Copper-loaded sustainable MOFs as photocatalysts for dye removal

Abstract

This work presents the effect of Cu loading, using incipient wetness impregnation method, on sustainably synthesized MIL-100(Fe), NH2-MIL-53(Al), Zr-BDC and NH2-Zr-BDC MOFs and their photocatalytic removal efficiency on target dye, rhodamine B (RhB), from aqueous solutions. Several Cu ratios have been tested, finding that 2 wt% of Cu load becomes optimum in terms of metal distribution and catalytic performance. Powder X-ray diffraction patterns (XRD) showed no difference from the parent supports in the case of MIL-100(Fe), NH2-MIL-53(Al) and Zr-BDC, whereas extra peaks are induced by Cu impregnation in NH2-Zr-BDC. In addition, several techniques indicate that Cu strongly interacts with the MOF in Cu@NH2-Zr-BDC, exhibiting the lowest bandgap of the series, the lowest photoluminescence intensity and a notable predominance of Cu in the oxidation state 2+. The above evidences lead Cu@NH2-Zr-BDC to behave as the most effective catalyst in the removal of RhB, reaching removal efficiency as high as 93 %, being able to efficiently and selectively remove basic dyes from mixed samples, such as RhB and MB, but not for acidic dyes like MO, and also showing a very good performance (46 % photodegradation) in real waste water from Hawassa textile factory, in Ethiopia. Moreover, this catalyst can be recycled 3 times by simple washing and drying. Scavengers test suggested that h+ is the most active species in the photocatalytic degradation.