Density of Grafted Chains in Thioglycerol-Capped CdS Quantum Dots Determines Their Interaction with Aluminum(III) in Water.

We aimed to quantify the interaction of water-soluble-functionalized CdS quantum dots (QDs) with metal cations from their composition and physical properties. From the diameter of thioglycerol-capped nanoparticles (TG-CdS QDs) measured by electronic microscopy ( D = 12.3 ± 0.3 nm), we calculated the molecular mass of the individual particle MAQD = (3 ± 0.5) × 106 g·mol-1 and its molar absorption coefficient ε450 = 21 × 106 M-1·cm-1. We built a three-dimensional model of the TG-CdS QDs in agreement with the structural data, which allowed us to quantify the number of thioglycerol grafted chains to ∼2000 per QD. This value fully matches the saturation binding curve of Al3+ cations interacting with TG-CdS QDs. The reaction occurred with a slow association rate ( kon = 2.1 × 103 M-1·s-1), as expected for heavy QDs. The photophysical properties of the functionalized QDs were studied using an absolute QD concentration of 7 nM, which allowed us to investigate the interaction with 14 metallic cations in water. The fluorescence intensity of TG-CdS QDs could be quenched only in the presence of Al3+ ions in the range 0.2-10 µM but not with other cations and was not observed with other kinds of grafting chains.

Three novel polysulfide-based conjugated polymers and characterization of their optoelectronic properties.

The aim of this study was to investigate the effect of side chain size on the optical and charge transport properties of thin films prepared from novel conjugated polysulfide-based polymers. Three polymers, labeled P1, P2, and P3, were derived from polysulfide derivatives and had different arylene groups (5,5'- biphenylene, 4,4'-biphenylene, and 2,6-pyridylene). Optical analysis was performed using photoluminescence (PL) and UV-visible absorption spectroscopy, revealing an energy band gap of 2.41-3.02 eV; P1 emitted yellow, P2 blue-green, and P3 green. Cyclic voltammetry measurements of the electrochemical band gap and HOMO and LUMO energy levels revealed that the polymer exhibited p-type semiconductor activity; the electrical properties of diodes based on the ITO/polysulfide derivative/Al structure were explored through analysis of current-voltage characteristics. The current space charge limitation (SCLC) mechanism was used to model the behavior of these diodes; the P2 thin film layer exhibited higher mobility than the other layers. The relationship between the geometry of the polymer thin films and their optical and electrical properties was thoroughly investigated.

Removal of textile pollutants from aqueous medium using biosynthesized CuO nanoparticles: Theoretical comparative investigation via analytical model.

The work deals with the removal of two dyes, namely methylene blue (MB) and methyl orange (MO), from polluted water by adsorption onto CuO nanoparticles synthesized with a green synthesis procedure, starting from plant resources. Adsorption isotherms are determined at different temperatures aiming at investigating the adsorption mechanisms of the two dyes. The experimental results indicate that, for both MB and MO, the adsorption capacity increases with increasing temperature, with slight differences in the case of MO. Comparatively, the CuO nanoparticles show a higher MB adsorption capacity with respect to MO. A modelling analysis is carried out with a multilayer model derived from statistical physics, selected among a group of models, each hypothesizing a different number of adsorbed molecules layers. The analysis of model parameters allows determining that the adsorbate molecules exhibit a non-parallel orientation on the surface of biosynthesized CuO nanoparticles and each functional group of the adsorbent binds multiple molecules, simultaneously.The model also allows determining the number of dye molecule layers formed on adsorbent surface, in all the cases resulting higher than three, also confirming the effect of temperature on the maximum adsorption capacity.Specifically, the total number of dye layers formed on biosynthesized CuO nanoparticles surface exhibited a range of 4.17-4.55 for MB dye and of 3.01-3.51 for MO dye.Finally, the adsorption energies reveal that adsorption likely involves physical forces (all resulting all below 22 kJ/mol), i.e. hydrogen bonding and van der Waals forces. The adsorption energies for the interactions between dye molecules are lower than those calculated for the interactions between the dye molecules and the adsorbent surface.

Design, synthesis, and density functional theory studies of a new selective chemosensor for Pb2.

Herein, we have focused on a new colorimetric ligand synthesized from the reaction of 2-hydroxy-5-methylbenzene-1,3-dialdehyde with 2-amino-thiophenol, and investigated its activity as a sensor. In this regard, the sensory activity of the ligand towards different ions (Mn2+, Cu2+, Co2+, Fe2+, Fe3+, Zn2+, Ni2+, Cd2+, Ag+, Na+, Cs+, Mg2+, Al3+, Ba2+, K+, and Pb2+) was studied. The specificity of ion bindings is discussed through UV-Vis analysis. The ligand that was synthesized showed remarkable sensitivity, with a detection limit of 0.001 ppb. Additionally, the presence of Pb2+ ions can be visually detected through a color change from colorless to yellow. In the last part of this work, we seek to predict the available experimental measurements. Density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) are employed to examine the bonding between the ligand and the Pb2+ ion. The effect of water solvent was thoroughly examined for all the steps via the conductor-like Polarizable Continuum Model (CPCM). The theoretical findings revealed that electronic properties, including energy gap, adsorption energy, charge/energy transfer, and optical characteristics, undergo significant changes when Pb2+ cations are present. Hence, it can be inferred that the newly synthesized chemosensor (NC) is highly efficient in detecting Pb2+.

Green synthesis of copper oxide nanoparticles using Ephedra Alata plant extract and a study of their antifungal, antibacterial activity and photocatalytic performance under sunlight.

In the present work, copper oxide (CuO NPs) was synthesized by an eco-friendly, simple, low-cost, and economical synthesis method using Ephedra Alata aqueous plant extract as a reducing and capping agent. The biosynthesized CuO-NPs were compared with chemically obtained CuO-NPs to investigate the effect of the preparation method on the structural, optical, morphological, antibacterial, antifungal, and photocatalytic properties under solar irradiation. The CuO NPs were characterized using X-ray diffraction (XRD), UV-VIS spectroscopy, Fourier transform infrared spectrometer (FTIR) analysis, and field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDX). The photocatalytic activities of biosynthetic CuO-NPs and chemically prepared CuO-NPs were studied using methylene blue upon exposure to solar irradiation. The results showed that the biosynthesized CuO photocatalyst was more efficient than the chemically synthesized CuO-NPs for Methylene Blue (MB) degradation under solar irradiation, with MB degradation rates of 93.4% and 80.2%, respectively. In addition, antibacterial and antifungal activities were evaluated. The disk diffusion technique was used to test the biosynthesized CuO-NPs against gram-negative bacteria, Staphylococcus aureus and Bacillus subtilis, as well as C. Albicans and S. cerevisiae. The biosynthesized CuO-NPs showed efficient antibacterial and antifungal activity. The obtained results revealed that the biosynthesized CuO-NPs can play a vital role in the destruction of pathogenic bacteria, the degradation of dyes, and the activity of antifungal agents in the bioremediation of industrial and domestic waste.

Highly Luminescent and Photostable Core/Shell/Shell ZnSeS/Cu:ZnS/ZnS Quantum Dots Prepared via a Mild Aqueous Route.

An aqueous-phase synthesis of 3-mercaptopropionic acid (3-MPA)-capped core/shell/shell ZnSeS/Cu:ZnS/ZnS QDs was developed. The influence of the Cu-dopant location on the photoluminescence (PL) emission intensity was investigated, and the results show that the introduction of the Cu dopant in the first ZnS shell leads to QDs exhibiting the highest PL quantum yield (25%). The influence of the Cu-loading in the dots on the PL emission was also studied, and a shift from blue-green to green was observed with the increase of the Cu doping from 1.25 to 7.5%. ZnSeS/Cu:ZnS/ZnS QDs exhibit an average diameter of 2.1 ± 0.3 nm and are stable for weeks in aqueous solution. Moreover, the dots were found to be photostable under the continuous illumination of an Hg-Xe lamp and in the presence of oxygen, indicating their high potential for applications such as sensing or bio-imaging.

Role of surface defects in colloidal cadmium selenide (CdSe) nanocrystals in the specificity of fluorescence quenching by metal cations.

This study aimed to answer the question as whether crystal defects at the surface of soluble capped CdSe nanocrystals (or quantum dots, QDs) in water colloidal suspension are involved in the mechanism of fluorescence quenching induced by metal cations. Nanocrystals of CdSe were synthesized by an aqueous protocol, varying the ratio between the CdSe precursors and the grafted ligand mercaptosuccinic acid (MSA). Changing the MSA/CdSe ratio during synthesis impacts the crystal nucleation growth, which plays an important role in surface construction of CdSe QDs and changes the surface state. In this way, we could modulate the crystal surface defects of CdSe, as verified by analysis of the individual bands which constitute the emission spectra and are associated with different relaxation processes. We found that the various tested metal cations, which interact in solution with the MSA ligand grafted on the QDs, quench their fluorescence differently, depending on the MSA/CdSe ratio used in synthesis. The crystal defects modulate the excitonic relaxation in CdSe and we demonstrated here that the surface defects intervene in the quenching of QDs induced by the binding of cations.

New zinc phthalocyanine derivatives for nitrogen dioxide sensors: A theoretical optoelectronic investigation.

Zinc-phthalocyanines ZnPc derivatives including quinoleinoxy groups have been studied through DFT calculations. The most stable geometries were characterized for the unsubstituted to the tetra substituted ZnPcs. The energy gap decreased from 2.146 eV for ZnPc to 2.050 eV for ZnPcR4, in agreement with the experimental trend, and indicating the reliability of the electrochemical evaluation of LUMO and HOMO energy levels. Optical transitions computed at the CAM-B3LYP-D3 with triple zeta basis sets were found to be in good agreement with experimental values for both the B and Q bands. Subsequently, structures were also characterized for NO2 adsorbed complexes, in order to assess the potential role of ZnPc as a NO2 sensor. A clear sigma bonding chemisorption of NO2 on Zn atom is observed for all derivatives, followed by a charge transfer from the π Pc conjugated system to the Zn-NO2 moiety. More importantly, after NO2 chemisorption on ZnPc derivative a remarkable red-shift is observed in the optical spectra, particularly for NO2/ZnPcR4 complex, thus offering a good index to detect the binding of NO2. The optical spectra and the vibrational spectra can therefore be used to detect the presence of NO2 and ZnPc derivatives show appropriate properties to constitute good NO2 sensors.

Use of MPA-capped CdS quantum dots for sensitive detection and quantification of Co2+ ions in aqueous solution.

Water soluble CdS quantum dots (QDs) were synthesized by a simple aqueous chemical route using mercaptopropionic acid (MPA) as a stabilizer. These QDs had a fluorescence emission band maximum at 540 nm with a FWHM ∼130 nm and a quantum yield of ∼12%. Transmission electronic microscopy images were used to determine the QD diameter of 8.9 ±â€¯0.4 nm. From this value we calculated the molecular mass M(QD) = 1.17 × 106 g mol-1 and the extinction coefficient at the band edge (450 nm) ε450 = 4.7 × 106 cm-1 M-1, which allowed to determine the true molar concentration of 17 nM for spectroscopic measurements in solution. The fluorescence intensity of MPA-CdS QDs was quenched only in the presence of Co2+ ions, but not in the presence of thirteen other metal cations. The fluorescence quenching of MPA-CdS QDs appeared proportional to the Co2+ concentration in the range 0.04-2 µM. Based on a fluorescence peak position and a lifetime both independent from Co2+ concentration, the quenching mechanism of MPA-CdS QDs appeared static. Because the strong electronic absorption of Co2+ overlaps the emission of QDs, our results can be explained by Förster energy transfer from QD to the bound Co2+ cations.