Boric acid pyrolysis modulating secondary-shell boron coordination in iron single-atom catalysts for high-efficiency peracetic acid activation and bisphenol A degradation

In this study, we incorporated boric acid into the synthesis of single-atom catalysts (SACs), where it served dual roles by facilitating iron dispersion and introducing boron coordination. Our results show that boron oxide formed from molten boric acid acts as both an efficient high-temperature carbonization agent and a metal-blocking medium, effectively suppressing iron nanoparticle formation in the resulting iron SAC material (Fe@NBC). The material features predominantly nitrogen-coordinated single iron atoms, with boron atoms successfully incorporated into secondary coordination shells. Fe@NBC demonstrates excellent Fenton-like catalytic activity, completely removing 10 mg/L bisphenol A (BPA) within 30 min through peracetic acid (PAA) activation. Increasing the boron content from 2.78 % to 4.23 % improved BPA removal efficiency from 52.1 % to 100 %. Density functional theory (DFT) calculations reveal that electron-deficient boron atoms adjust the electronic structure of Fe-N₄ active sites. As the boron coordination number in the second shell increases from 1 to 2, the central iron atom loses more electrons (1.20e^- to 2.25e^-). This strengthens the oxidant’s adsorption at the Fe site (−0.96 eV to −1.07 eV), boosts electron transfer between PAA and the Fe active center while reducing the energy barrier for hydroxyl radical formation. This work provides critical insights for designing boron-mediated Fenton-like catalysts to efficiently degrade organic pollutants in water.