Visible light-assisted photocatalytic degradation of methylene blue in water by highly chemically stable Cd-coordination polymers at room temperature

Abstract

Methylene blue is widely used in industrial and agricultural production and daily life, leading to the prevalence of methylene blue in the environment, which is toxic and persistent in large quantities. Coordination polymers (CPs), as a type of novel photocatalytic material with special structural characteristics and tunability, have high potential for efficient removal of methylene blue. A novel Cd-CP material [Cd₂(dda)(bibp)₂]·H₂O (YAU-10, H₄dda = 3,3,5,5-azodibenzoic acid, bibp = 4,4′-di(1H-imidazol-1-yl)-1,1′-biphenyl) was successfully prepared by a solvothermal method. Single-crystal X-ray diffraction studies of YAU-10 reveal a three-dimensional (3D) network structure consisting of a Cd₂ cluster, [dda]⁴⁻ and bibp ligands as nodes having a (2,3,8)-connected binodal net with {4⁴·6¹⁰·8}{4⁴·6²} topology. In the 3D network structure, there are several types of strong weak interaction forces, such as π–π stacking and hydrogen bonds, which further enhance the stability of YAU-10. Investigation of YAU-10 for visible light-assisted photocatalytic degradation of methylene blue at room temperature resulted in a high degradation rate. The remarkable high, visible-light catalytic performance of YAU-10 has been attributed to the cooperative effect of its structural characteristics, light, H₂O₂, pH and other factors. Conversely, the CP [Cd(dda)_0.5(bibp)₂]·3H₂O, with a Cd²⁺ mononuclear node and one-dimensional structure, does not show good photocatalytic activity under similar conditions. Furthermore, the frame structures and photocatalytic activity of YAU-10 did not change significantly after six cycles of experiment. To the best of our knowledge, YAU-10 is the first example of a CP based on a binuclear 3D structure that exhibits visible light-assisted degradation of methylene blue in the presence of H₂O₂ and pH = 10 without the assistance of noble metal cocatalysts.