Understanding the coordination behavior of antibiotics: Take tetracycline as an example.

Gaining insight into the occurrence states of residual antibiotics is crucial to demystify their environmental behavior. However, the complexation of heteroatoms functioned on antibiotic molecules to metal ions in the water environment is not fully understood. This study reports that a fluorescence response was unexpectedly triggered by tetracycline (TC) and Al3+, serving as solid evidence to visualize the Al3+-TC coordination reaction. Differential electron absorption spectroscopy shows a quantifiable signal of the redshifted n-π* transition with a coordination reaction, which is also proportional to the fluorescence. The occurrence of Al3+-complexed TC also caused a split in retention time in liquid chromatogram. The TC ligands were re-released in the presence of stronger ligands competing for central Al3+. The complex ratio of Al3+-TC is confirmed to be 1:1 using Job's plot with a stability constant of 1.01 × 106. Quantum chemical computations coupled with Gibbs free energy analysis simulated the formation of octahedral Al3+-TC configuration through a spontaneous bidentate chelation. This study helps convey a broad consensus and opens a new door in the mechanistic study of metal-involved antibiotic transformation process, leading to a better understanding that can ultimately be essential to reach the final goal of alleviating the antibiotic crisis.

Molten-salts assisted preparation of iron-nitrogen-carbon catalyst for efficient degradation of acetaminophen by periodate activation.

Highly efficient and stable heterogeneous catalysts were desired to activate periodate (PI) for sustainable pollution control. Herein, iron-nitrogen-carbon catalyst was synthesized using a facile molten-salts mediated pyrolysis strategy (denoted as FeNC-MS) and employed to activate PI for the degradation of acetaminophen (ACE). Compared with iron-nitrogen-carbon catalyst prepared by direct pyrolysis method (marked as FeNC), FeNC-MS exhibited superior catalytic activity due to its large specific surface area (1600 m2 g-1) and the abundance of FeNx sites. The batch experiments revealed that FeNC/PI process achieved 37 % ACE removal within 20 min, while ACE removal in FeNC-MS/PI process was 98 % under the identical conditions. Integrated with electron paramagnetic resonance tests, quenching experiments, chemical probe identification, and electrochemical experiments, we demonstrated that FeNC-MS-PI complexes-mediated electron transfer was the predominant mechanism for the oxidation of ACE. Further analysis disclosed that FeNx sites in FeNC-MS were the main active sites for the activation of PI. Additionally, FeNC-MS/PI process exhibited significant resistance to humic acid and background electrolyte, and avoided the secondary pollution imposed by Fe leaching. The possible degradation pathways of ACE were proposed. The germination experiments of lettuce seeds showed that the ecotoxicity of ACE solution was significantly reduced after treatment with FeNC-MS/PI process. Overall, this study provided a facile strategy for the synthesis of efficient iron-nitrogen-carbon catalysts and gained fundamental insight into the mechanism of PI activation by iron-nitrogen-carbon catalysts for pollutants degradation.

Understanding the nonradical activation of peroxymonosulfate by different crystallographic MnO2: The pivotal role of MnIII content on the surface.

Manganese oxide-activated persulfate plays a critical role in water purification and in situ chemical oxidation processes, but the underlying mechanism needs to be further revealed. Herein, the detailed mechanism of MnO2 with various crystallographic structures (α-, ß-, γ-, and δ-MnO2) towards peroxymonosulfate (PMS) activation was investigated. PMS activated by tunnel structured α-, ß-, and γ-MnO2 showed higher acetaminophen (ACE) removal than layer structured δ-MnO2 with the removal efficiency following an order of α-MnO2 (85%) ≈ Î³-MnO2 (84%) > ß-MnO2 (65%) > Î´-MnO2 (31%). Integrated with chemical quenching experiments, electron paramagnetic resonance, Raman spectra, X-ray photoelectron spectroscopy, and Langmuir-Hinshelwood model on kinetic data, both surface-bound PMS complexes and direct oxidation by surface manganese species (Mn(Ⅳ, Ⅲ)(s)) were disclosed as the dominant oxidation mechanism for ACE degradation in α-, ß-, and γ-MnO2/PMS, which were rarely observed in previous reports. Moreover, the catalytic activity of α-, ß-, and γ-MnO2 was positively correlated to the MnIII(s) content on the catalyst surface. Higher content of MnIII(s) would stimulate the generation of more oxygen vacancies, which was conducive to the adsorption of PMS and the formation of reactive complexes. Overall, this study might provide deeper insight into the nonradical activation mechanism of PMS over different crystallographic MnO2.

Effects of foreign metal doping on the step-by-step oxidation process in M-OMS-2 catalyzed activation of PMS.

Various metal cations M (M = Mg2+, Ca2+, Zn2+, Cu2+, Fe3+) were doped into the tunnel of manganese octahedral molecular sieve (OMS-2). Redox-inactive metal (Ca, Mg and Zn) doped OMS-2 exhibited better peroxymonosulfate (PMS) catalytic activity than redox metal-doped Cu-OMS-2 and Fe-OMS-2. Redox-inactive metals doping improves the conductivity and reducibility of the catalyst, while transition metal doping reduces the dispersion of manganese. More importantly, the degradation of ACE can be divided into two stages. In the first stage, ACE was oxidized dominantly through mediated electron transfer process. Subsequently, singlet oxygen (1O2) gradually dominated oxidative degradation in the second stage, which was derived from the reaction between superoxide radical (O2•-) and metastable manganese intermediates. The long half-life of O2•- on the surface of OMS-2 ensured the delay generation of 1O2. This study not only provides a new idea for improving the efficiency of heterogeneous catalysts activation of PMS, but also meaningful for the in-depth study of multiple reaction mechanisms in PMS activation processes.