Selective adsorption behaviours of MOFs@SiO2 with different pore sizes and shell thicknesses

Polyethylene upcycling to aromatics by pulse pressurized catalytic pyrolysis

To address the challenging issues of waste plastic pollution and petroleum shortage, we report herein a pulse pressurized catalytic pyrolysis process where polyethylene is continuously converted into aromatics using HZSM-5 catalyst incorporated with hydrated SiO2. Pressurization improves the activity of single-pulse pyrolysis of polyethylene by 14.42%. In contrast to the linear decrease of BTEXS relative yield with a K value of - 0.23 under non-pressurized conditions, pressurization results in a notable stability in the latter stage, characterized by a K value of only - 0.063. Comprehensive catalyst characterization demonstrates that pressurization promotes the release of water from hydrated SiO2, enabling HZSM-5 to effectively undergo dealumination and obtain suitable acidity and pore structure, and ultimately enhancing the resistance to carbon deposition. In summary, pressurization improves both pyrolysis activity and catalysis stability, offering a promising strategy for the high-value utilization of waste plastics.

Grafting (S)-2-Phenylpropionic Acid on Coordinatively Unsaturated Metal Centers of MIL-101(Al) Metal-Organic Frameworks for Improved Enantioseparation

Chiral metal-organic frameworks (cMOFs) are emerging chiral stationary phases for enantioseparation owing to their porosity and designability. However, a great number of cMOF materials show poor separation performance for chiral drugs in high-performance liquid chromatography (HPLC). The possible reasons might be the irregular shapes of MOFs and the low grafting degree of chiral ligands. Herein, MIL-101-Ppa@SiO₂ was synthesized by a simple coordination post-synthetic modification method using (S)-(+)-2-Phenylpropionic acid and applied as the chiral stationary phase to separate chiral compounds by HPLC. NH₂-MIL-101-Ppa@SiO₂ prepared via covalent post-synthetic modification was used for comparison. The results showed that the chiral ligand density of MIL-101-Ppa@SiO₂ was higher than that of NH₂-MIL-101-Ppa@SiO₂, and the MIL-101-Ppa@SiO₂ column exhibited better chiral separation performance and structural stability. The binding affinities between MIL-101-Ppa@SiO₂ and chiral compounds were simulated to prove the mechanism of the molecular interactions during HPLC. These results revealed that cMOFs prepared by coordination post-synthetic modification could increase the grafting degree and enhance the separation performance. This method can provide ideas for the synthesis of cMOFs.

Application of Metal-Organic Framework-Based Composites for Gas Sensing and Effects of Synthesis Strategies on Gas-Sensitive Performance

Gas sensing materials, such as semiconducting metal oxides (SMOx), carbon-based materials, and polymers have been studied in recent years. Among of them, SMOx-based gas sensors have higher operating temperatures; sensors crafted from carbon-based materials have poor selectivity for gases and longer response times; and polymer gas sensors have poor stability and selectivity, so it is necessary to develop high-performance gas sensors. As a porous material constructed from inorganic nodes and multidentate organic bridging linkers, the metal-organic framework (MOF) shows viable applications in gas sensors due to its inherent large specific surface area and high porosity. Thus, compounding sensor materials with MOFs can create a synergistic effect. Many studies have been conducted on composite MOFs with three materials to control the synergistic effects to improve gas sensing performance. Therefore, this review summarizes the application of MOFs in sensor materials and emphasizes the synthesis progress of MOF composites. The challenges and development prospects of MOF-based composites are also discussed.