Interfacial self-assembly of manganese multiporphyrin arrays on multi-walled carbon nanotubes as heterogeneous catalysts for degradation of toxic naphthols in aqueous solution

Artificial pigments of metalloporphyrin derivatives are effective catalysts for the degradation of toxic organic dyes, phenols, and other pollutants. We reported here an interfacial layer-by-layer (LBL) assembly of multiporphyrin arrays on the surface of multi-walled carbon nanotubes (MWNTs) with the use of Na 2 PdCl 4 as a connector and manganese (III) meso-tetra(4-pyridyl)porphine acetate (MnTPyP) as a linker, respectively. Thermogravimetric analysis revealed that the relative content of organic species in the MWNT@(Pd-MnTPyP) n nanocomposites increased gradually with more layers of Pd-MnTPyP assembled. The Soret absorption band of MnTPyP displayed approximately 20-nm redshift in the nanocomposites due to the increase of porphyrin-porphyrin interaction within the Pd-MnTPyP ultrathin films. The specific surface area was about 513.1 and 47.7 m 2 /g for the original MWNTs and MWNT@(Pd-MnTPyP) 3 nanocomposites, respectively. Finally, the nanocomposites were used as heterogeneous catalysts for catalytic degradation of toxic 1-naphthol, 1,5-dihydroxynaphthalene, 5-amino-1-naphthol, and 1-naphthol-5-sulphonic acid in phosphate buffer, using H 2 O 2 as the oxidant. It was revealed that, when the nanocomposites were used, the catalytic efficiency could increase by 2 to 3 orders of magnitude. Higher catalytic efficiency was observed for the naphthols bearing the electron-donating group of hydroxyl or amino than those bearing an electron-withdrawing group of sulfonic acid. Graphical abstract