixtures is related to the attraction or repulsion between the guest molecules.

Transport Diffusion of Linear Alkanes (C5-C16) through Thin Films of ZIF-8 as Assessed by Quartz Crystal Microgravimetry

We report uptake capacities and transport diffusivities, D, for each of eight linear alkanes (ranging from C₅ to C₁₆) in quartz crystal-supported films of solvent-evacuated ZIF-8. Analyses of the alkane uptake profiles revealed that the transport dynamics are governed by guest diffusion through metal-organic framework (MOF) (ZIF-8) crystallites rather than by rates of entry into films at the MOF/vapor interface. The obtained diffusivities range from just over 10^-18 m²/s to just under 10^-14 m²/s. Notably, minimum cross-sectional widths for all guests exceed the crystallographically measured width of ZIF-8's largest apertures and imply consistently with previous experimental and computational studies that apertures expand to accommodate guest uptake. On average, each additional carbon decreases the transport diffusivity of an alkane by twofold. Closer examination, however, reveals an odd-even effect such that linear alkanes having even numbers of carbons diffuse more rapidly than alkanes featuring one more or one less carbon atom. Thus, ZIF-8's differentiation of transport diffusivities for pairs of alkanes differing in length by only one carbon atom can be significantly greater than the aforementioned factor of 2. Elucidation of the microscopic basis for the odd-even behavior, however, awaits the outcome of molecular dynamics calculations that are beyond the scope of the present study. For compact, solvothermally prepared films, guest transport is dominated by 1D diffusion from the film/vapor interface and toward the underlying quartz crystal. For much lower density, electrophoretically deposited (EPD) films, crystallites behave nearly independently, and guest transport can be adequately modeled by assuming rapid permeation of macroscopic voids between crystallites, followed by entry and rate-limiting radial diffusion into isolated crystallites. One consequence is that EPD films can be much more rapidly infiltrated by molecular guests than can compact, solvothermally grown films. The combined results have potentially favorable implications for the development of kinetic separation schemes for closely related analytes.

Solvent-Dependent Adsorption-Driven Mechanism for MOFs-Based Yolk-Shell Nanostructures

Metal-organic frameworks (MOFs)-based yolk-shell nanostructures have drawn enormous attention recently due to their multifunctionality. However, the regulations of the size and morphology of yolk-shell nanostructures are still limited by the unclear formation mechanism. Herein, we first demonstrated a solvent-dependent adsorption-driven mechanism for synthesizing yolk-shelled MOFs-based nanostructures coated with mesoporous SiO₂ shells (ZIF-8@mSiO₂ ) with tunable size and morphology. The selective and competitive adsorption of methanol (CH₃ OH) and water (H₂ O) on ZIF-8 core were found to have decisive effects on inducing the morphology evolution of yolk-shell nanostructures. The obtained yolk-shelled ZIF-8@mSiO₂ nanostructures show great promise in generating acoustic cavitation effect for sonodynamic cancer therapy in vitro. We believe that this work will not only help us to design novel MOFs-based yolk-shell nanostructures, but also promote the widespread application of MOFs materials.

Porous Copper/Zinc Bimetallic Oxides Derived from MOFs for Efficient Photocatalytic Reduction of CO2 to Methanol

A novel metal organic framework (MOF)-derived porous copper/zinc bimetallic oxide catalyst was developed for the photoreduction of CO2 to methanol at a very fast rate of 3.71 mmol gcat−1 h−1. This kind of photocatalyst with high activity, selectivity and a simple preparation catalyst provides promising photocatalyst candidates for reducing CO2 to methanol.

Rhodamine B degradation by nanosized zeolitic imidazolate framework-8 (ZIF-8)

Adsorption and photodegradation of rhodamine B by ZIF-8 nanocrystals were studied using spectroscopic techniques coupled with density functional theory (DFT) cluster calculations. A fast adsorption rate was observed in the dark, but upon exposure to visible light or UV irradiation the adsorption rate noticeably increased. Although several studies previously reported this phenomenon involving bulk ZIF-8 powder, this is the first mechanistic study to our knowledge that demonstrates adsorption and degradation of rhodamine B by nanosized ZIF-8 under various light conditions. The combined study of N2 sorption pore analysis and surface-sensitive X-ray photoelectron spectroscopy (XPS) confirmed the surface adsorption was mainly due to the open metal sites and surface groups of nanoporous ZIF-8. The fluorescence studies suggested ZIF-8 nanocrystals were able to generate hydroxyl radicals in water but only under UV illumination. The work presented here provides an insight into understanding nanoscale metal-organic frameworks (MOFs) in the removal of organic molecules from wastewater.

Molecular Dynamics Simulations for Loading-Dependent Diffusion of CO2, SO2, CH4, and Their Binary Mixtures in ZIF-10: The Role of Hydrogen Bond

The loading-dependent diffusion behavior of CH₄, CO₂, SO₂, and their binary mixtures in ZIF-10 has been investigated in detail by using classical molecular dynamics simulations. Our simulation results demonstrate that the self-diffusion coefficient D_i of CH₄ molecules decreases sharply and monotonically with the loading while those of both CO₂ and SO₂ molecules initially display a slight increase at low uptakes and follow a slow decrease at high uptakes. Accordingly, the interaction energies between CH₄ molecules and ZIF-10 remain nearly constant regardless of the loading due to the absence of hydrogen bonds (HBs), while the interaction energies between CO₂ (or SO₂) and ZIF-10 decease rapidly with the loading, especially at small amounts of gas molecules. Such different loading-dependent diffusion and interaction mechanisms can be attributed to the relevant HB behavior between gas molecules and ZIF-10. At low loadings, both the number and strength of HBs between CO₂ (or SO₂) molecules and ZIF-10 decrease obviously as the loading increases, which is responsible for the slight increase of their diffusion coefficients. However, at high loadings, their HB strength increases with the loading. Similar loading-dependent phenomena of diffusion, interaction, and HB behavior can be observed for CH_4, CO₂, and SO₂ binary mixtures in ZIF-10, only associated with some HB competition between CO₂ and SO₂ molecules in the case of the CO₂/SO₂ mixture.

MOF the beaten track: unusual structures and uncommon applications of metal-organic frameworks

Over the past few decades, metal-organic frameworks (MOFs) have proved themselves as strong contenders in the world of porous materials, standing alongside established classes of compounds such as zeolites and activated carbons. Following extensive investigation into the porosity of these materials and their gas uptake properties, the MOF community are now branching away from these heavily researched areas, and venturing into unexplored avenues. Ranging from novel synthetic routes to post-synthetic functionalisation of frameworks, host-guest properties to sensing abilities, this review takes a sidestep away from increasingly 'traditional' approaches in the field, and details some of the more curious qualities of this relatively young family of materials.

Study of Adsorption and Desorption Performances of Zr-Based Metal-Organic Frameworks Using Paper Spray Mass Spectrometry

The dynamic pore systems and high surface areas of flexible metal-organic framework materials make them excellent candidates to be used in different kinds of adsorption processes. However, the adsorption and desorption behaviors of therapeutic drugs on metal-organic frameworks in solution are not fully developed. Here, we systematically investigated the adsorption and desorption behaviors of a typical therapeutic drug, verapamil, over several Zr-based metal-organic frameworks [e.g., Zr-FUM, UiO-66(Zr), UiO-66(Zr)-NH₂ and UiO-66(Zr)-2COOH] as well as ZrO₂ in an acetonitrile solution by using paper spray mass spectrometry. In contrast to other materials, UiO-66(Zr)-2COOH demonstrated a superior adsorption performance to verapamil due to their strong acid-base and/or hydrogen-bond interactions, and the adsorption process fitted well with the pseudo-second-order kinetic model. As verapamil-adsorbed materials were used for desorption experiments, ZrO₂ demonstrated the most favorable desorption performance, whereas UiO-66(Zr)-2COOH yielded the poorest desorption capability. These Zr-based materials had also been coated at the surface with filter papers for the analysis of various drugs and proteins in the process of paper spray mass spectrometry. The results demonstrated that among the studied materials, ZrO₂-coated paper gave the most favorable desorption performance as a pure drug solution, whereas the paper from UiO-66(Zr) demonstrated the optimal capability in the analyses of therapeutic drugs in a complex matrix (e.g., blood) and a protein (e.g., myoglobin).

Cationic Ionic Liquids Organic Ligands Based Metal-Organic Frameworks for Fabrication of Core-Shell Microspheres for Hydrophilic Interaction Liquid Chromatography

In this study, new metal-organic frameworks (MOFs) nanocrystals modified SiO2 core-shell microspheres were designed with cationic ionic liquids (ILs) 1,3-bis(4-carboxybutyl)imidazolium bromide (ILI) as organic ligands. By further adjustment the growth cycles, the new ILI-01@SiO2 core-shell stationary phase was facilely fabricated. The developed stationary phase was respectively characterized via element analysis, thermogravimetric analysis, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectrometry. Because the introduction of cationic imidazolium-based ILs ILI for fabrication of the MOFs nanocrystals shell, the new stationary phase exhibits the retention mechanism of hydrophilic interaction liquid chromatography (HILIC). Many polar samples, such as amides, vitamins, nucleic acid bases, and nucleosides, were utilized to investigate the performance of the prepared ILI-01@SiO2 column. Compared to the conventional aminosilica column, the new ILI-01@SiO2 column displays high separation selectivity in a shorter separation time. Furthermore, the new ILI-01@SiO2 column was also used for detection of illegal melamine addition in the baby formula. All the above results demonstrate the new ILI-01@SiO2 core-shell stationary phase is of good potentials for high-selectivity separation the polar samples.