Construction strategies to modulate the photocatalytic efficiency of Cd(ii) MOFs to photodegrade organic dyes

Abstract

Metal–organic frameworks (MOFs), a sub-class of well-known coordination polymers, are assorted multidimensional materials that can be employed as photocatalysts for the decomposition of aromatic dyes present in wastewater discharge. Herein, two new Cd(II) MOFs [Cd₇(L)₄(μ₂-OH)₂(H₂O)₄(bbi)₃] (1) and [Cd₃(L)₂(bbm)₂] (2) (H₃L = 3-(4-carboxyphenoxy)-5-methylbenzoic acid, bbi = 1,4-di(1H-imidazol-1-yl)butane and bmp = 1,3-bis(2-methylimidazolyl)pentane) have been synthesized and characterized. Single-crystal X-ray diffraction analysis reveals that 1 possesses a 3D (3,16)-connected pillar-bilayer network with a {3²·4}₂{3⁸·4⁵⁰·5³⁴·6²⁴·7⁴} topology and comprises [Cd₇(COO)₁₄] SBUs. Meanwhile, 2 exhibits a 2D (3,8)-connected framework with a {3·4²}₂{3⁴·4⁶·5⁶·6⁸·7³·8} topology comprising [Cd₃(COO)₆] SBUs. Both MOFs have been used as photocatalysts for the photodegradation of aromatic dyes, and experiments demonstrate that 1 and 2 exhibit 95.5% and 86.2% photodegradation of methyl violet (MV), respectively, in a time span of 100 min. Moreover, both MOFs offer better photodegradation of MV than other model dyes such as rhodamine B, methyl blue and methyl orange. Additionally, the effects of catalyst amount and dye concentration on dye degradation have been explored. Further, trapping experiments indicate that ˙OH and ˙O₂⁻ are the active species responsible for the degradation of MV in the presence of 1. Both MOFs could be recycled and used repeatedly as photocatalysts for the degradation of MV, which showcases their highly stable nature. Density of states plots and Hirshfeld surface analyses have been performed to address the plausible photocatalytic mechanistic pathways.