One-pot in situ synthesis of an NS-ligand co-doped metal–organic framework for the enhanced adsorption-assisted photocatalytic decontamination of metronidazole

Abstract

Doping active agents into metal–organic frameworks (MOFs) is widely sought after owing to its potential to enhance adsorption and photocatalytic efficiency, surpassing the potential of bare frameworks. This study incorporated a catalytically active NS-ligand (1,2-benzisothiazolin-3-one) into a very stable and porous PCN-600 MOF via an in situ synthesis approach. The NS-ligand, which matched with the host ligands of PCN-600, enabled the highly efficient synthesis of NS-co-doped MOFs. The pristine PCN-600 framework and morphology were retained in the MOF altered with the NS-ligand, as demonstrated by XRD, FTIR, and SEM characterizations. A high electron density was generated due to the synergistic effect between the defects in the NS-co-doped photocatalyst and engineered active sites. This facilitated the adsorption-assisted photocatalytic decontamination of metronidazole with an 87% removal by PCN-600-NS-10 compared to 43% by pristine PCN-600 within a total time of 150 min. The MOF doped with the NS-ligand exhibited a reduced band gap and enhanced adsorption and photocatalytic capabilities compared to pristine PCN-600. The impact of operational parameters, such as catalyst dosage, initial solution pH, and MNZ concentration, was also explored. Pseudo-second and pseudo-first order models were found to describe the adsorption and degradation kinetics of metronidazole and the Dubinin–Radushkevich model was found to fit the equilibrium adsorption results. The thermodynamic characteristics of adsorption processes (ΔG_ads, ΔH_ads, and ΔS_ads) demonstrated that adsorption was physical, spontaneous, and exothermic and resulted in increased entropy.