Identification of Fenton-like active Cu sites by heteroatom modulation of electronic density

Abstract

Developing heterogeneous catalysts with atomically dispersed active sites is vital to boost peroxymonosulfate (PMS) activation for Fenton-like activity, but how to controllably adjust the electronic configuration of metal centers to further improve the activation kinetics still remains a great challenge. Herein, we report a systematic investigation into heteroatom-doped engineering for tuning the electronic structure of Cu-N4 sites by integrating electron-deficient boron (B) or electron-rich phosphorus (P) heteroatoms into carbon substrate for PMS activation. The electron-depleted Cu-N4/C-B is found to exhibit the most active oxidation capacity among the prepared Cu-N4 single-atom catalysts, which is at the top rankings of the Cu-based catalysts and is superior to most of the state-of-the-art heterogeneous Fenton-like catalysts. Conversely, the electron-enriched Cu-N4/C-P induces a decrease in PMS activation. Both experimental results and theoretical simulations unravel that the long-range interaction with B atoms decreases the electronic density of Cu active sites and down-shifts the d-band center, and thereby optimizes the adsorption energy for PMS activation. This study provides an approach to finely control the electronic structure of Cu-N4 sites at the atomic level and is expected to guide the design of smart Fenton-like catalysts.

Origin of the Excellent Activity and Selectivity of a Single-Atom Copper Catalyst with Unsaturated Cu-N2 Sites via Peroxydisulfate Activation: Cu(III) as a Dominant Oxidizing Species

“…High-valent metal species becomes the dominant active species for pollutant degradation in certain transition metal/persulfate systems. ,,, The generation of Cu­(III) can be determined by the Raman spectra in homogeneous and heterogeneous systems. , As shown in Figure f, Cu SA -NC does not exhibit obvious peaks and the peaks only occur in the range of 400–500 cm –1 in PDS solution. Obviously, the new peak around 616 cm –1 is observed in the Cu SA -NC + PDS system, confirming the formation of Cu­(III), because it is the typical Cu–O stretching vibration peak of a metastable Cu­(III). , BA and NB ( • OH probe compound) with electron-poor groups can hardly be degraded in the Cu SA -NC system (Figure d), which is attributed to the selective oxidation of Cu­(III) reported in previous studies. , From the EPR spectra (Figure S19), Cu SA -NC alone exhibits a signal at g = 2.003, and its intensity decreases significantly with the addition of PDS solution, and this result is consistent with the phenomenon during the transformation of Cu­(II) to Cu­(III) . In addition, the main intermediates of 2,4-DCP in the Cu SA -NC system were identified by gas chromatography–mass spectrometry (GC–MS).…”

Single–atom catalysts based on Fenton-like/peroxymonosulfate system for water purification: design and synthesis principle, performance regulation and catalytic mechanism

“…Instead, Fentonlike catalytic reactions are completed on the active units formed by coordination between isolated metal atoms and surrounding electronegative heteroatoms (e.g., C, O, N, S and B). [106][107][108][109][110] At present, the widely studied active centers (e.g., M-Cx, M-Nx and M-N-C) are composed of transition metal species interacting with heteroatoms in ligands in the form of covalent or ionic bonds. 111,112 Importantly, the existence of coordination atoms, especially the electrostatic interaction between anchored non-metallic atoms and transition metal elements, prevents the agglomeration trend of isolated metal elements, thus improving the chemical and structural stability of Fenton-like SACs.…”

“…, C, O, N, S and B). 106–110 At present, the widely studied active centers ( e.g. , M–C x , M–N x and M–N–C) are composed of transition metal species interacting with heteroatoms in ligands in the form of covalent or ionic bonds.…”

A nanoclay-confined single atom catalyst: tuning uncoordinated N species for efficient water treatment

“…To date, various strategies including pyrolysis and thermal activation, atomic layer deposition, and photochemical reduction, have been proposed for the synthesis of NG-SACs. 2,10,16,17 However, specific strategies are usually formed for a given structure; it remains unclear how the synthetic methods are relevant to the adjusted structures of NG-SACs. 10 There is thus a lack of controllable preparation strategies that could regulate the uncoordinated N species of NG-SACs while guaranteeing NG-SACs with a similar exposure area, pore structure, TM and N contents.…”