Vacancy-rich structure inducing efficient persulfate activation for tetracycline degradation over Ni-Fe layered double hydroxide nanosheets

Layered double hydroxide (LDH)-based catalysts have been corroborated to be effective for persulfate (PS) activation towards wastewater remediation. However, the effect of vacancies especially the role of cation vacancies in LDH has not been well illustrated. In this study, NiFe-LDH with Ni(II) vacancies (NiFe-LDH-V-Ni) or Fe (III) vacancies (NiFe-LDH-V-Fe) were fabricated via defect-engineering to tune catalytic activity on PS activation for tetracycline (TC) degradation. Characterizations of X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy confirmed cation vacancies were successfully implanted in NiFe-LDH catalyst. Experiments demonstrated that cation vacancies enhance the catalytic performance while NiFe-LDH-V-Ni exhibited better activation performance since vacancies could facilitate the electron transfer, thereby forming more reactive oxygen species. Meanwhile, theoretical calculations disclosed that the NiFe-LDH with Ni(II) or Fe(III) vacancies possessed larger surface energy, lower Fermi energy and more positive Mulliken atomic charges than bare NiFe-LDH. About 80% of 30 mg.L-1 TC could be mineralized through the catalysis of NiFe-LDH-V-Ni/PS system in 90 min. Furthermore, quenching experiments confirmed that the SO4-center dot & nbsp;and (OH)-O-center dot generated by interface reaction accounted for the TC degradation. O-1(2) and O-2(-center dot)& nbsp;species were also identified in the presence of oxygen vacancies through nitrogen gas cleaning experiments. Ultimately, a possible mechanism of TC degradation was proposed in NiFe-LDH/PS system with Ni(II) or Fe(III) vacancies. This study provides a possible guideline to discover the appropriate cation vacancies that contribute to the activation process and also provides a strategy to rationally design high-activity catalysts based on defect engineering.

Automated summary

In this study, NiFe-LDH catalysts with cation vacancies were fabricated via defect engineering to enhance the activation of persulfate (PS) and the degradation of tetracycline (TC). Experimental and theoretical results showed that cation vacancies improved the catalytic performance by facilitating electron transfer and generating more reactive oxygen species. The study provides a guideline for the design of high-activity catalysts based on defect engineering.