In situ stable growth of β-FeOOH on g-C3N4 for deep oxidation of emerging contaminants by photocatalytic activation of peroxymonosulfate under solar irradiation

Peroxymonosulfate (PMS) activation with the generation of strongly oxidizing hydroxyl radicals (center dot OH) and sulfate radicals (SO4 center dot-) has attracted widespread attention for the elimination of organic contaminants. However, the design of an eco-friendly catalytic system with high mineralization rate and high stability remains a challenge. Here, an iron-based photocatalyst (beta-FeOOH@g-C3N4) for the activation of PMS was prepared by a cyclic microwave-assisted reaction, whereby Fe3+ was introduced at the nitrogen sites of g-C3N4, resulting in in situ growth and a uniform distribution of nano-beta-FeOOH thereon. beta-FeOOH@g-C3N4 maintained high catalytic activity after acid treatment or repeated tests, demonstrating excellent stability and reusability. Moreover, compared with the catalytic systems with beta-FeOOH or g-C3N4 alone, the catalytic activity of beta-FeOOH@g-C3N4 was increased 5-10 times for the catalytic oxidation of carbamazepine (CBZ) and other emerging contaminants under solar irradiation. Importantly, the CBZ mineralization rate with the beta-FeOOH@g-C3N4/PMS system under solar irradiation was as high as 92%. From the results of electron paramagnetic resonance spectroscopy and radical trapping experiments, large amounts of O-2(center dot-), O-1(2), and Fe-V = O are present at the beginning of the reaction, which contribute to the rapid oxidative removal of CBZ, while SO4 center dot- and (OH)-O-center dot contribute to the deep oxidation, leading to a significantly enhanced total organic carbon (TOC) removal efficiency. This work provides an alternative method for the design of a highly efficient and stable catalyst for PMS activation to eliminate emerging contaminants.