Regulating B-Site Metals in Delafossite to Reach Efficient and Selective Peroxymonosulfate Activation for Water Remediation

Transition metals (TMs) are excellent active sites to activate peroxymonosulfate (PMS) for water remediation; however, the factors determining the efficiency and selectivity of PMS activation over different TMs remain blurred. Herein, delafossite with different B-site metals (denoted as CuBO2, B = Mn, Fe, Co, Cr) was synthesized to activate PMS for Orange I (OI) degradation. Their catalytic activity order followed CuCrO2 (91.5%) approximate to CuCoO2 (91.2%) > CuMnO2 (46.9%) > CuFeO2 (27.9%); especially the degradation rate (k) of CuCrO2 (CuCoO2) was 14.0 (12.6)-fold and 30.0 (27.1)-fold higher than that of CuMnO2 > CuFeO2, respectively. Mechanism analysis showed that sulfate radical (SO4 center dot-) was the main oxidant responsible for OI degradation in the CuCoO2/PMS system, while CuCrO2 interacted with PMS to execute an electron transfer pathway (ETP) for degrading OI. Experimental and density functional theory calculation results deciphered that the d-band centers of CuCoO2 (E-d = -1.22 eV) and CuCrO2 (E-d = 0.62 eV) were closest to the Fermi level (E-F), thereby facilitating the interfacial electron transfer process and enhancing the PMS activation efficiency. Moreover, it was important to note that the E-d value of CuCoO2 was located below the E-F, which led CuCoO2 to easily lose electrons to PMS, thereby generating sulfate radicals SO4 center dot-. On the other hand, the E-d value of CuCrO2 was situated above the E-F, which facilitated the catalyst to obtain electrons, acting as electron shuttles and driving a nonradical ETP. Finally, the established CuBO2-activated PMS systems also exhibited excellent stability and robust resistance against coexisting substances. These findings provided an alternative perspective to understanding the inherent nature of TM-based catalysts for regulating the efficiency and selectivity of PMS activation in water remediation.