Construction of ultra-high defective iron-based metal organic frameworks with small molecule acid regulator for enhanced degradation of sulfamethoxazole

In this study, Several small molecule acid FA (formic acid), HBC (benzoic acid), OA (oxalic acid), and CA (citric acid) were applied as the modulator in the preparation of high-activity defective Fe(II)-MOFs with coordinatively unsaturated sites (CUS). Due to the competitive effect caused between organic ligand and carboxyl functional group of the modulator, the addition of modulator create more CUS for PS activation. Moreover, sulfamethoxazole (SMX) degradation rates raised from 40.41% to 80.19%, 73.50%, 63.89%, and 91.96%, respectively. Fe(II)MOF-CA displayed the most ideal catalytic activity during PS activation. Through typical physical and chemical characterizations (XRD, XPS, CV, BET, and EIS), as well as performance tests, CA was observed as the most robust modulator for improving the degree of crystallinity, porosity and coordination by slowing the rate of Fe releasing via chelation. Based on Electron paramagnetic resonance (EPR), chemical quenching experiment, and LC-MS detection results, main free radicals and degradation intermediates were identified, and the degradation pathways of SMX in the Fe(II)-MOF-CA/PS system was proposed. According to XPS, CV, and EIS results, the possible catalytic mechanism was raised. This research provided a new perspective for improving the performance of Fe based MOFs toward PS via the construction of defect using small molecule acid, which was meaningful for further investigation and application of pollution control based on MOFs.

Automated summary

In this study, different small molecule acids were used as modulators to prepare high-activity defective Fe(II)-MOFs with unsaturated coordination sites. The addition of the modulators created more unsaturated sites for PS activation, leading to enhanced degradation of sulfamethoxazole. Citric acid was found to be the most effective modulator, improving the crystallinity, porosity, and coordination of the Fe(II)-MOFs. The study also proposed a degradation pathway for sulfamethoxazole in the Fe(II)-MOF-CA/PS system and proposed a possible catalytic mechanism based on experimental results.