| Phenolic compound is one of organic contaminated wastewater which is widespread, difficult to degrade and tremendously harm to the natural environment. It is one of organic pollutants which require to be serious controlled not only in china but also in abroad. The traditional advanced oxidation technology suffer from the problems of low utilization of H2O2, poor catalytic activity of refractory organic pollutants and the difficulty to reuse of catalysts. Therefore, designing a kind of catalysts with highly efficient catalytic oxidization of target pollutants can be of great significance.Metallophthalocyanine derivatives, having analogous structure to the active center of cytochrome P-450. The catalytic activity and selectivity are similar to biological enzymes, which catalytic reaction occurs generally following the coordination between central metal ions and reactants. Carbon nanotubes can be an ideal carrier material which determined by its unique physical properties and structure, excellent electrochemical performance, large specific surface area, good physical adsorption capacity and high stability under different conditions. Therefore, we can explore new methods to improve the supported catalyst by studying catalytic properties of the metal phthalocyanine supported on modified carbon nanotubes system.In this paper, two different ligands(4-aminopyridine(Py) and mercaptoethylamine(CS)) were used to modify carbon nanotubes, deamination and amidation methods were used to modify carbon nanotubes respectively and obtained MWCNTs-Py and MWCNTs-CS. Then, two novel bioinspired composite catalysts(FePc-Py-MWCNTs, FePc-CS-MWCNTs) made from iron phthalocyanine with axial ligands, Py and CS, were anchored on multi-walled carbon nanotubes to degrade 4-chlorophenol. FePc was successfully coordinated on carbon nanotubes by axial ligands under the characterizations of UV-vis, XPS, FTIR and other methods. The effect of pH, temperature, and sustained catalytic stability during cycling were investigated in the presence of two catalysts. The experimental results showed that different axial ligands that donated electrons to the central iron of iron phthalocyanine improved the catalytic activity and stability during hydrogen peroxide activation significantly. The FePc-CS-MWCNTs had a stronger catalytic oxidation capability under neutral conditions and better stability than the composite FePc-Py-MWCNTs with Py as axial ligand. H2O2 was not sufficiently powerful to oxidize by FePc-PyMWCNTs under neutral conditions, possibly because of the lower electronic interaction between N atoms in Py to Fe in FePc. Electron paramagnetic resonance spin-trapping experiments indicated that catalytic oxidation is dominated by hydroxyl radicals in both catalytic systems(both ?OH and ?OOH radicals were detected), which was different from the high-valent metal-oxo that is generated in common biomimetic catalytic systems with iron-porphyrins in the presence of a fifth species of ligands. The high catalytic activity and strong durability were distinct from traditional peroxide-activating catalysts of metal complexes dominated by ?OH radicals, where catalytic oxidation had a poor stability and was self-destructive in repetitive cyclic oxidation. In the catalytic system of this paper, the axial ligand affected the electronic structure of the central iron in which electron-donor substituents shifted the FeIII/II potential to more negative values, and increased the rate of the step from FeIII to FeII, which occurred slowly in the traditional Fenton system with hydrogen peroxide. This work offers a new perspective coordination between metal phthalocyanine and its supports, based on the appropriate selection of axial ligand for catalyst design and optimization. |
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