Ibuprofen degradation by a synergism of facet-controlled MIL-88B(Fe) and persulfate under simulated visible light

The photocatalysis/persulfate (PS) hybrid system has proven to be a promising method for degrading organic pollutants from aqueous solutions. In this study, three MIL-88B(Fe) iron-based metal-organic framework (MOF) phases with different facet content were prepared and used both as photocatalysts and catalysts for PS activation to remove ibuprofen (IBP). The results showed that there was a close correlation between the exposed facets and the catalytic activity. MIL-88B(Fe)-1 (M88B1) with exposed {100} facets and proportionally more {101} facets showed the best catalytic activity. The optimum PS dosage used in this study was 60 mg/L. The presence of Cl-, SO42-, and NO3- all inhibited the degradation of IBP. X-ray photoelectron spectroscopy (XPS) showed that M88B1 possessed more Fe2+ than the other two MIL-88B(Fe) MOF phases, making it easier to generate active radicals through PS activation. The UV-vis diffuse reflectance spectra (DRS), photoluminescence (PL), and electrochemical analysis indicated that M88B1 possessed the highest light absorption, most active sites, and fastest charge transfer ability. Radical scavenging and electron spin resonance (ESR) experiments demonstrated that SO4-•, •OH, O2-•, and 1O2 species participated in the IBP degradation process. Furthermore, density functional theory (DFT) calculations were performed to identify the crystallographic facets, band structure, and total density of states of MIL-88B(Fe) to further confirm the mechanism of MIL-88B(Fe) as a photocatalyst and a PS activator. This work provides new insights into the synergism between photocatalysis and persulfate activation by facet-controlled MOFs for environmental remediation.