Sulfur-functionalized porphyrin-based covalent organic framework as a metal-free dual-functional catalyst for photodegradation of organophosphorus pesticides under visible-LED-light.

Parathion and diazinon are two significant organophosphorus pesticides broadly used in agriculture. However, these compounds are toxic and can enter into the environment and atmosphere via various processes. Herein, we synthesized and post-functionalized a porphyrinic covalent organic framework (COF), COF-366, with elemental sulfur under solvent-free conditions to give polysulfide-functionalized COF-366, namely PS@COF. The resulting material consisting of porphyrin sensitizer and sulfur nucleophilic sites was used as a dual-functional heterogeneous catalyst for the degradation of these organic compounds using visible-LED-light. Accordingly, the effects of several pertinent parameters such as pH (3-9), the catalyst dosage (5-30 mg), time (up to 80 min), and substrate concentration (10-50 mg L-1) were studied in detail and optimized. The post-modified COF showed excellent photocatalytic activity (>97%) in the detoxification of diazinon and parathion for 60 min at pH 5.5. Kinetic studies indicated a fast degradation rate with pseudo-second order model for 20 mg L-1 of diazinon and parathion. The total organic carbon detection and gas chromatography-mass spectrometry (GC-MS) confirmed the organic intermediates and byproducts formed during the process. PS@COF displayed good recyclability and high reusable efficiency for six cycles without a noteworthy lose in its catalytic activity, owing to its robust structure.

Cooperativity of pi-stacking and hydrogen bonding interactions and substituent effects on X-ben//pyr...H-F complexes.

Quantum chemical calculations have been performed to gauge the effect of pi-stacking and hydrogen bonding interactions on each other in X-ben//pyr...H-F (X = NO(2), CF(3), CN, F, Cl, CH(3) and OH) complexes. The results indicate the cooperativity of interactions in these complexes where face-to-face aromatic interactions and hydrogen bonding interactions coexist. The effects of substituents on the X-ben//pyr...H-F complexes have also been studied with the MP2 method using 6-31G** basis set. The total binding energy increases in both electron-donating and withdrawing substituents. Herein, computational results indicate an enhanced pi-stacking interaction for all substituted complexes related to an unsubstituted case. On the other hand, H...N hydrogen bond interaction is declined by strong electron withdrawing substituents (NO(2) and CN) only. The cooperativity of pi-stacking and H...N hydrogen bond interaction has also been studied by using the atoms in molecules (AIM), natural bond orbital (NBO) and molecular electrostatic potential (MEP) analyses. There are good relationships between the Hammett constants and energy data, geometrical parameters, and the results of population analysis in X-ben//pyr...H-F and X-ben//pyr complexes. The characteristics of interactions are directly related to the electrostatic interaction between the rings.