Cu anchored on manganese residue through mechanical activation to prepare a Fe-Cu@SiO2/starch-derived carbon composites with highly stable and active visible light photocatalytic performance

To harmlessly treat and effectively utilize manganese residue (MR), a novel MR-based catalyst, mechanical activation (MA)-pretreated MR-derived Fe-Cu@SiO2/starch-derived carbon (MAMR-Fe-Cu@SiO2/SC) composite, was prepared through a facial method by reduction roasting of MA-pretreated precursors. The prepared catalysts were systematically characterized to explore the formation and catalytic activities. The results showed that the formation of CuFeO2 anchored on the MR could be ascribed to the close contact and mutual diffusion between solid components caused by MA, and the higher specific surface area, strong interaction of Fe-Cu and more accessible reactive sites of MAMR-Fe-Cu@SiO2/SC contributed to the greater catalytic activity in photo-Fenton system for tetracycline (TC) degradation. The MAMR-Fe-Cu@SiO2/SC catalyst showed excellent degradation efficiency at pH range of 2.5-9.5, and about 100% TC removal in 40 min and 85.6% TOC removal in 120 min could be obtained. The MAMR-Fe-Cu@SiO2/SC exhibited the highest apparent reaction rate constant of 0.066 min(-1), being about 4.0, 2.8, and 2.2 times that for the catalyst of Cu/SC, MAMR-Fe3O4@SiO2/SC and MR-Fe-Cu@SiO2/SC, respectively. This enhancement could be attributed to that anchored Cu could accelerate the charge transfer, and short the reaction pathway between photo and Fenton reaction. XPS results showed that the presence of Fe2+-Fe3+, Mn2+-Mn3+ and Cu+-Cu2+ cycles were responsible for the radical generation on the surface of the catalyst. This environmentally-friendly method for the preparation of composite catalysts may provide new insights for harmless fixed treatment and valorization of MR and large-scale production of catalyst.