Investigations on Iron Sulfide Nanosheets Prepared via a Single-Source Precursor Approach

Two-dimensional (2D) magnetic pyrrhotite (Fe7S8) and greigite (Fe3S4) nanosheets were synthesized by pyrolyzing, respectively, single-source precursors such as Fe(Ddtc)2(Phen) (Phen = 1,10-phenanthroline; Ddtc = diethyldithiocarbamate) and Fe(Ddtc)3 in oleylamine. Under optimized reaction temperature of 280 °C, both monoclinic Fe7S8 and cubic Fe3S4 obtained presented hexagonal sheet structure with sizes of 500–800 nm and 100–500 nm, respectively. AFM measurements revealed that both of these two types of nanosheets had a nearly identical thickness of 50 nm. Further XRD measurements revealed that the reaction temperature played a critical role in determining the crystalline structure as well as the chemical composition of the resultant nanosheets. In the reaction temperature range of 240−320 °C, a higher reaction temperature generally favored the transformations of monoclinic Fe7S8 to hexagonal FeS, and cubic Fe3S4 to hexagonal Fe7S8, respectively. The magnetic properties of the resultant nanosheets were accordingly altered against the reaction temperature. Further experimental results obtained by combining different types of solvents suggested that oleylamine was necessary for the formation of hexagonal Fe7S8 nanosheets. In contrast, it only helped prevent the hexagonal Fe3S4nanosheets from agglomeration. It was also found that both pyrrhotite (Fe7S8) and greigite (Fe3S4) nanosheets were metastable under ambient conditions. Systematic XPS measurements were carried out to investigate the air stabilities of the resultant nanosheets

From Ultrathin Two-Dimensional Djurleite Nanosheets to One-Dimensional Nanorods Comprised of Djurleite Nanoplates: Synthesis, Characterization, and Formation Mechanism

Sn-doped ultrathin copper sulfide nanosheets of 209 ± 33 nm and nanoplates of 36.0 ± 5.9 nm were synthesized by pyrolyzing copper(II) acetylacetonate (Cu(acac)2) in dodecanethiol in the presence of different amounts of SnCl4·5H2O. The large nanosheets appeared in hexagonal and quasi-triangular shapes, while the small nanoplates presented mainly triangular shapes. Transmission electron microscopy (TEM) studies revealed that both nanosheets and nanoplates tended to form face-to-face stacking, which was further confirmed by X-ray diffraction studies. Such a self-assembling tendency became so strong for the small nanoplates that they formed one-dimensional (1D) self-assembled nanorods of 365 ± 145 nm. Atomic force microscopy studies revealed that the thickness of nanosheets was around 6.4−6.6 Å. The powder X-ray diffraction and high resolution TEM investigations demonstrated that the resultant two-dimensional (2D) nanocrystals are of monoclinic djurleite (Cu31S16). Further investigations on different control samples revealed that Sn could partly replace Cu in forming lamellar supramolecular structures which actually acted as the precursors for the ultrathin 2D djurleite nanocrystals. Because of the excellent thermal stability and protective effects, the Sn-dodecanethiol complexes survived the pyrolysis of Cu(acac)2 and preferentially attached on {100} facets of the resultant djurleite nanocrystals. Consequently, the growth of djurleite nanocrystals along the [100] direction was blocked, resulting in 2D Cu31S16 nanocrystals. The dipole−dipole interaction along the [100] direction and the hydrophobic interaction between the nanoplates were the main driving force for the formation of 1D superstructures of the nanoplates

Electroluminescence Studies on Self-Assembled Films of PPV and CdSe Nanoparticles

Electrooptical and structural studies on self-assembled films composed of CdSe nanoparticles, poly(p-phenylene vinylene) (PPV), and different nonconjugated polyelectrolytes are reported. It is demonstrated by optical spectroscopy and X-ray reflectivity measurements that CdSe nanoparticles and PPV can successfully be incorporated into homogeneous ultrathin films by the self-assembly method. The surface roughness obtained from the X-ray measurements is 2.7 and 1.3 nm respectively for CdSe/PAH (PAH, poly(allylamine) hydrochloride) and PSS/PPV (PSS, poly(styrenesulfonic acid)) multilayer films. This allows us to stack a (PSS/PPV)*n film on top of a (CdSe/PAH)*n film to build up well-defined two-layer composite film devices. Electroluminescence studies show that pure (PSS/PPV)*n film devices exhibit green light emission but with a very short lifetime (several seconds) if operated in ambient air. During operation, the PPV emission shifts toward the blue, which indicates that the mean conjugation length of PPV is shortened due to oxidation. Oxidation of CdSe particles is also observed in (CdSe/PAH)*n devices during operation. However, the stability of CdSe particles is enhanced if they are combined alternately with PPV, and a (CdSe/PPV)*n device gives a broad, nearly white emission. The turn-on voltage of it is much smaller and better defined than that for a (CdSe/PAH)*20 device. This proves that PPV works like a charge-transportation layer rather than an emitting layer in the (CdSe/PPV)*n film device. In an ITO//PEI(CdSe/PAH)*10/(PSS/PPV)*10//Al two-layer composite film device the lifetime of PPV electroluminescence can be prolonged for at least 1 order of magnitude only after the device is first operated under backward bias (positive pole on Al electrode). This suggests that the oxygen within the film is removed by this operation due to oxidation of the particles. Afterward, this two-layer composite film device presents emission from PPV and CdSe, respectively, when the sign of the external voltage is changed

Flow Synthesis of Biocompatible Fe₃O₄ Nanoparticles: Insight into the Effects of Residence Time, Fluid Velocity, and Tube Reactor Dimension on Particle Size Distribution

PEGylated Fe₃O₄ nanoparticles were prepared through flow synthesis upon the pyrolysis of ferric acetylacetonate (Fe­(acac)₃) in anisole at 250 °C under pressure of 33 bar, in the presence of α,ω-dicarboxyl-terminated polyethylene glycol (HOOC–PEG–COOH) and oleylamine. In combination with theoretical analysis, the effects of linear velocity, residence time, and reactor dimension on particle size distribution were systematically investigated. In addition, the impact of Ostwald ripening on particle size distribution was also revealed. In particular, the impacts of monomer concentration distributions along both axial and radial directions of the tube reactor on the particle size distribution were carefully investigated. Under optimized conditions, PEGylated Fe₃O₄ nanoparticles with the relative standard deviation of particle size down to 10.6% were thus obtained. The resulting 4.6 nm particles exhibited excellent colloidal stability and high longitudinal relaxivity (<i>r</i>₁) up to 11.1 mM^–1·s^–1, which manifested the reliability of flow synthesis in preparing PEGylated Fe₃O₄ nanoparticles as contrast agents for magnetic resonance imaging applications

Coating Aqueous Quantum Dots with Silica via Reverse Microemulsion Method: Toward Size-Controllable and Robust Fluorescent Nanoparticles

Fluorescent core−shell CdTe@SiO2 particles with controllable particle sizes were prepared via a reverse microemulsion method by hydrolyzing tetraethyl orthosilicate within microwater droplets. Aqueous CdTe nanocrystals and CdS nanocrystals stabilized by different types of thiol molecules were prepared for elucidating the mechanism leading to the core−shell structures. Photo-oxidation experiments were performed to show the enhancement effect of the silica shell on the photostability of the CdTe nanocrystals encapsulated. Further surface modifications were also performed for grafting amino groups on the surface of the resultant fluorescent CdTe@SiO2 particles

Coating Aqueous Quantum Dots with Silica via Reverse Microemulsion Method: Toward Size-Controllable and Robust Fluorescent Nanoparticles

Fluorescent core−shell CdTe@SiO2 particles with controllable particle sizes were prepared via a reverse microemulsion method by hydrolyzing tetraethyl orthosilicate within microwater droplets. Aqueous CdTe nanocrystals and CdS nanocrystals stabilized by different types of thiol molecules were prepared for elucidating the mechanism leading to the core−shell structures. Photo-oxidation experiments were performed to show the enhancement effect of the silica shell on the photostability of the CdTe nanocrystals encapsulated. Further surface modifications were also performed for grafting amino groups on the surface of the resultant fluorescent CdTe@SiO2 particles

Wearable Plant Sensors Based on Nanometer-Thick Ag Films on Polyethylene Glycol Terephthalate Substrates for Real-Time Monitoring of Plant Growth

The real-time monitoring of growth status, pest and disease prevention, and the extraction of physical and chemical signals of plant are essential for precision and postharvest agriculture. Although multifunctional wearable plant sensors have been used in leaf wetness and growth monitoring, their high fabrication costs and low performance are drawbacks. Herein, a bionic plant sensor with a nanometer-thick Ag film and double V-shaped grooves was fabricated and operated as a scorpion microscale slit receptor to monitor plant growth. The bionic plant sensor showed ultrasensitive vibration detection capability and was fabricated using a very simple and scalable strategy, requiring only 1 h/per and costing $1.3/per. Furthermore, the wireless sensor enabled continuous and real-time growth monitoring of bamboo, which showed a day/night growth tendency consistent with previous intrusive reports. In addition, the wearable plant sensor demonstrated great potential for real-time plant growth detection

Wearable Plant Sensors Based on Nanometer-Thick Ag Films on Polyethylene Glycol Terephthalate Substrates for Real-Time Monitoring of Plant Growth

The real-time monitoring of growth status, pest and disease prevention, and the extraction of physical and chemical signals of plant are essential for precision and postharvest agriculture. Although multifunctional wearable plant sensors have been used in leaf wetness and growth monitoring, their high fabrication costs and low performance are drawbacks. Herein, a bionic plant sensor with a nanometer-thick Ag film and double V-shaped grooves was fabricated and operated as a scorpion microscale slit receptor to monitor plant growth. The bionic plant sensor showed ultrasensitive vibration detection capability and was fabricated using a very simple and scalable strategy, requiring only 1 h/per and costing $1.3/per. Furthermore, the wireless sensor enabled continuous and real-time growth monitoring of bamboo, which showed a day/night growth tendency consistent with previous intrusive reports. In addition, the wearable plant sensor demonstrated great potential for real-time plant growth detection

Generation, Characterization, and Application of Hierarchically Structured Self-Assembly Induced by the Combined Effect of Self-Emulsification and Phase Separation

Hierarchically structured magnetic single-hole hollow spheres (MSHS) have been successfully obtained via a facile self-assembly strategy. This methodology allows the double emulsions generated via the combined effect of self-emulsification and phase separation to provide confinement for directing the self-assembly of magnetic nanoparticles (MNPs). The resulting MSHS fully capitalize on both the multifunctional properties of MNPs and container features of single-hole hollow spheres. Moreover, the magnetic properties showed obvious improvement and can be tuned by modulating the assembled structure. Thus, MSHS can be used as a smart platform with multiple functionalities including image contrast enhancement, selective encapsulation for biomacromolecules, on-demand release, and magnetically guided transport. This strategy is very promising in the design of hierarchically structured assemblies for desired applications in biomedicine and other fields

Synthesis and Shape-Tailoring of Copper Sulfide/Indium Sulfide-Based Nanocrystals

Heterostructured Cu2S−In2S3 nanocrystals with various shapes and compositions were synthesized by a high-temperature precursor-injection method using the semiconductor nanocrystal Cu1.94S as a catalyst. The intrinsic cationic deficiencies formed at high temperature by Cu ions made the Cu1.94S nanocrystal a good candidate for catalyzing the nucleation and subsequent growth of In2S3 nanocrystals, eventually leading to the formation of heterostructured Cu2S−In2S3 nanocrystals. Gelification of the reaction systems, which were composed of different types of nanocrystal precursors and solvent, was found to be a very effective measure for controlling the growth kinetics of the heterostructured particles. Consequently, matchsticklike Cu2S3−In2S3 heterostructured nanorods, teardroplike quasi-core/shell Cu2S@In2S3 nanocrystals, and pencil-like In2S3 nanorods were successfully obtained by manipulating the gelification of the reaction system; this formed a solid experimental basis for further discussion of the growth mechanisms for differently shaped and structured nanocrystals. By reaction with 1,10-phenanthroline, a reagent that strongly and selectively binds to Cu+, a compositional transformation from binary matchsticklike Cu2S−In2S3 nanorods to pure In2S3 nanorods was successfully achieved