Manganese-based metal-organic framework preferentially photocatalytically degraded high electronegativity groups in methyl orange

Abstract

The photophysical properties, electronic structure, and surface active sites of metal-organic framework (MOF) photocatalysts influence their performance. In this paper, a manganese (Mn) based MOF {[Mn(L)]∙2H₂O}_n (Mn-MOF) and its nano photocatalyst (Mn-MOF-N) with strong visible light response (E_g = 2.48 eV) were synthesized by MnAc₂∙4H₂O and 2,2′-bipyridine-4,4′-dicarboxylic acid (H₂L) as raw materials. X-ray single crystal diffraction analysis shows that L²⁻ in Mn-MOF bridges adjacent Mn(II) in a μ₅-η¹:η¹:η¹:η¹:η¹ mode to generate a three-dimensional structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the particle diameter of Mn-MOF-N is about 100 nm. The degradation of methyl orange (MO) by Mn-MOF-N was found to follow pseudo-first-order degradation kinetics with a photocatalytic degradation rate of 2.500 mg L⁻¹ h⁻¹ under optimal conditions (pH = 3.00, dosage was 0.0100 g), which is higher than that of P25 and some MOF photocatalysts. The degradation mechanism was confirmed through density functional theory (DFT) and electrospray ionization mass spectrometry (ESI-MS), revealing that the highly electronegative azo groups in MO were reduced by hydroxyl radicals and were degraded subsequently through catalytic oxidation. Mn-MOF-N emerged favourable structural stability and performance stability in cycling experiments, giving it a chance to prospective application in photocatalytic degradation of actual wastewater.