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

Abstract

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.