Designing hierarchically porous zero-valent iron via 3D printing to degrade organic pollutants by activating peroxymonosulfate using high-valent iron-oxo species

Zero-valent iron (ZVI) has emerged as an efficient catalyst for facilitating the decomposition of organic pollutants. However, practical applications of ZVI remain limited owing to its susceptibility towards oxidation and agglomeration. Herein, we utilize 3D printing to fabricate hierarchically porous ZVI (3D-ZVI), which displays a high level of printing precision and superb compression resistance. The 3D-ZVI catalyst can effectively activate peroxymonosulfate (PMS) to degrade a diverse selection of organic contaminants. Notably, while the catalytic activity of 3D-ZVI is comparable to that of Fe powder under similar conditions, the concentration of leached Fe ions of the former is 6.3 times lower than that of the latter. Moreover, 3D-ZVI is capable of maintaining an efficient catalytic performance throughout 45 continuous reactions, which is significantly superior to most previously reported powder catalysts. The high-valent iron-oxo species generated in the 3D-ZVI/PMS system are primarily responsible for contaminant removal, while hydroxyl and sulfate radicals play a lesser role. Additionally, the degradation intermediates and their toxicity levels are investigated. This work provides insight into the practical applications of the ZVI/PMS system, and it also serves as a guide for the rational design of efficient and stable catalysts that can be conveniently recovered from aqueous environments.