Controlling the morphology of metal–organic frameworks and porous carbon materials: metal oxides as primary architecture-directing agents

Owing to their large ratio of surface area to mass and volume, metal–organic frameworks and porous carbons have revolutionized many applications that rely on chemical and physical interactions at surfaces. However, a major challenge today is to shape these porous materials to translate their enhanced performance from the laboratory into macroscopic real-world applications. In this review, we give a comprehensive overview of how the precise morphology control of metal oxides can be transferred to metal–organic frameworks and porous carbon materials. As such, tailored material structures can be designed in 0D, 1D, 2D, and 3D with considerable implications for applications such as in energy storage, catalysis and nanomedicine. Therefore, we predict that major research advances in morphology control of metal–organic frameworks and porous carbons will facilitate the use of these materials in addressing major needs of the society, especially the grand challenges of energy, health, and environment

Hydrothermal Synthesis of ZnO Superstructures with Controlled Morphology via Temperature and pH Optimization

Zinc oxide, as a widely used material in optics, electronics, and medicine, requires a complete overview of different conditions for facile and easily reproducible syntheses. Two types of optimization of ZnO hydrothermal preparation from zinc acetate and sodium hydroxide solution are presented, which allowed for obtaining miscellaneous morphologies of materials. The first was a temperature-controlled synthesis from 100 to 200 °C, using citric acid as a capping agent. The formation of hexagonal rods at the lowest temperature was evidenced, which agglomerated to flower-like structures at 110 and 120 °C. It was followed by transformation to flake-like roses at 160 °C, up to disordered structures composed of nanosized plates (>180 °C). The transformations were generated through a temperature change, which had an impact on the diffusion effect of hydroxide and citrate complexes. The second optimization was the hydrothermal synthesis free of organic additives and it included only a pH variation from 7.5 to 13.5. It was found that by utilizing a slow-dropping process and varying amounts of NaOH solutions, it is possible to obtain well-formed hexagonal pellets at pH 8.0–8.5. Strongly basic conditions of pH 11.0 and 13.5 impeded superstructure formations, giving small elongated particles of ZnO. All samples were characterized by high phase purity and crystallinity, with a specific surface area of 18–37 m2/g, whereas particle size distribution indicated a predominance of small particles (<1 μm)

Biocompatible Fe-Based Metal-Organic Frameworks as Diclofenac Sodium Delivery Systems for Migraine Treatment

Migraine is now the sixth most common disease in the world and affects approximately 15% of the population. Non-steroidal anti-inflammatory drugs, including ketoprofen, diclofenac sodium, and ibuprofen, are often used during migraine attacks. Unfortunately, their efficiency can be reduced due to poor water solubility and low cellular uptake. This requires the design of appropriate porous carriers, which enable drugs to reach the target site, increase their dissolution and stability, and contribute to a time-dependent specific release mode. In this research, the potential of the MIL-88A metal-organic frameworks with divergent morphologies as diclofenac sodium delivery platforms was demonstrated. Materials were synthesized under different conditions (temperature: 70 and 120 °C; solvent: distilled water or N,N-Dimethylformamide) and characterized using X-ray diffraction, low-temperature nitrogen adsorption/desorption, thermogravimetric analysis, infrared spectroscopy, and scanning electron microscopy. They showed spherical, rod- or diamond-like morphologies influenced by preparation factors. Depending on physicochemical properties, the MIL-88A samples exhibited various sorption capacities toward diclofenac sodium (833–2021 mg/g). Drug adsorption onto the surface of MIL-88A materials primarily relied on the formation of hydrogen bonds, metal coordination, and electrostatic interactions. An in vitro drug release experiment performed at pH 6.8 revealed that diclofenac sodium diffused to phosphate buffer in a controlled manner. The MIL-88A carriers provide a high percentage release of drug in the range of 58–97% after 24 h

Insight into the Photocatalytic Activity of Cobalt-Based Metal&ndash;Organic Frameworks and Their Composites

Nowadays, materials with great potential for environmental protection are being sought. Metal&ndash;organic frameworks, in particular those with cobalt species as active sites, have drawn considerable interest due to their excellent properties. This review focuses on describing cobalt-based MOFs in the context of light-triggered processes, including dye degradation, water oxidation and splitting, carbon dioxide reduction, in addition to the oxidation of organic compounds. With the use of Co-based MOFs (e.g., ZIF-67, Co-MOF-74) as photocatalysts in these reactions, even over 90% degradation efficiencies of various dyes (e.g., methylene blue) can be achieved. Co-based MOFs also show high TOF/TON values in water splitting processes and CO2-to-CO conversion. Additionally, the majority of alcohols may be converted to aldehydes with efficiencies exceeding 90% and high selectivity. Since Co-based MOFs are effective photocatalysts, they can be applied in the elimination of toxic contaminants that endanger the environment

Insight into the Photocatalytic Activity of Cobalt-Based Metal–Organic Frameworks and Their Composites

Nowadays, materials with great potential for environmental protection are being sought. Metal–organic frameworks, in particular those with cobalt species as active sites, have drawn considerable interest due to their excellent properties. This review focuses on describing cobalt-based MOFs in the context of light-triggered processes, including dye degradation, water oxidation and splitting, carbon dioxide reduction, in addition to the oxidation of organic compounds. With the use of Co-based MOFs (e.g., ZIF-67, Co-MOF-74) as photocatalysts in these reactions, even over 90% degradation efficiencies of various dyes (e.g., methylene blue) can be achieved. Co-based MOFs also show high TOF/TON values in water splitting processes and CO2-to-CO conversion. Additionally, the majority of alcohols may be converted to aldehydes with efficiencies exceeding 90% and high selectivity. Since Co-based MOFs are effective photocatalysts, they can be applied in the elimination of toxic contaminants that endanger the environment