Examining the Effect of Cu and Mn Dopants on the Structure of Zinc Blende ZnS Nanopowders

It is known that doping zinc sulfide (ZnS) nanoparticles with Mn or Cu ions significantly affects their luminescent properties. Herein, we investigated how dopant atoms are incorporated into the structure of ZnS using X-ray diffraction and multi-edge X-ray absorption spectroscopy. The observed broadening of the X-ray diffraction patterns indicates an average crystallite size of about 6 nm. By analyzing the Zn, Mn, and Cu K-edge extended X-ray absorption fine structure (EXAFS) spectra using the reverse Monte Carlo method, we were able to determine the relaxations of the local environments around the dopants. Our findings suggested that upon the substitution of Zn by Mn or Cu ions, there is a shortening of the Cu-S bonds by 0.08 Å, whereas the Mn-S bonds exhibited lengthening by 0.07 Å. These experimental results were further confirmed by first-principles density functional theory calculations, which explained the increase in the Mn-S bond lengths due to the high-spin state of Mn2+ ions.

New Fluorescent Nanosensor for Determination of Diazepam Using Molecularly Imprinted Mn-doped ZnS Quantum Dots

In this study, molecularly imprinted Mn-doped ZnS quantum dots were used as nanosensors to determine diazepam and its metabolites. Mn-doped ZnS quantum dots (QDs) capped with L-cysteine were prepared using a sodium thiosulfate precursor and characterized by various methods. Methacrylic acid was used as a precursor for the synthesis of MIP Mn-doped ZnS QDs and then used to measure diazepam in various samples. The linear dynamic range, coefficient of determination, and detection limit were found to be 0.3 - 250 µmol/L, 0.989 and 8.78 × 10^-2 µmol/L, respectively. The interference studies showed that the prepared nanosensor was selective for diazepam and its metabolites.

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

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.

Effect of the exposure to Mn-doped ZnS nanoparticles on biomarkers in the freshwater western mosquitofish Gambusia affinis

Synthesized Mn-doped ZnS nanoparticles, with 10% of Mn dopant, were used to investigate their environmental toxicity. Mn-doped ZnS quantum dots (QDs) stabilized by 3-mercaptopropionic acid (MPA) were synthesized in a basic aqueous solution using the nucleation doping. The optical properties and structure of the obtained Mn (10%):ZnS QDs have been characterized by X-ray diffraction, UV-vis, photoluminescence spectroscopies and transmission electron microscopy. The brain, gills and liver stained sections from Gambusia affinis were dissected. Antioxidant enzyme activities (acetylcholinesterase and catalase), as well as malondialdehyde and H₂O₂ levels, were determined after exposure (94 h) to 14 and 28 mg/L of nanoparticles. The obtained nearly monodisperse Mn(10%):ZnS@MPA QDs have an average diameter of ca. 2.8 nm and a zinc-blende crystal structure. Mn-doped ZnS acts differently on the activities of the biomarkers in a dose-dependent manner. The recorded alterations varied between organs. Such findings provide information on the biological target of nanoparticles and their behaviour within the environment.

A facile method for the preparation of bifunctional Mn:ZnS/ZnS/Fe3O4 magnetic and fluorescent nanocrystals

Bifunctional magnetic and fluorescent core/shell/shell Mn:ZnS/ZnS/Fe3O4 nanocrystals were synthesized in a basic aqueous solution using 3-mercaptopropionic acid (MPA) as a capping ligand. The structural and optical properties of the heterostructures were characterized by X-ray diffraction (XRD), dynamic light scattering (DLS), transmission electron microscopy (TEM), UV-vis spectroscopy and photoluminescence (PL) spectroscopy. The PL spectra of Mn:ZnS/ZnS/Fe3O4 quantum dots (QDs) showed marked visible emission around 584 nm related to the (4)T1 → (6)A1 Mn(2+) transition. The PL quantum yield (QY) and the remnant magnetization can be regulated by varying the thickness of the magnetic shell. The results showed that an increase in the thickness of the Fe3O4 magnetite layer around the Mn:ZnS/ZnS core reduced the PL QY but improved the magnetic properties of the composites. Nevertheless, a good compromise was achieved in order to maintain the dual modality of the nanocrystals, which may be promising candidates for various biological applications.

Aqueous synthesis of highly luminescent glutathione-capped Mn²⁺-doped ZnS quantum dots

In this paper, an aqueous-based route has been developed to prepare highly luminescent glutathione (GSH)-capped Mn-doped ZnS quantum dots (QDs). The dots obtained have an average diameter of 4.3 nm and exhibit the Mn(2+)-related orange luminescence with very low surface defect density. The highest photoluminescence was observed for a Mn(2+) to Zn(2+) molar ratio of 3%. Consecutive overcoating of the Mn:ZnS@GSH QDs by a ZnS shell was done, and the core/shell structured QDs exhibit a PL quantum yield of 23%. Transmission electron microscopy, X-ray powder diffraction, electron spin resonance, X-ray photoelectron spectroscopy, UV-visible spectroscopy and spectrofluorometry have been used to characterize the crystal structure, the doping status, and the optical properties of the doped-QDs. Our systematic investigation shows that Mn:ZnS/ZnS@GSH QDs are highly promising fluorescent labels in biological applications.