A novel multi-flaw MoS2 nanosheet piezocatalyst with superhigh degradation efficiency for ciprofloxacin

Abstract

Multi-flaw MoS₂ nanosheets were synthesized by a hydrothermal method by controlling the molar ratio of Mo and S. The physical and chemical properties and structures of the samples were characterized by SEM, TEM, N₂ adsorption/desorption isotherms, XRD, Raman spectroscopy, and XPS. The construction of flaws with abundant exposed edges in the ultrathin MoS₂ nanosheets played an important role in improving the piezocatalytic performance for the degradation of antibiotic ciprofloxacin (CIP) by forming the active sites. Compared with flaw-free MoS₂, multi-flaw MoS₂ nanosheets had a high number of atomic layers (abundant odd numbers of atomic layers) and exhibited excellent adsorption-piezocatalytic ability, decomposing 99% of CIP in 30 s under ultrasonic irradiation. Furthermore, the total organic carbon (TOC) analysis indicated that 56% of CIP was completely mineralized after 5 min of ultrasonic irradiation. The eradication mechanism of CIP followed pseudo-second-order kinetics with a maximum degradation rate constant of 1.29 L mg⁻¹ s⁻¹. The superior piezocatalytic performance of multi-flaw MoS₂ nanosheets was mainly attributed to the highly efficient separation of electron–hole pairs caused by the strain-induced piezoelectric field (an internal electric field). Active species trapping and terephthalic acid (TA) fluorescence experiments demonstrated that the hydroxyl radicals (˙OH) were the major reactive oxygen species that degraded CIP. In addition, UPLC-MS analysis was used for monitoring the intermediates in CIP decomposition. The complete opening of the piperazine and quinolinic rings and the formation of simpler aliphatic compounds were observed. A possible degradation pathway was proposed based on the UPLC-MS data. The ultrafast degradation efficiency of multi-flaw MoS₂ nanosheets could be used for practical environmental remediation applications.