Optimizing the Visible Light Degradation of Methylene Blue Dye Using UiO-Series Metal-Organic Frameworks

Abstract

Wastewater pollution has become a globally problematic issue, increasing the need for more efficient and sustainable methods of aqueous pollutant removal. Photocatalysis using metal-organic frameworks (MOFs) has emerged as one such method, where MOFs absorb light energy to degrade pollutants. Current MOF-based photocatalytic applications typically involve UV irradiation, which is energy-intensive and costly; as such, optimizing MOFs for visible light usage is much more desirable. This study investigated three strategies to optimize the visible light degradation efficiency of the zirconium-based UiO-series MOF (UiO-66 and UiO-67) for the degradation of a model wastewater pollutant, methylene blue dye. These strategies included: 1.) crystal size alteration, 2.) pore size expansion via linker modulation, and 3.) secondary metal (Cu) incorporation. Crystal size alteration and secondary metal incorporation were found to be relatively ineffectual for enhancing visible light photocatalytic effects, mostly due to small particle agglomeration tendencies inherent to the former and independent Cu dendrite depositions inherent to the latter. Linker modulation through the use of UiO-67 rather than UiO-66 was found to be a more effective and promising strategy due to UiO-67’s strong initial adsorptive properties and increased pore sizes that allowed for improved internal active site usage. Synergistic explorations, in which the above three strategies were combined and tested in tandem, were additionally found to be mostly unavailing for enhancing degradation efficiency in the context of this study, mostly because of difficulties related to crystal size syntheses as well as due to Cu incorporation’s lacking effect. Based on the body of this work, future research strategies focused on prolonging the use of MOF internal active sites were deemed to have the most potential for improving photocatalytic degradation efficiency under visible light irradiation.