Water-soluble CdSe Quantum Dots Research Articles

A high-efficiency photocatalytic hydrogen evolution system based on nickel-quinoxaline dithiolate complexes and water-soluble CdSe quantum dots

Photocatalytic water splitting of water for hydrogen evolution is one of the effective methods to obtain clean hydrogen energy. In the present work, the following materials were synthesized: two nickel quinoxaline thiolate complexes [NBu4]2 [Ni(qdt)2] (1, Bu = n-butyl, qdt = quinoxaline-dithiol), [NBu4]2 [Ni(qdt)2(NO2)2] (2) and water-soluble MPA-CdSe quantum dots (MPA-CdSe QDs, MPA = 3-mercaptopropionic acid). Subsequently, an efficient three-component photocatalytic hybrid system for hydrogen evolution was developed and tested under visible light irradiation, in which one of the target complex 1 or 2 was used as the catalyst, triethylamine (TEA) was used as the sacrificial electron donor, and MPA-CdSe QDs were used as the light harvesting reagent. The turnover numbers (TON) for H2 evolution of 8974 (vs. complex 1) and 6532 (vs. complex 2) were obtained under the optimal conditions with TEA concentration of 5 %, pH = 12, and concentration of complex 1 or 2 of 1 × 10−5 mol L−1 after 13 h of irradiation (λ > 420 nm) in pure water. The mechanism investigation indicated that critical steps of hydrogen production was formation of hydride intermediates Ni(II)-H and Ni(I)-H spices, followed by the reaction of two Ni(II)-H or Ni(I)-H species with protons generating H2 molecules and regenerating the catalyst Ni(II).

Coupling Ni-substituted polyoxometalate catalysts with water-soluble CdSe quantum dots for ultraefficient photogeneration of hydrogen under visible light

The development of robust and efficient hydrogen-evolving system remains a substantial but promising challenge to convert solar energy into clean fuel. Herein, we report the construction of water-compatible, robust, and ultraefficient hydrogen-evolving system by coupling water-soluble CdSe light-absorbers with Ni-substituted polyoxometalate (Ni-POM) catalysts and AA electron donor. Such facile catalytic system exhibits superior and robust hydrogen production activity to date even among known semiconductor/POM hybrids-based hydrogen production systems. Multiple stability experiments confirm the molecular stability of Ni-POM catalysts under turnover conditions. Various experimental and spectroscopic analyses reveal that the synergistic cooperation between high photostability of CdSe light-absorber, outstanding reversible multi-electron-transferring property of Ni-POM catalyst, and the fast hole-removing ability of AA electron donor account for the exceptional performance of present catalytic system. Our present work provides new research insights into the continued development of effective hydrogen-evolving systems through coupling other QDs-based light-absorbers and earth-abundant transition-metal-substituted POM catalysts.

Cover Feature: Visible‐Light‐Driven Oxidative Cleavage of Alkenes Using Water‐Soluble CdSe Quantum Dots (ChemSusChem 22/2021)

The Cover Feature shows the oxidative cleavage of alkenes and oxidation of sulfides via water soluble CdSe quantum dots. The reactions were carried out in the water with oxygen as oxidant, with turnover numbers up to 37000. In a word, this approach is green and sustainable. More information can be found in the Full Paper by J. Li et al.

Positive Sorption Behaviors in the Ligand Exchanges for Water-Soluble Quantum Dots and a Strategy for Specific Targeting.

N,N,N',N'-Tetramethylethylenediamine (TMEDA) and ethylenediamine (EDA) were investigated in-depth in the ligand exchanges for water-soluble CdSe quantum dots (QDs). TMEDA could assist the phase transfer of QDs from apolar solvents to the aqueous solutions as stabilized by mercaptopropionic acid (MPA). We successfully maintained the stability of a series of MPA-capped QDs of different ligand densities for NMR characterizations in aqueous solutions. The proton NMR spectroscopies of MPA of the binding state were used to analyze the ligand densities on the surface of QDs, which were not explored in the past. The binding thermodynamics of the surface ligands of QDs, as analyzed using the Hill equation, demonstrated a positive promoting effect and possible interactions between ligands. EDA in the purification process underwent a spontaneous adsorption with two-stage thermodynamic behaviors as characterized by isothermal titration calorimetry. Due to the positive role of the already adsorbed ligands, excess EDA would further attach to the surface of QDs in the form of non-bonded physisorption, greatly improving the quantum yield (QY) of QDs, and the ligand of this part would almost not change the stability of QDs. We proposed a strategy for the preparation of aqueous QDs with a high QY, followed by fluorescence quenching-enhancement cycles caused by purification-adsorption operations. The strategy made it possible for the preparation of functional QDs with small molecules after purification operations. Kinetics of the sorption of ligands on the surface of QDs were determined by fluorescence spectroscopy. Modified pseudo-second-order kinetics after consideration of the ligand-ligand interaction effect could well analyze the kinetic data. This kinetic model had advantages over the previous ligand exchange model in terms of accuracy, reproducibility, and physical significance. Finally, we used the above strategy for the design of fluorescent QDs for bioimaging of lysosomes, mitochondria, and cancer cells. This work can simplify the preparation of multifunctional fluorescent QDs and avoid complicated ligand design.

Visible-Light-Driven Oxidative Cleavage of Alkenes Using Water-Soluble CdSe Quantum Dots.

The oxidative cleavage of C=C bonds is an important chemical reaction, which is a popular reaction in the photocatalytic field. However, high catalyst-loading and low turnover number (TON) are general shortcomings in reported visible-light-driven reactions. Herein, the direct oxidative cleavage of C=C bonds through water-soluble CdSe quantum dots (QDs) is described under visible-light irradiation at room temperature with high TON (up to 3.7×104 ). Under the same conditions, water-soluble CdSe QDs could also oxidize sulfides to sulfoxides with 51-84 % yields and TONs up to 3.4×104 . The key features of this photocatalytic protocol include high TONs, wide substrates scope, low catalyst loadings, simple and mild reaction conditions, and molecular O2 as the oxidant.

Water-soluble CdSe quantum dots synthesis via facile seed-mediated approach and their characterization studies

In this paper, we are reporting the water-soluble quantum dots exhibiting emission in visible range from 550 to 650 nm. These have been synthesized by a simple seed-mediated approach using cadmium chloride, sodium borohydrate, selenium powder and thioglycolic acid as precursors. The as-prepared cadmium selenide (CdSe) quantum dots were characterized by UV-Vis spectroscopy (UV-Vis), photo luminescence (PL) spectroscopy, Fourier transfer infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM). The obtained water-soluble quantum dots exhibited excellent composition, spherical geometry, strong emission and good stability which can be suitable for biomedical imaging applications.

Site- and Spatial-Selective Integration of Non-noble Metal Ions into Quantum Dots for Robust Hydrogen Photogeneration

Summary Artificial photosystems consisting of semiconductor quantum dots (QDs) and non-noble metal ions (e.g., Fe2+, Co2+, Ni2+) show intrinsic advantages in efficient and cost-effective hydrogen (H2) evolution. However, well-controlled integration of these metal ions into ultra-small QDs is a major challenge. Here, we present a two-step strategy to realize site- and spatial-selective integration of earth-abundant Fe2+ ions in CdSe QDs; i.e., CdSe QDs are modified with a thin and anisotropic ZnS shell, and partial Zn2+ ions are selectively substituted by Fe2+ via cation exchange. The anisotropic ZnS layer not only passivates CdSe core but also works as an ideal medium to intimately anchor Fe2+. The multifunctional CdSe/Zn1−xFexS QD exhibits extraordinary activity and stability toward H2 photogeneration. Specifically, more than 880 mL (∼39,300 μmol) H2 gas is produced from 6 mL of aqueous solution during a consecutive 172 h (>1 week) experiment, thus achieving a turnover number of >600,000 per QD.

Absorption and photoluminescence properties of CdSe quantum dots prepared by hydrothermal method

Herein, we investigated the preparation and optical properties of water-soluble CdSe quantum dots (QDs). CdSe QDs with a narrow size distribution were hydrothermally prepared by reacting Cd2+ with NaHSe in the presence of N-acetyl-L-cysteine as ligand. Furthermore, photoluminescence quantum yield increased to ∼47% when a ZnS shell was applied to prepare the CdSe/ZnS core/shell QDs.

Fluorescent determination of trinitrotoluene with bovine serum albumin mediated enhancement of thioglycolic acid capped cadmium selenium quantum dots

Here, a spectroscopic investigation of the interaction between bovine serum albumin protein and thioglycolic acid capped cadmium selenide (CdSe) quantum dots is presented. Luminescent water-soluble CdSe quantum dots were synthesized at room temperature by a one-step proctocol. Selenium powder and thioglycolic acid were used as the precursor and stabilizer, respectively. The synthesized thioglycolic acid capped CdSe quantum dots were activated by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride/N-hydroxysuccinimide treatment and conjugated with bovine serum albumin protein. The fluorescence signal of CdSe quantum dots was enhanced proportionally with the bovine serum albumin concentration from 0.25 to 5 µg/mL. This nano-bioconjugate was employed for the determination of trinitrotoluene with a detection limit of 5.65 ppm trinitrotoluene across a linear range of 4.4 × 10−6 M to 35.2 × 10−6 M.

Total Count of Salmonella typhimurium Coupled on Water Soluble CdSe Quantum Dots by Fluorescence Detection

Health diseases due to the ingestion of water or food contaminated with pathogenic microorganisms are a main health problem around the world. The traditional methods for detecting foodborne pathogens are time-consuming (on the order of days). The development of methods that can help to detect and identify foodborne pathogens with high sensitivity and specificity have been proposed to overcome the limitations of traditional methods. Accordingly, this research is focused on the development of an experimental protocol for a high-sensitivity detection and quantification of bacterial pathogens with reduced detection times. This will lead to the development of a portable and low-cost technology with the opportunity to make onsite detection of pathogenic species. The proposed approach has modified the route reported in the literature; the method proposed is expected to be sensitive enough to detect a low limit of 102 CFU/mL counts of bacteria. The fluorescence-based method was tested in presence of Salmonella typhimurium (ATCC 14020) and Escherichia coli (ATCC 25922). CdSe water-soluble quantum dots (QDs) were synthesized in aqueous phase in presence of thioglycolic acid (TGA) as a capping agent. As-synthesized QDs were characterized by x-ray diffraction, near infrared and Fourier transform infrared spectroscopy, UV–Vis and photoluminescence techniques. Results of the CdSe/TGA-bacteria coupling and the determination of the corresponding quantification profiles (calibration curves) will be presented and discussed.

Synthesis and luminescent properties of water-soluble nanobiocomposite CdSe/polysaccharide quantum dots

Water-soluble nanobiocomposite CdSe quantum dots were obtained using the stabilizing potential of natural biologically active polysaccharides galactomannan and κ-carrageenan. A complex of physicochemical methods was used to investigate the biphasic amorphous-crystalline structure of the obtained nanocomposites, the size range (4.8—6.9 nm) of the formed CdSe particles was determined, and, additionally, it was shown that aqueous solutions of the nanocomposites in question were characterized by the presence of photoluminescence in two spectral regions, namely, 410—450 and 510—580 nm.

Interaction of l-cysteine functionalized CdSe quantum dots with metallic cations and selective binding of cobalt in water probed by fluorescence

Water-soluble CdSe quantum dots (QDs) capped with l-cysteine (Cys-CdSe) were synthesized in aqueous medium and analyzed by X-ray diffraction, electronic microscopy, absorption spectroscopy and time-resolved fluorescence spectroscopy. We have measured the average diameter of Cys-CdSe QDs, 4.15nm, the true molecular mass, 1.43×105gmol−1 and the molar extinction coefficient, ε480=3×105cm−1M−1 at maximum of band edge (480nm). The number of grafted l-cysteine chains per individual QD was measured to be ∼100. The interaction of these functionalized Cys-CdSe QDs at a concentration of 0.2μM with seventeen different metal ions were evaluated by fluorescence. Only the interaction with Co2+ ions resulted in fluorescence quenching in the range 0.5–20μM when the true concentration of QDs is 0.2μM, with a saturation behavior at Co2+ concentration of ∼20μM, in agreement with 100 grafted l-cysteines per QD. The quenching mechanism involves both static and dynamic fluorescence quenching processes. A model of interaction is derived for the selective binding of Co2+ to Cys-CdSe QDs, involving the carboxyl functions of l-cysteine. The comparison with other QD-systems shows the need for a systematic analysis of the parameters influencing the QD-ions interaction and fluorescence emission, especially their true concentration, in order to understand the fundamental mechanisms at the origin of the specificity for metal binding to a particular QD.

Synthesis, Optical Characterization, and Size Distribution Determination by Curve Resolution Methods of Water-Soluble CdSe Quantum Dots

In this work a colloidal approach to synthesize water-soluble CdSe quantum dots (QDs) bearing a surface ligand, such as thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), glutathione (GSH), or thioglycerol (TGH) was applied. The synthesized material was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), UV-visible spectroscopy (UV-Vis), and fluorescence spectroscopy (PL). Additionally, a comparative study of the optical properties of different CdSe QDs was performed, demonstrating how the surface ligand affected crystal growth. The particles sizes were calculated from a polynomial function that correlates the particle size with the maximum fluorescence position. Curve resolution methods (EFA and MCR-ALS) were employed to decompose a series of fluorescence spectra to investigate the CdSe QDs size distribution and determine the number of fraction with different particle size. The results for the MPA-capped CdSe sample showed only two main fraction with different particle sizes with maximum emission at 642 and 686 nm. The calculated diameters from these maximum emission were, respectively, 2.74 and 3.05 nm.

Synthesis, characterization and spectral temperature-dependence of thioglycerol-CdSe nanocrystals

Water-soluble CdSe quantum dots (QDs) have been synthesized with thioglycerol as a stabilizer through a novel hydrothermal route. The obtained thioglycerol capped CdSe (TG-CdSe) nanocrystals were characterized regarding their morphology and structural, thermal and optical properties. The resulting nanocrystals were synthesized in the cubic structure with a near spherical shape, as confirmed by X-ray diffraction and transmission electron microscopy. Combining transmission electron microscopy imaging and calculations using UV–visible absorption spectrum and X-ray diffraction pattern, the diameter of the synthesized nanocrystals was estimated to 2.26nm. As confirmed by its Fourier transform IR spectrum, thioglycerol was successfully liganded on the surface of the resulting nanocrystals. Band structure parameters of the TG-CdSe nanoparticles were determined and quantum confinement effect was evidenced by optical absorption, fluorescence and Raman measurements. The thermal properties of the TG-CdSe were explored by thermal gravimetric analysis and differential scanning calorimetry. The temperature dependence of both the absorption and fluorescence spectra in the physiological range makes the TG-CdSe nanocrystals sensitive temperature markers, a property that must be taken into account when developing any probing applications, especially for cellular imaging.

Mechanistic evaluation of the size dependent antimicrobial activity of water soluble QDs

Water soluble size variable (2.43–5.09 nm) CdSe quantum dots.

Thioglycerol-functionalized CdSe quantum dots detecting cadmium ions

Water-soluble CdSe quantum dots (QDs) were synthesized using thioglycerol (TG) as the surface capping agent through a one-step process at low temperature T (100°C). The CdSe quantum dots were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, UV–visible absorption and fluorescence spectroscopies. These measurements revealed that the TG-capped CdSe QDs possess a high crystalline quality with an average diameter in the range 2.5–2.8nm and exhibit particular optical properties. The UV–visible absorption of CdSe QDs is enhanced by the addition of cadmium ions, with a simultaneous shift of the edge band (400nm), while seventeen other tested metal cations have no effect on the absorption of QDs. Moreover, the binding of Cd2+ ions induces a quenching of the fluorescence emission of TG-CdSe QDs. At particular absorption wavelengths, the response is linearly proportional to the cadmium ions concentration ranging from 1.0 to 22μM with a detection limit of 0.32μM (37μgL−1). Based on these optical properties, the TG-CdSe QDs could be used as a highly selective probe for the detection of Cd2+ ions in aqueous solutions, a species highly toxic for cells.

Quantum dots and ionic liquid-sensitized effect as an efficient and green catalyst for the sensitive determination of glucose

A novel fluorescence (FL) method using water-soluble CdSe quantum dots (QDs) is proposed for the fluorometric determination of hydrogen peroxide and glucose. Water-soluble CdSe QDs were synthesized by using thioglycolic acid as stabilizer in aqueous solutions. The nanoparticles were structurally and optically characterized by X-ray powder diffraction (XRD), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), UV–Vis absorption spectroscopy, photoluminescence (PL) emission spectroscopy and transmission electron microscope (TEM). Ionic liquid-sensitized effect in aqueous solution was then investigated. In the presence of ionic liquid as catalyst, H2O2 was decomposed into radical that could quench the fluorescence of CdSe QDs more efficiently and rapidly. Then the oxidization of glucose by glucose oxidase was coupled with the fluorescence quenching of CdSe QDs by H2O2 producer with ionic liquid catalyst, which can be used to detect glucose. Therefore, a new FL analysis system was developed for the determination of glucose. Under the optimum conditions, there is a good linear relationship between the relative PL emission intensity and the concentration of glucose in the range of 5.0×10−7–1.0×10−4M of glucose with a correlation coefficient (R2) of 0.9973. The limit of detection of this system was found to be 1.0×10−7M. This method is not only simple, sensitive and low cost, but also reliable for practical applications.

Nickel Complexes for Robust Light-Driven and Electrocatalytic Hydrogen Production from Water

A series of nickel bis(chelate) complexes having square planar coordination are studied for light-driven and electrocatalytic hydrogen production from water. The complexes Ni(abt)2 (abt = 2-aminobenzenethiolate), Ni(mp)2 (mp = 2-mercaptophenolate) and Ni(mpo)2 (mpo = 2-mercaptopyridyl-N-oxide) are found to be active catalysts under light-driven conditions, using fluorescein (Fl) as the photosensitizer (PS) and triethanolamine (TEOA) as the sacrificial electron donor in water under basic pH (pH = 9.8). These molecular systems achieve a turnover number (TON) of ∼6000 (relative to catalyst) and are stable for more than 100 h under H2-generating conditions. When water-soluble CdSe quantum dots with tripodal S-donor capping agents are employed as PS and ascorbic acid (AA) is used as the sacrificial electron donor at pH 4.5, an active and robust system is obtained for the light-driven generation of H2 from aqueous protons. A TON of over 280 000 is achieved for the three active catalysts. These complexes are also examined electrochemically in organic solvents with weak organic acids as the proton source and in aqueous and aqueous/organic media for proton reduction. The most active photochemical catalysts also show excellent electrocatalytic activity in neutral pH water, achieving Faradaic yields close to 100% under anaerobic conditions and ∼80% under aerobic conditions.

One-Step Synthesis of High-Quality Water-Soluble CdSe Quantum Dots Capped byN-Acetyl-L-cysteineviaHydrothermal Method and Their Characterization

Novel water-soluble CdSe quantum dots (QDs) have been prepared withN-acetyl-L-cysteine as new stabilizer through a one-step hydrothermal route. The influence of experimental conditions, including reaction time, molar ratio of reactants, and pH value, on the luminescent properties of the obtained CdSe QDs has been systematically investigated. The characterization of as-prepared QDs was carried out through different methods. In particular, we realized qualitative and semiquantitative studies on CdSe QDs through X-ray photoelectron spectroscopy and electron diffraction spectroscopy. The results show that the as-prepared CdSe QDs exhibit a high quantum yield (up to 26.7%), high stability, and monodispersity and might be widely used in biochemical detection and biochemical research.

Synthesis of water-soluble CdSe quantum dots with various fluorescent properties and their application in immunoassay for determination of C-reactive protein.

Effects of various factors on synthesis and fluorescent properties of CdSe quantum dots were studied. It was shown that variation of pH, stabilizer and concentration of precursors brings to obtaining of quantum dots with various fluorescent properties. The nanoparticles prepared were conjugated with rabbit antibodies to C-Reactive protein and C-Reactive protein for competitive immunoassay for determination of CRP. It was shown that interaction of these dots as a result of antigen-antibody reaction brings to resonance energy transfer and these changes in fluorescence spectra correlate with concentration of CRP. This approach permits to determine CRP in range between 4-100ng.