Cu-doped Ni-LDH with abundant oxygen vacancies for enhanced methyl 4-hydroxybenzoate degradation via peroxymonosulfate activation: key role of superoxide radicals

• Published in: Journal of colloid and interface science Vol. 610; pp. 504 - 517
• Main Authors: Zhu, Jingyi, Zhu, Yixin, Zhou, Wenjun
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.03.2022
• Subjects: 4-hydroxybenzoic acid; catalytic activity; Cu-doped Ni-LDH; dissolved oxygen; oxidation; Oxygen; Oxygen vacancies; Parabens; Peroxides; Peroxymonosulfate; singlet oxygen; sulfates; Superoxide radicals; Superoxides; Cu-doped Ni-LDH; Oxygen vacancies; Superoxide radicals; Peroxymonosulfate
• ISSN: 0021-9797; 1095-7103; 1095-7103
• DOI: 10.1016/j.jcis.2021.11.097

[Display omitted] •Cu doping facilitated the formation of oxygen vacancies (OVs) in NixCu-LDHs.•OVs introduction enhanced the catalytic activation of PMS by NixCu-LDHs.•O2•− and 1O2 worked as the main ROSs in Ni15Cu-LDHs/PMS system.•DO or adsorbed oxygen could acquire electron from OVs to generate O2•−.•Synergy among Mn+/M(n+1)+ and active oxygen species ensured ROS generation. Oxygen vacancies (OVs) were introduced into Ni-based layered double hydroxides (LDHs) through Cu doping, and the catalytic performance of the resulting NixCu-LDHs were investigated for peroxymonosulfate (PMS) activation and methyl 4-hydroxybenzoate (MeP) degradation. Compared with that of Ni-LDH, the catalytic performance of NixCu-LDHs were significantly enhanced and increased with increasing OV content in the catalysts, indicating that Cu doping introduced OVs into NixCu-LDHs and greatly improved their catalytic activity with PMS. Quenching experiments and EPR analyses confirmed that oxidation processes dominated by superoxide radicals (O2•−) and singlet oxygen (1O2), rather than sulfate radicals (SO4•−) or hydroxyl radicals (•OH) used by traditional LDH catalysts, were responsible for MeP degradation by Ni15Cu-LDHs. In addition, quenching experiments with different systems showed the fate of reduced SO4•−and •OH, and demonstrated that O2•− and 1O2 concentrations grew with increasing OV content, confirming that the presence of OVs affected the process of PMS activation. Notably, O2•− mainly originated from adsorbed oxygen or dissolved oxygen (DO) by acquiring electrons from OVs in Ni15Cu-LDHs, since OVs possess abundant localized electrons. Consequently, an OV-mediated oxidative mechanism was proposed for Ni15Cu-LDHs/PMS. This study provides new clues for enhancing the catalytic performance of LDH catalysts by introducing OVs via metal doping in PMS-based AOPs systems.