Influence of Ag+ and Mn2+ ions on structural, optical and photoluminescence features of ZnS quantum dots

Synthesis, Structure, Morphology, Element composition, Electrochemical, and Optical studies of Zn0.98-XMn0.02CeX Quantum dots

Quantum dots (QDs) are semiconductors whose size falls in a range between 1 and 10 nm; they are generally known as zero-dimension materials. It finds various applications in optical industries including light-emitting diodes, display technology, imaging, and labelling. ZnS is one of the excellent QDs in its class of II-VI semiconductors. In this paper, It is reported that the preparation of Mn-doped ZnS and Mn, Ce co-doped ZnS QDs using facile co-precipitation technique. XRD and HR-TEM results confirmed the cubic structure, particle size, and phase of the synthesized particles, and the crystallite is measured as ∼ 2 nm. The surface morphology, elemental analysis, and FT-IR spectra revealed the purity of the samples and confirmed the presence of dopants as expected. Cyclic voltammetry studies expressed the electrochemical behaviour of the samples, which increased as a function of Ce3+ doping concentration. UV-visible absorbance and transmittance spectra disclosed the optical characteristics of the samples. A wide band gap (4.02 eV) was received for 2% Ce-doped Zn: MnS QDs. Week Blue and strong yellow emissions were received for 4% Ce-doped Zn:MnS QDs. Whereas, high intensity red-emission was received for 2% Ce-doped Zn:MnS QDs. The different colour emissions are discussed in terms of defects produced.

Effect of metal ion on optical, photoluminescence, morphological, and photocatalytic properties of ZnS nanoparticles

The semiconducting materials of pure zinc sulfide (ZnS), 2.5 wt%, 5.0 wt%, 7.5 wt%, and 10 wt% of Ag-doped ZnS nanoparticles were prepared using the sol-gel technique. The prepared nanoparticles were analyzed by powder X-ray diffraction (PXRD), Fourier transformed infrared (FTIR), UV-visible absorption, diffuse reflectance photoluminescence (PL), high-resolution transmission electron microscope (HRTEM), and field emission scanning electron microscope (FESEM) to study the properties of pure ZnS and Ag-doped ZnS nanoparticles (NPs). The Ag-doped ZnS nanoparticles have a polycrystalline nature, which is confirmed by PXRD analysis. The functional groups were identified by the FTIR technique. The bandgap values decrease with increasing Ag concentration compared to pure ZnS NPs. The crystal size lies between 12 and 41 nm for pure ZnS and Ag-doped ZnS NPs. The presence of Zn, S, and Ag elements was confirmed by EDS analysis. Using methylene blue (MB), the photocatalytic activity of pure ZnS and Ag-doped ZnS NPs was performed. The highest degradation efficiency was observed for 7.5 wt% Ag-doped ZnS NPs.

Photocatalytic degradation of organic pollutants in water by N-doping ZnS with Zn vacancy: enhancement mechanism of visible light response and electron flow promotion

In order to improve the visible light response, N-doping ZnS (N-ZnS) nanospheres with Zn vacancy and porous surface were prepared by a simple one-pot hydrothermal method. Characterizations and density functional theory simulations showed excellent visible light response of N-ZnS. N-doping introduced impurity energy levels, which led to orbital hybridization and changed the original dipole moment. The presence of ortho Zn vacancy (O-Znv) can effectively reduce e--h+ recombination and photocorrosion. Furthermore, O-Znv caused lattice distortion (twisted the -S-Zn-N-(O-Znv)-S-Zn-S- chemical bond chain), resulting in "vacancy effect" to accelerate e- flow. Under visible light, the photocatalytic degradation efficiency of tetracycline (TC) and 2,4-dichlorophenol (2,4-DCP) was 90.31% and 60.84%, respectively. TOC degradation efficiency was 31.4% and 25.6%, respectively. Combined with Fukui index and LC-MS methods, it was found that TC and 2,4-DCP were degraded under the constant attack of active substances such as ·OH. This work can provide a reference for the application of catalytic materials in the field of visible light photocatalysis.

Drug Release Profiles of Mitomycin C Encapsulated Quantum Dots-Chitosan Nanocarrier System for the Possible Treatment of Non-Muscle Invasive Bladder Cancer

Nanotechnology-based drug delivery systems are an emerging technology for the targeted delivery of chemotherapeutic agents in cancer therapy with low/no toxicity to the non-cancer cells. With that view, the present work reports the synthesis, characterization, and testing of Mn:ZnS quantum dots (QDs) conjugated chitosan (CS)-based nanocarrier system encapsulated with Mitomycin C (MMC) drug. This fabricated nanocarrier, MMC@CS-Mn:ZnS, has been tested thoroughly for the drug loading capacity, drug encapsulation efficiency, and release properties at a fixed wavelength (358 nm) using a UV-Vis spectrophotometer. Followed by the physicochemical characterization, the cumulative drug release profiling data of MMC@CS-Mn:ZnS nanocarrier (at pH of 6.5, 6.8, 7.2, and 7.5) were investigated to have the highest release of 56.48% at pH 6.8, followed by 50.22%, 30.88%, and 10.75% at pH 7.2, 6.5, and 7.5, respectively. Additionally, the drug release studies were fitted to five different pharmacokinetic models including pesudo-first-order, pseudo-second-order, Higuchi, Hixson-Crowell, and Korsmeyers-Peppas models. From the analysis, the cumulative MMC release suits the Higuchi model well, revealing the diffusion-controlled mechanism involving the correlation of cumulative drug release proportional to the function square root of time at equilibrium, with the correlation coefficient values (R2) of 0.9849, 0.9604, 0.9783, and 0.7989 for drug release at pH 6.5, 6.8, 7.2, and 7.5, respectively. Based on the overall results analysis, the formulated nanocarrier system of MMC synergistically envisages the efficient delivery of chemotherapeutic agents to the target cancerous sites, able to sustain it for a longer time, etc. Consequently, the developed nanocarrier system has the capacity to improve the drug loading efficacy in combating the reoccurrence and progression of cancer in non-muscle invasive bladder diseases.

Role of Bi3+ ions on structural, optical, photoluminescence and electrical performance of Cd0.9-xZn0.1BixS QDs

In this work, the Cd0.9-xZn0.1BixS QDs with different compositions of Bi3+ ions (0 ≤ x ≤ 0.05) were synthesized using a facile chemical route. The prepared QDs were characterized for analyzing the structural, morphological, elemental, optical, band gap, photoluminescence and electrochemical properties. XRD results confirmed that the Cd0.9-xZn0.1BixS QDs have a cubic structure. The mean crystallite size was increased from ~ 2 to ~ 5 nm for the increase of Bi3+ ions concentration. The optical transmittance behavior was decreased with increasing Bi3+ ions. The scanning electron microscope images showed that the prepared QDs possessed agglomerated morphology and the EDAX confirmed the presence of doped elements as per stoichiometry ratio. The optical band gap was slightly blue-shifted for initial substitution (Bi3+  = 1%) of Bi3+ ions and red-shifted for further increase of Bi3+ compositions. The optical band gap was ranged between 3.76 and 4.0 eV. High intense red emission was received for Bi3+ (1%) doped Zn:CdS QDs. The red emission peaks were shifted to a higher wavelength side due to the addition of Bi3+ ions. The PL emission on UV-region was raised for Bi3+ (1%) and it was diminished. Further, a violet (422 nm) and blue (460 nm) emission were received for Bi3+ ions doping. The cyclic voltammetry analysis showed that Bi3+ (0%) possessed better electrical properties than other compositions of Bi3+ ions.

Novel synthesis of Mn: ZnSe@ZnS core-shell quantum dots based on photoinduced fluorescence enhancement

A novel Type-I Mn: ZnSe@ZnS core-shell quantum dots (QDs) was reported through a two-step procedure by using low-cost inorganic salts and naturalbiomacromolecule as raw materials. Based on a designed structure of L-cysteine-capped Mn: ZnSe QDs in aqueous media with the controllable surface, Mn: ZnSe@ZnS core-shell QDs were formed due to photoactive ions and defect curing under continuous constant light. The influences of experimental variables, including synthesis conditions of Mn: ZnSe QDs, different types and affecting factors of photo irradiation had been systematically investigated. Under the effect of photoinduced fluorescence enhancement, the photoluminescence (PL) intensity increases significantly by about 5-10 times after 1-3 h of UV irradiation. The position of the fluorescence peak was red-shifted by about 17 nm, emitting orange-red fluorescence. The photoluminescence quantum yield (PL QY) was markedly improved (up to 35%). The structure and morphology of Mn: ZnSe@ZnS core-shell QDs were also confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS) in detail. The mechanism of photoinduced fluorescence enhancement was attributed to L-cysteine allowed to release S^2- to form a ZnS shell, and the passivated surface non-radiative relaxation centers of Mn: ZnSe@ZnS QDs was successfully synthesized with highuniform size, excellent photoluminescence performance, and good stability, all ofwhichmakethemgood potential candidates for white LEDs, and biological labels.