A novel catalyst of MIL-101(Fe) doped with Co and Cu as persulfate activator: synthesis, characterization, and catalytic performance

In this work, effective and novel heterogeneous catalysts of Metal–organic framework MIL-101(Fe) doped with cobalt (Co2+) or copper (Cu2+) have been synthesized by post-synthesis method, namely Co–MIL-101(Fe) and Cu–MIL-101(Fe). The initial and metal-doped samples were tested to activate persulfate (PS) for removal of Acid Orange 7 (AO7) in water. The surface of samples were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, N2 adsorption, scanning electron microscopy and transmission electron microscopy. The addition of Cu2+ and Co2+ could alter structure characteristics of MIL-101(Fe) in crystal structure and morphology. The unusual octahedron morphology of MIL-101(Fe) turned to be irregular, disorder and a rod-like morphology was shaped. What is more, Co doping caused greater changes in structure characteristics in comparison with Cu doping. The alteration was reflected in the catalytic capacity of PS activation. An interesting note was that, whether Co or Cu doping, metal-doped MIL-101(Fe) greatly improved the PS activation as compared to unmodified MIL-101(Fe). The removal rate of AO7 was about 66, 92, 98% in MIL-101(Fe)/PS, 6%wtCu–MIL-101(Fe)/PS and 6%wtCo–MIL-101(Fe)/PS system, respectively. Some results also suggested the performance of Co–MIL-101(Fe) was superior to that of Cu–MIL-101(Fe). Additionally, a series of parameters were designed to achieve maximum capacity of PS activation. Such an enhancement in activity may be attributed to the main reasons: the new active sites created by metal additives; an increase in number of active Fe sites produced by Co and Cu doping which results in alteration of morphology and structure of catalysts.