APTES-functionalized Fe3O4 microspheres supported Cu atom-clusters with superior catalytic activity towards 4-nitrophenol reduction

A kind of APTES-functionalized Fe3O4 microspheres supported Cu atom-clusters (Cu-APTES@Fe3O4) has been successfully synthesized. The composite material was monodispersed with particle size of ca. 170 nm. Cu clusters (ca. 8-10 nm) containing about 30-40 Cu atoms were trapped by the amino groups of APTES on the surface of Fe3O4 microspheres. The reduction catalysis of Cu-APTES@Fe3O4 has been investigated using 4-nitrophenol as a probe molecule. Under the optimum conditions, i.e., 0.17 mmol L-1 of 4-nitrophenol, 0.067 mol L-1 of NaBH4 and 9.9 mgL(-1) of Cu-APTES@Fe3O4, the as-obtained Cu-APTES@Fe3O4 catalyst showed superior reducibility. Almost complete reduction of 4-nitrophenol to 4-aminophenol was accomplished within 10 min reaction. The kinetic constant k(app) was 0.27 min(-1), and the calculated apparent activation energy was about 50.5 kJ/mol, both of which were comparable to those for the reported noble metal-based catalysts. The desirable catalytic activity was attributed to the facilitation of electron transfer process by Cu atom-clusters, and the improvement of surface functionalization by APTES. Furthermore, the magnetic composite catalyst has satisfactory stability and reusability, which is a promising reducing agent for reduction of 4-nitrophenol to 4-aminophenol.