Magnetic-Field Response and Giant Electric-Field Modulation of Cu2S

Cu2S likely plays an important role in the sharp resistivity transition of LK-99. Nevertheless, this immediately arouses an intriguing question of whether the extraordinary room-temperature colossal magnetoresistance in the initial reports, which has been less focused, originates from Cu2S as well. To resolve this issue, we have systematically investigated the electrical transport and magnetotransport properties of near-stoichiometric Cu2S pellets and thin films. Neither Cu2S nor LK-99 containing Cu2S in this study was found to exhibit the remarkable magnetoresistance effect implied by Lee et al. This implies that Cu2S could not account for all of the intriguing transport properties of the initially reported LK-99, and the initially reported LK-99 samples might contain magnetic impurities. Moreover, based on the crystal-structure-sensitive electrical properties of Cu2S, we have constructed a piezoelectric-strain-controlled device and obtained a giant and reversible resistance modulation of 2 orders of magnitude at room temperature, yielding a huge gauge factor of 160,000.

Largely Enhanced Thermoelectric Power Factor of Flexible Cu2-xS Film by Doping Mn

Copper-sulfide-based materials have attracted noteworthy attention as thermoelectric materials due to rich elemental reserves, non-toxicity, low thermal conductivity, and adjustable electrical properties. However, research on the flexible thermoelectrics of copper sulfide has not yet been reported. In this work, we developed a facile method to prepare flexible Mn-doped Cu2-xS films on nylon membranes. First, nano to submicron powders with nominal compositions of Cu2-xMnyS (y = 0, 0.01, 0.03, 0.05, 0.07) were synthesized by a hydrothermal method. Then, the powders were vacuum-filtrated on nylon membranes and finally hot-pressed. Phase composition and microstructure analysis revealed that the films contained both Cu2S and Cu1.96S, and the size of the grains was ~20-300 nm. By Mn doping, there was an increase in carrier concentration and mobility, and ultimately, the electrical properties of Cu2-xS were improved. Eventually, the Cu2-xMn0.05S film showed a maximum power factor of 113.3 μW m-1 K-2 and good flexibility at room temperature. Moreover, an assembled four-leg flexible thermoelectric generator produced a maximum power of 249.48 nW (corresponding power density ~1.23 W m-2) at a temperature difference of 30.1 K, and had good potential for powering low-power-consumption wearable electronics.

Effect of Vacancy, As, and Sb Dopants on the Gold-Capturing Ability of Cu2S during Gold Collection in Matte Processes

The technique of gold collection in matte can effectively improve the trapping efficiency of precious metals such as gold, silver, and platinum. However, the underlying mechanism of gold collection from high-temperature molten matte is complex and not well understood. In this work, the first-principle calculations were utilized to investigate the adsorption behavior of gold atoms on a Cu2S surface. The effects of vacancies and As and Sb doping on the gold-trapping ability of Cu2S were also explored, and the electronic properties of each adsorption system, including the charge density difference, density of states, and charge transfer, were systematically analyzed. The results show that the Cu-terminated Cu2S(111) surface has the lowest surface energy, and the Au atom is chemically adsorbed on the Cu2S(111) with an adsorption energy of -1.99 eV. The large adsorption strength is primarily ascribed to the strong hybridizations between Au-5d and Cu-3d orbitals. Additionally, the Cu vacancy can significantly weaken the adsorption strength of Cu2S(111) towards Au atoms, while the S vacancy can notably enhance it. Moreover, due to the formation of strong covalent As-Au/Sb-Au bonds, doping As and Sb into Cu2S(111) can enhance the gold-trapping capability of Cu2S, and the Sb doping exhibits superior effectiveness. Our studied results can provide theoretical guidance for improving the gold collection efficiency of Cu2S.

Facile Synthesis of Needle-like Copper Sulfide Structures as an Effective Electrochemical Sensor Material for Neurotransmitter Detection in Biological Samples

Electrochemical sensors, due to their excellent and unique features, are of high interest nowadays for the detection and monitoring of several biological compounds. In such a case, serotonin (SRN), an important neurotransmitter, was herein studied for its detection in biological fluids since its presence is more crucial to be monitored and detected in clinical and medical applications. Several study strategies have been used to determine the chemical and physical properties. The crystalline size of the constructed copper sulfide (Cu2S) material was measured to be 25.92 nm. The Cu2S was fabricated over the working surface and further analyzed for several sensor parameters to be optimized. The charge transfer resistance of the copper sulfide-modified glassy carbon electrode (Cu2S/GCE) was determined to be about 277.0 Ω. With the linear range from about 0.029 μM to 607.6 μM for SRN, the limit of detection (LOD) was calculated as 3.2 nM, with a good sensitivity of 13.23 μA μM-1 cm2. The sensor experienced excellent repeatability, reproducibility, and long-term stability. The fabricated electrode was selective with the presence of different interfering compounds. The real sample analysis, as determined with the regular addition method with human serum and urine samples, revealed a good recovery percentage. Thus, the employed fabricated electrode material will be highly effective in sensing other analytes of choice.

Construction of Porous Carbon Nanosheet/Cu2S Composites with Enhanced Potassium Storage

Porous C nanosheet/Cu2S composites were prepared using a simple self-template method and vulcanization process. The Cu2S nanoparticles with an average diameter of 140 nm are uniformly distributed on porous carbon nanosheets. When used as the anode of a potassium-ion battery, porous C nanosheet/Cu2S composites exhibit good rate performance and cycle performance (363 mAh g-1 at 0.1 A g-1 after 100 cycles; 120 mAh g-1 at 5 A g-1 after 1000 cycles). The excellent electrochemical performance of porous C nanosheet/Cu2S composites can be ascribed to their unique structure, which can restrain the volume change of Cu2S during the charge/discharge processes, increase the contact area between the electrode and the electrolyte, and improve the electron/ionic conductivity of the electrode material.

Preparation and Characterization of Screen-Printed Cu2S/PEDOT:PSS Hybrid Films for Flexible Thermoelectric Power Generator

In recent years, flexible thermoelectric generators(f-TEG), which can generate electricity by environmental temperature difference and have low cost, have been widely concerned in self-powered energy devices for underground pipe network monitoring. This paper studied the Cu₂S films by screen-printing. The effects of different proportions of p-type Cu₂S/poly 3,4-ethylene dioxythiophene-polystyrene sulfonate (PEDOT:PSS) mixture on the thermoelectric properties of films were studied. The interfacial effect of the two materials, forming a superconducting layer on the surface of Cu₂S, leads to the enhancement of film conductivity with the increase of PEDOT:PSS. In addition, the Seebeck coefficient decreases with the increase of PEDOT:PSS due to the excessive bandgap difference between the two materials. When the content ratio of Cu₂S and PEDOT:PSS was 1:1.2, the prepared film had the optimal thermoelectric performance, with a maximum power factor (PF) of 20.60 μW·m^-1·K^-1. The conductivity reached 75% of the initial value after 1500 bending tests. In addition, a fully printed Te-free f-TEG with a fan-shaped structure by Cu₂S and Ag₂Se was constructed. When the temperature difference (ΔT) was 35 K, the output voltage of the f-TEG was 33.50 mV, and the maximum power was 163.20 nW. Thus, it is envisaged that large thermoelectric output can be obtained by building a multi-layer stacking f-TEG for continuous self-powered monitoring.

Ultrasmall Copper (I) Sulfide Nanoparticles Prevent Hepatitis B Virus Infection

Hepatitis B virus (HBV) poses a severe threat to public health and social development. Here, we synthesized 4±0.5 nm copper (I) sulfide (Cu₂ S) nanoparticles (NPs) with 46 mdeg chiroptical property at 530 nm to selectively cleavage HBV core antigen (HBcAg) and effectively blocked HBV assembly and prevented HBV infection both in vitro and in vivo under light at 808 nm. Experimental analysis showed that the chiral Cu₂ S NPs specific bound with the functional domain from phenylalanine₂₃ (F₂₃ ) to leucine₃₀ (L₃₀ ) from HBcAg primary sequence and the cutting site was between amino acid residues F₂₄ and proline₂₅ (P₂₅ ). Under excitation at 808 nm, the intracellular HBcAg concentration was reduced by 95 %, and in HBV transgenic mice, the levels of HBV surface antigen (HBsAg) and HBV DNA were decreased by 93 % and 86 %, respectively. Together, these results reveal the potential nanomedicine for HBV control and provide fresh tools for viral infection.

Biomineralization of Cu2S Nanoparticles by Geobacter sulfurreducens

Dissimilatory metal-reducing bacteria are ubiquitous in soils and aquifers and are known to utilize a wide range of metals as terminal electron acceptors. These transformations play an important role in the biogeochemical cycling of metals in pristine and contaminated environments and can be harnessed for bioremediation and metal bioprocessing purposes. However, relatively little is known about their interactions with Cu. As a trace element that becomes toxic in excess, Cu can adversely affect soil biota and fertility. In addition, biomineralization of Cu nanoparticles has been reported to enhance the mobilization of other toxic metals. Here, we demonstrate that when supplied with acetate under anoxic conditions, the model metal-reducing bacterium Geobacter sulfurreducens can transform soluble Cu(II) to Cu₂S nanoparticles. This study provides new insights into Cu biomineralization by microorganisms and suggests that contaminant mobilization enhanced by Cu biomineralization could be facilitated by Geobacter species and related organisms.

Biomineralization of Cu has been shown to control contaminant dynamics and transport in soils. However, very little is known about the role that subsurface microorganisms may play in the biogeochemical cycling of Cu. In this study, we investigate the bioreduction of Cu(II) by the subsurface metal-reducing bacterium Geobacter sulfurreducens. Rapid removal of Cu from solution was observed in cell suspensions of G. sulfurreducens when Cu(II) was supplied, while transmission electron microscopy (TEM) analyses showed the formation of electron-dense nanoparticles associated with the cell surface. Energy-dispersive X-ray spectroscopy (EDX) point analysis and EDX spectrum image maps revealed that the nanoparticles are rich in both Cu and S. This finding was confirmed by X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses, which identified the nanoparticles as Cu₂S. Biomineralization of Cu_xS nanoparticles in soils has been reported to enhance the colloidal transport of a number of contaminants, including Pb, Cd, and Hg. However, formation of these Cu_xS nanoparticles has only been observed under sulfate-reducing conditions and could not be repeated using isolates of implicated organisms. As G. sulfurreducens is unable to respire sulfate, and no reducible sulfur was supplied to the cells, these data suggest a novel mechanism for the biomineralization of Cu₂S under anoxic conditions. The implications of these findings for the biogeochemical cycling of Cu and other metals as well as the green production of Cu catalysts are discussed.

IMPORTANCE Dissimilatory metal-reducing bacteria are ubiquitous in soils and aquifers and are known to utilize a wide range of metals as terminal electron acceptors. These transformations play an important role in the biogeochemical cycling of metals in pristine and contaminated environments and can be harnessed for bioremediation and metal bioprocessing purposes. However, relatively little is known about their interactions with Cu. As a trace element that becomes toxic in excess, Cu can adversely affect soil biota and fertility. In addition, biomineralization of Cu nanoparticles has been reported to enhance the mobilization of other toxic metals. Here, we demonstrate that when supplied with acetate under anoxic conditions, the model metal-reducing bacterium Geobacter sulfurreducens can transform soluble Cu(II) to Cu₂S nanoparticles. This study provides new insights into Cu biomineralization by microorganisms and suggests that contaminant mobilization enhanced by Cu biomineralization could be facilitated by Geobacter species and related organisms.

Hierarchical Octahedra Constructed by Cu2 S/MoS2 ⊂Carbon Framework with Enhanced Sodium Storage

Metal sulfides have aroused considerable attention for efficient sodium storage because of their high capacity and decent redox reversibility. However, the poor rate capability and fast capacity decay greatly hinder their practical application in sodium-ion batteries. Herein, a self-template-based strategy is designed to controllably synthesize hierarchical microoctahedra assembled with Cu₂ S/MoS₂ heterojunction nanosheets in the porous carbon framework (Cu₂ S/MoS₂ ⊂PCF) via a facile coprecipitation method coupled with vulcanization treatment. The Cu₂ S/MoS₂ ⊂PCF microoctahedra with 2D hybrid nanosubunits reasonably integrate several merits including facilitating the diffusion of electrons and Na⁺ ions, enhancing the electric conductivity, accelerating the ion and charge transfer, and buffering the volume variation. Therefore, the Cu₂ S/MoS₂ ⊂PCF composite manifests efficient sodium storage performance with high capacity, long cycling life, and excellent rate capability.

An Innovative Lithium Ion Battery System Based on a Cu2S Anode Material

Cu₂S is considered as one of the potential anode paradigms for advanced rechargeable batteries because of its high theoretical capacity (∼335 mAh·g^-1), high and flat charge/discharge voltage plateaus (∼1.7 V vs Li⁺/Li), stable cycling performance, and its elemental abundance. However, many studies have shown that Cu₂S exhibits a dramatic capacity fade in carbonate-based electrolytes, which has precluded its commercialization when paired with high voltage cathodes in state-of-the-art lithium ion batteries. Here, we report on a fundamental mechanistic study of the electrochemical processes of Cu₂S in both ether- and carbonate-based electrolytes employing operando synchrotron X-ray methods. Based on our findings, we developed a Cu₂S/C composite material that suppresses its failure mechanism in carbonate-based electrolytes and further demonstrated its feasibility in lithium ion full cells for the first time. Our experiment provides the basis for the utilization of Cu₂S in industrial-scale applications for large-scale electrical energy storage.

Rationally Designed Three-Layered Cu2 S@Carbon@MoS2 Hierarchical Nanoboxes for Efficient Sodium Storage

Hybrid materials, integrating the merits of individual components, are ideal structures for efficient sodium storage. However, the construction of hybrid structures with decent physical/electrochemical properties is still challenging. Now, the elaborate design and synthesis of hierarchical nanoboxes composed of three-layered Cu₂ S@carbon@MoS₂ as anode materials for sodium-ion batteries is reported. Through a facile multistep template-engaged strategy, ultrathin MoS₂ nanosheets are grown on nitrogen-doped carbon-coated Cu₂ S nanoboxes to realize the Cu₂ S@carbon@MoS₂ configuration. The design shortens the diffusion path of electrons/Na⁺ ions, accommodates the volume change of electrodes during cycling, enhances the electric conductivity of the hybrids, and offers abundant active sites for sodium uptake. By virtue of these advantages, these three-layered Cu₂ S@carbon@MoS₂ hierarchical nanoboxes show excellent electrochemical properties in terms of decent rate capability and stable cycle life.

Decoupling Thermoelectric Performance and Stability in Liquid-Like Thermoelectric Materials

Liquid-like materials are one family of promising thermoelectric materials discovered in the past years due to their advantanges of ultrahigh thermoelectric figure of merit (zT), low cost, and environmental friendliness. However, their practial applications are greatly limited by the low service stability from the Cu/Ag metal deposition under large current and/or temperature gradient. Both high zT for high efficiency and large critical voltage for good stability are required for liquid-like materials, but they are usually strongly correlated and hard to be tuned individually. Herein, based on the thermodynamic analysis, it is shown that such a correlation can be decoupled through doping immobile ions into the liquid-like sublattice. Taking Cu2- δ S as an example, doping immobile Fe ions in Cu1.90S scarcely degrades the initial large critical voltage, but significantly enhances the zT to 1.5 at 1000 K by tuning the carrier concentration to the optimal range. Combining the low-cost and environmentally friendly features, these Fe-doped Cu2- δ S-based compounds show great potential in civil applications. This study sheds light on the realization of both good stability and high performance for many other liquid-like thermoelectric materials that have not been considered for real applications before.

High Thermoelectric Figure of Merit Achieved in Cu2S1- xTe x Alloys Synthesized by Mechanical Alloying and Spark Plasma Sintering

Chalcogenides have been considered as promising thermoelectric materials because of their low cost, nontoxicity, and environmental benignity. In this work, we synthesized a series of Cu₂S_{1- x}Te _x (0 ≤ x ≤ 1) alloys by a facile, rapid method of mechanical alloying combined with spark plasma sintering process. The Cu₂S_{1- x}Te _x system provides an excellent vision of the competition between pure phase and phase transformation, entropy-driven solid solution, and enthalpy-driven phase separation. When the Te concentration increases, the Cu₂S_{1- x}Te _x system changed from the pure monoclinic Cu₂S at x = 0 to monoclinic Cu₂S_{1- x}Te _x solid solution at 0.02 ≤ x ≤ 0.06 and then transforms to hexagonal Cu₂S_{1- x}Te _x solid solution at 0.08 ≤ x ≤ 0.1. The phase separation of hexagonal Cu₂Te in the hexagonal Cu₂S matrix occurs at 0.3 ≤ x ≤ 0.7 and finally forms the hexagonal Cu₂Te at x = 1. Owing to the changed band structure and the coexisted Cu₂S and Cu₂Te phases, greatly enhanced power factor was achieved in all Cu₂S_{1- x}Te _x (0 < x < 1) alloys. Meanwhile, the point defect introduced by the substitution of Te/S atoms strengthened the phonon scattering, resulting in a lowered lattice thermal conductivity in most of these solid solutions. As a consequence, Cu₂S_0.94Te_0.06 exhibits a maximum ZT value of 1.18 at 723 K, which is about 3.7 and 14.8 times as compared to the values of pristine Cu₂S (0.32) and Cu₂Te (0.08), respectively.

Reversible structure manipulation by tuning carrier concentration in metastable Cu2S

The optimal functionalities of materials often appear at phase transitions involving simultaneous changes in the electronic structure and the symmetry of the underlying lattice. It is experimentally challenging to disentangle which of the two effects--electronic or structural--is the driving force for the phase transition and to use the mechanism to control material properties. Here we report the concurrent pumping and probing of Cu₂S nanoplates using an electron beam to directly manipulate the transition between two phases with distinctly different crystal symmetries and charge-carrier concentrations, and show that the transition is the result of charge generation for one phase and charge depletion for the other. We demonstrate that this manipulation is fully reversible and nonthermal in nature. Our observations reveal a phase-transition pathway in materials, where electron-induced changes in the electronic structure can lead to a macroscopic reconstruction of the crystal structure.

Large-Size 2D β-Cu2 S Nanosheets with Giant Phase Transition Temperature Lowering (120 K) Synthesized by a Novel Method of Super-Cooling Chemical-Vapor-Deposition

2D triangular β-Cu₂ S nanosheets with large size and high quality are synthesized by a novel method of super-cooling chemical-vapor-deposition. The phase transition of this 2D material from β-Cu₂ S to γ-Cu₂ S occurs at 258 K (-15 °C), and such transition temperature is 120 K lower than that of its bulk counterpart (about 378 K).

Crystal-bound vs surface-bound thiols on nanocrystals

The use of thiol ligands as a sulfur source for nanocrystal synthesis has recently come en vogue, as the products are often high quality. A comparative study was performed of dodecanethiol-capped Cu2S prepared with elemental sulfur and thiol sulfur reagents. XPS and TGA-MS provide evidence for differing binding modes of the capping thiols. Under conditions where the thiol acts only as a ligand, the capping thiols are "surface-bound" and bond to surface cations in low coordination number sites. In contrast, when thiols are used as a sulfur source, "crystal-bound" thiols result that sit in high coordination sites and are the terminal S layer of the crystal. A (1)H NMR study shows suppressed surface reactivity and ligand exchange with crystal-bound thiols, which could limit further application of the particles. To address the challenge and opportunity of nonlabile ligands, dodecyl-3-mercaptopropanoate, a molecule possessing both a thiol and an ester, was used as the sulfur source for the synthesis of Cu2S and CuInS2. A postsynthetic base hydrolysis cleaves the ester, leaving a carboxylate corona around the nanocrystals and rendering the particles water-soluble.

Low-cost flexible nano-sulfide/carbon composite counter electrode for quantum-dot-sensitized solar cell

Cu2S nanocrystal particles were in situ deposited on graphite paper to prepare nano-sulfide/carbon composite counter electrode for CdS/CdSe quantum-dot-sensitized solar cell (QDSC). By optimization of deposition time, photovoltaic conversion efficiency up to 3.08% was obtained. In the meantime, this composite counter electrode was superior to the commonly used Pt, Au and carbon counter electrodes. Electrochemical impedance spectra further confirmed that low charge transfer resistance at counter electrode/electrolyte interface was responsible for this, implied the potential application of this composite counter electrode in high-efficiency QDSC.