Synthesis of a 3D Cu(II) MOF and its heterostructual g-C3N4 composite showing improved visible-light-driven photodegradation of organic dyes

Abstract

One 3D Cu(II)-based metal-organic framework {[Cu3(tmpa)2(1,2,3-btc)2(H2O)2].14H2O.2DMF}n (Cu(tmpa)) (tmpa ​= ​tris(4-(2-methyl-1H-imidazole-1-yl)phenyl)amine, 1,2,3-H3btc ​= ​1,2,3-benzenetricarboxylic acid) was prepared by hydrothermal method and characterized. Cu(tmpa) exhibits (3,3,4)-connected 3D topology showing point symbol of (6·8·9)2(6·8·10)2(62·82·102). The heterostructural Cu(tmpa)/CN composites with different mass proportions were prepared and characterized by XRD, FT-IR, SEM, EDS, UV-DRS, TGA, PL and EIS. The photocatalytic activities of Cu(tmpa) and Cu(tmpa)/20%CN composite to degrade methylene blue (MB), methyl violet (MV), malachite green (MG), and Congo red (CR) were investigated. The photocatalytic degradation of MB by Cu(tmpa)/CN with different mass proportions was studied, and the catalytic conditions catalyst dosage, H2O2 concentration and initial pH value with were optimized. The degradation rate of MB for Cu(tmpa)/20%CN could reach 92.0% within 20 ​min. Cu(tmpa)/20%CN could also degrade 92.0%, 92.9% and 98.2% of MV, MG and CR in 60 ​min, 35 ​min and 3 ​min, respectively. The degradation mechanisms for MB and CR were studied. The enhanced photocatalytic activities of Cu(tmpa)/CN composite might be attributed not only to the vigorous visible-light absorption of Cu(tmpa), but also to the heterojunction formed by doping g-C3N4, which accelerates the divorce and movement of photogenerated charges compared to Cu(tmpa). The holes were the primary active matters in the degradation for MB. The holes and superoxide radicals were the main reactive matters in degradation of CR. Cu(tmpa) and Cu(tmpa)/20%CN are good photocatalytic materials.