Coordination engineering strategy of iron single-atom catalysts boosts anti-Cu(II) interference detection of As(III)...

Mutual interference issues between heavy metal ions tremendously affect the detection reliability and accuracy in water quality analysis, especially the serious interference of Cu(II) on the detection of As(III) is greatly hard to overcome, which needs to be solved urgently. Herein, iron single-atom catalysts with different coordination structures of FeN₂C₂ and FeN₃P are constructed to selectively catalyze the detection of As(III) in the coexistence of Cu(II). FeN₃P achieves a high sensitivity of 3.90 µA ppb^-1 toward As(III) in NH₄Cl/NH₃·H₂O electrolyte (pH 8.0), completely avoiding Cu(II)-interference. Moreover, the turnover frequency (TOF) of FeN₃P is an order of magnitude higher than that of FeN₂C₂. X-ray absorption fine structure (XAFS) spectroscopy and density functional theory (DFT) calculations demonstrate that an As-O bond of H₃AsO₃ is broken by the strong affinities between both P and O atoms and Fe and As atoms, and H₃AsO₃ are preferentially reduced by FeN₃P during adsorptive process. Meanwhile, the low reaction energy barrier of the rate-determined step for As(III) reduction over FeN₃P also accelerates the deposition of As(III) and enhances its response signals. The free-Cu(II) are difficult to adsorb on FeN₃P and do not compete with As(III) for Fe active sites, which contributes to the excellent anti-Cu(II) interference capability.