Growth Mechanism and Surface State of CuInS2 Nanocrystals Synthesized with Dodecanethiol

Rigid CuInS2/ZnS Core/Shell Quantum Dots for High Performance Infrared Light-Emitting Diodes

CuInS2 (CIS) quantum dots (QDs) represent an important class of colloidal materials with broad application potential, owing to their low toxicity and unique optical properties. Although coating with a ZnS shell has been identified as a crucial method to enhance optical performance, the occurrence of cation exchange has historically resulted in the unintended formation of Cu-In-Zn-S alloyed QDs, causing detrimental blueshifts in both absorption and photoluminescence (PL) spectral profiles. In this study, we present a facile one-pot synthetic strategy aimed at impeding the cation exchange process and promoting ZnS shell growth on CIS core QDs. The suppression of both electron-phonon interaction and Auger recombination by the rigid ZnS shell results in CIS/ZnS core/shell QDs that exhibit a wide near-infrared (NIR) emission coverage and a remarkable PL quantum yield of 92.1%. This effect boosts the fabrication of high-performance, QD-based NIR light-emitting diodes with the best stability of such materials so far.

Fabrication of CuInZnS/ZnS Quantum Dot Microbeads by a Two-Step Approach of Emulsification-Solvent Evaporation and Surfactant Substitution and Its Application for Quantitative Detection

CuInS2 quantum dots (CIS QDs) are considered to be promising alternatives for Cd-based QDs in the fields of biology and medicine. However, high-quality hydrophobic CIS QDs are difficult to be transferred to water due to their 1-dodecylmercaptan (DDT) ligands. Therefore, the fluorescence and stability of the prepared aqueous CIS QDs is not enough to meet the requirement for sensitive detection. Here, as large as 13 nm CuInZnS/ZnS QDs with DDT ligands were first synthesized, and then, CuInZnS/ZnS microbeads (QBs) containing thousands of QDs were successfully fabricated by a two-step approach of emulsion-solvent evaporation and surfactant substitution. Through emulsion-solvent evaporation, the CuInZnS/ZnS QDs formed microbeads in the microemulsion with dodecyl trimethylammonium bromide (DTAB), and the Förster resonance energy transfer (FRET) has been effectively overcome. Then, CO-520 was introduced to substitute DTAB to improve the stability and water solubility. Lastly, the microbeads were coated with a SiO2 shell and carboxylated. Subsequently, the constructed QBs (∼210 nm) were used as labels in a fluorescence immunosorbent assay (FLISA) for quantitative detection of heart type fatty acid binding protein (H-FABP), and the limit of detection was 0.48 ng mL-1, which indicated a greatly improved detection sensitivity compared to that of the Cd-free QDs. The highly fluorescent and stable CuInZnS/ZnS QBs will have great application prospects in many biological fields.

Multipod Bi(Cu2-xS)n Nanocrystals formed by Dynamic Cation-Ligand Complexation and Their Use as Anodes for Potassium-Ion Batteries

We report the formation of an intermediate lamellar Cu-thiolate complex, and tuning its relative stability using alkylphosphonic acids are crucial to enabling controlled heteronucleation to form Bi(Cu_2-xS)_n heterostructures with a tunable number of Cu_2-xS stems on a Bi core. The denticity of the phosphonic acid group, concentration, and chain length of alkylphosphonic acids are critical factors determining the stability of the Cu-thiolate complex. Increasing the stability of the Cu-thiolate results in single Cu_2-xS stem formation, and decreased stability of the Cu-thiolate complex increases the degree of heteronucleation to form multiple Cu_2-xS stems on the Bi core. Spatially separated multiple Cu_2-xS stems transform into a support network to hold a fragmented Bi core when used as an anode in a K-ion battery, leading to a more stable cycling performance showing a specific capacity of ∼170 mAh·g^-1 after 200 cycles compared to ∼111 mAh·g^-1 for Bi-Cu_2-xS single-stem heterostructures.

Copper Phosphonate Lamella Intermediates Control the Shape of Colloidal Copper Nanocrystals

Understanding the structure and behavior of intermediates in chemical reactions is the key to developing greater control over the reaction outcome. This principle is particularly important in the synthesis of metal nanocrystals (NCs), where the reduction, nucleation, and growth of the reaction intermediates will determine the final size and shape of the product. The shape of metal NCs plays a major role in determining their catalytic, photochemical, and electronic properties and, thus, the potential applications of the material. In this work, we demonstrate that layered coordination polymers, called lamellae, are reaction intermediates in Cu NC synthesis. Importantly, we discover that the lamella structure can be fine-tuned using organic ligands of different lengths and that these structural changes control the shape of the final NC. Specifically, we show that short-chain phosphonate ligands generate lamellae that are stable enough at the reaction temperature to facilitate the growth of Cu nuclei into anisotropic Cu NCs, being primarily triangular plates. In contrast, lamellae formed from long-chain ligands lose their structure and form spherical Cu NCs. The synthetic approach presented here provides a versatile tool for the future development of metal NCs, including other anisotropic structures.

Entropy of Branching Out: Linear versus Branched Alkylthiols Ligands on CdSe Nanocrystals

Surface ligands of semiconductor nanocrystals (NCs) play key roles in determining their colloidal stability and physicochemical properties and are thus enablers also for the NCs flexible manipulation toward numerous applications. Attention is usually paid to the ligand binding group, while the impact of the ligand chain backbone structure is less discussed. Using isothermal titration calorimetry (ITC), we studied the effect of structural changes in the ligand chain on the thermodynamics of the exchange reaction for oleate coated CdSe NCs, comparing linear and branched alkylthiols. The investigated alkylthiol ligands differed in their backbone length, branching position, and branching group length. Compared to linear ligands, lower exothermicity and entropy loss were observed for an exchange with branched ligands, due to steric hindrance in ligand packing, thereby justifying their previous classification as "entropic ligands". Mean-field calculations for ligand binding demonstrate the contribution to the overall entropy originating from ligand conformational entropy, which is diminished upon binding mainly by packing of NC-bound ligands. Model calculations and the experimental ITC data both point to an interplay between the branching position and the backbone length in determining the entropic nature of the branched ligand. Our findings suggest that the most entropic ligand should be a short, branched ligand with short branching group located toward the middle of the ligand chain. The insights provided by this work also contribute to a future smarter NC surface design, which is an essential tool for their implementation in diverse applications.

Synthesis and Optical Properties of In2S3-Hosted Colloidal Zn-Cu-In-S Nanoplatelets

High-efficiency photoluminescence quaternary hexagon Zn-Cu-In-S (ZCIS) nanoplatelets (NPls) have been synthesized by a two-step cation exchange method, which starts with the In₂S₃ NPls followed by the addition of Cu and Zn. It is the first time that In₂S₃ NPls are used as templates to synthesize ZCIS NPls. In this paper, the reaction temperature of In₂S₃ is essential for the formation of NPls. The photoluminescence wavelength of NPls can be tuned by adjusting the temperature of Cu addition. To enhance the stability of the resulting NPls and to improve their optical properties, we introduced Zn²⁺ and obtained ZCIS NPls by cation exchange on the surface. It is worth noting that the obtained ZCIS NPls show a shorter fluorescence lifetime than other ternary copper sulfide-based NPls. This work provides a new way to synthesize high-efficiency, nontoxic, and no byproduct ZCIS NPls.

Magnetic and Highly Luminescent Heterostructures of Gd3+/ZnO Conjugated to GCIS/ZnS Quantum Dots for Multimodal Imaging

In recent years, the use of quantum dots (Qdots) to obtain biological images has attracted attention due to their excellent luminescent properties and the possibility of their association with contrast agents for magnetic resonance imaging (MRI). In this study, Gd³⁺/ZnO (ZnOGd) were conjugated with Qdots composed of a gadolinium-copper-indium-sulphur core covered with a ZnS shell (GCIS/ZnS Qdots). This conjugation is an innovation that has not yet been described in the literature, and which aims to improve Qdot photoluminescent properties. Structural and morphological Qdots features were obtained by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analyses (TGA). The photoluminescent properties were examined by emission (PL) and excitation (PLE) spectra. A new ZnOGd and GCIS/ZnS (ZnOGd-GCIS/ZnS) nanomaterial was synthesized with tunable optical properties depending on the ratio between the two native Qdots. A hydrophilic or lipophilic coating, using 3-glycidyloxypropyltrimethoxysilane (GPTMS) or hexadecyltrimethoxysilane (HTMS) on the surface of ZnOGd-GCIS/ZnS Qdots, was carried out before assessing their efficiency as magnetic resonance contrast agents. ZnOGd-GCIS/ZnS had excellent luminescence and MRI properties. The new Qdots developed ZnOGd-GCIS/ZnS, mostly constituted of ZnOGd (75%), which had less cytotoxicity when compared to ZnOGd, as well as greater cellular uptake.

Recent research on the luminous mechanism, synthetic strategies, and applications of CuInS2 quantum dots

We discuss the synthesis and luminescence mechanisms of CuInS₂ QDs, the strategies to improve their luminous performance and their potential application in light-emitting devices, solar energy conversion, and the biomedical field.

Shaping non-noble metal nanocrystals via colloidal chemistry

Non-noble metal nanocrystals with well-defined shapes have been attracting increasingly more attention in the last decade as potential alternatives to noble metals, by virtue of their earth abundance combined with intriguing physical and chemical properties relevant for both fundamental studies and technological applications. Nevertheless, their synthesis is still primitive when compared to noble metals. In this contribution, we focus on third row transition metals Mn, Fe, Co, Ni and Cu that are recently gaining interest because of their catalytic properties. Along with providing an overview on the state-of-the-art, we discuss current synthetic strategies and challenges. Finally, we propose future directions to advance the synthetic development of shape-controlled non-noble metal nanocrystals in the upcoming years.

Simple Synthesis of CuInS2/ZnS Core/Shell Quantum Dots for White Light-Emitting Diodes

In this study, the CuInS₂/ZnS core/shell quantum dots (QDs) were prepared via simple and environmentally friendly solvothermal synthesis and were used as phosphors for white light-emitting diodes (WLEDs). The surface defect of the CuInS₂ core QDs were passivated by the ZnS shell by forming CuInS₂/ZnS core/shell QDs. By adjusting the Cu/In ratio and the nucleation temperature, the photoluminescence (PL) peak of the CuInS₂ QDs was tunable in a range of 651-775 nm. After coating the ZnS layer and modifying oleic acid ligands, the PL quantum yield increased to 85.06%. The CuInS₂/ZnS QD powder thermal stability results showed that the PL intensity of the QDs remained 91% at 100°C for 10 min. High color rendering index values (CRI, 90) and correlated color temperature of 4360 K for the efficient WLEDs were fabricated using CuInS₂/ZnS QDs and (Ba,Sr)₂SiO₄:Eu²⁺ as color converters in combination with a blue GaN light-emitting diode chip.

Multinary copper-based chalcogenide nanocrystal systems from the perspective of device applications

Multinary chalcogenide semiconductor nanocrystals are a unique class of materials as they offer flexibility in composition, structure, and morphology for controlled band gap and optical properties. They offer a vast selection of materials for energy conversion, storage, and harvesting applications. Among the multinary chalcogenides, Cu-based compounds are the most attractive in terms of sustainability as many of them consist of earth-abundant elements. There has been immense progress in the field of Cu-based chalcogenides for device applications in the recent years. This paper reviews the state of the art synthetic strategies and application of multinary Cu-chalcogenide nanocrystals in photovoltaics, photocatalysis, light emitting diodes, supercapacitors, and luminescent solar concentrators. This includes the synthesis of ternary, quaternary, and quinary Cu-chalcogenide nanocrystals. The review also highlights some emerging experimental and computational characterization approaches for multinary Cu-chalcogenide semiconductor nanocrystals. It discusses the use of different multinary Cu-chalcogenide compounds, achievements in device performance, and the recent progress made with multinary Cu-chalcogenide nanocrystals in various energy conversion and energy storage devices. The review concludes with an outlook on some emerging and future device applications for multinary Cu-chalcogenides, such as scalable luminescent solar concentrators and wearable biomedical electronics.

Machado W, Wegner KD, Gontijo LAP, Bettini J, Schiavon MA, Reiss P, Aldakov D. Hydrothermal Synthesis of Aqueous-Soluble Copper Indium Sulfide Nanocrystals and Their Use in Quantum Dot Sensitized Solar Cells

A facile hydrothermal method to synthesize water-soluble copper indium sulfide (CIS) nanocrystals (NCs) at 150 °C is presented. The obtained samples exhibited three distinct photoluminescence peaks in the red, green and blue spectral regions, corresponding to three size fractions, which could be separated by means of size-selective precipitation. While the red and green emitting fractions consist of 4.5 and 2.5 nm CIS NCs, the blue fraction was identified as in situ formed carbon nanodots showing excitation wavelength dependent emission. When used as light absorbers in quantum dot sensitized solar cells, the individual green and red fractions yielded power conversion efficiencies of 2.9% and 2.6%, respectively. With the unfractionated samples, the efficiency values approaching 5% were obtained. This improvement was mainly due to a significantly enhanced photocurrent arising from complementary panchromatic absorption.

Polymer Lamellae as Reaction Intermediates in the Formation of Copper Nanospheres as Evidenced by In Situ X-ray Studies

The classical nucleation theory (CNT) is the most common theoretical framework used to explain particle formation. However, nucleation is a complex process with reaction pathways which are often not covered by the CNT. Herein, we study the formation mechanism of copper nanospheres using in situ X-ray absorption and scattering measurements. We reveal that their nucleation involves coordination polymer lamellae as pre-nucleation structures occupying a local minimum in the reaction energy landscape. Having learned this, we achieved a superior monodispersity for Cu nanospheres of different sizes. This report exemplifies the importance of developing a more realistic picture of the mechanism involved in the formation of inorganic nanoparticles to develop a rational approach to their synthesis.

New Unsymmetrical Bisacridine Derivatives Noncovalently Attached to Quaternary Quantum Dots Improve Cancer Therapy by Enhancing Cytotoxicity toward Cancer Cells and Protecting Normal Cells

The use of nanoparticles for the controlled drug delivery to cells has emerged as a good alternative to traditional systemic delivery. Quantum dots (QDs) offer potentially invaluable societal benefits such as drug targeting and in vivo biomedical imaging. In contrast, QDs may also pose risks to human health and the environment under certain conditions. Here, we demonstrated that a unique combination of nanocrystals core components (Ag-In-Zn-S) would eliminate the toxicity problem and increase their biomedical applications. The alloyed quaternary nanocrystals Ag-In-Zn-S (QD_green, Ag_1.0In_1.2Zn_5.6S_9.4; QD_red, Ag_1.0In_1.0Zn_1.0S_3.5) were used to transport new unsymmetrical bisacridine derivatives (UAs, C-2028 and C-2045) into lung H460 and colon HCT116 cancer cells for improving the cytotoxic and antitumor action of these compounds. UAs were coupled with QD through physical adsorption. The obtained results clearly indicate that the synthesized nanoconjugates exhibited higher cytotoxic activity than unbound compounds, especially toward lung H460 cancer cells. Importantly, unsymmetrical bisacridines noncovalently attached to QD strongly protect normal cells from the drug action. It is worth pointing out that QD_green or QD_red without UAs did not influence the growth of cancer and normal cells, which is consistent with in vivo results. In noncellular systems, at pH 5.5 and 4.0, which relates to the conditions of endosomes and lysosomes, the UAs were released from QD-UAs nanoconjugates. An increase of total lysosomes content was observed in H460 cells treated with QDs-UAs which can affect the release of the UAs from the conjugates. Moreover, confocal laser scanning microscopy analyses revealed that QD-UAs nanoconjugates enter H460 cells more efficiently than to HCT116 and normal cells, which may be the reason for their higher cytotoxicity against lung cancer. Summarizing, the noncovalent attachment of UAs to QDs increases the therapeutic efficiency of UAs by improving cytotoxicity toward lung H460 cancer cells and having protecting effects on normal cells.

Gram-Scale Synthesis of Tetrahedrite Nanoparticles and Their Thermoelectric Properties

Here, we report a method for facile gram-scale synthesis of tetrahedrite (Cu₁₂Sb₄S₁₃) nanoparticles (NPs) with high quality and good reproducibility. The obtained NPs had a well-defined tetrahedral shape with a mean edge length of ∼70 nm. We sintered the NPs by the hot press technique to fabricate a nanostructured pellet for thermoelectric measurements. The figure of merit (ZT) value of the pellet was 0.52 at 675 K, which was comparable with the ZT value of the non-nanostructured counterpart.

Insights into Reaction Intermediates to Predict Synthetic Pathways for Shape-Controlled Metal Nanocrystals

Understanding nucleation phenomena is crucial across all branches of physical and natural sciences. Colloidal nanocrystals are among the most versatile and tunable synthetic nanomaterials. While huge steps have been made in their synthetic development, synthesis by design is still impeded by the lack of knowledge of reaction mechanisms. Here, we report on the investigation of the reaction intermediates in high temperature syntheses of copper nanocrystals by a variety of techniques, including X-ray absorption at a synchrotron source using a customized in situ cell. We reveal unique insights into the chemical nature of the reaction intermediates and into their role in determining the final shape of the metal nanocrystals. Overall, this study highlights the importance of understanding the chemistry behind nucleation as a key parameter to predict synthetic pathways for shape-controlled nanocrystals.

Correlation of near-unity quantum yields with photogenerated excitons in X-type ligand passivated CsPbBr3 perovskite quantum dots

We investigated the exciton decay dynamics of CsPbBr₃ perovskite quantum dots (PQDs) through an X-type ligand passivation process. 1-Dodecanethiol (DDT), as an X-type ligand, covers Br vacancies of PQDs and then the photoluminescence quantum yield (PLQY) sharply improved from 76.1% to 99.8%. Impressively, after passivation, the photoluminescence (PL) lifetime of PQDs decreased from 3.16 ns to 2.42 ns, contrary to the PLQY increase. To clarify this phenomenon, we observed exciton decay dynamics by varying the temperature. Thereby, we found that shallow traps from Br vacancies not only reduce the PLQY but also induce a longer lifetime related to the nonradiative exciton decay leading to an increase in the lifetime. Our results are novel and important in a way that we provide a systematic understanding of the exciton decay dynamics by combining two key concepts together: (1) near unity PLQY via ligand engineering and (2) temperature-dependent photogenerated excitons.

Synthesis and characterization of Ag2S and Ag2S/Ag2(S,Se) NIR nanocrystals

Syntheses of metal sulfide nanocrystals (NCs) by heat-up routes in the presence of thiols yield NC arrangements difficult to further functionalize and transfer to aqueous media. By means of different NMR techniques, and exemplified by Ag2S NCs, a metal-organic polymer formed during the synthesis acting as a ligand has been identified to be responsible for such aggregation. In this work, a new synthetic hot-injection strategy is presented to synthesize Ag2S NCs which are easily ligand exchangeable in water. Furthermore, the hot-injection route allows an extra NC treatment with Se to produce Ag2S/Ag2(S,Se) NCs with improved optical properties with respect to the Ag2S cores, and better resistance to oxidation, as demonstrated by X-ray absorption experiments.

Eco-Friendly Colloidal Quantum Dot-Based Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) have attracted significant attention as promising solar energy conversion devices for building integrated photovoltaic (PV) systems due to their simple architecture and cost-effective fabrication. Conventional LSCs are generally comprised of an optical waveguide slab with embedded emissive species and coupled PV cells. Colloidal semiconductor quantum dots (QDs) have been demonstrated as efficient emissive species for high-performance LSCs because of their outstanding optical properties including tunable absorption and emission spectra covering the ultraviolet/visible to near-infrared region, high photoluminescence quantum yield, large absorption cross sections, and considerable photostability. However, current commonly used QDs for high-performance LSCs consist of highly toxic heavy metals (i.e., cadmium and lead), which are fatal to human health and the environment. In this regard, it is highly desired that heavy metal-free and environmentally friendly QD-based LSCs are comprehensively studied. Here, notable advances and developments of LSCs based on unary, binary, and ternary eco-friendly QDs are presented. The synthetic approaches, optical properties of these eco-friendly QDs, and consequent device performance of QD-based LSCs are discussed in detail. A brief outlook pointing out the existing challenges and prospective developments of eco-friendly QD-based LSCs is provided, offering guidelines for future device optimizations and commercialization.

Water-Dispersible Copper Sulfide Nanocrystals via Ligand Exchange of 1-Dodecanethiol

In colloidal Cu_2-x S nanocrystal synthesis, thiols are often used as organic ligands and the sulfur source, as they yield high-quality nanocrystals. However, thiol ligands on Cu_2-x S nanocrystals are difficult to exchange, limiting the applications of these nanocrystals in photovoltaics, biomedical sensing, and photocatalysis. Here, we present an effective and facile procedure to exchange native 1-dodecanethiol on Cu_2-x S nanocrystals by 3-mercaptopropionate, 11-mercaptoundecanoate, and S^2- in formamide under inert atmosphere. The product hydrophilic Cu_2-x S nanocrystals have excellent colloidal stability in formamide. Furthermore, the size, shape, and optical properties of the nanocrystals are not significantly affected by the ligand exchange. Water-dispersible Cu_2-x S nanocrystals are easily obtained by precipitation of the nanocrystals capped by S^2-, 3-mercaptopropionate, or 11-mercaptoundecanoate from formamide, followed by redispersion in water. Interestingly, the ligand exchange rates for Cu_2-x S nanocrystals capped with 1-dodecanethiol are observed to depend on the preparation method, being much slower for Cu_2-x S nanocrystals prepared through heating-up than through hot-injection synthesis protocols. XPS studies reveal that the differences in the ligand exchange rates are due to the surface chemistry of the Cu_2-x S nanocrystals, where the nanocrystals prepared via hot-injection synthesis have a less dense ligand layer due to the presence of trioctylphosphine oxide during synthesis. A model is proposed that explains the observed differences in the ligand exchange rates. The facile ligand exchange procedures reported here enable the use of high-quality colloidal Cu_2-x S nanocrystals prepared in the presence of 1-dodecanethiol in various applications.

New Lamellar Silver Thiolate Coordination Polymers with Tunable Photoluminescence Energies by Metal Substitution

The structures of two lamellar silver thiolate coordination polymers [Ag( p-SPhCO₂H)] _n (1) and [Ag( p-SPhCO₂Me)] _n (2) are described for the first time. Their inorganic part is composed of distorted Ag₃S₃ honeycomb networks separated by noninterpenetrated thiolate ligands. The main difference between the two compounds arises from dimeric hydrogen bonds present for the carboxylic acids. Indepth photophysical studies show that the silver thiolates exhibit multiemission properties, implying luminescence thermochromism. More interestingly, the synthesis of a heterometallic lamellar compound, [Ag_0.85Cu_0.15( p-SPhCO₂H)] _n (3), allows to obtain mixed metal thiolate coordination polymers and to tune the photophysical properties with the excitation wavelengths from a green vibronic luminescence to a single red emission band.

Ultra-low loading of Pd5 nanoclusters on carbon nanotubes as bifunctional electrocatalysts for the oxygen reduction reaction and the ethanol oxidation reaction

How to reduce the usage of precious metals in electrocatalysts is a big challenge for the development of fuel cells. Metal nanoclusters (NCs) are highly desirable as active catalysts, but palladium nanoclusters (Pd NCs) have been less well developed than other metal clusters, such as gold, silver and copper, owing partly to the difficulties in size-controlled synthesis. Here, based on N, N-dimethylformamide (DMF)-mediation and ligand-exchange reaction, atomically precise Pd₅(C₁₂H₂₅S)₁₃ nanoclusters are successfully synthesized. By loading the as-prepared Pd₅ nanoclusters on multiwalled carbon nanotubes (MWCNTs) and the following pyrolysis to remove the thiolate ligands, the surface-cleaned Pd₅ clusters (Pd₅ NCs/MWCNTs) can serve as efficient electrocatalysts for the oxygen reduction reaction (ORR) and the ethanol oxidation reaction (EOR). With ultra-low mass loading of Pd (2%), the Pd₅ NCs showed higher mass and specific activities and better durability than the commercial Pd/C catalyst (5 wt%) for the ORR. At 0.8 V, the mass and specific activities of Pd₅ NCs/MWCNTs are 5.70 and 4.53 times higher than the commercial Pd/C catalyst, respectively. As for the EOR, the Pd₅ NCs/MWCNTs exhibited lower onset potential (0.39 V) and peak potential (0.81 V) than the commercial Pd/C catalyst (0.44 and 0.89 V). Electrochemical impedance spectroscopy (EIS) measurements indicated that for the EOR, the Pd₅ nanoclusters have a much smaller charge transfer resistance (R_ct) than the commercial Pd/C. The high-performance electrocatalytic properties of Pd₅ NCs for the ORR and EOR could be ascribed to the relatively high surface area-to-volume ratio and high density of exposed surface atoms of the Pd₅ nanoclusters.

Red light-driven photoelectrochemical biosensing for ultrasensitive and scatheless assay of tumor cells based on hypotoxic AgInS2 nanoparticles

A novel red light-driven photoelectrochemical (PEC) biosensing platform based on hypotoxic ternary mercaptopropionic acid (MPA)-capped AgInS₂ nanoparticles (NPs) with excellent hydrophily and biocompatibility was proposed. AgInS₂ NPs as a PEC sensing substrate exhibited high photon-to-current conversion efficiency under red light excitation, generating an intensive photocurrent for enhancing the sensitivity of PEC determination. After the introduction of the amino-terminated sgc8c aptamer onto the interface of AgInS₂ NPs, the overexpressed protein tyrosine kinase-7 on the surface of lymphoblast CCRF-CEM cells could be efficiently captured. Using CCRF-CEM cell as a model analyte, an ultrasensitive PEC biosensor for scatheless assay of cells at the applied potential of 0.15 V under a red light excitation of 630 nm was designed based on the significant decline of photocurrent intensity after capturing CCRF-CEM cells. The developed PEC cytosensor demonstrated an excellent cell-capture ability, as well as a wide linear range from 1.5 × 10² to 3.0 × 10⁵ cells/mL and a low detection limit of 16 cells/mL for CCRF-CEM cells. In addition, the resulting assay method verified high selectivity and negligible cytotoxicity for cells assay. This work provided an alternative method for scatheless assay of tumor cells, which would have promising prospect in clinical diagnoses of cancer.

In Situ X-ray Scattering Guides the Synthesis of Uniform PtSn Nanocrystals

Compared to monometallic nanocrystals (NCs), bimetallic ones often exhibit superior properties due to their wide tunability in structure and composition. A detailed understanding of their synthesis at the atomic scale provides crucial knowledge for their rational design. Here, exploring the Pt-Sn bimetallic system as an example, we study in detail the synthesis of PtSn NCs using in situ synchrotron X-ray scattering. We show that when Pt(II) and Sn(IV) precursors are used, in contrast to a typical simultaneous reduction mechanism, the PtSn NCs are formed through an initial reduction of Pt(II) to form Pt NCs, followed by the chemical transformation from Pt to PtSn. The kinetics derived from the in situ measurements shows fast diffusion of Sn into the Pt lattice accompanied by reordering of these atoms into intermetallic PtSn structure within 300 s at the reaction temperature (∼280 °C). This crucial mechanistic understanding enables the synthesis of well-defined PtSn NCs with controlled structure and composition via a seed-mediated approach. This type of in situ characterization can be extended to other multicomponent nanostructures to advance their rational synthesis for practical applications.

Interplay between Surface Chemistry, Precursor Reactivity, and Temperature Determines Outcome of ZnS Shelling Reactions on CuInS2 Nanocrystals

ZnS shelling of I-III-VI₂ nanocrystals (NCs) invariably leads to blue-shifts in both the absorption and photoluminescence spectra. These observations imply that the outcome of ZnS shelling reactions on I-III-VI₂ colloidal NCs results from a complex interplay between several processes taking place in solution, at the surface of, and within the seed NC. However, a fundamental understanding of the factors determining the balance between these different processes is still lacking. In this work, we address this need by investigating the impact of precursor reactivity, reaction temperature, and surface chemistry (due to the washing procedure) on the outcome of ZnS shelling reactions on CuInS₂ NCs using a seeded growth approach. We demonstrate that low reaction temperatures (150 °C) favor etching, cation exchange, and alloying regardless of the precursors used. Heteroepitaxial shell overgrowth becomes the dominant process only if reactive S- and Zn-precursors (S-ODE/OLAM and ZnI₂) and high reaction temperatures (210 °C) are used, although a certain degree of heterointerfacial alloying still occurs. Remarkably, the presence of residual acetate at the surface of CIS seed NCs washed with ethanol is shown to facilitate heteroepitaxial shell overgrowth, yielding for the first time CIS/ZnS core/shell NCs displaying red-shifted absorption spectra, in agreement with the spectral shifts expected for a type-I band alignment. The insights provided by this work pave the way toward the design of improved synthesis strategies to CIS/ZnS core/shell and alloy NCs with tailored elemental distribution profiles, allowing precise tuning of the optoelectronic properties of the resulting materials.

Near-Infrared-Emitting CuInS2/ZnS Dot-in-Rod Colloidal Heteronanorods by Seeded Growth

Synthesis protocols for anisotropic CuInX₂ (X = S, Se, Te)-based heteronanocrystals (HNCs) are scarce due to the difficulty in balancing the reactivities of multiple precursors and the high solid-state diffusion rates of the cations involved in the CuInX₂ lattice. In this work, we report a multistep seeded growth synthesis protocol that yields colloidal wurtzite CuInS₂/ZnS dot core/rod shell HNCs with photoluminescence in the NIR (∼800 nm). The wurtzite CuInS₂ NCs used as seeds are obtained by topotactic partial Cu⁺ for In³⁺ cation exchange in template Cu_2–xS NCs. The seed NCs are injected in a hot solution of zinc oleate and hexadecylamine in octadecene, 20 s after the injection of sulfur in octadecene. This results in heteroepitaxial growth of wurtzite ZnS primarily on the Sulfur-terminated polar facet of the CuInS₂ seed NCs, the other facets being overcoated only by a thin (∼1 monolayer) shell. The fast (∼21 nm/min) asymmetric axial growth of the nanorod proceeds by addition of [ZnS] monomer units, so that the polarity of the terminal (002) facet is preserved throughout the growth. The delayed injection of the CuInS₂ seed NCs is crucial to allow the concentration of [ZnS] monomers to build up, thereby maximizing the anisotropic heteroepitaxial growth rates while minimizing the rates of competing processes (etching, cation exchange, alloying). Nevertheless, a mild etching still occurred, likely prior to the onset of heteroepitaxial overgrowth, shrinking the core size from 5.5 to ∼4 nm. The insights provided by this work open up new possibilities in designing multifunctional Cu-chalcogenide based colloidal heteronanocrystals.

From Large-Scale Synthesis to Lighting Device Applications of Ternary I-III-VI Semiconductor Nanocrystals: Inspiring Greener Material Emitters

Quantum dots with fabulous size-dependent and color-tunable emissions remained as one of the most exciting inventories in nanomaterials for the last 3 decades. Even though a large number of such dot nanocrystals were developed, CdSe still remained as unbeatable and highly trusted lighting nanocrystals. Beyond these, the ternary I-III-VI family of nanocrystals emerged as the most widely accepted greener materials with efficient emissions tunable in visible as well as NIR spectral windows. These bring the high possibility of their implementation as lighting materials acceptable to the community and also to the environment. Keeping these in mind, in this Perspective, the latest developments of ternary I-III-VI nanocrystals from their large-scale synthesis to device applications are presented. Incorporating ZnS, tuning the composition, mixing with other nanocrystals, and doping with Mn ions, light-emitting devices of single color as well as for generating white light emissions are also discussed. In addition, the future prospects of these materials in lighting applications are also proposed.

Colloidal Synthesis and Thermoelectric Properties of CuFeSe₂ Nanocrystals

Copper-based chalcogenides that contain abundant, low-cost and environmentally-friendly elements, are excellent materials for numerous energy conversion applications, such as photocatalysis, photovoltaics, photoelectricity and thermoelectrics (TE). Here, we present a high-yield and upscalable colloidal synthesis route for the production of monodisperse ternary I-III-VI₂ chalcogenides nanocrystals (NCs), particularly stannite CuFeSe₂, with uniform shape and narrow size distributions by using selenium powder as the anion precursor and CuCl₂·2H₂O and FeCl₃ as the cationic precursors. The composition, the state of valence, size and morphology of the CuFeSe₂ materials were examined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM), respectively. Furthermore, the TE properties characterization of these dense nanomaterials compacted from monodisperse CuFeSe₂ NCs by hot press at 623 K were preliminarily studied after ligand removal by means of hydrazine and hexane solution. The TE performances of the sintered CuFeSe₂ pellets were characterized in the temperature range from room temperature to 653 K. Finally, the dimensionless TE figure of merit (ZT) of this Earth-abundant and intrinsic p-type CuFeSe₂ NCs is significantly increased to 0.22 at 653 K in this work, which is demonstrated to show a promising TE materialand makes it a possible p-type candidate for medium-temperature TE applications.