APTES-functionalized Fe 3 O 4 microspheres supported Cu atom-clusters with superior catalytic activity towards 4-nitrophenol reduction

Abstract A kind of APTES-functionalized Fe 3 O 4 microspheres supported Cu atom-clusters (Cu-APTES@Fe 3 O 4 ) 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 Fe 3 O 4 microspheres. The reduction catalysis of Cu-APTES@Fe 3 O 4 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 NaBH 4 and 9.9 mg L −1 of Cu-APTES@Fe 3 O 4 , the as-obtained Cu-APTES@Fe 3 O 4 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.