A Facile Phosphine‐Free Method for Synthesizing PbSe Nanocrystals with Strong Optical Limiting Effects

PbSe semiconductor nanocrystals (NCs) have attracted ever‐growing interest owing to both their fundamental physics and potential applications in a diverse range of fields such as optoelectronic devices and nonlinear optics. The current fabrication strategy for colloidal PbSe NCs, however, frequently involves acutely toxic reagents and tedious reaction procedures, and is plagued by products with poorly controlled size and morphology. Herein, we report a facile, low‐cost, and phosphine‐free method for synthesizing PbSe NCs, which provides highly uniform NCs with tunable mid‐IR absorption, and they are promising for bio‐related applications. These high quality NCs were obtained by the reaction of elemental Se and PbCl₂ in oleylamine as both the ligand and reaction medium. The high flexibility and reproducibility of the method reported in this study allows us to synthesize monodispersed PbSe NCs with well‐controlled size and morphology. In addition, these products show strong optical limiting effects, and thus hold potential for developing nonlinear optical devices.     

Glycine-Functionalized CsPbBr3 Nanocrystals for Efficient Visible-Light Photocatalysis of CO2 Reduction

Capping ligands are indispensable for the preparation of metal-halide-perovskite (MHP) nanocrystals (NCs) with good stability; however, the long alkyl-chain capping ligands in conventional MHP NCs will be unfavorable for CO₂ adsorption and hinder the efficient carrier separation on the surface of MHP NCs, leading to inferior catalytic activity in artificial photosynthesis. Herein, CsPbBr₃ nanocrystals with short-chain glycine as ligand are constructed through a facile ligand-exchange strategy. Owing to the reduced hindrance of glycine and the presence of the amine group in glycine, the photogenerated carrier separation and CO₂ uptake capacity are noticeably improved without compromising the stability of the MHP NCs. The CsPbBr₃ nanocrystals with glycine ligands exhibit a significantly increased yield of 27.7 μmol g⁻¹ h⁻¹ for photocatalytic CO₂-to-CO conversion without any organic sacrificial reagents, which is over five times higher than that of control CsPbBr₃ NCs with conventional long alkyl-chain capping ligands.     

Hyperbranched polymers meet colloid nanocrystals: a promising avenue to multifunctional,robust nanohybrids

Colloid nanocrystals (NCs) mainly include metal nanocrystals, semiconductor nanocrystals, and insulator nanocrystals, exhibiting interesting size-dependent electrical, optical, magnetic, and chemical properties that cannot be achieved by their bulk counterparts. However, there’s a critical problem that NCs tend to aggregate, which induces degradation of their performance. Hyperbranched polymers (HPs) possess excellent attributes of three-dimensional topology, low viscosity, good solubility, and plenty of modifiable terminal groups. The combination of NCs and HPs to form nanohybrids cannot only endow NCs with multifunctionality, uniform dispersibility, and splendid solubility but also can impart extra properties to HPs. This article reviews the recent progress and state-of-the-art of the synthesis and applications of NCs-HPs nanohybrids (NHBs). NHBs can be obtained by three approaches: HPs first (i.e., NCs are formed with the stabilizer of HPs), NCs first (i.e., HPs are grafted on the surface of as-prepared NCs), and ligand exchange (the original ligand of NCs is replaced with HPs). Various HPs including hyperbranched poly(amidoamine), polyethylenimine, polyglycerol, polyester, polyamide, polyurethane, and poly(3-ethyl-3-hydroxymethyloxetane), as well as sorts of NCs such as metals (e.g., Ag, Au, Pd, Pt, and Rh), quantum dots (e.g., ZnO, CdS, CdTe, CdSe, and SnO₂), magnetic oxides (e.g., Fe₃O₄), rare earth compounds, and so forth, have been used to obtain NHBs. The NHBs can be applied in nanocatalysis, antimicrobia, biosensor, biological labeling, and other fields promising their bright future.     

Capillary electrophoretic separation of nanoparticles

In the present work, CdSe nanocrystals (NCs) synthesized with a trioctylphosphine surface passivation layer were modified using amphiphilic molecules to form a surface bilayer capable of providing stable NCs aqueous solutions. Such modified nanocrystals were used as a test solute in order to analyze new electrophoretic phenomena, by applying a micellar plug as a separation tool for discriminating nanocrystals between micellar and micelle-free zones during electrophoresis. The distribution of NCs between both zones depended on the affinity of nanocrystals towards the micellar zone, and this relies on the kind of surface ligands attached to the NCs, as well as electrophoretic conditions applied. In this case, the NCs that migrated within a micellar zone can be focused using a preconcentration mechanism. By modifying electrophoretic conditions, NCs were forced to migrate outside the micellar zone in the form of a typical CZE peak. In this situation, a two-order difference in separation efficiencies, in terms of theoretical plates, was observed between focused NCs (N ~ 10⁷) and a typical CZE peak for NCs (N ~ 10⁵). By applying the amino-functionalized NCs the preconcentration of NCs, using a micellar plug, was examined, with the conclusion that preconcentration efficiency, in terms of the enhancement factor for peak height (SEF_height) can be, at least 20. The distribution effect was applied to separate CdSe/ZnS NCs encapsulated in silica, as well as surface-modified with DNA, which allows the estimation of the yield of conjugation of biologically active molecules to a particle surface.     

Impact of Zn-doping on the composition,stability, luminescence properties of silica coated all-inorganic cesium lead bromide nanocrystals and their biocompatibility

Cesium lead halide (CsPbX₃: X = I, Br, Cl) nanocrystals (NCs) are believed to be potential candidates for bioimaging applications. However, their low structural stability against polar solvents remains as a major limitation. To improve the NCs stability and maintain high emission intensity, we synthesized silica coated Zn-doped core@shell perovskite NCs via modified ligand assisted reprecipitation (LARP) synthetic method under relatively high humid condition. We systemically varied the composition inside the perovskite structure and then studied their photophysical properties and stability. Interestingly, the Zn-doping amount controls the ratio of CsPbBr₃ to Cs₄PbBr₆ perovskites inside the core and also facilitates the growth of (OA)₂PbBr₄ shell, enables overall increase in NCs emission intensity and stability. We observed green color emission from these NCs in the spectral range of 494-506 nm with a maximum photoluminescence quantum yield (PLQY) up to 88%. The optimized Zn-doped NCs exhibited nearly four times better water stability compared to the bare NCs and retain emission properties for several months even in highly polar solvents. Finally, we performed biocompatibility test of the NCs generated on biological samples and hydroponics test in a gardenia leaf for their potential bioimaging applications.     

SnFe2O4 Nanocrystals as Highly Efficient Catalysts for Hydrogen‐Peroxide Sensing

SnFe₂O₄ nanocrystals (NC), prepared with a simple one‐step carrier‐solvent‐assisted interfacial reaction process, were developed as highly efficient catalysts for hydrogen peroxide sensing. These NCs, with a size of around 7 nm, served as the sensing catalyst and were decorated onto the pore surfaces of a porous fluorine‐doped tin oxide (PFTO) host electrode, prepared from commercial FTO glass with a simple anodic treatment, to form the sensing electrode for hydrogen peroxide. The SnFe₂O₄ NCs‐loaded PFTO electrode exhibited an ultra‐high sensitivity of 1027 mA m ^?1 cm^?2 toward hydrogen peroxide, outperforming Pt NCs‐loaded PFTO electrodes. The SnFe₂O₄ NCs‐loaded PFTO electrode proved a promising relatively low cost, high performance sensing electrode for hydrogen peroxide.     

Highly Luminescent Cesium Lead Halide Perovskite Nanocrystals with Tunable Composition and Thickness by Ultrasonication

We describe the simple, scalable, single‐step, and polar‐solvent‐free synthesis of high‐quality colloidal CsPbX₃ (X=Cl, Br, and I) perovskite nanocrystals (NCs) with tunable halide ion composition and thickness by direct ultrasonication of the corresponding precursor solutions in the presence of organic capping molecules. High angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) revealed the cubic crystal structure and surface termination of the NCs with atomic resolution. The NCs exhibit high photoluminescence quantum yields, narrow emission line widths, and considerable air stability. Furthermore, we investigated the quantum size effects in CsPbBr₃ and CsPbI₃ nanoplatelets by tuning their thickness down to only three to six monolayers. The high quality of the prepared NCs (CsPbBr₃) was confirmed by amplified spontaneous emission with low thresholds. The versatility of this synthesis approach was demonstrated by synthesizing different perovskite NCs.     

Facile Synthesis of PdCu Echinus‐Like Nanocrystals as Robust Electrocatalysts for Methanol Oxidation Reaction

Exploiting high‐performance and inexpensive electrocatalysts for methanol electro‐oxidation is conductive to promoting the commercial application of direct methanol fuel cells. Here, we present a facile synthesis of echinus‐like PdCu nanocrystals (NCs) via a one‐step and template‐free method. The echinus‐like PdCu NCs possess numerous straight and long branches which can provide abundant catalytic active sites. Owing to the novel nanoarchitecture and electronic effect of the PdCu alloy, the echinus‐like PdCu NCs display high electrocatalytic performance toward methanol oxidation reaction in an alkaline medium. The mass activity of echinus‐like PdCu NCs is 1202.1 mA mg_Pd^?1, which is 3.7 times that of Pd/C catalysts. In addition, the echinus‐like structure, as a kind of three‐dimensional self‐supported nanoarchitecture, endows PdCu NCs with significantly enhanced stability and durability. Hence, the echinus‐like PdCu NCs hold prospect of being employed as electrocatalysts for direct alcohol fuel cells.     

Nitrogen-doped TiO2 Nanocrystals for Highly Sensitive Electrochemical Immunoassay of Carcinoembryonic Antigen

Nitrogen-doped TiO₂ nanocrystals (N−TiO₂ NCs) were simply synthesized and then functionalized with streptavidin for highly sensitive electrochemical immunoassay of tumor marker. Scanning electron microscopy, transmission electron microscopy, static water contact angle, and cyclic voltametric measurement were adapted to examine the properties of N−TiO₂ NCs and resultant immunosensor. The functionalized N−TiO₂ NCs sensing platform shows high electrochemical conductivity, large surface area and excellent hydrophilicity. The features make them to produce high current response, capture more antibody molecules, and maintain the bioactivity of immobilized antibodies. By means of carcinoembryonic antigen (CEA) as model tumor marker, a wide linear range of 0.005–3 ng/mL and a low detection limit of 0.005 ng/mL (signal-to-noise ratio of 3) were achieved by the proposed CEA immunosensor. Furthermore, the resultant CEA immunosensor displays high specificity and was employed to determine CEA in clinical serum samples.     

CdTe nanocrystals sensitized chemiluminescence and the analytical application

It was found that the mixing of CdTe semiconductor nanocrystals (NCs) with luminol in the presence of KMnO₄ can induce a great sensitized effect on chemiluminescence (CL) emission. When the concentration of luminol, KMnO₄ and NaOH were fixed at 1 μM, 1 μM and 0.05 M, respectively, the most excellent performance can be obtained for the CdTe NCs sensitized CL. By means of CL and photoluminescence spectra, we suppose the enhanced CL signals resulted from the accelerated luminol CL induced by the oxidized species of CdTe NCs. Based on the finding, using thioglycolic acid-capped CdTe NCs as label and immunoglobulin G (IgG) as a model analyte, a CL immunoassay protocol for IgG content detection was developed. The strong inhibition effect of phenol compounds on luminol-KMnO₄-CdTe NCs CL system was also observed. All these findings demonstrated the possibility of semiconductor nanocrystals induced chemiluminescence to be utilized for more practical applications.     

Mechanism of Phosphine Borane Deprotection with Amines: The Effects of Phosphine,Solvent and Amine on Rate and Efficiency

The kinetics of borane transfer from simple tertiary phosphine borane adducts to a wide range of amines have been determined. All data obtained, including second‐order kinetics, lack of cross‐over, and negative entropies of activation for reaction of triphenylphosphine borane with quinuclidine and triethylamine, are consistent with a direct (S_N2‐like) transfer process, rather than a dissociative (S_N1‐like) process. The identities of the amine, phosphine, and solvent all impact substantially on the rate (k) and equilibrium (K) of the transfer, which in some cases vary by many orders of magnitude. P‐to‐N transfer is more efficient with cyclic amines in apolar solvents due to reduced entropic costs and ground‐state destabilisation. Taken as a whole, the data allow informed optimisation of the deprotection step from the stand‐point of rate, or synthetic convenience. In all cases, both reactants should be present at high initial concentration to gain kinetic benefit from the bimolecularity of the process. Ultimately, the choice of amine is dictated by the identity of the phosphine borane complex. Aryl‐rich phosphine boranes are sufficiently reactive to allow use of diethylamine or pyrrolidine as a volatile low polarity solvent and reactant, whereas more alkyl‐rich phosphines benefit from the use of more reactive amines, such as 1,4‐diaza[2.2.2]bicyclooctane (DABCO), in apolar solvents at higher temperatures.     

Heterochiral Self-Discrimination-Driven Supramolecular Self-Assembly of Decanuclear Gold(I)-Sulfido Complexes into 2D Nanostructures with Chiral Anions-Tuned Morphologies

Chiral self-recognition and self-discrimination are of vital importance to biological processes. In this work, 2D regular rhombic nanocrystals ( RS -NC ) were fabricated through heterochiral self-discrimination between chiral polynuclear gold(I)-sulfido complex enantiomers, [(R-BINAP)₄Au₁₀S₄]Cl₂ ( R -Au₁₀ ) and [(S-BINAP)₄Au₁₀S₄]Cl₂ ( S -Au₁₀ ), in MeOH without the need for any surfactants or templates. The monitoring of nanocrystals (NCs) formation by TEM and DLS has uncovered the self-assembly process and shape evolution of the NCs and revealed a screw-dislocation dictated spiral growth of the rhombic NCs. Upon addition of chiral anions, the morphology of the gold NCs was found to change from rhombic to strip and quasi-hexagonal nanosheets, arising from reverse and rotational layer-by-layer stacking to give the bilayer NCs. By applying a high temperature, rhombic gold nanoisland films were obtained from the rhombic NCs. The current study has provided a simple strategy towards the construction of regular geometric 2D NCs as well as their chiral anion-tuned and reverse and rotational stacking-determined morphology change by heterochiral self-discrimination.     

Emergence of Visible-Light Water Oxidation Upon Hexaniobate-Ligand Entrapment of Quantum-Confined Copper-Oxide Cores

The formation of small 1 to 3 nm organic-ligand free metal-oxide nanocrystals (NCs) is essential to utilization of their attractive size-dependent properties in electronic devices and catalysis. We now report that hexaniobate cluster-anions, [Nb₆O₁₉]⁸⁻, can arrest the growth of metal-oxide NCs and stabilize them as water-soluble complexes. This is exemplified by formation of hexaniobate-complexed 2.4-nm monoclinic-phase CuO NCs ( 1 ), whose ca. 350 Cu-atom cores feature quantum-confinement effects that impart an unprecedented ability to catalyze visible-light water oxidation with no added photosensitizers or applied potentials, and at rates exceeding those of hematite NCs. The findings point to polyoxoniobate-ligand entrapment as a potentially general method for harnessing the size-dependent properties of very small semiconductor NCs as the cores of versatile, entirely-inorganic complexes.     

Surface Functionalization of Micro Mechanical Cantilever Sensors by Organic Capped TiO2 and Fe2O3 Nanocrystals

A convenient and rapid procedure has been achieved to immobilize densely packed nanoporous 3D arrays of oleic acid (OLEA)-capped rod-shaped TiO₂ nanocrystals (NCs) and nearly spherical Fe₂O₃ NCs on the surface of micro mechanical cantilever sensors on SU-8. The NCs have been immobilized at room temperature and in the dark on the micro cantilevers before their release. AFM, SEM and XPS investigations attest for an effective and attachment of the NCs on the SU-8 which occurs with not modifying the original morphology and chemical composition of the nano-objects allowing for an effective accomplishment of the cantilever fabrication.     

Colloidal Synthesis and Optical Properties of All‐Inorganic Low‐Dimensional Cesium Copper Halide Nanocrystals

Low‐dimensional metal halides have recently attracted extensive attention owing to their unique structure and photoelectric properties. Herein, we report the colloidal synthesis of all‐inorganic low‐dimensional cesium copper halide nanocrystals (NCs) by adopting a hot‐injection approach. Using the same reactants and ligands, but different reaction temperatures, both 1D CsCu₂I₃ nanorods and 0D Cs₃Cu₂I₅ NCs can be prepared. Density functional theory indicates that the reduced dimensionality in 1D CsCu₂I₃ compared to 0D Cs₃Cu₂I₅ makes the excitons more localized, which accounts for the strong emission of 0D Cs₃Cu₂I₅ NCs. Subsequent optical characterization reveals that the highly luminescent, strongly Stokes‐shifted broadband emission of 0D Cs₃Cu₂I₅ NCs arises from the self‐trapped excitons. Our findings not only present a method to control the synthesis of low‐dimensional cesium copper halide nanocrystals but also highlight the potential of 0D Cs₃Cu₂I₅ NCs in optoelectronics.     

Preparation of CdS nanocrystals within supramolecular self-assembled nanoreactors and their phase transfer behavior

A new strategy for the synthesis of CdS nanocrystals (NCs) within supramolecular self-assembly nanoreactors has been described. The self-assembly nanoreactors were readily constructed through the electrostatic interactions and ion pairs between palmitic acid and the terminal amine groups of hyperbranched polymer. In a chloroform/water two-phase system, aqueous Cd (2+) ions were spontaneously encapsulated into the cavities of self-assembly nanoreactors in chloroform. After reaction with S (2-) ions, the CdS NCs with high stability were obtained. By the addition of excess triethylamine, CdS NCs formed in the self-assembly nanoreactors were transferred from organic phase into aqueous phase. After dialysis and rotorary evaporation, aqueous CdS NCs could be redispersed into chloroform solution containing palmitic acid.     

Completely Amine-Free Open-Atmospheric Synthesis of High-Quality Cesium Lead Bromide (CsPbBr3) Perovskite Nanocrystals

Cesium lead halide perovskite nanocrystals (NCs) CsPbX₃ (X=Cl, Br, and I) have been prominent materials in the last few years due to their high photoluminescence quantum yield (PLQY) for light-emitting diodes and other significant applications in photovoltaics and optoelectronics. In colloidal CsPbX₃ synthesis, the most commonly used ligands are oleic acid and oleylamine. The latter plays an important role in surface passivation but may also be responsible for poor colloidal stability as a result of facile proton exchange leading to the formation of labile oleylammonium halide, which pulls halide ions out of the NC surface. Herein, a facile, efficient, completely amine-free synthesis of cesium lead bromide perovskite nanocrystals using hydrobromic acid as halide source and tri-n-octylphosphane as ligand under open-atmospheric conditions is demonstrated. Hydrobromic acid serves as labile source of bromide ion, and thus this three-precursor approach (separate precursors for Cs, Pb, Br) gives more control than a conventional single-source precursor for Pb and Br (PbBr₂). The use of HBr paved the way to eliminate oleylamine, and thus the formation of labile oleylammonium halide can be completely excluded. Various Cs:Pb:Br molar ratios were studied and optimum conditions for making very stable CsPbBr₃ NCs with high PLQY were found. These completely amine-free CsPbBr₃ perovskite NCs synthesized under bromine-rich conditions exhibit good stability and durability for more than three months in the form of colloidal solutions and films, respectively. Furthermore, stable tunable emission across a wide spectral range through anion exchange was demonstrated. More importantly, this work reports open-atmosphere-stable CsPbBr₃ NCs films exhibiting strong PL, which can be further used for optoelectronic device applications.     

Epitaxial Seeded Growth of Rare‐Earth Nanocrystals with Efficient 800 nm Near‐Infrared to 1525 nm Short‐Wavelength Infrared Downconversion Photoluminescence for In Vivo Bioimaging

Novel β‐NaGdF₄/Na(Gd,Yb)F₄:Er/NaYF₄:Yb/NaNdF₄:Yb core/shell 1/shell 2/shell 3 (C/S1/S2/S3) multi‐shell nanocrystals (NCs) have been synthesized and used as probes for in vivo imaging. They can be excited by near‐infrared (800 nm) radiation and emit short‐wavelength infrared (SWIR, 1525 nm) radiation. Excitation at 800 nm falls into the “biological transparency window”, which features low absorption by water and low heat generation and is considered to be the ideal excitation wavelength with the least impact on biological tissues. After coating with phospholipids, the water‐soluble NCs showed good biocompatibility and low toxicity. With efficient SWIR emission at 1525 nm, the probe is detectable in tissues at depths of up to 18 mm with a low detection threshold concentration (5 nM for the stomach of nude mice and 100 nM for the stomach of SD rats). These results highlight the potential of the probe for the in vivo monitoring of areas that are otherwise difficult to analyze.     

Synthesis of double perovskite and quadruple perovskite nanocrystals through post-synthetic transformation reactions

Lead-free halide perovskite nanocrystals (NCs) represent a group of emerging materials which hold promise for various optical and optoelectronic applications. Exploring facile synthetic methods for such materials has been of great interest to not only fundamental research but also technological implementations. Herein, we report a fundamentally new method to access lead-free Bi-based double perovskite (DP) and quadruple perovskite (or layered double perovskite, LDP) NCs based on a post-synthetic transformation reaction of Cs₃BiX₆ (X = Cl, Br) zero-dimensional (0D) perovskite NCs under mild conditions. The produced NCs show good particle uniformity, high crystallinity, and comparable optical properties to the directly synthesized NCs. The relatively slow kinetics and stop-on-demand feature of the transformation reaction allow real-time composition–structure–property investigations of the reaction, thus elucidating a cation-alloyed intermediate-assisted transformation mechanism. Our study presented here demonstrates for the first time that post-synthetic transformation of 0D perovskite NCs can serve as a new route towards the synthesis of high-quality lead-free perovskite NCs, and provides valuable insights into the crystal structures, excitonic properties and their relationships of perovskite NCs.

Lead-free perovskite nanocrystals are synthesized by post-synthetic transformation reactions. The post-synthetic transformations show the structural flexibility of zero-dimensional perovskite nanocrystal materials.     

Stabilizing RbPbBr3 Perovskite Nanocrystals through Cs+ Substitution

ABX₃-type halide perovskite nanocrystals (NCs) have been a hot topic recently due to their fascinating optoelectronic properties. It has been demonstrated that A-site ions have an impact on their photophysical and chemical properties, such as the optical band gap and chemical stability. The pursuit of halide perovskite materials with diverse A-site species would deepen the understanding of the structure–property relationship of the perovskite family. In this work we have attempted to synthesize rubidium-based perovskite NCs. We have discovered that the partial substitution of Rb⁺ by Cs⁺ help to stabilize the orthorhombic RbPbBr₃ NCs at low temperature, which otherwise can only be obtained at high temperature. The inclusion of Cs⁺ into the RbPbBr₃ lattice results in highly photoluminescent Rb_1−xCs_xPbBr₃ NCs. With increasing amounts of Cs⁺, the band gaps of the Rb_1−xCs_xPbBr₃ NCs decrease, leading to a redshift of the photoluminescence peak. Also, the Rb_1−xCs_xPbBr₃ NCs (x=0.4) show good stability under ambient conditions. This work demonstrates the high structural flexibility and tunability of halide perovskite materials through an A-site cation substitution strategy and sheds light on the optimization of perovskite materials for application in high-performance optoelectronic devices.