Valorization of manganese residue to construct amorphous MnO2/α-Fe2O3@geopolymer Z-scheme heterojunction for efficient Cr(VI) reduction and ciprofloxacin degradation

Abstract

To effectively utilize the hazardous industrial solid waste manganese residue (MR), a MR-derived Fe2O3-baesd photocatalyst with efficient charge transfer, abundant reactive sites and high redox performance was developed for simultaneously removing organic pollutants and heavy metals. Herein, a novel “confined growth” strategy was proposed to fabricate an amorphous MnO2 decorated α-Fe2O3@geopolymer sphere (A-MnO2/Fe2O3@GS) Z-scheme heterojunction by ion exchange method, which was used as a photo-Fenton catalyst for efficiently reducing Cr(VI) and degrading ciprofloxacin (CIP). Characterization results reveal that the 3D hydrangea-like MnO2 with low crystallinity could not only capture and accelerate electron transfer but also act as an electron conduction bridge and a surface oxygen adsorption site, resulting in efficient separation and utilization of charge. More importantly, the photocatalytic reduction capacity was greatly enhanced in Z-scheme heterojunction owing to the lower conduction band potential of MnO2. A-MnO2/Fe2O3@GS showed excellent photocatalytic activity with CIP removal of 99.1% within 40 min and Cr(VI) removal of 97.6% within 50 min, which were 8.13 and 3.47 times higher than those catalyzed by Fe2O3@GS, respectively. This can be ascribed to the formation of intimate interface, internal electrostatic field, and rich structure defects in the Z-scheme heterojunction. This work offers a new idea to construct Z-scheme photocatalysts with high reactivity for environmental modification.