Metal Sulfide Quantum Dots Research Articles

Bioinspired, Non-Enzymatic, Aqueous Synthesis of Size-Tunable CdS Quantum Dots for Sustainable Optoelectronic Applications.

The enzymatic production of hydrogen sulfide (H2S) from cysteine in various metabolic processes has been exploited as an intrinsically "green" and sustainable mode for the aqueous biomineralization of functional metal sulfide quantum dots (QDs). Yet, the reliance on proteinaceous enzymes tends to limit the efficacy of the synthesis to physiological temperature and pH, with implications for QD functionality, stability, and tunability (i.e., particle size and composition). Inspired by a secondary non-enzymatic biochemical cycle that is responsible for basal H2S production in mammalian systems, we establish how iron(III)- and vitamin B6 (pyridoxal phosphate, PLP)-catalyzed decomposition of cysteine can be harnessed for the aqueous synthesis of size-tunable QDs, demonstrated here for CdS, within an expanded temperature, pH, and compositional space. Rates of H2S production by this non-enzymatic biochemical process are sufficient for the nucleation and growth of CdS QDs within buffered solutions of cadmium acetate. Ultimately, the simplicity, demonstrated robustness, and tunability of the previously unexploited H2S-producing biochemical cycle help establish its promise as a versatile platform for the benign, sustainable synthesis of an even wider range of functional metal sulfide nanomaterials for optoelectronic applications.

Dynamic Bond-Directed Synthesis of Stable Mesoporous Metal–Organic Frameworks under Room Temperature

Stable metal-organic frameworks (MOFs) with mesopores (2-50 nm) are promising platforms for immobilizing nanosized functional compounds, such as metal-oxo clusters, metal-sulfide quantum dots, and coordination complexes. However, these species easily decompose under acidic conditions or high temperatures, hindering their in situ encapsulation in stable MOFs, which are usually synthesized under harsh conditions involving excess acid modulators and high temperatures. Herein, we report a route for the room-temperature and acid-modulator-free synthesis of stable mesoporous MOFs and MOF catalysts with acid-sensitive species encapsulated: (1) we initially construct a MOF template by connecting stable Zr6 clusters with labile Cu-bipyridyl moieties; (2) Cu-bipyridyl moieties are subsequently exchanged by organic linkers to afford a stable version of Zr-MOFs; (3) acid-sensitive species, including polyoxometalates (POMs), CdSeS/ZnS quantum dots, and Cu-coordination cages, can be encapsulated in situ into the MOFs during step 1. The room-temperature synthesis allows the isolation of mesoporous MOFs with 8-connected Zr6 clusters and reo topology as kinetic products, which are inaccessible by traditional solvothermal synthesis. Furthermore, acid-sensitive species remain stable, active, and locked within the frameworks during MOF synthesis. We observed high catalytic activity for VX degradation by the POM@Zr-MOF catalysts as a result of the synergy between redox-active POMs and Lewis-acidic Zr sites. The dynamic bond-directed method will accelerate the discovery of large-pore stable MOFs and offer a mild route to avoid the decomposition of catalysts during MOF synthesis.

Structural characterization of cystathionine γ-lyase smCSE enables aqueous metal quantum dot biosynthesis

The development and utilization of inorganic material biosynthesis have evolved into single macromolecular systems. A putative cystathionine γ-lyase of bacteria Stenotrophomonas maltophilia (smCSE) is a newly identified biomolecule that enables the synthesis of nanomaterials. Due to the lack of structural information, the mechanism of smCSE biosynthesis remains unclear. Herein, we obtain two atomic-resolution smCSE-form X-ray structures and confirm that the conformational changes of Tyr108 and Lys206 within the enzyme active sites are critical for the protein-driven synthesis of metal sulfide quantum dots (QDs). The structural stability of tetramer and the specificity of surface amino acids are the basis for smCSE to synthesize quantum dots. The size of QD products can be regulated by predesigned amino acids and the morphology can be controlled through proteolytic treatments. The growth rate is enhanced by the stabilization of a flexible loop in the active site, as shown by the X-ray structure of the engineered protein which fused with a dodecapeptide. We further prove that the smCSE-driven route can be applied to the general synthesis of other metal sulfide nanoparticles. These results provide a better understanding of the mechanism of QD biosynthesis and a new perspective on the control of this biosynthesis by protein modification.

Decoration of upconversion nanocrystals with metal sulfide quantum dots by a universal in situ controlled growth strategy.

Conjugating transition-metal sulfide quantum dots and upconversion nanocrystals (UCNCs) has aroused widespread concern due to enhanced physical and chemical properties in contrast to only their simple sum. However, the synthesis of such hybrid nanoparticles by a universal in situ growth strategy has been scarcely reported so far. Herein, we developed a facile approach to functionalize NaYF4:Yb/Er with chitosan (NaYF4:Yb/Er@CS), which not only could improve the hydrophilicity of NaYF4:Yb/Er, but also can form stable chelates with transition-metal ions. Then, ultrasmall metal sulfide (Mn+S, M = Ag, Cu, Cd) quantum dots (QDs) can be conjugated homogeneously on the surface of NaYF4:Yb/Er@CS. Taking Ag2S as an example, the growth behavior of Ag2S QDs on the surface of NaYF4:Yb/Er@CS was studied specifically. The influence of the Ag : Y ratio, S : Ag ratio, pH value, reaction time and reaction temperature on the growth behavior of Ag2S on the surface of NaYF4:Yb/Er@CS was investigated systematically. Meanwhile, this innovative strategy is also suitable for the growth of ultrasmall QDs in various shapes, including plates, spheres and rods. The resultant NaYF4:Yb/Er@CS@Ag2S system possesses both upconversion luminescence (UCL) properties of NaYF4:Yb/Er and a good photothermal conversion effect of Ag2S, and is a promising candidate for UCL imaging guided PTT of cancer.

High-order harmonic generation using quasi-phase matching and two-color pump in the plasmas containing molecular and alloyed metal sulfide quantum dots

As high-order harmonic emitters, quantum dots are produced through laser-induced plasmas. Subsequently, we generate high-order harmonics with 800-nm and 30-fs pulses from laser-produced plasmas containing quantum dots of different metal sulfides (Ag2S, CdS, and Cd0.5Zn0.5S). The high-order harmonic generation is analyzed using different approaches, including two-color (800 nm + 400 nm) pump, application of alloyed quantum dots, and quasiphase matching of interacting waves. We discuss the self-phase modulation induced splitting of harmonics, the difference in the application of thick and thin crystals for second harmonic (400 nm) emission during two-color pumping of the quantum dot plasma, the spatial modulation of the quantum dot plasma for quasiphase matching, and the comparison of harmonic yields from monomer and quantum dot plasmas. This study allows us to determine the mechanisms of coherent extreme ultraviolet radiation generation using a few nanometer-sized emitters as well as optimal methods for further enhancing the high-order harmonic generation efficiency.

Effective high-order harmonic generation from metal sulfide quantum dots.

In the past, common media for high-order harmonic generation (HHG) has been atoms and molecules. More recently, clusters, and nanoparticles have been introduced as HHG emitting media. Multi-particle media can enhance HHG yields but have more stringent requirements in determining the optimal parameters. Here, we demonstrate, for the first time, the effective application of 1-3 nm metal sulfide quantum dots (QDs) for harmonic generation in the 20 - 115 nm extreme ultraviolet range. We report on the syntheses, ablation of Ag2S, CdS, and ZnS QDs, and HHG from laser-produced plasmas by using single- and two-color pumps. We compare HHG efficiency from the ablated QDs to that of bulk metal sulfides and show a seven-fold increase in harmonic yields. Further, the study also allows us to understand the effects of QD-contained plasma spreading dynamics on HHG yield.

Gum Arabic Microgels As Template for In Situ Metal-Sulfide Based Quantum Dots Preparation and Their Thermal, Spectroscopic, Optical, and Magnetic Characterization

Here, gum arabic (GA) microgel in 5–50 μm size range was used as a template for in situ quantum dot (QD) preparation. The in situ synthesis of metal sulfide quantum dots (QDs) such as CdS, PbS, CuS, ZnS, CoS, and MnS was accomplished by the absorption of the corresponding metal ions from aqueous solutions and then in situ precipitation with S2− treatments within GA microgels. Transmission electron microscopy (TEM) confirmed the existence of the evenly distributed QDs within GA microgel matrices for each of the prepared QDs. All the fabricated GA-QD composites have shown excellent semiconducting behaviors with relatively larger band gap values of 4.87 eV, 4.60 eV, 6.71 eV, 4.81 eV, 3.68 eV, 5.2 eV, and 4.0 eV for CdS, PbS, ZnS, CuS, CoS, MoS, and MnS, respectively. The results revealed that CdS and ZnS are found to be the most efficient florescence materials amongst the all QDs with 630 and 70 cd/cm2 fluorescence intensities, respectively. Moreover, the magnetic susceptibility study suggests that Mn(IV), Co(III), and Mo(IV), have mononuclear octahedral geometries whereas Zn(II), Cd(II), and Pb(II) show binuclear geometries.

Magneto-controlled aptasensor for simultaneous electrochemical detection of dual mycotoxins in maize using metal sulfide quantum dots coated silica as labels

Currently there is an urgent need for multi-mycotoxin detection methods due to the co-occurrence of multiple mycotoxins in food raw materials and their augmented toxicity. Herein, a magneto-controlled aptasensor has been developed for simultaneous electrochemical detection of ochratoxin A (OTA) and fumonisin B1 (FB1), two typical mycotoxins found in food crops world-wide. This aptasensor was designed using the high specificity between the target and aptamer with heavy CdTe or PbS quantum dots (QDs) coated silica as labels and the complementary DNA functionalized magnetic beads as capture probes. In presence of targets, the aptamer preferred to form the target-aptamer binding which forced the partial release of the preloaded labels from the magnetic beads. After a one-step incubation and a simple magnetic separation, the electrochemical signals of Cd2+ and Pb2+ dissolved from the reserved labels which had negative correlation with targets contents, was measured based on the difference of peak potentials. This aptasensor provided a wide detection range of 10pgmL−1 to 10ngmL−1 for OTA and 50pgmL−1 to 50ngmL−1 for FB1, and succeeded in real maize samples. This method provides a new avenue for high throughput screen of mycotoxins due to the advantages of simple instrument, low sample consumption, short assay times, and lower detection costs per assay. Moreover, it could be readily expanded for the simultaneous detection of a large panel of mycotoxins by using different metal sulfide QDs when their specific aptamers are available.

Metal sulfide precursor aqueous solutions for fabrication of Ag-doped ZnxCd1−xS quantum dots thin films

Aqueous solution deposition of metal chalcogenide semiconductor thin films is considered a green and low-cost approach. So it is hard to find a general aqueous solution approach to deposit various kinds of high-quality metal sulfide quantum dots thin films. Here, we describe a green and robust aqueous solution approach, and five types of metal sulfide precursor solutions (Cu(CH3COO)2, AgNO3, Zn(CH3COO)2, Cd(CH3COO)2·2H2O, Ni(CH3COO)2·4H2O) can be prepared at room temperature under air atmosphere. By this green route, luminescent Ag-doped ZnxCd1−xS semiconductor films have been successfully synthesized via a facile and green method in the open air at 260°C using precursors. NH3·H2O (28–30%) were used as solvent, and 3-mercaptopropionic acid was used as the capping agents. As-prepared quantum dot thin films exhibit a tunable emission covering the whole visible light region. The absolute photoluminescence quantum yields can reach as high as 24.6%, which have a high potential application in luminescent, transparent, and conductive thin films.

Kelvin probe imaging of photo-injected electrons in metal oxide nanosheets from metal sulfide quantum dots under remote photochromic coloration.

Metal oxide and quantum dot (QD) heterostructures have attracted considerable recent attention as materials for developing efficient solar cells, photocatalysts, and display devices, thus nanoscale imaging of trapped electrons in these heterostructures provides important insight for developing efficient devices. In the present study, Kelvin probe force microscopy (KPFM) of CdS quantum dot (QD)-grafted Cs4W11O36(2-) nanosheets was performed before and after visible-light irradiation. After visible-light excitation of the CdS QDs, the Cs4W11O36(2-) nanosheet surface exhibited a decreased work function in the vicinity of the junction with CdS QDs, even though the Cs4W11O36(2-) nanosheet did not absorb visible light. X-ray photoelectron spectroscopy revealed that W(5+) species were formed in the nanosheet after visible-light irradiation. These results demonstrated that excited electrons in the CdS QDs were injected and trapped in the Cs4W11O36(2-) nanosheet to form color centers. Further, the CdS QDs and Cs4W11O36(2-) nanosheet composite films exhibited efficient remote photochromic coloration, which was attributed to the quantum nanostructure of the film. Notably, the responsive wavelength of the material is tunable by adjusting the size of QDs, and the decoloration rate is highly efficient, as the required length for trapped electrons to diffuse into the nanosheet surface is very short owing to its nanoscale thickness. The unique properties of this photochromic device make it suitable for display or memory applications. In addition, the methodology described in the present study for nanoscale imaging is expected to aid in the understanding of electron transport and trapping processes in metal oxide and metal chalcogenide heterostructure, which are crucial phenomena in QD-based solar cells and/or photocatalytic water-splitting systems.

ChemInform Abstract: Carbon Nanotube‐Based Heterostructures for Solar Energy Applications

AbstractReview: 152 refs.

Carbon nanotube-based heterostructures for solar energy applications

One means of combining the unique physical and chemical properties of both carbon nanotubes and complementary material motifs (such as metal sulfide quantum dots (QDs), metal oxide nanostructures, and polymers) can be achieved by generating carbon nanotube (CNT)-based heterostructures. These materials can be subsequently utilized as novel and interesting constituent building blocks for the assembly of functional light energy harvesting devices and because of their architectural and functional flexibility, can potentially open up novel means of using and taking advantage of existing renewable energy sources. In this review, we present the reliable and reproducible synthesis of several unique model CNT-based heterostructured systems as well as include an accompanying discussion about the charge transfer and energy flow properties of these materials for their potential incorporation into a range of practical solar energy conversion devices.

ChemInform Abstract: Photodeposition of Metal Sulfide Quantum Dots on Titanium(IV) Dioxide and the Applications to Solar Energy Conversion

AbstractReview: 87 refs.

A facile synthesis of graphene–metal (Pb, Zn, Cd, Mn) sulfide composites

We propose a general approach for the preparation of graphene-metal sulfide quantum dots (QDs) composites by π–π stacking of pyridine-capped metal sulfide QDs and chemically converted graphene (CCG) in aqueous solution. CCG sheets disperse stably in water without the assistance of dispersing agents, only by electrostatic repulsion. The aromatic structures of pyridine capped on metal sulfide QDs make these QDs dispersible in ethanol or water, and further introduce a π–π stacking interaction between CCG and QDs, and extend the conjugated structure of CCG. The structural details, formation mechanism, and textural properties of the resultant graphene-metal sulfide QDs composites are characterized by X-ray diffraction, UV–vis absorption, electron microscopy, and Raman scattering studies. The CCG–metal sulfide composites disperse stably in aqueous solution, allowing them to be potentially used in biological tissues and easy-to-form filtered films for further research and application.

Photodeposition of metal sulfide quantum dots on titanium(iv) dioxide and the applications to solar energy conversion

Heteronanojunction systems consisting of narrow gap semiconductors represented by metal sulfides and TiO(2) are highly expected as visible-light-active photocatalysts and the key materials for various photoelectrochemical devices. The common central issue is increasing efficiency of the light-induced interfacial electron transfer from the metal sulfide quantum dots (QDs) to TiO(2). We have newly developed simple and versatile low-temperature photodeposition techniques for directly coupling metal sulfide QDs and TiO(2) by taking advantage of its photocatalysis and the photoinduced surface superhydrophilicity. This critical review summarizes the recent developments in the photodeposition techniques and their unique characteristics. Subsequently to the Introduction, a theoretical view of the interfacial electron transfer is presented to obtain the guidelines for the design of the heteronanojunction systems. Then, the itemized description is given for the photodepositions of several kinds of metal sulfides on TiO(2) followed by the summary of the features of the photodeposition technique. Finally, the applications of the resulting heteronanojunction systems to the photocatalysts and QD-sensitized solar cells are described, and the excellent performances are discussed by relating with the features of the photodeposition technique (87 references).

Photodeposition of Metal Sulfide Quantum Dots on Titanium(IV) Dioxide and its Applications

ABSTRACTIn situ photodeposition techniques taking advantage of the TiO2 photocatalysis have been developed for coupling metal sulfide quantum dots (QDs) and TiO2 at a nonoscale. The coupled metal sulfide-TiO2 systems possess the following characteristics: (I) a large amount of metal sulfides can be directly formed on TiO2 during a fairly short period with excellent reproducibility, (II) the band energies of metal sulfides QDs are widely tunable by irradiation time, (III) metal sulfide QDs can be deposited on not only the external surfaces but also the inner ones of mesoporous TiO2 nanocrystalline films without pore-blocking, (IV) the simple solution-based technique at low temperature enables the low-cost production, (V) this technique has a wide possibility for coupling TiO2 and narrow gap metal sulfides. These unique features produce the excellent performances of the resulting heteronanojunaction systems as the photoanodes for QD-sensitized solar cells.