In-situ growth of amorphous MnO2 on C-decorated Fe-based geopolymer sphere with rich structure defects for efficient solar light-induced photo-thermal-Fenton reaction

Crystalline MnO2 exhibits excellent photo-thermal conversion and adjustability of valence states properties, but the weak near-infrared light absorption, poor charge transportation and utilization limit its environmental applications. Herein, a novel Na-doped amorphous MnO2/C-decorated Fe-based geopolymer sphere (A-MnO2/C-FeGS) with rich structure vacancies was constructed by ion exchange anchoring strategy and used to degrade tetracycline hydrochloride (TC) in solar light-induced photo-thermal-Fenton process. Manganese residue (MR), an industrial solid waste, was used as the source of Fe and Si. A-MnO2/C-FeGS exhibited excellent catalytic performance with TC removal of 98.2% within 30 min, being about 4.5 and 3.3 times faster than crystalline MnO2 and C-FeGS, respectively. The improved photocatalytic activity was attributed to that rich oxygen vacancies could provide more catalytic active sites and accelerate Fe3+/Fe2+ and Mn4+/(Mn2++Mn3+) conversion for more ·OH generation. Moreover, Na-doped amorphous MnO2 and C decoration synergistically contributed to high photo-thermal conversion rate, which could in-situ heat the catalyst and induce the activation of H2O2. This promoted the activation of the surface lattice oxygen and accelerated the secondary transition and utilization of the thermal electrons captured by the defect sites. This work provides a novel strategy for the development of highly reactive catalysts and valorization of MR in the field of environmental remediation.