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The covellite phase of copper sulfide thin film (CuS), due to its excellent electronic, optical and chemical properties, has attracted enormous attention in cutting-edge research. This is a comprehensive study of the structural, optical, morphological and electrical properties of CuS thin films deposited by chemical bath deposition technique on flexible polyethylene terephthalate (PET) substrates at different deposition temperatures, i.e. 25 °C, 40 °C, 55 °C and 70 °C for the fabrication of flexible photodetectors. X-ray diffraction and Raman spectral studies reveal the presence of hexagonal covellite phase (CuS), whereas the root mean square (RMS) roughness of CuS thin film increases with an increase in deposition temperature. The optical bandgap of CuS thin film is found to be decreased with an increase in deposition temperature. The optimized CuS thin film, deposited at 70 °C, exhibits a homogeneous surface with RMS roughness of 13.72 nm, mobility of 25.09 cm2 V−1s−1 and bandgap of 1.86 eV. The mobility of CuS thin film is found to be increased with the increase in deposition temperature. The flexible CuS photodetector, fabricated at 70 °C, exhibits better photoresponse characteristics, with the highest responsivity of 0.18 mA W−1, specific detectivity of 1.39 × 108 Jones and sensitivity of 173.25 % upon light illumination. The established photocurrent possesses an outstanding dependence on various intensities of illuminated light. Furthermore, the bending test of flexible CuS photodetectors reveals the absence of any sign of deterioration up to bending angle of 30°. This suggests that the Al/CuS-PET/Al photodetector device could be used in various wearable optoelectronic device applications. [ABSTRACT FROM AUTHOR]

The complete reaction of chalcopyrite at ≥220 °C under pressure oxidation conditions (10 or 20% w/w pulp density, PO2 700 kPa) is a clean process producing a residue consisting of hematite and un-reacted gangue minerals. However, when the process water contains chloride ions, covellite intermediate formation is significant and subsequently generates elemental sulphur that can persist for up to 60 min. Increasing the temperature to 230 °C reduces this time, although the dissolution of copper and the oxidation of sulphur still follows non-parallel reaction pathways. At 245 °C, the production of elemental sulphur in the presence of moderate chloride levels, 15 g/L, is no longer significant. The effects of other chemical additions (including enhancement of aluminium content) are also examined. Particular emphasis is given to the mineralogy of the leach residues and the deportment of iron in these residues to various phases that include hematite, basic ferric sulphate and natrojarosite. The residues are found to also contain a number of other intermediate phases in addition to covellite and sulphur, such as antlerite and clinoatacamite, depending upon the leach conditions employed. [ABSTRACT FROM AUTHOR]

Recrystallization of the copper sulfide occurs during the thermal treatment of the samples and directly affects the size of the nanoparticles. Since particle size is one of the most important characteristics of copper sulfides, in determining the electrochemical and optical properties of nanostructured sulfides, the investigation of the thermal stability of copper sulfides is relevant. In this work, the mechanism of the thermal decomposition of synthetic covellite was investigated and proposed. According to the literature, thermal decomposition and oxidation presumably occur up to 600 °C, and therefore, the experiments were carried out in a temperature range of 25–600 °C. The thermal behavior and decomposition were investigated and characterized by XRD, DSC, and SEM–EDX analysis methods. It was determined that the duration of synthesis had an influence on the temperature of decomposition of synthetic covellite, because by prolonging the duration of synthesis from 0.5 to 4 h, the temperature range of the stability of covellite increased by 100 °C (from 300 to 400 °C). Furthermore, the application of different sulfurizing agents for hydrothermal synthesis insignificantly affected the mineral changes of the annealing products in the temperature range of 250–400 °C. It was established that minor reactions of covellite decomposition started in 300 °C, by forming Cu7S4 and Cu9S5. The majority of digenite formed at a temperature higher than 400 °C. It was determined that at a temperature higher than 450 °C, Cu1.81S and Cu2S formed and copper sulfide oxidation to copper sulfate occurred. [ABSTRACT FROM AUTHOR]

The complete reaction of chalcopyrite at ≥220 °C under pressure oxidation conditions (10 or 20% w/w pulp density, PO2 700 kPa) is a clean process producing a residue consisting of hematite and un-reacted gangue minerals. However, when the process water contains chloride ions, covellite intermediate formation is significant and subsequently generates elemental sulphur that can persist for up to 60 min. Increasing the temperature to 230 °C reduces this time, although the dissolution of copper and the oxidation of sulphur still follows non-parallel reaction pathways. At 245 °C, the production of elemental sulphur in the presence of moderate chloride levels, 15 g/L, is no longer significant. The effects of other chemical additions (including enhancement of aluminium content) are also examined. Particular emphasis is given to the mineralogy of the leach residues and the deportment of iron in these residues to various phases that include hematite, basic ferric sulphate and natrojarosite. The residues are found to also contain a number of other intermediate phases in addition to covellite and sulphur, such as antlerite and clinoatacamite, depending upon the leach conditions employed.

The flotation separation of enargite from copper sulfide minerals is difficult owing to the similar floatability and reagent adsorption characteristics of these minerals. In this study, the effect of oxidation treatment using NaClO flow with FeCl3 on the flotation separation of covellite and enargite was systematically investigated. Micro-flotation tests and contact angle measurements indicated that the addition of NaClO and FeCl3 increased the hydrophobicity difference between covellite and enargite. The bench-scale flotation test results show that the bulk copper concentrate could be separated into two products: a low-arsenic-containing (0.46%) and a high-arsenic-containing (5.18%) copper concentrate. X-ray photoelectron spectroscopy and scanning electron microscopy revealed that the oxidization treatment of NaClO caused the accumulation of oxides on the covellite surface, but not on the enargite surface. The varying precipitation of ferric hydroxide on the surfaces of covellite and enargite further exacerbated the difference in the hydrophilicity of these minerals. Thus, a possible method for separating enargite from covellite was obtained through oxidation treatment using NaClO and FeCl3. [ABSTRACT FROM AUTHOR]

The graphical abstract image illustrating the formation of clove structured CuS and their application towards benzene detection. [Display omitted] • A reliable and sensitive approach for the detection of benzene in gas phase. • The fabricated hexagonal structured CuS microcloves showed excellent photoresponse against benzene under visible light exposure. • The lattice parameters are calculated to be a = b = 3.798 ± 5 Å and c = 16.358 ± 10. • CuS MCs showed excellent selectivity, sensitivity and fast response time against benzene. We have reported CuS microcloves (MCs) for highly selective detection of benzene using scanning kelvin probe (SKP) technique. The electron microscopy investigations revealed the formation of clove shaped CuS with a size of about 1–2 µm at 180 °C and 6 h. The time of reaction significantly affected the crystallinity as well as the morphology of resulting CuS materials. The investigations on adsorption behavior of different types of common volatile organic compounds (VOCs) with varying charge and nature revealed an outstanding selectivity towards benzene when compared to other VOCs. The difference in work function between gold tip and sensor surface modified with CuS MCs was decreased under the exposure of light, most likely caused by transfer of electrons to conduction band of CuS under illumination of light. As a result, the CuS MCs showed enhanced photo response in visible light exposure in the presence of benzene. A chemiresistive type sensor device was fabricated using CuS MCs and exposed to benzene vapor in a concentration ranging from 2.8 to 11.2 ppm. The sensitivity was found to be 1.63 × 10-3 ppm−1. Notably, a rapid response time of ∼6 s and recovery time of ∼ 16 s was achieved for the sensor at a benzene concentration of 5.6 ppm at room temperature. Also, considerable and repeatable sensor response was observed for 560 ppb of benzene vapor at 70 °C. Hence, these results suggested that the CuS MCs have huge potential as novel material for selective benzene detection in gas phase towards breath analysis and other environmental monitoring. [ABSTRACT FROM AUTHOR]

Nonstoichiometric minerals form during the leaching of chalcocite; they form the following sequential row between chalcocite and covellite: djurleite (Cu1.93–1.96S), roxbyite (Cu1.72–1.82S), digenite (Cu1.75–1.78S), anilite (Cu1.75S), geerite (Cu1.5–1.6S), spionkopite (Cu1.4S), and yarrowite (Cu1.1S). A hypothesis that the oxidation of chalcocite (Cu2S) ends in villamaninite (CuS2) rather than covellite (CuS) has been put forward and substantiated. The formation of various copper sulfides during the oxidation of chalcocite is related to the fact that copper has a variable valence and sulfur can be in them in both mono- and disulfide form. A scientific substantiation and chemical reactions are proposed for the formation of elemental orthorhombic sulfur at the last stage of chalcocite leaching, and the possibility of appearance of its other allotropes is shown. When chalcocite and other sulfides are leached below the melting temperature of sulfur (low-temperature regime), cyclic sulfur molecules, which are essentially liquid (molten) sulfur, form. During leaching, sulfate ions and elemental sulfur do not precipitate in two independent processes: they form in one way through the formation of polysulfides, which are transitional phases to molecular sulfur. [ABSTRACT FROM AUTHOR]

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The flotation separation of enargite from copper sulfide minerals is difficult owing to the similar floatability and reagent adsorption characteristics of these minerals. In this study, the effect of oxidation treatment using NaClO flow with FeCl3 on the flotation separation of covellite and enargite was systematically investigated. Micro-flotation tests and contact angle measurements indicated that the addition of NaClO and FeCl3 increased the hydrophobicity difference between covellite and enargite. The bench-scale flotation test results show that the bulk copper concentrate could be separated into two products: a low-arsenic-containing (0.46%) and a high-arsenic-containing (5.18%) copper concentrate. X-ray photoelectron spectroscopy and scanning electron microscopy revealed that the oxidization treatment of NaClO caused the accumulation of oxides on the covellite surface, but not on the enargite surface. The varying precipitation of ferric hydroxide on the surfaces of covellite and enargite further exacerbated the difference in the hydrophilicity of these minerals. Thus, a possible method for separating enargite from covellite was obtained through oxidation treatment using NaClO and FeCl3.

We report on the properties of the (0001) covellites surfaces, which we investigate by periodic slab density functional theory calculations. The absolute surface energies have been computed for all bulk terminations, showing that surfaces terminated by the flat CuS layer are associated with the lowest surface energy. Cleavage is predicted to occur across the [0001] interlayer Cu-S bond. The surfaces obtained by lowest energy cleavage are analyzed in terms of the atomic vertical relaxation, workfunction, and surface band structure. Our study predicts the presence of a shallow pz-derived surface state located 0.26 eV below the Fermi level, which is set to play an important role in the surface reactivity of covellite. [ABSTRACT FROM AUTHOR]

Morphology and phase have significant role in the performance of catalysts. Herein, we fabricated various novel and highly hierarchical flower-like copper sulfide superstructures of CuS and Cu 1.8 S phase through self-assembly of nanoplates or nanosheets via solvothermal reaction by adjusting the ratio of precursors and the type of solvent (i.e. 2-propanol, methanol, and mixed 2-propanol: water). Subsequently, the growth mechanism of superstructures was systematically investigated. These results demonstrate that the copper sulfide superstructures display surface area, morphology, and phase-dependent catalytic activity for decolorization of organic dye in an aqueous medium. Additionally, the rose like CuS structures showed the highest rate constant and reusability property. Thus they could be useful for environmental pollution cleanup as an efficient catalyst. [ABSTRACT FROM AUTHOR]

Dissolution kinetics of digenite (Cu9S5) was studied in Fe3+-H2SO4-NaCl media. The temperature range for the study was between 297 and 373 K (24 and 100°C), with a ferric concentration between 0.0100 and 0.0806 mol/dm3, a sulfuric acid concentration of 0.05 to 1.5 mol/dm3 and a NaCl concentration of 1.5 to 5 mol/dm3. Agitation speed and particle size were also studied. Results indicate that the dissolution mechanisms of digenite occurs in two stages: i) generation of covellite (CuS) with the formation of cupric ion (Cu2+) and ii) dissolution of covellite (CuS) with copper production in the system, as well as amorphous sulfur (S°). The second stage occurred very slowly compared to the first stage, the above variables studied directly affected the second stage. Temperature, Fe3+ and H2SO4 concentration positively affected dissolution of covellite formed (second stage), while the presence of NaCl did not increase dissolution of Cu9S5 or CuS. Results showed that stirring speed had an important role in the dissolution rate of CuS. Dissolution kinetics was analyzed using the model of diffusion through the porous layer. Covellite dissolution reaction order was 2.3 and 0.2 with respect to the concentration of ferric and sulfuric acid, respectively, and the rate was inversely proportional to particle size. The calculated activation energy was 36.1 kJ/mol, which is a typical value for a reaction controlled by diffusion in the porous layer at temperature between 297 and 373 K (24 and 100°C). [ABSTRACT FROM AUTHOR]

We report on a systematic study on the physicochemical attributes of synthetic Fe-Cu-sulfide nanoparticles (NPs) precipitated under conditions similar to the anoxic, low-temperature aqueous, sedimentary, soil, and subsurface environments where these NPs have been repeatedly identified. Characterizing the basic attributes of these NPs is the first step in understanding their behaviors in various processes including in the bio-availability of essential and toxic metals, environmental remediation, and resource recovery. Abiotic experiments are compared to biotic experiments in the presence of the sulfate-reducer Desulfovibrio vulgaris to elucidate biological controls on NP formation. First, the single-metal end-member NPs are determined by precipitation in a solution containing either aqueous Fe(II) or Cu(II). Limited differences are observed between biogenic and abiogenic precipitates aged for up to one month; the Fe-only experiments resulted in 4 -- 10 nm mackinawite (FeS) NPs that aggregate to form nanosheets up to ~1000 nm in size, while the Cu-only experiments resulted in mixtures of covellite (CuS) NPs comprised of <10 nm fine nanocrystals, 20 -- 40 × 6 -- 9 nm nanorods, and ~30 nm nanoplates. The crystal sizes of biogenic mackinawite and covellite are, respectively, larger and smaller than their abiogenic counterparts, indicating a mineral-specific response to biological presence. Structural defects are observable in the fine nanocrystals and nanorods of covellite in both biogenic and abiogenic experiments, indicative of intrinsic NP instability and formation mechanism via particle attachment. In contrast, covellite nanoplates are defect free, indicating high stability and potentially rapid recrystallization following particle attachment. Next, mixed-metal sulfide NPs are precipitated at variable initial aqueous Fe-to-Cu ratios (2:1, 1:1, and 1:5). With an increasing ratio of Fe-to-Cu, Fe-rich covellite, nukundamite (Cu5.5FeS6.5), chalcopyrite (CuFeS2), and Cu-rich mackinawite are formed. The Fe-rich covellite NPs are larger (100 -- 200 nm) than covellite precipitated in the absence of Fe, indicating a role for Fe in promoting crystal growth. Chalcopyrite and nukundamite are formed through the incorporation of Fe into precursor covellite NPs while retaining the original crystal morphology, as confirmed by doping a covellite suspension with aqueous Fe(II), resulting in the formation of chalcopyrite and nukundamite within days. Additionally, in the biological systems, we observe the recrystallization of mackinawite to greigite (Fe3S4) after six months of incubation in the absence of Cu and the selective formation of chalcopyrite and nukundamite at lower initial Fe-to-Cu ratios compared to abiotic systems. These observations are consistent with NP precipitation that are influenced by the distinct (sub)micro-environments around bacterial cells compared to the bulk solution. Comparative TEM analyses indicate that the synthetic NPs are morphologically similar to NPs identified in natural environments, opening ways to studying behaviors of natural NPs using experimental approaches. [ABSTRACT FROM AUTHOR]

Abstract The effect of calcium hypochlorite (Ca(ClO) 2) on the flotation separation of covellite and pyrite with ammonium dibutyl dithiophophate (ADD) has been investigated through micro-flotation tests, zeta-potential measurements, infrared spectroscopy (IR) analyses, adsorption measurements and X-ray photoelectron (XPS) analyses. The flotation results illustrate that Ca(ClO) 2 depressed pyrite selectively and had little effect on covellite at pH 10. The zeta-potential measurements indicate that a potential change occurred on covellite and pyrite because of the adsorption of ADD. The selective adsorption of Ca(OH)+ on pyrite causes a sharp decrease in the negative potential. In addition, adsorption studies and IR analyses demonstrate that the adsorption of ADD on pyrite is strongly inhibited by Ca(ClO) 2 , whereas that on covellite is affected only slightly. Furthermore, XPS analyses confirm that pyrite is preferentially oxidized by Ca(ClO) 2 to form CaSO 4 and Fe(OH) 3 on its surface; thus, the adsorption of ADD on pyrite is prevented, resulting in the depression of pyrite. Graphical abstract Unlabelled Image Highlights • Selective separation of covellite from pyrite was achieved by flotation. • Ca(ClO) 2 selectively depressed the flotation of pyrite rather than that of covellite. • Pyrite surface was oxidized by Ca(ClO) 2 to prevent ADD adsorption. • Oxidative mechanism of pyrite was proposed based on electrochemical theory. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Bimetal Cu Ni OS oxysulfide nanoflower was prepared by a feasible method. • Cu Ni OS performed high redox activity in the dark without additional reagents. • The Cu+/Cu2+ ratio in Cu Ni OS affected its catalytic activity for redox reactions. • Redox reactions involve the electron or hole transport between Cu+ and Cu2+. • Kinetic mechanism is schematically proposed to explain for the fast redox reactions. Abstract Cu Ni OS bimetal oxysulfide catalysts with catalytic activity in the dark were synthesized by a feasible solution method below 100 °C. It has a hexagonal CuS covellite structure with the Cu+/(Cu++Cu2+) molar ratio above 0.6. S6+ was formed to balance the deficiency in positive charge due to a high Cu+ content. The effect of hydrazine (N 2 H 4) amount added during the Cu Ni OS synthesis on the redox reactions was evaluated. The N 2 H 4 -free Cu Ni OS showed the fast methylene blue (MB) degradation capability and the [N 2 H 4 ]-high Cu Ni OS had the high Cr(VI) reduction capability all in the dark condition. The adjustable redox reactions by the Cu Ni OS catalyst system are demonstrated and explained. The catalytic reaction mechanism is elucidated, depending upon the Cu+/Cu2+ ratio for different charge transports. Cu Ni OS also exhibited relatively good stability and durability during its reusability tests. The catalytic reactions under the mild conditions without heat and electrical and thermal energies are encouraging for green synthesis. [ABSTRACT FROM AUTHOR]

CuS, or covellite (hexagonal symmetry), was compressed in a diamond anvil cell at room temperature up to a pressure of 45 GPa, and studied using x rays from both a Mo Kα source and a synchrotron. The x-ray diffraction spectrum of CuS disappears by about 18 GPa. The presence of Cu fluorescence lines in all spectra and the reappearance of diffraction lines upon decompression confirm that CuS undergoes reversible pressure-induced amorphization at this pressure. A third-order Birch–Murnaghan equation of state fit to the diffraction data below 11 GPa yields a bulk modulus of 89±10 GPa with a pressure derivative of -2±2 for covellite. Further compression up to 45 GPa shows three to four diffraction lines of very low intensity, implying some high pressure ‘‘ordering’’ of the amorphous phase. The Raman spectra obtained indicate that the changes in structure are probably due to the twisting or the distortion of covalently bonded CuS4–CuS4 units in different directions. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The study demonstrates the process of anion exchanger modification in order to obtain a reactive organic polymer containing Cu x S dispersed within its matrix. As starting materials, two strongly basic commercial anion exchangers were used – macroreticular and gel-type – previously modified by deposition of cuprite or tenorite within their structure. The pre-formed composites were sulphidated using an Na 2 S solution to obtain materials containing Cu x S (5.3–6.7 wt% Cu and 4.5–6.7 wt% S), which were further studied using Raman and XPS spectroscopy, and XRD and SEM/EDS analyses. Depending on the sulphidation precursor, Cu 2 O or CuO, its distribution within the polymeric matrix, and the porous structure of the supporting anion exchanger, products with different Cu x S content were obtained. The main sulphidation product – covellite – was accompanied by admixtures of copper-rich phases such as digenite and djurleite, but products of sulphide oxidation were also identified. The conversion of Cu 2 O into CuS was more efficient and selective in comparison to CuO. The sulphidation process remained within the initial distribution of the precursor particles within the polymeric matrix. The morphology of the obtained covellite particles was strongly dependent on the porous structure of the supporting anion exchanger. The conversion of the Cu 2 O and CuO within the macroporous matrix led respectively to spiky burr-like CuS and more densely packed elongated needle-shaped CuS particles, while the CuS particles obtained in the gel-type matrix were spherical. The spherical particles obtained from Cu 2 O conversion exhibited a hollow structure, which was the result of solid-state diffusion during the sulphidation, the so-called Kirkendall effect. [Display omitted] • Sulfidation of CuO and Cu 2 O into covellite in the structure of anion exchangers. • Obtained composites contained 5.3–6.7 wt% Cu and 4.5–6.7 wt% S. • Covellite was accompanied by digenite, djurlecite and brochantite. • Conversion of Cu 2 O particles was more selective than CuO transformation. • Covellite particles exhibited different morphology: spheres, needles, burr-like. [ABSTRACT FROM AUTHOR]

Copper sulfide (CuS) thin films were deposited on a glass substrate at room temperature using the radio-frequency (RF) magnetron-sputtering method at RF powers in the range of 40−100 W, and the structural and optical properties of the CuS thin film were investigated. The CuS thin films fabricated at varying deposition powers all exhibited hexagonal crystalline structures and preferred growth orientation of the (110) plane. Raman spectra revealed a primary sharp and intense peak at the 474 cm−1 frequency, and a relatively wide peak was found at 265 cm−1 frequency. In the CuS thin film deposited at an RF power of 40 W, relatively small dense particles with small void spacing formed a smooth thin-film surface. As the power increased, it was observed that grain size and grain-boundary spacing increased in order. The binding energy peaks of Cu 2p3/2 and Cu 2p1/2 were observed at 932.1 and 952.0 eV, respectively. Regardless of deposition power, the difference in the Cu2+ state binding energies for all the CuS thin films was equivalent at 19.9 eV. We observed the binding energy peaks of S 2p3/2 and S 2p1/2 corresponding to the S2− state at 162.2 and 163.2 eV, respectively. The transmittance and band-gap energy in the visible spectral range showed decreasing trends as deposition power increased. For the CuS/tin sulfide (SnS) absorber-layer-based solar cell (glass/Mo/absorber(CuS/SnS)/cadmium sulfide (CdS)/intrinsic zinc oxide (i-ZnO)/indium tin oxide (ITO)/aluminum (Al)) with a stacked structure of SnS thin films on top of the CuS layer deposited at 100 W RF power, an open-circuit voltage (Voc) of 115 mA, short circuit current density (Jsc) of 9.81 mA/cm2, fill factor (FF) of 35%, and highest power conversion efficiency (PCE) of 0.39% were recorded.

Many researchers found that the Fe2+ together with less amount of Cu2+ can accelerate the leaching of chalcopyrite. In this work, the leaching of chalcopyrite with Cu2+ was investigated. The leaching residuals were examined by Raman spectroscopy. Based on the leaching experiments, the chemical equilibrium in solution was calculated using Visual MINTEQ. The results showed that the Fe in chalcopyrite lattice was replaced by Cu2+; therefore, the chalcopyrite transformed into covellite. Furthermore, the formation of chalcocite occurred when Fe2+ and Fe3+ were added to the solution containing Cu2+. The copper extraction increased with a decrease of the initial redox potential (or the ratio of Fe3+/Fe2+). [ABSTRACT FROM AUTHOR]

Copper sulfides (Cu2−xS) comprises a family of sulfides which possess good electrical and photovoltaic properties due to their self-doping (p-type) nature, attributed from the copper vacancies in their structure. Recently, metal sulfide thin films have been investigated for their resistive RAM behaviour due to the reversible formation of conductive bridges between crystalline structures. In this letter, 2D self-assembled finned covellite (CuS) was prepared via RF Magnetron Sputtering. This 2D finned CuS was found to be polycrystalline via TEM, exhibiting ReRAM behaviour with resistances having two orders of magnitude differences between 0 and −0.5 V. This fin structure eliminates the need for a multi-layered device which until now is the primary method of harnessing the ReRAM behaviour in copper sulphide. It gives rise to very low voltages of −3 V and 1 V for writing and reset, respectively, with a writing time of 20 ms. [ABSTRACT FROM AUTHOR]

In the present study, the mechanochemically prepared covellite, CuS and chalcocite, Cu 2 S nanocrystals are compared in detail. Concretely, the SEM, EDS, N 2 adsorption, UV–Vis, PL, FTIR, ZP measurement, PCCS, XPS and DTA/TG were used. SEM, EDS and elemental mapping have shown that the agglomerates containing nanoparticles of the corresponding phases were formed as a result of milling. The nitrogen adsorption method has documented richer surface properties in the case of CuS sample. The specific surface area values were 2.7 m 2  g −1 and 1.4 m 2  g −1 for CuS and Cu 2 S, respectively. UV–Vis and PL measurements have shown that these materials might be suitable for optoelectronic applications, as the optical bandgaps were 1.92 eV and 3 eV for CuS and Cu 2 S, respectively. FTIR spectrum of CuS exhibited a peak at 621 cm −1 , which is characteristic for this material. ZP values were more negative in the case of CuS and PCCS has confirmed the finer character of this sample (x 50 values were 680 nm and 617 nm for Cu 2 S and CuS, respectively). XPS method documented the surface oxidation of the prepared Cu 2 S. The thermal stability measurement up to 550 °C has shown that Cu 2 S does not undergo significant changes (only 1.4% weight loss was observed), whereas CuS is losing sulfur and is transformed into digenite and chalcocite (14.3% weight loss was observed). The mechanochemically synthesized copper sulfides show high activities in photodecolorization of Methyl Orange dye under visible light irradiation, as Cu 2 S was able to completely decompose the dye in 150 min and CuS caused 80% decomposition after the same time of treatment. [ABSTRACT FROM AUTHOR]

For Kupferschiefer mining established pyrometallurgical and acidic bioleaching methods face numerous problems. This is due to the finely grained and dispersed distribution of the copper minerals, the complex mineralogy, comparably low copper content, and the possibly high carbonate and organic content in this ore. Leaching at neutral pH seemed worth a try: At neutral pH the abundant carbonates do not need to be dissolved and therewith would not consume excessive amounts of provided acids. Certainly, copper solubility at neutral pH is reduced compared to an acidic environment; however, if copper complexing ligands would be supplied abundantly, copper contents in the mobile phase could easily reach the required economic level. We set up a model system to study the effect of parameters such as pH, microorganisms, microbial metabolites, and organic ligands on covellite leaching to get a better understanding of the processes in copper leaching at pH ≥ 6. With this model system we could show that glutamic acid and the microbial siderophore desferrioxamine B promote covellite dissolution. Both experimental and modeling data showed that pH is an important parameter in covellite dissolution. An increase of pH from 6 to 9 could elevate copper extraction in the presence of glutamic acid by a factor of five. These results have implications for both development of a biotechnological process regarding metal extraction from Kupferschiefer, and for the interaction of bacterial metabolites with the lithosphere and potential mobilization of heavy metals in alkaline environments. [ABSTRACT FROM AUTHOR]

Thin films of covellite copper sulphide (CuS) were deposited on FTO substrates using chemical spray pyrolysis technique. Influence of Cu-to-S molar ratio on structural, surface morphological, optical and electrical properties were systematically investigated using variety of characterization techniques. Formation of covellite CuS films was confirmed by low angle-XRD and Raman spectroscopy. The field emission scanning electron microscopy analysis revealed the formation of faceted CuS particles without secondary growth. Optical studies exhibited decrease in optical band gap (from 2.21 to 1.69 eV) with increase in Cu-to-S molar ratio. Electrical properties were investigated using Van der Pauw four point probe method and Hall measurements revealed that as-synthesized CuS films have low sheet resistance (1.47–2.45 Ω/□), high carrier mobility (8.90–54.89 cm2/Vs) and high sheet concentration (1016–1018/cm2). The CuS films deposited at optimized Cu-to-S molar ratio (1:2.5) were then further studied for electrochemical impedance spectroscopy and photovoltaic characteristics. A quantum-dot sensitized solar cell incorporating optimized CuS film as counter electrode showed power conversion efficiency of ~ 1.05% with Voc ~ 0.46 V, Isc ~ 1.01 mA/cm2 and fill factor ~ 0.34%. Although the cell is not fully optimized and better results can be anticipated. [ABSTRACT FROM AUTHOR]

Synthesis of copper sulfide-based nanomaterials by cation incorporation into copper deficient copper sulfide (Cu2-xS) is of interest as a powerful means to obtain nanostructures with otherwise inaccessible combinations of size, shape, composition, and crystal phase. Incorporation of a heterocation (M) may produce heterogeneous Cu2-xS-MS nanocrystals (NCs) or homogeneous Cu-M-S alloys. However, the factors determining whether heterogeneous NCs or homogeneous alloy NCs are produced have not been fully elucidated. In this report, we incorporate diverse cations into covellite CuS nanoplatelet (NPl) templates in the presence of dodecanethiol (DDT). These cations are categorized by their valencies. We demonstrate that trivalent and tetravalent cations can be incorporated into reduced CuS NPls to produce homogeneous ternary alloy NPls, while the divalent cations cannot coexist with Cu+ ions in the Cu2-xS phase. In turn, the incorporation of divalent cations leads to formation of heterogeneous NPls and finally produces copper-free metal sulfide NPls. The cation valence selectivity arises from conflicts between charge balance and coordination between Cu+ and divalent cations. This study not only provides better understanding of the relationship among the composition, morphology, and crystal structure of copper sulfide-based nanomaterials but also provides a pathway to controllable synthesis of complex nanostructures. [ABSTRACT FROM AUTHOR]

Copper sulfide (CuS) thin films have been used in many applications such as solar cells, photo-thermal, electro-conductive, and microwave shielding. In this work, copper sulfide thin films were deposited on glass and silicon substrates by thermal evaporation of in situ synthesized CuS powder. XRD analysis of these films revealed a single-crystal structure, AFM measurements indicated the films have a surface roughness (14.1 nm) and agglomerates of multiple monocrystalline particles with average size (66 nm), and the optical properties were investigated by UV-Vis spectrophotometer showing the films have high transmission (>80%) in the visible region and low absorbance with wide energy gap (3.813 eV). This novel structure with outstanding optical properties makes it very promising optical materials in optoelectronics. [ABSTRACT FROM AUTHOR]

The Bukovik-Kadiica mineralized system is hosted by Tertiary dacitic and andesitic volcanic rocks which have intruded the basement of Palaeozoic schists in the Serbo-Macedonian Massif of eastern Macedonia. The latest geological exploration has confirmed that this porphyry copper mineralizationis characterized by a dominance of chalcocite and covellite with associated chalcopyrite, emplectite, and bornite, with the highest grades in a zone of supergene enrichment. Silicification is the dominant alteration within the mineralized system, whilst zones of potassic, phyllic, argillic, propylitic, and advanced argillic alteration are also present. Silicification and sulphide mineralization are located in stockworks in altered dacite and andesite breccia. Dissolution of primary sulphides and chemical leaching are evident in the zones of oxidation, dominated by limonite breccia.The main copper mineralization has a vertical extent between 90 and 220 m. Fluid inclusion studies of mineralized quartz veins have identified three separate groups of fluids: saline inclusions which homogenize at 326-501 °C and have a salinity of 32-45 wt% NaCl equiv., vapour-dominated inclusions which homogenize at 438-497 °C and have a salinity of 6-16 wt% NaCl equiv., and more dilute, two-phase vapour-liquid inclusions that homogenize at 360-627 °C and have a salinity of 3-24 wt% NaCl equiv. [ABSTRACT FROM AUTHOR]

Thin films of the covellite phase of CuS are of special importance due to their properties for optoelectronic device applications. Their preparation by chemical solution methods could enable their deposition on flexible substrates at low temperature for large area applications. Successive Ionic Layer Adsorption and Reaction (SILAR) is a promising option because it is simple, inexpensive, and allows the control of thickness and composition. However, low crystalline CuS thin films have been reported so far. In this work, highly polycrystalline CuS thin films were successfully grown at room temperature by SILAR using CuSO4 and Na2S as the ionic solutions without post-deposition annealing. The films obtained at different SILAR cycles resulted in good appearance, uniformity, well adhered to the substrate, and presented the covellite structure as the predominant crystalline phase. X-ray diffraction analysis showed important details about the films growth evolution, which were in agreement with results from atomic force microscopy and ellipsometry. All the films exhibited low electrical resistivity in agreement with the metallic behavior observed in the infrared region of their transmittance spectra. These results demonstrate a direct method of obtaining highly polycrystalline CuS thin films at low temperature, which could open a new range of applications. [ABSTRACT FROM AUTHOR]

Covellite, CuS and chalcocite, CuS nanoparticles prepared in the explosive manner from elemental precursors were further ball-milled in order to observe additional changes caused by mechanical action. Three phases of chalcocite were interchanging during milling, monoclinic one being major at the equilibrium after 30 min. In the case of covellite synthesis, milling for 15 min brought about a significant diminishment in the content of digenite, CuS, impurity. Covellite powder exhibited finer character than chalcocite, as documented by crystallite size, grain size and specific surface area analysis. Finally, the effect of milling speed on the explosive character of the reaction and phase composition of chalcocite was investigated. The most drastic conditions favored the formation of the monoclinic phase with the lowest symmetry and the time and intensity of the explosion was found to depend on the milling speed. The whole process is mechanically driven. [ABSTRACT FROM AUTHOR]

A detailed study of the anodic behaviour of synthetic covellite in acidic chloride solutions has been conducted as part of an overall program on the fundamental aspects of the heap leaching of copper sulfide minerals. The anodic behaviour in chloride solutions is characterized by active (but slow) dissolution at low potentials below about 0.65 V, passivation at potentials above 0.70 V that continues to potentials greater than 1.4 V above which rapid transpassive dissolution occurs. These characteristics are also typical of chalcopyrite under similar conditions. The anodic characteristics at potentials in the region of the measured mixed potentials in the presence of copper(II) show that there are two peaks in the voltammetric sweeps at about 0.65 V and 0.75 V, the magnitude of which increase with increasing chloride concentration. The two peaks merge into a single peak at very high chloride concentrations. Potentiostatic current-time transients at various potentials in the region of the mixed potential show the slow passivation typical of chalcopyrite and the data can similarly be described quantitatively in terms of rate limiting solid-state diffusion. The rate of oxidative dissolution of covellite under ambient temperature conditions is slow but about an order of magnitude greater than that of chalcopyrite. The voltammetric response of chalcopyrite after pre-treatment with a chloride solution containing a low concentration of copper(II) shows the presence of the same two peaks observed for covellite confirming the surface conversion of chalcopyrite to covellite. A mechanism similar to that previously proposed for the dissolution of chalcopyrite has been described in terms of which the formation of polysulfides (typically CuS 2 ) by dissolution of a fraction of the copper in the covellite lattice is responsible for the passivation that increases slowly as the polysulfide layer increases in thickness. Novel measurements of the mixed potential and the solution potential at a covellite surface at the bottom of a capillary have been used to simulate the situation within ore particles. The results have been simulated using a simple linear diffusion model that show that the potential at the covellite surface can be 50–100 mV lower than that in the bulk of the solution. This has important consequences for the rate of heap leaching. [ABSTRACT FROM AUTHOR]

A series of copper rods were reacted with sulfur vapour in evacuated glass ampoules at ∼445 °C. Product materials were characterised by powder X-ray diffraction and reflected polarised light microscopy. Copper sulfurised rapidly to digenite, γ-Cu 2-x S, under these conditions, whereas the subsequent sulfurisation to covellite, CuS, was notably slower, yielding texturally distinguishable inner (secondary) and outer (primary) CuS regions. A two-stage partial sulfurisation of γ-Cu 1.8 S resulted in the external growth of two successive layers of primary CuS, which demonstrates decisively that covellite − besides being a p-type metal − is ionically conducting at 445 °C, although considerably less so than digenite. We infer that the growth of platy covellite crystals and their radial alignment in the primary CuS layer are a consequence of copper ion mobility being restricted to the basal plane of the covellite structure. Sulfurising a coil of copper wire at ∼445 °C is an effective method for synthesising covellite. [ABSTRACT FROM AUTHOR]

The promising application of CuS (covellite) nanoparticles in the biomedical field has motivated the present work with the aim of studying the stability of stoichiometric CuS surfaces and nanoparticles (NPs) under different conditions of pressure (p), temperature (T), and sulfur chemical potential (μS) by computational techniques using the density functional theory (DFT) formalism. Using the ab initio atomistic thermodynamic approach, the stability of several CuS surfaces is investigated by means of the linear relationship between surface energy γ and μS. A mixed surface labeled (001)-Cu/S has emerged as the most stable in all chemical potential ranges, whereas the surfaces with rich sulfur terminations labeled (020)-S, (100)-S, and (001)-S-2 are stable depending on the thermodynamic conditions. Additionally, we also investigate the composition and shape of CuS NPs as a function of μS using the Wulff construction method. These NPs show cylindrical and hexagonal prism shapes with top and bottom surfaces formed by (001)-Cu/S facets and the other surfaces are constituted by other facets depending on μS. Our description of the NPs, consistent with the reported experimental evidence, contributes significantly to the knowledge of CuS surfaces of the nanoparticle facets. [ABSTRACT FROM AUTHOR]

The focus of this experimental work is to characterize interaction of bentonite with possible used-fuel waste container materials. Experiments were performed up to 300 °C at 150–160 bars for five to six weeks. Bentonite was saturated with a 1900 ppm K-Ca-Na-Cl-bearing water with Cu-foils. Copper rapidly degrades into chalcocite (CuS 2 ) and minor covellite (CuS) in the presence of H 2 S. Chalcocite growth and corrosion pit depths were measured for four different experimental runs yielding corrosion rates between 8.8 and 116 μm/yr depending on duration of experiment, brine composition, and clay type (bentonite vs. Opalinus Clay). Results of this research show that although pit-corrosion is demonstrated on Cu substrates, experiments show that the reactions that ensue, and the formation of minerals that develop, are extraordinarily slow. This supports the use of Cu in nuclide-containment systems as a possible engineered barrier system material. [ABSTRACT FROM AUTHOR]

As a result of LA ICP MS analysis of sulfides of the Semenov-2 hydrothermal field, it is established that covellite, which replaces Zn sulfides, is enriched in most trace elements. The Ga, Ni, and In contents in it do not vary, whereas Mn, Co, and Cd are lower than in sphalerite. The distribution of trace elements in covellite, which replaces Cu-Fe sulfides, is distinct: it is enriched in Cd, Sb, Pb, and Bi, whereas the contents of other elements are either lower or invariant. Covellite, which replaces Zn sulfides, is enriched in all trace elements relative to that replacing Cu-Fe sulfides. Enrichment of covellite in trace elements relative to primary sulfides was favored by oxidation of the hydrothermal fluid by seawater, which is similar to the processes of submarine oxidation of ancient massive sulfide deposits. Covellite is also a host to invisible gold and silver in ores of the Semenov-2 field along with toxic elements such as As, Se, Te, Tl, and Cd. [ABSTRACT FROM AUTHOR]