Assessing the Photocatalytic Degradation of Fluoroquinolone Norfloxacin by Mn:ZnS Quantum Dots: Kinetic Study, Degradation Pathway and Influencing Factors

Abstract

Norfloxacin (NOFX), a broadly used fluoroquinolone antibiotic, has been a subject of great concern in the past few years due to its undesirable effect on human beings and aquatic ecosystems. In this study, novel Mn doped ZnS (Mn:ZnS) quantum dots (QDs) were prepared through a facile chemical precipitation method and used as photocatalysts for NOFX degradation. Prior to photodegradation experiments, morphological and optical parameters of the QDs were examined through transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray analysis, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, fluorescence spectroscopy, Brunauer–Emmett–Teller analysis, and differential thermal and thermogravimetric analyses. Mn:ZnS QDs exhibited excellent properties of photodegradation, not only under UV irradiation but also in sunlight, which induced NOFX to photodegrade. The utmost photodegradation efficiency was obtained under optimal conditions (25 mL of NOFX, 15 mg/L, pH 10, 60 min UV irradiation, 60 mgs QDs), adopting first order kinetics. In addition, hydroxyl radicals produced by the conduction band electrons were found to be the primary reason dominating the transformation of NOFX in basic conditions, while holes, oxygen atoms, as well as the doped metal (Mn) enhanced the degradation. The QDs showed excellent reusability and stability in four repeated cycles. Finally, four different pathways were predicted, derived from the identified intermediates, with piperazinyl ring transformation being the primary one. It is expected that the synthesized Mn:ZnS QDs could be utilized as efficient photocatalytic materials for energy conversion and ecological remediation.

Photocatalytic Degradation of Malachite Green Dye Using Zinc Sulfide Nanostructures

“…There is a random aggregation between smaller particles, which leads to the development of irregular shaped crystallites. [30,31] EDS spectrum (Figure 7.b) indicates the presence of zinc (Zn) and sulfur(S).Also there is an impurity peak corresponds to oxygen(O) originated due to the metal salts which are unreacted. [32,33]…”

Solochrome Dark Blue Azo Dye Removal by Sonophotocatalysis Using Mn2+ Doped ZnS Quantum Dots

“…Their dimension is comparable to the excitonic Bohr radius and they are well-known for their tunable size, broad absorption and narrow emission spectra, high photo-stability and strong signal intensity [4]. In recent years, much interest was shown towards semiconductor-based photocatalytic degradation of hazardous organic pollutants [5,6]. To enlarge the light absorption of these nanomaterials, modifications were made using semiconductor coupling, dye sensitization, impurity doping, and metal deposition, using coordination metal complexes, etc.…”

Nano-Photocatalytic Materials: Possibilities and Challenges

“…There is great concern about the degradation of pharmaceutically active compounds such as antibiotics: these are not degraded in conventional wastewater treatment plants and they are discharged into the environment. Photocatalysis has shown its power in this challenge, and several works of this Special Issue test their materials with this kind of probe molecule [ 1 , 9 , 10 , 11 ]. J. Patel et al [ 10 ] synthesized ZnS quantun dots doped with manganese to degrade a fluoroquinolone antibiotic, norfloxacin, while H. Zhang et al [ 11 ] combined a UiO-66-NH 2 metal–organic framework (MOF) with g-C 3 N 4 and CdS to eliminate tetracycline.…”

“…Photocatalysis has shown its power in this challenge, and several works of this Special Issue test their materials with this kind of probe molecule [ 1 , 9 , 10 , 11 ]. J. Patel et al [ 10 ] synthesized ZnS quantun dots doped with manganese to degrade a fluoroquinolone antibiotic, norfloxacin, while H. Zhang et al [ 11 ] combined a UiO-66-NH 2 metal–organic framework (MOF) with g-C 3 N 4 and CdS to eliminate tetracycline. MOFs have attracted increasing attention due to their many advantages, such as high specific surface area, tunable porous structure and large number of active sites.…”