Effects of the peripheral substituents (–NH2, –OH, –CH3, –H, –C6H5, –Cl, –CO2H and –NO2) on molecular properties of a Ni-Porphyrazine dimers family

Electronic structure modulation of iron sites with fluorine coordination enables ultra-effective H2O2 activation

Electronic structure modulation of active sites is critical important in Fenton catalysis as it offers a promising strategy for boosting H2O2 activation. However, efficient generation of hydroxyl radicals (•OH) is often limited to the unoptimized coordination environment of active sites. Herein, we report the rational design and synthesis of iron oxyfluoride (FeOF), whose iron sites strongly coordinate with the most electronegative fluorine atoms in a characteristic moiety of F-(Fe(III)O3)-F, for effective H2O2 activation with potent •OH generation. Results demonstrate that the fluorine coordination plays a pivotal role in lowering the local electron density and optimizing the electronic structures of iron sites, thus facilitating the rate-limiting H2O2 adsorption and subsequent peroxyl bond cleavage reactions. Consequently, FeOF exhibits a significant and pH-adaptive •OH yield (~450 µM) with high selectivity, which is 1 ~ 3 orders of magnitude higher than the state-of-the-art iron-based catalysts, leading to excellent degradation activities against various organic pollutants at neutral condition. This work provides fundamental insights into the function of fluorine coordination in boosting Fenton catalysis at atomic level, which may inspire the design of efficient active sites for sustainable environmental remediation.

Room-temperature preparation of highly efficient NH2-MIL-101(Fe) catalyst: The important role of -NH2 in accelerating Fe(III)/Fe(II) cycling

The slow redox rate of Fe(III)/Fe(II) couples is a rate-limiting step for Fenton-like performance of Fe-MOFs. In this study, a series of catalysts (MIL-101) with various p-phthalic acid/2-aminoterephthalic acid (H₂BDC/NH₂-H₂BDC) molar ratios were prepared using a simple and mild chemical method and applied for catalyzed degradation of bisphenol A (BPA). Interestingly, the -NH₂ modified MIL-101(Fe) can adjust Fe-Oxo node by increasing the electron density of Fe(III) in the presence of -NH₂ group with high electron density, thus forming Fe(II) in situ in MOFs. Meanwhile, the -NH₂ groups used as electron-donors can promote electron transfer, resulting in faster Fe(III)→Fe(II) half-reaction and active H₂O₂ to continuously generate •OH radical. The BPA degradation and rate constant of Fe-BDC-NH₂/H₂O₂ system are 15.4-fold and 86.8-fold higher than that of Fe-BDC/H₂O₂ system, respectively. The density functional theory (DFT) calculations showed that Fe-BDC-NH₂ possesses higher Fermi level energy (-4.88 eV) and lower activation energy barriers (0.32 eV) compared with Fe-BDC. Moreover, Fe-BDC-NH₂ showed good reusability and stability. This work offers a highly efficient and stable MOFs-based Fenton-like catalyst to rapidly degrade organic pollutants over a wide pH range for potential applications in wastewater treatment.