Cu2 xS Research Articles

Metal‐Support Interaction Boosts Au Catalysts for Hydrogen Evolution‐Coupled Ethanol Electro‐Oxidation Reaction

AbstractElectrochemical hydrogen and acetate cogeneration from ethanol is a promising green hydrogen production technique with low hydrogen production energy consumption and high profitability. However, the poor catalytic stability of the anodic ethanol electro‐oxidation reaction (EOR) retards the device application. We adopted a metal support interaction strategy to reinforce small‐sized Au active sites using cuprous sulfide supports. The Au−Cu2–xS/C showed a superior activity of 1055 mA mgAu−1 at 1.1 V vs. RHE and retained the high activity in the chronopotentiometric test, surpassing the Au/C catalyst. It was demonstrated that the Cu2–xS support facilitated the formation of Au−OH and prevented the gold sites from aggregation, leading to high activity and stability for EOR. Finally, an electrochemical cogeneration electrolyzer assembled with the Au−Cu2–xS/C anodic catalyst continuously ran for over 100 hours, suggesting the device‘s applicability.

The state of gold in phases of the Cu-Fe-S system: In situ X-ray absorption spectroscopy study

Chalcopyrite and bornite are the main Au-bearing minerals at Cu porphyry deposits, volcanogenic massive sulfide (VMS) deposits, Cu-Ni deposits of the mafic magmatic complexes, and ores of submarine sulfide edifices. Bornite and intermediate solid solutions with wide compositional variations (bnss and iss – high-temperature chalcopyrite, correspondingly), which can scavenge economic concentrations of Au, appear in the Cu-Fe-S system at ore-forming conditions. However, the state of Au in bnss and iss is yet unknown. To solve this conundrum, we synthesized samples with net chemical composition of bnss and iss, studied them by in situ X–ray absorption spectroscopy (XAS), and used the experimental data to explain the Au distribution among natural ore-forming minerals. The sulfide samples were obtained at 495–700 °C in Au-saturated system by means of salt flux method. The bnss contained ∼1.2–1.6 log units more Au than iss: up to 18 wt.% Au in bnss vs 0.4 wt.% Au in iss at 700 °C. An increase of temperature resulted in the sharp increase of Au concentration in both phases, ∼1 log unit per 100 °C at f(S2) close to S(l) saturation. Analysis of Au L3-edge spectra recorded at 25–675 °C revealed that at 25 °C Au exists mainly in the metallic state. At t > 500 °C the spectral features of Au° disappear, and “chemically bound” Au predominates. The Au form of occurrence in the iss field is interpreted as Au-bearing clusters with a stromeyerite-like (CuAgS) structure. Digenite Cu2–xS and bnss contain Au in a mixture of stromeyerite-like and petrovskaite-like (Au0.8Ag1.2S) clusters. The chemical composition of both forms is close to CuAuS, where the nearest Au neighbors are two S atoms at RAu-S = 2.34–2.36 Å. Results of the present study allow to determine the state of Au and its concentration in the main Cu-bearing minerals of sulfide ores as a function of the T-f(S2)-compositional parameters. Due to the sharp increase of the CuAuS clusters stability with increasing temperature, in high-temperature ores formed at t > 350 °C Au enriches Cu-bearing minerals in comparison with Cu-free or Cu-deficient ones. As a result, in these ores native gold, being a product of decomposition of the Au-bearing clusters, is associated with Cu-rich minerals – chalcopyrite, bornite, digenite, chalcocite.

Subsuming the Metal Seed to Transform Binary Metal Chalcogenide Nanocrystals into Multinary Compositions.

Direct colloidal synthesis of multinary metal chalcogenide nanocrystals typically develops dynamically from the binary metal chalcogenide nanocrystals with the subsequent incorporation of additional metal cations from solution during the growth process. Metal seeding of binary and multinary chalcogenides is also established, although the seed is solely a catalyst for nanocrystal nucleation and the metal from the seed has never been exploited as active alloying nuclei. Here we form colloidal Cu–Bi–Zn–S nanorods (NRs) from Bi-seeded Cu2–xS heterostructures. The evolution of these homogeneously alloyed NRs is driven by the dissolution of the Bi-rich seed and recrystallization of the Cu-rich stem into a transitional segment, followed by the incorporation of Zn2+ to form the quaternary Cu–Bi–Zn–S composition. The present study also reveals that the variation of Zn concentration in the NRs modulates the aspect ratio and affects the nature of the majority charge carriers. The NRs exhibit promising thermoelectric properties with very low thermal conductivity values of 0.45 and 0.65 W/mK at 775 and 605 K, respectively, for Zn-poor and Zn-rich NRs. This study highlights the potential of metal seed alloying as a direct growth route to achieving homogeneously alloyed NRs compositions that are not possible by conventional direct methods or by postsynthetic transformations.

Improvement of Plasmonic CuS Nanocrystals’ Optoelectronic Properties via Cation Exchange for Infrared Detection Enhancement

Colloidal quantum dot (CQD) active thin films benefitting from plasmonic light trapping have emerged as an ideal platform to boost the performance of optoelectronic devices. Copper chalcogenides exhibit infrared absorption in concomitance with tunable localized surface plasmon resonances (LSPRs) within the near to mid infrared range. Regardless of the facile adjustment of the plasmonic oscillation and strong absorption in the infrared range, the application is limited due to very short-living photo-carriers followed by carrier recombination (∼100 ps). Herein, CuS nanocrystals (NCs) are developed as an infrared photoactive material to be functionalized via Pb2+ cation substitution. A short period of cation exchange causes a large reduction in photoluminescence, reaching efficient photo-response in near infrared as a consequence of charge separation. Estimated detectivity and responsivity as high as 2.16 × 1011 Jones and 870 mA W–1 at 750 nm illumination, respectively, were achieved. Increased reaction time and Pb2+ contents result in a growing trend in photoluminescence intensity, consistent with trap passivation: detectivity = 2.15 × 1011 Jones and responsivity = 730 mA W–1 at 950 nm illumination and 1.94 × 1011 Jones and 659 mA W–1 at 840 nm. Manipulation of optical and electrical properties of Cu2–xS NCs with precise cation substitution may open up possibilities for the application of plasmonic semiconductor NCs in optoelectronic devices.

The Layered Semiconductor Cu(Sb2S3)[AlCl4

AbstractSb2S3 and CuCl were reacted in the ionic liquid [BMIm]Cl ⋅ 4.4AlCl3 (BMIm=1‐n‐butyl‐3‐methylimidazolium) at 200 °C. Upon cooling to room temperature, orange‐red colored, air‐sensitive crystals of Cu(Sb2S3)[AlCl4] precipitated. X‐ray diffraction on a single‐crystal revealed an orthorhombic crystal structure, in which cationic [Cu(Sb2S3)]+ layers are separated by tetrahedral [AlCl4]− anions. The uncharged Sb2S3 partial structure consists of one‐dimensional strands with covalent Sb−S single bonds. The copper(I) cation is coordinated by three sulfur atoms and by one of chlorine atoms of the [AlCl4]– anion. An optical band gap of 2.14 eV was deduced from UV/Vis spectra. In very good agreement, a band gap of 2.07 eV results from DFT‐based calculations involving a new implementation of the bifunctional formalism for the exchange energy. By treatment with 0.1 molar hydrochloric acid, AlCl3 was leached from Cu(Sb2S3)[AlCl4] yielding a compound with the presumed composition Cu(Sb2S3)Cl. Hydrolysis at higher pH resulted in Cu2–xS and Sb4O5Cl2.

Effect of Surface Ligand on Chemical Interface Damping in Nonstoichiometric Cu2–xS Semiconductor Nanocrystals: A Direct Correlation between Ultrafast Carrier Dynamics and Photoconductivity

Effect of Surface Ligand on Chemical Interface Damping in Nonstoichiometric Cu_2–<i>x</i>S Semiconductor Nanocrystals: A Direct Correlation between Ultrafast Carrier Dynamics and Photoconductivity

A Flash Vacuum‐Induced Reaction in Preparing High Performance Thermoelectric Cu2S

AbstractSynthesis of high‐performance thermoelectric (TE) materials with tunable compositions and nanostructures normally require sophisticated and high‐cost methods, such as high‐temperature melting and solid‐state reactions, which consume a large amount of time and energy and incur high costs. Herein, a fast, reliable, low‐cost, and environmentally friendly method, namely the vacuum‐induced method, is developed to rapidly synthesize Cu2S‐based materials with high TE performance. By mixing finely ground powders of metal‐Cu and S at room temperature, Cu2–xS compounds with a tunable x varied from 0–0.07 can be instantly formed by a quick sulfurization reaction once the mixture is placed inside a low vacuum (≈about 30 Pa and beyond). The atomic mechanism of Cu2–xS formation is studied by transmission electron microscopy, as a heterogeneous growth with the diffusion of both Cu+‐cations and S2−‐anions. In a low vacuum, the sulfur vapor is preferably attached to the copper surface with rich defected sites such as atomic vacancies, steps, and edges. The synthesized Cu2–xS powders with further plasma‐activated sintering treatment show high TE performance with ZT ≈ 1.56 around 800 K. Such a simple synthesis method may provide an effective and low‐cost way to prepare sulfides with potential applications in TE materials and solid electrolytes.

Nanostructured materials with localized surface plasmon resonance for photocatalysis

Localized surface plasmon resonance (LSPR) enhanced photocatalysis has fascinated much interest and considerable efforts have been devoted toward the development of plasmonic photocatalysts. In the past decades, noble metal nanoparticles (Au and Ag) with LSPR feature have found wide applications in solar energy conversion. Numerous metal-based photocatalysts have been proposed including metal/semiconductor heterostructures and plasmonic bimetallic or multimetallic nanostructures. However, high cost and scarce reserve of noble metals largely limit their further practical use, which drives the focus gradually shift to low-cost and abundant nonmetallic nanostructures. Recently, various heavily doped semiconductors (such as WO3-x, MoO3-x, Cu2–xS, TiN) have emerged as potential alternatives to costly noble metals for efficient photocatalysis due to their strong LSPR property in visible-near infrared region. This review starts with a brief introduction to LSPR property and LSPR-enhanced photocatalysis, the following highlights recent advances of plasmonic photocatalysts from noble metal to semiconductor-based plasmonic nanostructures. Their synthesis methods and promising applicability in plasmon-driven photocatalytic reactions such as water splitting, CO2 reduction and pollution decomposition are also summarized in details. This review is expected to give guidelines for exploring more efficient plasmonic systems and provide a perspective on development of plasmonic photocatalysis.

Synthesis and Formation Mechanism of Colloidal Janus-Type Cu2-xS/CuInS2 Heteronanorods via Seeded Injection.

Colloidal heteronanocrystals allow for the synergistic combination of properties of different materials. For example, spatial separation of the photogenerated electron and hole can be achieved by coupling different semiconductors with suitable band offsets in one single nanocrystal, which is beneficial for improving the efficiency of photocatalysts and photovoltaic devices. From this perspective, axially segmented semiconductor heteronanorods with a type-II band alignment are particularly attractive since they ensure the accessibility of both photogenerated charge carriers. Here, a two-step synthesis route to Cu2–xS/CuInS2 Janus-type heteronanorods is presented. The heteronanorods are formed by injection of a solution of preformed Cu2–xS seed nanocrystals in 1-dodecanethiol into a solution of indium oleate in oleic acid at 240 °C. By varying the reaction time, Janus-type heteronanocrystals with different sizes, shapes, and compositions are obtained. A mechanism for the formation of the heteronanocrystals is proposed. The first step of this mechanism consists of a thiolate-mediated topotactic, partial Cu+ for In3+ cation exchange that converts one of the facets of the seed nanocrystals into CuInS2. This is followed by homoepitaxial anisotropic growth of wurtzite CuInS2. The Cu2–xS seed nanocrystals also act as sacrificial Cu+ sources, and therefore, single composition CuInS2 nanorods are eventually obtained if the reaction is allowed to proceed to completion. The two-stage seeded growth method developed in this work contributes to the rational synthesis of Cu2–xS/CuInS2 heteronanocrystals with targeted architectures by allowing one to exploit the size and faceting of premade Cu2–xS seed nanocrystals to direct the growth of the CuInS2 segment.

Stoichiometric Doping of Highly Coupled Cu2–xS Nanocrystal Assemblies

The hole density of individual copper sulfide nanocrystals (Cu2-xS NCs) is determined from the stoichiometric mismatch (x) between copper and sulfide atoms. Consequently, the electronic properties of the material vary over a range of x. To exploit Cu2-xS NCs in devices, assemblies of NCs are typically required. Herein, we investigate the influence of x, referred to as the stoichiometric doping effect, on the structural, optical, electrical, and thermoelectric properties of electronically coupled Cu2-xS NC assemblies. The doping process is done by immersing the solid NC assemblies into a solution containing a Cu(I) complex for different durations (0-10 min). As Cu+ gradually occupied the copper-deficient sites of Cu2-xS NCs, x could be controlled from 0.9 to less than 0.1. Consequently, the near-infrared (NIR) absorbance of Cu2-xS NC assemblies changes systematically with x. With increasing x, electrical conductivity increased and the Seebeck coefficient decreased systematically, leading to the maximal thermoelectric power factor from a film of Cu2-xS NCs at an optimal doping condition yielding x = 0.1. The physical characteristics of the Cu2-xS NC assemblies investigated herein will provide guidelines for exploiting this emerging class of nanocrystal system based on doping.

MoSe2–Cu2–xS/GaAs Heterostructure-Based Self-Biased Two Color-Band Photodetectors with High Detectivity

Two-dimensional (2D) MoSe2–Cu2–xS nanocomposite-based heterojunction two color-band photodetectors on n-type GaAs have been fabricated and are reported for the first time. MoSe2–Cu2–xS nanocomposit...

Double-Phase Heterostructure within Fe-Doped Cu2–xS Quantum Dots with Boosted Electrocatalytic Nitrogen Reduction

Electrochemical nitrogen reduction reaction (NRR) is considered as one of the most promising methods for NH₃ synthesis under room temperature and ambient pressure. A grand challenge of NRR is the development of efficient electrocatalysts, for which the delicate nanostructuring of catalysts plays an important role. Herein, a series of Fe-doped Cu₂–ₓS quantum dots (QDs) are synthesized with multiple active sites and interface engineering, in which the double-phase heterostructure plays a key role for boosting NRR activity. The yield of NH₃ was obviously improved with the increase of Fe content from 0 to 3% but started to decrease with Fe from 3 to 9%. The optimized Fe₃%–Cu₂–ₓS QDs show an outstanding NH₃ yield of 26.4 μg h–¹ mg–¹cₐₜ at −0.7 V (vs the reversible hydrogen electrode), which is 5 times higher than that of Cu₂–ₓS QDs. More importantly, we observed that the highest NRR activity in Fe₃%–Cu₂–ₓS QDs was ascribed to the formation of an inherent double-phase heterostructure of Cu₂–ₓS/Cu₅FeS₄, whereas the complete conversion to single-phase Cu₅FeS₄ with increased Fe doping (9%) resulted in the activity decrease. Further, N₂ temperature-programmed desorption and electrochemical impedance spectra characterizations confirm the stronger chemical adsorption of N₂ and faster charge transfer in the Cu₂–ₓS/Cu₅FeS₄ QDs. A plausible mechanism was proposed for the double-phase Cu₂–ₓS/Cu₅FeS₄ heterostructure, where the interface provides efficient charge transfer and more active sites of Cu, Fe, and S for the synergetic adsorption and activation of N₂. Our work provides a simple strategy for the design of NRR electrocatalysts, which may also bring new inspiration for the preparation of the inherent double-phase heterostructure within other doped QDs.

Preparation of Cu2ZnSnS4 nanoparticles by laser ablation in liquid and characterization

Cu2ZnSnS4 (CZTS) nanoparticles were successfully prepared by laser ablation in liquid. CZTS powders were irradiated with nanosecond-pulsed laser (Nd:YAG, second harmonic generation) to prepare nanoparticles. The primary particle size of prepared nanoparticles was decreased with the increase in laser fluence, and the decrease was saturated around 11 nm. The secondary particle size of them was increased with the increase in laser fluence because aggregation would proceed. A by-product such as Cu2–xS was created by this method, and the amount was increased with laser fluence and irradiation time.

Seeded Growth Combined with Cation Exchange for the Synthesis of Anisotropic Cu2-x S/ZnS, Cu2-x S, and CuInS2 Nanorods.

Colloidal copper(I) sulfide (Cu2–xS) nanocrystals (NCs) have attracted much attention for a wide range of applications because of their unique optoelectronic properties, driving scientists to explore the potential of using Cu2–xS NCs as seeds in the synthesis of heteronanocrystals to achieve new multifunctional materials. Herein, we developed a multistep synthesis strategy toward Cu2–xS/ZnS heteronanorods. The Janus-type Cu2–xS/ZnS heteronanorods are obtained by the injection of hexagonal high-chalcocite Cu2–xS seed NCs in a hot zinc oleate solution in the presence of suitable surfactants, 20 s after the injection of sulfur precursors. The Cu2–xS seed NCs undergo rapid aggregation and coalescence in the first few seconds after the injection, forming larger NCs that act as the effective seeds for heteronucleation and growth of ZnS. The ZnS heteronucleation occurs on a single (100) facet of the Cu2–xS seed NCs and is followed by fast anisotropic growth along a direction that is perpendicular to the c-axis, thus leading to Cu2–xS/ZnS Janus-type heteronanorods with a sharp heterointerface. Interestingly, the high-chalcocite crystal structure of the injected Cu2–xS seed NCs is preserved in the Cu2–xS segments of the heteronanorods because of the high-thermodynamic stability of this Cu2–xS phase. The Cu2–xS/ZnS heteronanorods are subsequently converted into single-component Cu2–xS and CuInS2 nanorods by postsynthetic topotactic cation exchange. This work expands the possibilities for the rational synthesis of colloidal multicomponent heteronanorods by allowing the design principles of postsynthetic heteroepitaxial seeded growth and nanoscale cation exchange to be combined, yielding access to a plethora of multicomponent heteronanorods with diameters in the quantum confinement regime.

Highly Enhanced Full Solar Spectrum‐Driven Photocatalytic CO2 Reduction Performance in Cu2–xS/g‐C3N4 Composite: Efficient Charge Transfer and Mechanism Insight

An efficient full solar spectrum ultraviolet–visible–near infrared (UV–vis–NIR) light‐driven Cu2–xS/g‐C3N4 composite photocatalyst is reported, which is fabricated by a facile solvothermal process for CO2 photoreduction into CO and CH4, as confirmed by product analysis and 13C isotopic test. The composite exhibits superior full solar‐spectrum‐driven CO2 photoreduction performance than pure Cu2–xS and g‐C3N4, which is attributed to the efficient charge transfer due to the formation of intimate interface contact and SC bond coupling between Cu2–xS and g‐C3N4 based on experimental analyses and theoretical calculations. In particular, the activities of the best composite for CO2 photoreduction into CO and CH4 under NIR light irradiation are about 2.6 times and 6.6 times higher than that of Cu2–xS, whereas no production is measured over g‐C3N4. A possible mechanism of photocatalytic CO2 reduction is given based on in situ Fourier transform infrared (FTIR) analysis. This study paves the way to prepare carbon nitride–based photocatalysts with full‐spectrum‐responsive property for efficient CO2 photoreduction.

Synthesis and study of structure and phase composition in Cu2–xS, SnxSy, ZnS, CuxSnSy and CuZnSnS pellets

Synthesis of pure single-phase Cu2ZnSnS4 (CZTS) has attracted much attention of some laboratories and investigation centers around the world. This is important in order to eliminate secondary phases which are detrimental to the final conversion efficiency of the CZTS solar cells. Pseudo-ternary phase diagram showed the formation of pure CZTS using the mixture of Cu2S, SnS2 and ZnS binary sulfides; nevertheless, the gap is very narrow. An additional problem lies in the effective determination of the CZTS purity, because some secondary phases display similar X-ray diffraction and Raman spectra as those of CZTS. The present work addresses a simple, fast and economical synthesis method for the preparation of some binary, ternary and CZTS pellets, which were prepared from their corresponding co-precipitated powders. These tablets can be used not only as a sputtering target but also as a precursor in a solid-state reaction. Among the various prepared compounds, Cu2−xS–SnxSy–ZnS and CuxSnSy are included and characterized to identify their presence in the CZTS pellets. From the obtained results, the usefulness of co-precipitation as a method to produce highly pure single-phase CZTS is discussed.

Selective Growth of Metal Sulfide, Metal, and Metal-Alloy on 2D CdS Nanoplates

Two-dimensional CdS-based hybrid nanostructures are intriguing materials with an application prospect in different fields such as sensing (i.e., photoresistors) and solar energy harvesting (photocatalysis, photovoltaics, and so forth). We report herein a colloidal synthetic path for interfacing metal and semiconductor with 2D CdS nanoplates. Selective growth of Au, Pt, and a PtNi alloy as well as Cu2–xS semiconductor is achieved on CdS nanoplates using controlled reduction of metallic precursors and thermal decomposition of a metal-sulfide single-source precursor using standard organic-phase colloidal chemistry.

Ultrafast Plasmon Dynamics and Hole–Phonon Coupling in NIR Active Nonstoichiometric Semiconductor Plasmonic Cu2–xS Nanocrystals

Nonstoichiometric Cu2–xS nanocrystals (NCs) have been synthesized by hot-injection method after changing the copper to sulfur ratio. Optical studies confirmed well-defined localized surface plasmon...

Near-Infrared Absorbing Solid Lipid Nanoparticles Encapsulating Plasmonic Copper Sulfide Nanocrystals

A novel near-infrared-absorbing nanoformulation is fabricated by efficiently encapsulating plasmonic Cu2–xS nanocrystals (NCs) within the core of low-density lipoprotein (LDL)-mimetic solid lipid nanoparticles (SLNs). Cu2–xS NCs are ideal candidates as photothermal or imaging agents for in vivo cancer treatment, thanks to their plasmonic properties, low toxicity, biodegradability, and low cost. Their incorporation in the LDL-mimetic nanocarriers enhances the nanoformulation potential in biomedical applications, resulting in nanosystems able to provide the concomitant delivery of anticancer molecules and cancer diagnosis and/or therapy. Besides the comprehensive characterization of the prepared nanostructures, the paper aims to tackle the accurate determination of the NC concentration in the final nanoformulation. Since both photothermal therapy and imaging efficiency strongly depend on the concentration of the nanoagents, the availability of a real-time and nondestructive approach for the determination of...

Structure-Selective Synthesis of Wurtzite and Zincblende ZnS, CdS, and CuInS2 Using Nanoparticle Cation Exchange Reactions.

For polymorphic solid-state systems containing multiple distinct crystal structures of the same composition, identifying rational pathways to selectively target one particular structure is an important synthetic capability. Cation exchange reactions can transform a growing library of metal chalcogenide nanocrystals into different phases by replacing the cation sublattice, often while retaining morphology and crystal structure. However, only a few examples have been demonstrated where multiple distinct phases in a polymorphic system could be selectively accessed using nanocrystal cation exchange reactions. Here, we show that roxbyite (hexagonal) and digenite (cubic) Cu2- xS nanoparticles transform upon cation exchange with Cd2+, Zn2+, and In3+ to wurtzite (hexagonal) and zincblende (cubic) CdS, ZnS, and CuInS2, respectively. These products retain the anion and cation sublattice features programmed into the copper sulfide template, and each phase forms to the exclusion of other known crystal structures. These results significantly expand the scope of structure-selective cation exchange reactions in polymorphic systems.