Beneficial features of biocompatible high-capacity UiO-66 nanoparticles, mesoporous SiO₂, and folate-conjugated pluronic F127 were combined to prepare the core–shell UiO-66@SiO₂/F127-FA drug delivery carrier for targeted cellular uptake in cancer treatment. UiO-66 and UiO-66-NH₂ nanoparticles with a narrow size and shape distribution were used to form a series of core–shell MOF@SiO₂ structures. The duration of silanization was varied to change the thickness of the SiO₂ shell, revealing a nonlinear dependence that was attributed to silicon penetration into the porous MOF structure. Doxorubicin encapsulation showed a similar final loading of 5.6 wt % for both uncoated and silica-coated particles, demonstrating the potential of the nanocomposite’s application in small molecule delivery. Silica coating improved the colloidal stability of the composites in a number of model physiological media, enabled grafting of target molecules to the surface, and prevented an uncontrolled release of their cargo, with the drawback of decreased overall porosity. Further modification of the particles with the conjugate of pluronic and folic acid was performed to improve the biocompatibility, prolong the blood circulation time, and target the encapsulated drug to the folate-expressing cancer cells. The final DOX-loaded UiO-66@SiO₂/F127-FA nanoparticles were subjected to properties characterization and in vitro evaluation, including studies of internalization into cells and antitumor activity. Two cell lines were used: MCF-7 breast cancer cells, which have overexpressed folate receptors on the cell membranes, and RAW 264.7 macrophages without folate overexpression. These findings will provide a potential delivery system for DOX and increase the practical value of MOFs.

Three UiO-66 samples were prepared by solvothermal synthesis using the defect engineering approach with benzoic acid as a modulator. They were characterized by different techniques and their acidic properties were assessed by FTIR spectroscopy of adsorbed CO and CD₃CN. All samples evacuated at room temperature contained bridging μ₃-OH groups that interacted with both probe molecules. Evacuation at 250 °C leads to the dehydroxylation and disappearance of the μ₃-OH groups. Modulator-free synthesis resulted in a material with open Zr sites. They were detected by low-temperature CO adsorption on a sample evacuated at 200 °C and by CD₃CN even on a sample evacuated at RT. However, these sites were lacking in the two samples obtained with a modulator. IR and Raman spectra revealed that in these cases, the Zr⁴⁺ defect sites were saturated by benzoates, which prevented their interaction with probe molecules. Finally, the dehydroxylation of all samples produced another kind of bare Zr sites that did not interact with CO but formed complexes with acetonitrile, probably due to structural rearrangement. The results showed that FTIR spectroscopy is a powerful tool for investigating the presence and availability of acid sites in UiO-66, which is crucial for its application in adsorption and catalysis.

Here, we report a new photosensitive metal–organic framework (MOF) that was constructed via the modification of UiO-66-NH₂ with diarylethene molecules (DAE, 4-(5-Methoxy-1,2-dimethyl-1H-indol-3-yl)-3-(2,5-dimethylthiophen-3-yl)-4-furan-2,5-dione). The material that was obtained was a highly crystalline porous compound. The photoresponse of the modified MOF was observed via UV–Vis and IR spectroscopy. Most of the DAE molecules inside of the UiO-66-pores had an open conformation after synthesis. However, the equilibrium was able to be shifted further toward an open conformation using visible light irradiation with a wavelength of 520 nm. Conversely, UV-light with a wavelength of 450 nm initiated the transformation of the photoresponsive moieties inside of the pores to a closed modification. We have shown that this transformation could be used to stimulate hydrogen adsorption–desorption processes. Specifically, visible light irradiation increased the H₂ capacity of modified MOF, while UV-light decreased it. A similar hybrid material with DAE moieties in the UiO-66 scaffold was applied for hydrogen storage for the first time. Additionally, the obtained results are promising for smart H₂ storage that is able to be managed via light stimuli.

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.

Sulfation is a common strategy to enhance the acidity and modify the adsorption properties of metal–organic frameworks (MOFs), yet its impact on the coordination and accessibility of active sites remains unclear. In this study, we investigate two structurally related systems—sulfated UiO-66 (UiO-66-SO₄) and sulfated tetragonal zirconia (S-ZrO₂)—by FTIR spectroscopy with probe molecules. Isotope exchange experiments on S-ZrO₂ reveal that dehydration above 250 °C induces tridentate SO₄ coordination, while hydration leads to a reversible transition to a bidentate coordination mode. In UiO-66-SO₄, sulfates are coordinated in a bidentate fashion to Zr₆O₆ clusters, significantly affecting the accessibility of Zr sites in defective pores. This coordination prevents CO adsorption but allows acetonitrile adsorption even after room temperature activation. Unlike S-ZrO₂, due to its lower thermal stability, UiO-66-SO₄ cannot be evacuated at high temperatures and dehydration at 250 °C does not induce tridentate coordination. The presence of H-bonded hydroxyls in UiO-66-SO₄ after activation at 250 °C supports this coordination model, indicating the formation of OH-coordinated Zr sites that are inaccessible to CO but interact with stronger bases like acetonitrile. Overall, this study provides new insights into the coordination chemistry of sulfated UiO-66 and highlights that sulfation can tune acidity and adsorption in MOFs for potential catalytic and adsorption applications.