Coordination engineering of Pd single-atom catalysts for non-radical organohalide degradation

Abstract

Palladium (Pd) single-atom catalysts (SACs) demonstrate significant potential for practical implementation in organohalide degradation. However, Pd SACs may suffer from low reactivity because of their uncontrollable coordination environments, and the rational modulation of coordination environments in Pd SACs remains challenging. In this work, a series of Pd SACs on carbon nitride support with controlled coordination environments, achieved by doping specific amounts of p-block elements (B or P), were synthesized. The catalytic performances of these catalysts in degrading para-chlorophenol (4-CP, as a representative organohalide) by activating peroxymonosulfate (PMS) were systematically examined. B-doped Pd SACs outperformed P-doped Pd SACs (1 g L⁻¹), achieving over 99% degradation of 4-CP (100 mg L⁻¹) within 10 min. Mechanistically, p-block element doping modulated the electronic structure of Pd SACs, thereby redirecting electron transfer from organohalides to PMS, which enabled a PMS-driven non-radical oxidation pathway rather than a singlet oxygen or radical-dominated reaction. The B doping induced electron-deficient Pd sites with elevated valence states, which effectively reduced the PMS adsorption energy barrier while facilitating interfacial electron transfer kinetics, resulting in superior catalysis performance in PMS activation and 4-CP degradation compared to most state-of-art transition metal catalysts. The superiority of B-doped Pd SACs was more evident in the presence of interfering species such as Cl⁻, HCO₃⁻, SO₄²⁻, and natural organic matter, as well as under pH variation, highlighting their immunity to ion poisoning. This work establishes a universal strategy for precise coordination engineering of Pd SACs and fundamentally advances the mechanistic understanding of non-radical oxidation pathways in Pd-based advanced oxidation processes.