This research focuses on identifying the accessibility of active sites within the defect-engineered UiO-66 framework. The task is particularly challenging due to reversible changes in the framework during dehydroxylation: the loss of mu 3-OH groups with simultaneous reduction of the Zr coordination number and the possible creation of Zr4+ Lewis acid sites in defect MOFs. We used in-situ FTIR and XANES analyses, as well as interaction with probe molecules, to monitor the changes in Zr coordination and the host-guest interaction. The defects were introduced using benzoic acid as a modulator, which coordinated to Zr4+ in defective pores. Our results showed that the UiO-66 sample synthesized with benzoic acid contained defects, but these were concealed under benzoate residues and thus inaccessible. Standard washing and heating did not remove benzoate anions. Dehydroxylation of the sample leads to the development of "hidden" Lewis acidity: some Zr4+ sites were not able to form complexes with the weak base CO, but they interact with the stronger bases acetonitrile. Additionally, insitu XANES analysis revealed that the effect of acetonitrile adsorption is similar to that of water rehydration. Treatment of the sample with HCl and DMF led to the replacement of benzoates with formate ions, exposing the bare Zr4+ sites within the defective pores. These cationic sites acted as true Lewis acids and were able to coordinate both CO and acetonitrile. Our findings emphasize that the active sites in UiO-66 highly depend on synthesis conditions and post-synthetic treatments. Comprehensive site-specific methods are crucial for accurately predicting and identifying these active sites.

Novel proton-conducting hybrid membranes consisting of sulfonated multiblock copolymer of polysulfone and polyphenylsulfone (SPES) reinforced with a HKUST-1 metal-organic framework (MOF) (5, 10, and 20 wt. %) were prepared and characterized for fuel cell applications. The presence of the MOF in the copolymer was confirmed by means of FE-SEM and EDS. The hybrid membranes show a lower contact angle value than the pure SPES, in agreement with the water uptake (WU%), i.e., by adding 5 wt. % of the MOF, this parameter increases by 20% and 40% at 30 °C and 60 °C, respectively. Additionally, the presence of the MOF increases the ion exchange capacity (IEC) from 1.62 to 1.93 mequivH+ g−1. Thermogravimetric analysis reveals that the hybrid membranes demonstrate high thermal stability in the fuel cell operation temperature range (<100 °C). The addition of the MOF maintains the mechanical stability of the membranes (TS > 85 MPa in the Na+ form). Proton conductivity was analyzed using EIS, achieving the highest value with a 5 wt. % load of the HKUST-1. This value is lower than that observed for the HKUST-1/Nafion system. However, polarization and power density curves show a remarkably better performance of the hybrid membranes in comparison to both the pure SPES and the pure Nafion membranes.

Two metal-organic frameworks (MOFs), UiO-66 and UiO-66-NH2, were considered as containers for bioactive chemicals. We provide a synthesis technique, which allowed the production of these materials suitable for biomedical applications. Both MOFs were characterized as single-phase porous materials composed of nanoparticles (30-65 nm) with a ζ-potential of more than 40 mV in water suspension. D,L-Leucine was applied as a model molecule, which allowed us to trace the mechanism of the loading process. We showed that after synthesis, amino groups of UiO-66-NH2 are coordinated with solvent residuals. It results in a similar route of leucine loading in UiO-66 and UiO-66-NH2 samples. Using joint data of thermogravimetric analysis and calorimetry, infrared spectroscopy, and nitrogen adsorption, we revealed that methyl groups of leucine molecules are responsible for bonding of an MOF matrix. We proposed the formation of bonds between CH3 groups and benzene rings of linkers via CH-π interaction. We also assessed the toxicity of the synthesized MOFs toward HeLa cells at 50 μg/mL after 24 h incubation and revealed no negative effects on the viability of the cells, prompting further biomedical research in the areas of small-molecule delivery and cell signaling and metabolism modulation.

We report on a synthesis procedure for obtaining a UiO-66 metal-organic framework in the form of nanoparticles with a modified surface. A distinctive feature of the developed procedure is that modification occurs directly during synthesis. Biocompatible polyethylene glycol (PEG) is selected as the organic polymer covering the surface of the UiO-66 nanoparticles. The effect of the degree of PEG polymerization on the size, morphology, and surface charge of UiO-66 nanoparticles is studied. The presence of PEG molecules is confirmed by infrared (IR) spectroscopy. The materials obtained are single phase and characterized by a high degree of crystallinity. The particle size varies from 80 to 120 nm, depending on the type of PEG used. A high surface charge in an aqueous medium (ζ-potential over 20 mV) indicates the possibility of forming a stable suspension. Thus, the obtained materials are promising as nanocontainers for the delivery of biologically active substances.

Abstract —The prototype of an apparatus for studying the X-ray fluorescence properties of nanomaterials for X-ray photodynamic therapy is developed. The X-ray fluorescence characteristics of nanomaterials based on gadolinium fluorides are studied. For a series of samples, X-ray fluorescence spectra are obtained in the region of 600–700 nm, which allows the conclusion that such materials are promising for use as components of radiosensitizers for X-ray photodynamic therapy. The data obtained are important for optimizing the characteristics of nanomaterials and for further modification of the parameters of methods for synthesizing new materials for X-ray photodynamic therapy.

In this paper, we calculate the geometry and band structure of iron sulfide (mackinawite) nanosheets. This material is one of the representatives of a new class of two-dimensional nanocatalysts for the hydrogen evolution reaction. Calculations show the absence of a band gap for model structures of crystalline and nanoscale mackinawite. In the model of oxidized nanoscale mackinawite, half of the sulfur atoms are replaced by oxygen atoms, and the band gap is 0.37 eV. The band-gap broadening can explain the appearance of catalytic activity in oxidized nanoscale mackinawite. The X-ray absorption spectra show a high sensitivity of the method to changes in the local atomic environment, especially in the first coordination sphere of iron atoms. The calculated model spectra allow determination of the features of the local atomic and electronic structure of the nanoscale mackinawite surface during the hydrogen evolution reaction.

This paper presents a new eco-friendly technique for the microfluidic synthesis of metal–organic framework MIL-88a in an aqueous medium at room temperature. Acetic acid as a modulator was used to control the morphology and size of the resulting particles during the synthesis. An increase of acetic acid concentration in a certain range of molar ratios leads to a decrease in the linear size of obtained particles and makes it possible to obtain a material with monodisperse porosity. The synthesized samples were comprehensively characterized by powder X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetry, and transmission electron microscopy. The porosity of the obtained materials was calculated according to the BET model, based on the data of low-temperature nitrogen adsorption.

Synthesis of the MIL-100 metal-organic framework particles was carried out by hydrothermal (HT) and microwave (MW)-assisted methods. Transmission electron microscopy showed formation of microparticles in the course of hydrothermal synthesis and nanoparticles for microwave-assisted synthesis. Powder X-ray diffraction confirmed formation of larger crystallites for hydrothermal synthesis. Particle aggregation in aqueous solution was observed by dynamic light scattering. However, the stability of both samples could be improved in acetic acid solution. Nitrogen sorption isotherms showed high porosity of the particles. ᶫ-leucine molecule was used as a model molecule for loading in the porous micro- and nanoparticles. Loading was estimated by FTIR spectroscopy and thermogravimetric analysis. UV-VIS spectroscopy quantified ᶫ-leucine release from the particles in aqueous solution. Cytotoxicity studies using the HeLa cell model showed that the original particles were somewhat toxic, but ᶫ-leucine loading ameliorated the toxic effects, likely due to signaling properties of the amino acid.

Experimental X-ray absorption spectra near the Fe K edge for as-synthesized MIL-88а metal–organic framework (MIL stands for Materials Institute Lavoisier) before and after activation have been obtained and analyzed for the first time. The theoretical analysis of experimental spectra has revealed changes in the local atomic structure of iron at the desorption of water from pores of the studied material in the process of activation.