Alternative synthesis of CuFeSe2 nanocrystals with magnetic and photoelectric properties

Multi-target photothermal immunochromatography for simultaneous detection of three mycotoxins in foods

BACKGROUND

Mycotoxin contaminated food poses a threat to human health. On-site detection of mycotoxin contamination is of significance to reduce the agricultural and food industries loss. Lateral flow immunochromatography (LFIC) as on-site detection method for mycotoxins has the advantages of low cost, easy to operate and short time-consuming. Of the various types of LFIC, photothermal LFIC possesses better sensitivity and stronger quantitative capability, but is unable to conduct synchronous multi-target analysis because that the laser can only activate one test area at a time. It was clear that a synchronous multi-target photothermal LFIC method was needed.

RESULTS

In this study, a photothermal LFIC method for the simultaneous detection of three mycotoxins, deoxynivalenol (DON), aflatoxin B1 (AFB1) and zearalenone (ZEN), was developed. We broadened the laser source with a beam expander and realized the irradiation and activation of three test zones simultaneously. In addition, the competitive photothermal LFIC was constructed by using Cu2-xSe-Au nanocomposites with excellent photothermal properties (η = 87.47%) as photothermal signal probes and thermal imager as photothermal signal collector. Under optimized experimental conditions, the limits of detection (LOD) were 73 ng L-1, 45 ng L-1 and 43 ng L-1 for DON, AFB1 and ZEN, respectively. The method had good linearity in three orders of magnitude and good specificity. The recoveries of the three mycotoxins in oat, cornmeal and millet samples ranged from 78.6% to 112.4%.

SIGNIFICANCE

Compared with previous studies, this method improved the sensitivity, broadened the linear range of detection without large equipment and realized synchronous multi-target analysis for DON, AFB1 and ZEN. We addressed a key limitation of photothermal LFIC by a simple way, facilitating the application of this technique in multi-target on-site detection in wider fields.

Oleic acid/oleylamine ligand pair: a versatile combination in the synthesis of colloidal nanoparticles

A variety of colloidal chemical approaches has been developed in the last few decades for the controlled synthesis of nanostructured materials in either water or organic solvents. Besides the precursors, the solvents, reducing agents, and the choice of surfactants are crucial for tuning the composition, morphology and other properties of the resulting nanoparticles. The ligands employed include thiols, amines, carboxylic acids, phosphines and phosphine oxides. Generally, adding a single ligand to the reaction mixture is not always adequate to yield the desired features. In this review, we discuss in detail the role of the oleic acid/oleylamine ligand pair in the chemical synthesis of nanoparticles. The combined use of these ligands belonging to two different categories of molecules aims to control the size and shape of nanoparticles and prevent their aggregation, not only during their synthesis but also after their dispersion in a carrier solvent. We show how the different binding strengths of these two molecules and their distinct binding modes on specific facets affect the reaction kinetics toward the production of nanostructures with tailored characteristics. Additional functions, such as the reducing function, are also noted, especially for oleylamine. Sometimes, the carboxylic acid will react with the alkylamine to form an acid-base complex, which may serve as a binary capping agent and reductant; however, its reducing capacity may range from lower to much lower than that of oleylamine. The types of nanoparticles synthesized in the simultaneous presence of oleic acid and oleylamine and discussed herein include metal oxides, metal chalcogenides, metals, bimetallic structures, perovskites, upconversion particles and rare earth-based materials. Diverse morphologies, ranging from spherical nanoparticles to anisotropic, core-shell and hetero-structured configurations are presented. Finally, the relation between tuning the resulting surface and volume nanoparticle properties and the relevant applications is highlighted.

Solution-phase controlled synthesis of Cu3NbSe4 nanocrystals for optoelectronic applications

Cu3NbSe4 nanocrystals with a cubic phase, monodisperse size and uniform shape synthesized by a facile colloidal method exhibit excellent optoelectronic properties.

Progress of Phototherapy Applications in the Treatment of Bone Cancer

Bone cancer including primary bone cancer and metastatic bone cancer, remains a challenge claiming millions of lives and affecting the life quality of survivors. Conventional treatments of bone cancer include wide surgical resection, radiotherapy, and chemotherapy. However, some bone cancer cells may remain or recur in the local area after resection, some are highly resistant to chemotherapy, and some are insensitive to radiotherapy. Phototherapy (PT) including photodynamic therapy (PDT) and photothermal therapy (PTT), is a clinically approved, minimally invasive, and highly selective treatment, and has been widely reported for cancer therapy. Under the irradiation of light of a specific wavelength, the photosensitizer (PS) in PDT can cause the increase of intracellular ROS and the photothermal agent (PTA) in PTT can induce photothermal conversion, leading to the tumoricidal effects. In this review, the progress of PT applications in the treatment of bone cancer has been outlined and summarized, and some envisioned challenges and future perspectives have been mentioned. This review provides the current state of the art regarding PDT and PTT in bone cancer and inspiration for future studies on PT.

Folic Acid-Conjugated CuFeSe2 Nanoparticles for Targeted T2-Weighted Magnetic Resonance Imaging and Computed Tomography of Tumors In Vivo

Background

Development of new long-circulating contrast agents for computed tomography (CT) and magnetic resonance imaging (MRI) of different biological systems still remains a great challenge. Here, we report the synthesis of folic acid (FA)-targeted CuFeSe₂ nano-contrast agent for CT and MRI imaging in vitro and in vivo.

Methods and Results

In our study, CuFeSe₂ was fabricated through a facile and green aqueous reaction and then further aminated through silanization. The amine-functionalized CuFeSe₂-NH₂ nanoparticles enable the covalent conjugation of folate-conjugated polyethylene glycol (FA-PEG-COOH) as a targeting ligand onto their surface, which could improve the dispersion and endue the targetability of nanoparticles, respectively. The formed multifunctional CuFeSe₂-PEG-FA nanoparticles were characterized via different techniques, which exhibited outstanding dispersion, good biocompatibility and excellent FA-targeted capability. Meanwhile, the nanoparticles were quite safe in the given concentration range as confirmed by in vitro and in vivo toxicity assay. Importantly, CuFeSe₂-PEG-FA nanoparticles were successfully applied in CT/MRI dual-modality imaging in vitro and in vivo, which showed a better imaging performance and targeted capability.

Conclusion

Therefore, the constructed CuFeSe₂-PEG-FA nanoparticles have a great potential as an efficient contrast agent for dual-modality imaging of different biological systems.

Discovery of a Wurtzite-like Cu2FeSnSe4 Semiconductor Nanocrystal Polymorph and Implications for Related CuFeSe2 Materials

I₂-II-IV-VI₄ and I-III-VI₂ semiconductor nanocrystals have found applications in photovoltaics and other optoelectronic technologies because of their low toxicity and efficient light absorption into the near-infrared. Herein, we report the discovery of a metastable wurtzite-like polymorph of Cu₂FeSnSe₄, a member of the I₂-II-IV-VI₄ family of semiconductors containing only earth-abundant metals. Density functional theory calculations on this metastable polymorph of Cu₂FeSnSe₄ indicate that it may be a superior semiconductor for solar energy and optoelectronics applications compared to the thermodynamically preferred stannite polymorph, since the former displays a sharper dispersion of energy levels near the conduction band minimum that can enhance electron mobility and suppress hot electron cooling. The experimental optical band gap was measured by the inverse logarithmic derivative method to be direct, in agreement with theory, and in the range of 1.48-1.59 eV. Mechanistic studies reveal that this metastable phase derives from intermediate Cu₃Se₂ nanocrystals that serve as a structural template for the final hexagonal wurtzite-like product. We compare the chemistry of wurtzite-like Cu₂FeSnSe₄ to the related CuFeSe₂ material system. Our experimental and computational comparisons between Cu₂FeSnSe₄ and CuFeSe₂ help explain both the crystal chemistry of CuFeSe₂ that prevents it from forming wurtzite-like polymorphs and the essential role of Sn in stabilizing the metastable structure of Cu₂FeSnSe₄. This work provides insight into the importance of elemental composition when designing syntheses for metastable materials.

Stand-Alone CuFeSe2 (Eskebornite) Nanosheets for Photothermal Cancer Therapy

Two-dimensional CuFeSe2 nanosheets have been successfully obtained via solution-phase synthesis using a sacrificial template method. The high purity was confirmed by X-ray diffraction and the two-dimensional morphology was validated by transmission electron microscopy. The intense absorption in the 400-1400 nm region has been the basis for the CuFeSe2 nanosheets' photothermal capabilities testing. The colloidal CuFeSe2 (CFS) nanosheets capped with S2- short ligands (CFS-S) exhibit excellent biocompatibility in cell culture studies and strong photothermal effects upon 808 nm laser irradiation. The nanosheets were further loaded with the cancer drug doxorubicin and exposed to laser irradiation, which accelerated the release of doxorubicin, achieving synergy in the therapeutic effect.

Gadolinium-chelate functionalized magnetic CuFeSe2 ternary nanocrystals for T1-T2 dual MRI and CT imaging in vitro and in vivo

CuFeSe2 nanomaterial with high thermal conversion efficiency, well superparamagnetism, effective x-ray attenuation ability, multifunctional groups and excellent biocompatibility is beneficial to the construction of multimodal imaging probes which can combine various imaging modes to provide a synergistic advantage over a single imaging mode. This study aimed to develop a novel multimodal nanocontrast agent CuFeSe2@diethylenetriaminepentaacetic acid (DTPA)-Gd to obtain imaging information with high specificity, high sensitivity and high contrast. The morphology and physical characteristics of CuFeSe2@DTPA-Gd were detected by transmission electron microscope, scanning electron microscope, x-ray single crystal diffraction, vibrating sample magnetometer and fourier transform infrared spectrometer. The toxicity of CuFeSe2@DTPA-Gd in vivo was evaluated by hematoxylin-eosin staining. The imaging capability of CuFeSe2@DTPA-Gd in vitro and in vivo was evaluated by magnetic resonance imaging (MRI) and computed tomography (CT). This study successfully prepared nanoparticles CuFeSe2@DTPA-Gd, and experimental results in this study demonstrated CuFeSe2@DTPA-Gd is expected to be a useful CT and MRI T1-weighted imaging/T2-weighted imaging three-modal contrast agent in clinic.

Controllable synthesis of non-layered two-dimensional plate-like CuGaSe2 materials for optoelectronic devices

CuGaSe2 semiconductor materials, as an important member of the I-III-VI2 family, have sparked tremendous attention due to their fascinating structure-related properties and promising applications in solar energy storage and conversion. Nevertheless, the controllable preparation of two-dimensional (2D) CuGaSe2 structures is still a daunting challenge owing to the intrinsic non-layered crystal structure and inaccessible reactivity-matching of multiple reaction precursors, which will seriously impede the much deeper research progress on their properties and applications. Herein, non-layered 2D CuGaSe2 plates possessing high crystallinity, and uniform size and morphology have been first synthesized by a feasible cation exchange strategy. Because the fabrication of 2D CuGaSe2 crystals is rarely reported, a particular highlight is laid on the compositional analysis, structural characterization, and formation mechanism. Furthermore, the optical absorption and optoelectronic measurements reveal that the as-synthesized CuGaSe2 plates exhibit high light harvesting capacity and excellent photoelectric performance. This study opens up a new avenue for the feasible fabrication of non-layered CuGaSe2 plates possessing a high-quality crystalline structure and provides a promising candidate for the development of novel solar energy conversion and storage devices.

CuFeSe2-based thermo-responsive multifunctional nanomaterial initiated by a single NIR light for hypoxic cancer therapy

A thermo-responsive CuFeSe₂-based multifunctional nanomaterial was used for NIR light initiated hypoxic cancer therapy and CT/MR imaging.

Scalable Synthesis of a Sub-10 nm Chalcopyrite (CuFeS2) Nanocrystal by the Microwave-Assisted Synthesis Technique and Its Application in a Heavy-Metal-Free Broad-Band Photodetector

A heavy-metal-free chalcopyrite (CuFeS₂) nanocrystal has been synthesized via microwave-assisted growth. Large-scale nanocrystals with an average particle size of 5 nm are fabricated by this technique within a very short period of time without any need for organic ligands. Scanning electron microscopy study (SEM) of individual synthesis steps indicates that aggregates of nanocrystals are formed as flakes during microwave-assisted synthesis. The colloidal solution of the CuFeS₂ nanocrystal was prepared by sonicating these flakes. Transmission electron microscopy (TEM) study reveals the growth of sub-10 nm CuFeS₂ nanocrystals that are further characterized by X-ray diffraction. UV-visible absorption spectroscopic study shows that the band gap of this nanocrystal is ∼1.3 eV. To investigate the photosensitive nature of this nanocrystal, a bilayer p-n heterojunction photodetector has been fabricated using this nontoxic CuFeS₂ nanocrystal as a photoactive material and n-type ZnO as a charge-transport layer. The detectivity of this photodetector reaches above 10¹² Jones in visible and near-infrared (NIR) regions under 10 V external bias, which is significantly high for a nontoxic nanocrystal-based photodetector.

Synthesis and optoelectronic properties of Cu3VSe4 nanocrystals

The ternary chalcogenide Cu₃VSe₄ (CVSe) with sulvanite structure has been theoretically predicted to be a promising candidate for photovoltaic applications due to its suitable bandgap for solar absorption and the relatively earth-abundant elements in its composition. To realize the absorber layer via an inexpensive route, printed thin-films could be fabricated from dispersions of nano-sized Cu₃VSe₄ precursors. Herein, cubic Cu₃VSe₄ nanocrystals were successfully synthesized via a hot-injection method. Similar with reported Cu₃VS₄ nanocrystals, Cu₃VSe₄ nanocrystals with cubic structure exhibit three absorption bands in the UV-Visible range indicative of a potential intermediate bandgap existence. A thin film fabricated by depositing the nanoparticles Cu₃VSe₄ on FTO coated glass substrate, exhibited a p-type behavior and a photocurrent of ~ 4 μA/cm² when measured in an electrochemical cell setting. This first demonstration of photocurrent exhibited by a CVSe nanocrystals thin film signifies a promising potential in photovoltaic applications.

Hyperthermia and Controllable Free Radical Coenhanced Synergistic Therapy in Hypoxia Enabled by Near-Infrared-II Light Irradiation

Tumor cell metabolism and tumor blood vessel proliferation are distinct from normal cells. The resulting tumor microenvironment presents a characteristic of hypoxia, which greatly limits the generation of oxygen free radicals and affects the therapeutic effect of photodynamic therapy. Here, we developed an oxygen-independent free radical generated nanosystem (CuFeSe₂-AIPH@BSA) with dual-peak absorption in both near-infrared (NIR) regions and utilized it for imaging-guided synergistic treatment. The special absorption provides the nanosystem with high photothermal conversion efficiency and favorably matched photoactivity in both I and II NIR biological windows. Upon NIR light irradiation, the generated heat could prompt AIPH release and decompose to produce oxygen-independent free radicals for killing cancer cells effectively. The contrastive research results show that the enhanced therapeutic efficacy of NIR-II over NIR-I is principally due to its deeper tissue penetration and higher maximum permission exposure that benefits from a longer wavelength. Hyperthermia effect and the production of toxic free radicals upon NIR-II laser illumination are extremely effective in triggering apoptosis and death of cancer cells in the tumor hypoxia microenvironment. The high biocompatibility and excellent anticancer efficiency of CuFeSe₂-AIPH@BSA allow it to be an ideal oxygen-independent nanosystem for imaging-guided and NIR-II-mediated synergistic therapy via systemic administration.

Cu-Fe-Se Ternary Nanosheet-Based Drug Delivery Carrier for Multimodal Imaging and Combined Chemo/Photothermal Therapy of Cancer

Ternary transition-metal chalcogenide nanosheets have shown great potential in diverse applications owing to their intrinsically amazing properties with a broad tunable window. Direct preparation of water-soluble and biocompatible ternary chalcogenide nanosheets for theranostic application remains a challenge. In this article, we prepared Cu-Fe-Se nanosheets (CFS NSs) in an aqueous solution under ambient conditions by a sequential coprecipitation method. They were functionalized with anticancer drug doxorubin (CFS@DOX) through electrostatic interactions and labeled with radioactive isotope ^99mTc through surface coordination effect. The resulting nanosheets have a size of 70 nm and a thickness of 5 nm, and can be well dispersed in water, phosphate-buffered saline, 10% fetal bovine serum, and 0.9% NaCl with an excellent colloidal stability. They also exhibit a high photothermal conversion efficiency of 78.9% for in vitro and in vivo photoacoustic imaging and photothermal therapy. The isotope-labeled nanosheets (^99mTc-CFS NSs) were used for single photon emission computed tomography/computed tomography imaging to quantify their blood circulation time (∼4.7 h) and biodistributions in major organs, which follow an order of liver > bladder > lung > spleen > heart > kidney. The DOX-functionalized nanosheets (CFS@DOX) were used for chemotherapy of cancer and exhibited excellent anticancer efficacy. Our research shows the great promise of ternary metal chalcogenide nanosheets for combined imaging and therapy of cancer.

Constructing two-dimensional CuFeSe2@Au heterostructured nanosheets with an amorphous core and a crystalline shell for enhanced near-infrared light water oxidation

Although substantial efforts have been made toward the synthesis of noble metal-semiconductor heteronanostructures, direct in situ synthesis of two-dimensional (2D) core-shell semiconductor@noble metal heterostructured nanosheets remains largely unexplored. Herein, we report the synthesis of a novel 2D core-shell CuFeSe₂@Au heterostructured nanosheet with an amorphous core and a crystalline shell based on the reversed growth of Au nanosheets on the CuFeSe₂ frameworks under near-infrared (NIR) illumination. The nanosheet exhibits strong absorbance in the NIR region, and the valence band top of CuFeSe₂@Au nanosheets is higher than the oxidation potential of O₂/H₂O. Owing to the unique structural features, the resulting nanosheets show excellent photocatalytic activity and high stability toward water oxidation with an O₂ generation rate up to 3.48 mmol h^-1 g^-1 compared to those of the constituent materials under NIR light irradiation (λ > 850 nm). This work brings new opportunities to prepare 2D core-shell semiconductor@noble metal heterostructured nanosheets, which can be applied as photocatalysts toward water splitting and solar energy conversion at long wavelengths.

A bifunctional scaffold with CuFeSe2 nanocrystals for tumor therapy and bone reconstruction

Bone tumor is one of major challenging issues clinically. After surgical intervention, a few bone tumor cells still remain around bone defects and then proliferate over days. Fabrication of specific biomaterials with dual functions of bone tumor therapy and bone regeneration is of great significance. In order to achieve this aim, we managed to prepare bioactive glass (BG) scaffolds functionalized by the CuFeSe₂ nanocrystals (BG-CFS) by combining 3D printing technique with solvothermal method. During the solvothermal reaction process, CuFeSe₂ nanocrystals could in situ grow on the strut surface of BG scaffolds and thus endow BG scaffolds excellent photothermal performance. The photothermal performance of BG-CFS scaffolds could be well regulated through altering the content of CuFeSe₂ nanocrystals and laser power density when exposed to the near infrared laser (808 nm). The BG-CFS scaffolds could not only effectively ablate the bone tumor cells (Saos-2 cells) in vitro, but also significantly inhibit bone tumor growth in vivo. Moreover, BG-CFS scaffolds could stimulate osteogenic gene expressions of rabbit bone marrow stromal cells (rBMSCs) and finally facilitate the formation of new bone in the bone defects. Our study, for the first time, combined the photothermal performance of semiconductor CuFeSe₂ nanocrystals with the bone-forming activity of bioactive glass scaffolds, which can offer a more extensive horizon for developing novel biomaterials with dual functions of bone tumor therapy and bone regeneration.

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.

High-index faceted CuFeS2 nanosheets with enhanced behavior for boosting hydrogen evolution reaction

A rational design of highly active and robust catalysts based on earth-abundant elements for hydrogen evolution reaction (HER) is essential for future renewable energy applications. Herein, we report the synthesis of a new class of ultrathin metallic CuFeS₂ nanosheets (NSs) with abundant exposed high-index {02[combining macron]4} facets. They serve as a robust catalyst for the HER with a lower onset potential of 28.1 mV, an overpotential of only 88.7 mV (at j = 10 mA cm^-2) and remarkable long-term stability in 0.5 M H₂SO₄, which make them the best system among all the reported non-noble metal catalysts. The theoretical calculations reveal that the mechanistic origin for such a high HER activity should be attributed to the excess S^2- active sites on the exposed {02[combining macron]4} high-index facets of CuFeS₂ NSs, which have a rather favorable Gibbs free energy for atomic hydrogen adsorption. The present work highlights the importance of designing ultrathin metallic chalcopyrite nanosheets with high-index facets in order to increase the number of active sites for boosting the HER performance.

Ultrasmall Magnetic CuFeSe2 Ternary Nanocrystals for Multimodal Imaging Guided Photothermal Therapy of Cancer

Nanoscale ternary chalcogenides have attracted intense research interest due to their wealth of tunable properties and diverse applications in energy and environmental and biomedical fields. In this article, ultrasmall magnetic CuFeSe₂ ternary nanocrystals (<5.0 nm) were fabricated in the presence of thiol-functionalized poly(methacrylic acid) by an environmentally friendly aqueous method under ambient conditions. The small band gap and the existence of intermediate bands lead to a broad NIR absorbance in the range of 500-1100 nm and high photothermal conversion efficiency (82%) of CuFeSe₂ nanocrystals. The resultant CuFeSe₂ nanocrystals show superparamagnetism and effective attenuation for X-rays. In addition, they also exhibit excellent water solubility, colloidal stability, biocompatibility, and multifunctional groups. These properties enable them to be an ideal nanotheranostic agent for multimodal imaging [e.g., photoacoustic imaging (PAI), magnetic resonance imaging (MRI), computed tomography (CT) imaging] guided photothermal therapy of cancer.

Compound Copper Chalcogenide Nanocrystals

This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), energy storage (lithium-ion batteries, hydrogen generation), emissive materials (plasmonics, LEDs, biolabelling), sensors (electrochemical, biochemical), biomedical devices (magnetic resonance imaging, X-ray computer tomography), and medical therapies (photochemothermal therapies, immunotherapy, radiotherapy, and drug delivery). The confluence of advances in the synthesis, assembly, and application of these NCs in the past decade has the potential to significantly impact society, both economically and environmentally.

Diorganyl dichalcogenides as useful synthons for colloidal semiconductor nanocrystals

The ability to synthesize colloidal semiconductor nanocrystals in a well-controlled manner (i.e., with fine control over size, shape, size dispersion, and composition) has been mastered over the past 15 years. Much of this success stems from careful studies of precursor conversion and nanocrystal growth with respect to phosphine chalcogenide precursors for the synthesis of metal chalcogenide nanocrystals. Despite the high level of success that has been achieved with phosphine chalcogenides, there has been a longstanding interest in exploring alternate chalcogenide precursors because of issues associated with phosphine chalcogenide cost, purity, toxicity, etc. This has resulted in a large body of literature on the use of sulfur and selenium dissolved in octadecene or amines, thio- and selenoureas, and silyl chalcogenides as alternate chalcogenide precursors for metal chalcogenide nanocrystal synthesis. In this Account, emerging work on the use of diorganyl dichalcogenides (R-E-E-R, where E = S, Se, or Te and R = alkyl, allyl, benzyl, or aryl) as alternate chalcogenide precursors for the synthesis of metal chalcogenide nanocrystals is summarized. Among the benefits of these dichalcogenide synthons are the following: (i) they represent the first and only common precursor type that can function as chalcogen transfer reagents for each of the group VI elements (i.e., to make metal oxide, metal sulfide, metal selenide, and metal telluride nanocrystals); (ii) they possess relatively weak E-E bonds that can be readily cleaved under mild thermolytic or photolytic conditions; and (iii) the organic substituents can be tuned to affect the reactivity. These combined attributes have allowed dichalcogenide precursors to be employed for a wide range of metal chalcogenide nanocrystal syntheses, including those for In2S3, SnxGe1-xSe, SnTe, Cu2-xSySe1-y, ZnSe, CdS, CdSe, MoSe2, WSe2, BiSe, and CuFeS2. Interestingly, a number of metastable phases of compositionally complex semiconductors can be kinetically accessed through syntheses utilizing dichalcogenide precursors, likely as a result of their ability to convert at relatively low temperatures. These include the hexagonal wurtzite phases of CuInS2, CuInSe2, Cu2ZnSn(S1-xSex)4, and Cu2SnSe3 nanocrystals. The discovery of crystal phases on the nanoscale that do not exist in their bulk analogues is a developing area of nanocrystal chemistry, and dichalcogenides are proving to be a useful synthetic tool in this regard. The most recent application of dichalcogenide synthons for semiconductor nanocrystals is their use as precursors for surface ligands. While there is a rich history of using thiol ligands for semiconductor nanocrystals, the analogous selenol and tellurol ligands have not been studied, likely because of their oxidative instability. Dichalcogenides have proven useful in this regard, as they can be reduced in situ with diphenylphosphine to give the corresponding selenol or tellurol ligand that binds to the nanocrystal surface. This chemistry has been applied to the in situ synthesis and ligand binding of selenols to PbSe nanocrystals and both selenols and tellurols to CdSe nanocrystals. These initial studies have allowed the photophysics of these nanocrystal-ligand constructs to be investigated; in both cases, it appears that the selenol and tellurol ligands act as hole traps that quench the photoluminescence of the semiconductor nanocrystals.

Synthesis of Cu2SnSe3-Au heteronanostructures with optoelectronic and photocatalytic properties

Cu2SnSe3-Au heteronanostructures have been successfully synthesized for the first time using a seed-mediated growth method. Such new Cu2SnSe3-Au heteronanostructures demonstrate enhanced and broadened optical absorption in the Vis-NIR region. We have also investigated the optoelectronic and photocatalytic properties of the Cu2SnSe3-Au heteronanostructures and proposed a mechanism to illustrate the improved photocurrent and photocatalytic performance as compared to bare Cu2SnSe3.