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 MnO 2 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 MnO 2 /C-decorated Fe-based geopolymer sphere (A-MnO 2 /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-MnO 2 /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 MnO 2 and C-FeGS, respectively. The improved photocatalytic activity was attributed to that rich oxygen vacancies could provide more catalytic active sites and accelerate Fe 3+ /Fe 2+ and Mn 4+ /(Mn 2+ +Mn 3+ ) conversion for more ·OH generation. Moreover, Na-doped amorphous MnO 2 and C decoration synergistically contributed to high photo-thermal conversion rate, which could in-situ heat the catalyst and induce the activation of H 2 O 2 . 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.