Regulating Oriented Adsorption on Targeted Nickel Sites for Antibiotic Oxidation with Simultaneous Hydrogen Energy Recovery by a Direct Electrochemical Process.

The efficiency of antibiotic oxidation by direct electrochemical processes based on transition metal electrodes is largely restricted by the adsorption capacity for single molecules on targeted active sites. Inspired by density functional theory (DFT) calculations, we found that the adsorption energy of sulfanilamide molecules on Ni sites could be markedly changed by regulating the local atomic environment of the Ni atoms (for NiCo2O4 and NiCoP, ΔGNi = -0.11 and +0.47 eV, respectively). The high electronegativity of oxygen changed the electron cloud density around the Ni atoms, leading to an oriented adsorption of SA on Ni sites. Moreover, the oriented adsorption on Ni sites occurs not only on NiCo2O4 but on the in situ-generated NiIIIOOH (ΔGNi = -0.09 eV). Consequently, utilizing NiCo2O4 as the anode resulted in superior removal performance (97% vs 55% efficiency) for SA oxidation, with a kinetic constant ∼10 times higher than that of NiCoP (0.031 min-1 vs 0.0029 min-1). Meanwhile, non-oriented adsorption reduced the competition between SA molecules and H+ for active sites, which benefitted the activity of the hydrogen evolution reaction at the NiCoP cathode (68 mV at j = 10 mA·cm-2, 0.5 mmol·L-1 SA added in). Furthermore, the in situ Raman spectra and DFT calculations confirmed that NiIIIOOH dominated the oxidation process and terminated it at the p-benzoquinone stage. These findings provide a feasible strategy to combine electrochemical antibiotic oxidation by Ni-based electrodes with hydrogen energy recovery.