Aqueous copper sulfide clusters as intermediates during copper sulfide formation

Bulk and Mapping Speciation Analyses Unveil the Pattern and Heterogeneity of Cu Species during Organic Waste Treatment

Organic wastes (OWs) can be a common source of copper (Cu) contamination of agricultural soils. Here we conducted a comprehensive study of 22 raw and treated OWs sampled at 6 different full-scale OW treatment plants. Bulk XANES analysis findings indicated that the Cu oxidation state was subject to changes throughout the OW treatment process, mostly depending on the anaerobic/aerobic conditions prevailing in each treatment stage. These changes were independent of the OW origin (agricultural, urban or industrial). Cu(I) prevailed in raw OWs and digestates (88-100%), whereas Cu(II) dominated in composts (46-100%). Bulk EXAFS analysis confirmed these observations and revealed that Cu(I) species in raw OWs and digestates consisted mainly of Cu(I)-sulfide (76-100%), while Cu(II) species (60-100%) in composts were Cu(II)-citrate, Cu(II)-carbonate and amorphous Cu(II)-phosphate. Interestingly, we observed that anaerobic digestion was conducive to the formation of crystallized Cu(I)-sulfides at the expense of nanosized and poorly crystalline Cu(I)-sulfide species, and that the recalcitrant Cu(I) species in composts was always crystallized Cu(I)-sulfide. XANES imaging analysis revealed Cu(II) species present in low proportions (2-4%) that were not detected using bulk XAS analysis in raw OWs and digestates. This demonstrated the potential of XANES imaging for probing minor species in complex matrices.

Solid phase speciation controls copper mobilisation from marine sediments by methanobactin

Although marine environments represent huge reservoirs of the potent greenhouse gas methane, they currently contribute little to global net methane emissions. Most of the methane is oxidized by methanotrophs, minimizing escape to the atmosphere. Aerobic methanotrophs oxidize methane mostly via the copper (Cu)-bearing enzyme particulate methane monooxygenase (pMMO). Therefore, aerobic methane oxidation depends on sufficient Cu acquisition by methanotrophs. Because they require both oxygen and methane, aerobic methanotrophs reside at oxic-anoxic interfaces, often close to sulphidic zones where Cu bioavailability can be limited by poorly soluble Cu sulphide mineral phases. Under Cu-limiting conditions, certain aerobic methanotrophs exude Cu-binding ligands termed chalkophores, such as methanobactin (mb) exuded by Methylosinus trichosporium OB3b. Our main objective was to establish whether chalkophores can mobilise Cu from Cu sulphide-bearing marine sediments to enhance Cu bioavailability. Through a series of kinetic batch experiments, we investigated Cu mobilisation by mb from a set of well-characterized sulphidic marine sediments differing in sediment properties, including Cu content and phase distribution. Characterization of solid-phase Cu speciation included X-ray absorption spectroscopy and a targeted sequential extraction. Furthermore, in batch experiments, we investigated to what extent adsorption of metal-free mb and Cu-mb complexes to marine sediments constrains Cu mobilisation. Our results are the first to show that both solid phase Cu speciation and chalkophore adsorption can constrain methanotrophic Cu acquisition from marine sediments. Only for certain sediments did mb addition enhance dissolved Cu concentrations. Cu mobilisation by mb was not correlated to the total Cu content of the sediment, but was controlled by solid-phase Cu speciation. Cu was only mobilised from sediments containing a mono-Cu-sulphide (CuSx) phase. We also show that mb adsorption to sediments limits Cu acquisition by mb to less compact (surface) sediments. Therefore, in sulphidic sediments, mb-mediated Cu acquisition is presumably constrained to surface-sediment interfaces containing mono-Cu-sulphide phases.

A Critical Look at Colloid Generation, Stability, and Transport in Redox-Dynamic Environments: Challenges and Perspectives

Colloid generation, stability, and transport are important processes that can significantly influence the fate and transport of nutrients and contaminants in environmental systems. Here, we critically review the existing literature on colloids in redox-dynamic environments and summarize the current state of knowledge regarding the mechanisms of colloid generation and the chemical controls over colloidal behavior in such environments. We also identify critical gaps, such as the lack of universally accepted cross-discipline definition and modeling infrastructure that hamper an in-depth understanding of colloid generation, behavior, and transport potential. We propose to go beyond a size-based operational definition of colloids and consider the functional differences between colloids and dissolved species. We argue that to predict colloidal transport in redox-dynamic environments, more empirical data are needed to parametrize and validate models. We propose that colloids are critical components of element budgets in redox-dynamic systems and must urgently be considered in field as well as lab experiments and reactive transport models. We intend to bring further clarity and openness in reporting colloidal measurements and fate to improve consistency. Additionally, we suggest a methodological toolbox for examining impacts of redox dynamics on colloids in field and lab experiments.

Rice straw biochar and lime regulate the availability of heavy metals by managing colloid-associated- but dissolved-heavy metals

Heavy metal (HM) pollution has extensively spread in agricultural soils, posing potential threats to food safety and human health. Biochar and lime are two amendments used to remediate the soils contaminated with HMs. However, colloids have been shown to increase the mobility of HMs in paddy soils. Nevertheless, limited investigations have been made into the impact of biochar and lime on the formation of colloid-associated (colloidal) HMs in paddy soils. In this study, column and microcosm incubation experiments were conducted to examine how biochar and lime affected the availability of HMs (arsenic, cadmium, copper, iron, manganese, lead, and zinc) in different layers of paddy soils. The results revealed that biochar significantly inhibited the formation of colloidal HMs in the soil flooding phase, whereas the lime increased the colloidal HMs. These colloids containing HMs were identified as poorly dissolved metal sulfides. When the soil was drained, colloidal HMs transformed into dissolved forms, thereby improving the availability of HMs. Biochar decreased HM availability by reducing colloidal- but dissolved- HMs, whereas lime had the opposite effect. Hence, biochar demonstrated a stable and reliable remediation ability to decrease HM availability in paddy soil during flooding and drainage processes. In conclusion, this study highlighted that biochar efficiently reduced HM availability by mitigating the formation of colloidal HMs during flooding and their transformation into dissolved HMs during drainage in paddy soils.

Inhibitory effect of exogenous mineral elements (Si, P, Zn, Ca, Mn, Se, Fe, S) on rice Cd accumulation and soil Cd bioavailability in Cd-contaminated farmlands: A meta-analysis

A promising strategy for safely remediating Cd-contaminated farmland has been the application of mineral elements, which can reduce Cd accumulation in rice and inhibit its bioavailability in Cd-contaminated farmlands. However, there is still a lack of systematic and quantitative evaluations regarding how different mineral elements affect rice Cd accumulation and soil Cd bioavailability. Here, a meta-analysis was conducted based on 1062 individual observations from 137 published works to explore the effects of Si, P, Zn, Ca, Mn, Se, Fe and S in rice Cd accumulation and soil Cd bioavailability, we aimed to identify key factors that control the reduction of Cd concentration in rice grains. The results showed that the presence of exogenous elements had dramatically reduced rice grains Cd concentrations in the following decreasing order: Fe (43.03%) > P (38.45%) > Si (33.24%) > Ca (31.90%) > Se (29.83%) > Zn (25.95%) > Mn (23.26%) > S (18.78%). The elements of Ca, P and Si had strongly reduced Cd bioavailability in soils by 29.87%, 27.80% and 22.70%, respectively. The effects of these elements on Cd bioavailability appeared to be controlled by soil physio-chemical properties, such as pH, soil organic carbon (SOC) but also water management, application amounts and elemental forms. Overall, this study provides valuable insights into the potential of using exogenous mineral elements to mitigate Cd contamination in rice and farmlands, and facilitates the selection and application of mineral elements for the safe utilization of Cd-contaminated farmlands, taking into account soil properties and other factors that affect their effect.

Inhibition of photosensitized degradation of organic contaminants by copper under conditions typical of estuarine and coastal waters

Dissolved organic matter (DOM) driven-photochemical processes play an important role in the redox cycling of trace metals and attenuation of organic contaminants in estuarine and coastal ecosystems. In this study, we evaluate the effect of Cu on 4-carboxybenzophenone (CBBP) and Suwannee River natural organic matter (SRNOM)-photosensitized degradation of seven target contaminants (TCs) including phenols and amines under pH conditions and salt concentrations typical of those encountered in estuarine and coastal waters. Our results show that trace amounts of Cu(II) (25 -500 nM) induce strong inhibition of the photosensitized degradation of all TCs in solutions containing CBBP. The influence of TCs on the photo-formation of Cu(I) and the decrease in the lifetime of transformation intermediates of contaminants (TC^•+/ TC^•_(-H)) in the presence of Cu(I) indicated that the inhibition effect of Cu was mainly due to the reduction of TC^•+/ TC^•_(-H) by the photo-produced Cu(I). The inhibitory effect of Cu on the photodegradation of TCs decreased with the increase in Cl^- concentration since less reactive Cu(I)-Cl complexes dominate at high Cl^- concentrations. The impact of Cu on the SRNOM-sensitized degradation of TCs is less pronounced compared to that observed in CBBP solution since the redox active moieties present in SRNOM competes with Cu(I) to reduce TC^•+/ TC^•_(-H). A detailed mathematical model is developed to describe the photodegradation of contaminants and Cu redox transformations in irradiated SRNOM and CBBP solutions.

Brine-Releasable Hydrogen Sulfide in Wine: Mechanism of Release from Copper Complexes and Effects of Glutathione

Copper-sulfhydryl complexes in wine can be disrupted by addition of brine to release free hydrogen sulfide (H₂S), and the resulting "brine-releasable H₂S" is reported to correlate with formation of H₂S during bottle storage. However, both the mechanism of the brine-release assay and factors affecting the stability of copper sulfhydryls under brine-release conditions are not well understood. By varying brine composition and concentration, it is shown that release of copper-complexed H₂S requires the presence of a halide (Cl^- and Br^-) and is not due to a general "salting-out" effect. Release of copper-complexed H₂S by the brine dilution assay is highly temperature-dependent. When H₂S and Cu(II) are added to a model wine, brine-releasable H₂S decreases markedly (∼10-fold) after a 20 min incubation period prior to performing the brine-release assay. In commercial wines, the fraction of added H₂S recovered through the brine-release assay was correlated with the initial glutathione (GSH) concentration (r² = 0.58) but not with initial Cu. Negligible additional release of H₂S from organopolysulfanes was observed following addition of a disulfide-reducing agent (tris(2-carboxyethyl)phosphine). As previous studies have reported a correlation between H₂S formed under brine-release conditions and normal storage, these results suggest that the susceptibility of a wine to form latent copper-sulfhydryl precursors of H₂S following copper addition is dependent on the concentration of sulfhydryls like GSH.

Copper transformation, speciation, and detoxification in anoxic and suboxic freshwater sediments

The complex chemistry of copper (Cu) in freshwater sediments at low concentrations is not well understood. We evaluated the transformation processes of Cu added to freshwater sediments under suboxic and anoxic conditions. Freshwater sediments from three sources in Michigan with different characteristics (Spring Creek, River Raisin, and Maple Lake) were spiked with 30 or 60 mg kg^-1 Cu and incubated under a nitrogen atmosphere. After 28-d, each treatment subset was amended with organic matter (OM) to promote anoxic conditions and evaluate its effects on Cu speciation. OM addition triggered a shift from suboxic to anoxic conditions, and sequential extractions showed that Cu accordingly shifted from acid-soluble to oxidizable fractions. Extended X-ray absorption fine-structure (EXAFS) spectroscopy revealed that Cu sulfides dominated all anoxic samples except for Spring Creek 30 mg kg^-1, where Cu(I) was predominantly complexed to thiol groups of OM. Covellite and chalcopyrite (CuFeS₂) were the predominant Cu species in nearly all anoxic samples, as determined by Raman spectroscopy, scanning electron microscopy, and X-ray absorption near-edge structure (XANES) spectroscopy. Copper reduction also occurred under suboxic conditions: for two of three sediments, around 80% had been reduced to Cu(I), while the remaining 20% persisted as Cu(II) complexed to OM. However, in the third coarsest (i.e., Spring Creek), around 50% of the Cu had been reduced, forming Cu(I)-OM complexes, while the remainder was Cu(II)-OM complexes. Toxicity tests showed that survival of H. azteca and D. magna were significantly lower in suboxic treatments. Anoxic sediments triggered a near-complete transformation of Cu to sulfide minerals, reducing its toxicity.

Improved extraction of acid-insoluble monosulfide minerals by stannous chloride reduction and its application to the separation of mono- and disulfide minerals in the presence of ferric iron

Metal sulfides, which are important indicators of sulfur cycling, are usually divided into two categories according to sulfur chemical valence: (1) monosulfides (S^2-) and (2) disulfides (S₂^2-). The two sulfur species are separated and quantified by a sequential-extraction method. Specifically, monosulfides are extracted as acid-volatile sulfide (AVS) using 6 M HCl prior to the extraction of disulfides using acidic CrCl₂, which is defined as chromium-reducible sulfur (CRS). However, the conventional AVS procedure does not result in the quantitative extraction of S^2- from the acid-insoluble metal monosulfide, copper sulfide (CuS). Consequently, residual sulfur in CuS (CuS-S) may be extracted as CRS resulting in the inaccurate separation of these two sulfur species. In this study, we used stannous chloride (SnCl₂) to improve CuS-S recovery in the AVS procedure and permit the separate extraction of sulfur from CuS and pyrite (FeS₂), the most abundant disulfide in nature. Our results show that the addition of SnCl₂ increased the recovery of CuS-S as AVS from less than 36% to as high as 92% in the absence of pyrite and Fe³⁺ and 89% in the presence of pyrite and Fe³⁺. In addition, based on the observed correlation between the concentration of SnCl₂ and the dissolution of FeS₂, we identified the appropriate concentration of SnCl₂ needed to avoid the dissolution of FeS₂ in the AVS procedure. SnCl₂ also minimized the oxidation of CuS-S by Fe³⁺ released from ferric minerals during the extraction of AVS. Based on the results of a series of sequential-extraction experiments, we show that an amendment of SnCl₂ in the AVS procedure followed by CRS permits the quantitative separation of CuS-S and FeS₂-S while also preventing interference by Fe³⁺. Our method will find application in research concerned with the fate of metals and the biogeochemistry of sulfur in the environment.

Free Radicals Produced from the Oxidation of Ferrous Sulfides Promote the Remobilization of Cadmium in Paddy Soils During Drainage

Most of the cadmium (Cd) accumulated in rice grains is derived from its remobilization in soils during the grain filling period when paddy water is drained. The factors affecting Cd remobilization upon drainage remain poorly understood. Here, we show that the free radical effect produced from the oxidation of ferrous sulfides is an important mechanism affecting the oxidative remobilization of Cd during soil drainage. When soils were flooded, microbial sulfate reduction results in the formation of various metal sulfides including CdS and FeS. Upon soil drainage, the oxidation of FeS produced considerable amounts of hydroxyl free radicals (OH^•), which could oxidize CdS directly and thereby promote the oxidative dissolution of CdS and increase Cd mobilization in soils. FeS and CdS could also form a within-sulfide voltaic cell, with FeS protecting the oxidative dissolution of CdS due to the lower electrochemical potential of the former. However, this voltaic effect was short-lived and was surpassed by the free radical effect. The amounts and composition of metal sulfides formed during soil flooding vary with soils, and the oxidative dissolution of CdS is affected by both the free radical and voltaic effects offered by different metal sulfides. These effects are also applicable to the biogeochemistry of other chalcophile trace elements coupled with sulfur and iron redox cycles during the anoxic-oxic transition in many environments.

Effect of the Annealing Atmosphere on Crystal Phase and Thermoelectric Properties of Copper Sulfide

Cu_2-xS has become one of the most promising thermoelectric materials for application in the middle-high temperature range. Its advantages include the abundance, low cost, and safety of its elements and a high performance at relatively elevated temperatures. However, stability issues limit its operation current and temperature, thus calling for the optimization of the material performance in the middle temperature range. Here, we present a synthetic protocol for large scale production of covellite CuS nanoparticles at ambient temperature and atmosphere, and using water as a solvent. The crystal phase and stoichiometry of the particles are afterward tuned through an annealing process at a moderate temperature under inert or reducing atmosphere. While annealing under argon results in Cu_1.8S nanopowder with a rhombohedral crystal phase, annealing in an atmosphere containing hydrogen leads to tetragonal Cu_1.96S. High temperature X-ray diffraction analysis shows the material annealed in argon to transform to the cubic phase at ca. 400 K, while the material annealed in the presence of hydrogen undergoes two phase transitions, first to hexagonal and then to the cubic structure. The annealing atmosphere, temperature, and time allow adjustment of the density of copper vacancies and thus tuning of the charge carrier concentration and material transport properties. In this direction, the material annealed under Ar is characterized by higher electrical conductivities but lower Seebeck coefficients than the material annealed in the presence of hydrogen. By optimizing the charge carrier concentration through the annealing time, Cu_2-xS with record figures of merit in the middle temperature range, up to 1.41 at 710 K, is obtained. We finally demonstrate that this strategy, based on a low-cost and scalable solution synthesis process, is also suitable for the production of high performance Cu_2-xS layers using high throughput and cost-effective printing technologies.

The Voltaic Effect as a Novel Mechanism Controlling the Remobilization of Cadmium in Paddy Soils during Drainage

Excessive cadmium (Cd) accumulation in rice grain is a global issue that affects human health. The drainage of paddy soils during the grain filling period leads to the remobilization of Cd in soils, resulting in most of the Cd accumulated in rice grain. The rate of Cd remobilization during drainage differs markedly among soils, but the mechanisms underlying these differences remain largely unknown. Using microcosm soil incubation, electrochemical experiments, isotope labeling, and microscopic and spectroscopic analyses, here, we discover the voltaic effect as a novel mechanism controlling the remobilization of Cd during soil drainage. During soil flooding, microbial sulfate reduction results in the formation of various metal sulfides. When the soils are subsequently drained, the various metal sulfides can form within sulfide voltaic cells. The metal sulfides with a lower electrochemical potential act as anodes and are prone to oxidative dissolution, whereas the metal sulfides with a higher potential act as cathodes and are protected from oxidation. This voltaic effect explains why the presence of ZnS (with a low potential) suppresses the oxidative dissolution of Cd sulfides, whereas the presence of CuS (with a high potential) promotes the oxidative dissolution of Cd sulfides. The voltaic effect is applicable to all chalcophile trace metals coupled with the sulfur redox cycle in periodically anoxic-oxic environments, thus playing an important role in the biogeochemistry of trace metals.

CuS nanoparticles in humid environments: adsorbed water enhances the transformation of CuS to CuSO4

Covellite copper sulfide nanoparticles (CuS NPs) have attracted immense research interest due to their widespread use in a range of biological and energy applications. As such, it is crucial to understand the transformations of these nanomaterials and how these transformations influence the behavior of these nanoparticles in environmental and biological systems. This study specifically focuses on understanding the role of water vapor and adsorbed water in the transformation of CuS NP surfaces to CuSO4 in humid environments. Surface sulfide ions are oxidized to sulfate by oxygen in the presence of water vapor, as detected by atomic force microscopy based photothermal infrared spectroscopy (AFM-PTIR) and in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. These results show that the transformation of CuS to CuSO4 is highly dependent on relative humidity (RH). While sulfide to sulfate conversion is not observed to a great extent at low RH (<20%), there is significant conversion at higher RH (>80%). X-ray photoelectron spectroscopy (XPS) analysis confirms that sulfide is irreversibly oxidized to sulfate. Furthermore, it shows that initially, the Cu ions possess the original oxidation state similar to the original covellite, i.e. Cu+, but they are oxidized to Cu2+ at higher RH. The formation of CuSO4 has also been confirmed by HRTEM. These analyses show that adsorbed water on the NP surfaces enhances the conversion of sulfide to sulfate and the oxidation of Cu+ to Cu2+ in the presence of molecular oxygen.

Copper Inhibition of Triplet-Sensitized Phototransformation of Phenolic and Amine Contaminants

Excited triplet states of natural organic matter (³NOM*) are important reactive intermediates in phototransformation of organic contaminants in sunlit waters. The main goal of this study was to explore the influence of Cu on triplet-sensitized transformation rates of 20 selected phenolic and amine contaminants. Fourteen of the compounds examined exhibited a marked decrease in their 4-carboxybenzophenone (CBBP)-mediated phototransformation rate in the presence of trace amounts of Cu(II) (25-500 nM). Both mathematical modeling of these rate data and transient absorption spectroscopy measurements support the hypothesis that the decrease in the rate and extent of phototransformation of organic contaminants is due to the reduction of radical intermediates of the contaminants by photochemically formed Cu(I). The Cu-induced inhibition of oxidation of organic contaminants photosensitized by Suwannee River NOM (SRNOM) could also take place in the presence of nanomolar concentrations of Cu. The inhibitory effect of Cu on the oxidation rates of amine contaminants in SRNOM solutions was found to be significantly weaker compared to that in CBBP solutions, but little difference was observed on depletion of phenols. This behavior was attributed to the intrinsic inhibitory effect of the antioxidant moieties present in NOM on phototransformation of amine compounds, partially neutralizing the potential for further Cu inhibition.

Copper(I) Promotes Silver Sulfide Dissolution and Increases Silver Phytoavailability

Metal sulfides, including acanthite (Ag₂S), are persistent in the environment. In colloidal form, however, they can serve as a "Trojan horse", facilitating the mobility of trace metal contaminants. The natural processes that lead to the in situ dissolution of colloidal metal sulfides in soil are largely unknown. In this study, the dissolution of colloidal Ag₂S in topsoil and Ag phytoavailability to wheat were examined in Ag₂S-Cu(II)-thiosulfate systems. Cu(II) and thiosulfate strongly increased silver release (up to 83% of total Ag) from Ag₂S in the dark. Electron paramagnetic resonance, X-ray photoelectron spectroscopy, and Cu K-edge X-ray absorption spectroscopy identified Cu(I) as the driving force of Ag₂S dissolution. Density functional theory calculations further demonstrated the ability of Cu(I) to substitute for surface Ag on Ag₂S in an energetically favorable manner. However, excess Cu(II) could enhance the formation of precipitates containing Cu(I), Ag, and S. Our results indicate that at ambient temperature and in the dark, Cu(I) can promote the dissolution of Ag₂S and act as a precipitating agent. These findings reveal previously unrecognized biogeochemical processes of colloidal Ag₂S and their importance in determining the fate of metal sulfides in the environment and probably also in vivo.

Copper Mobilization and Immobilization along an Organic Matter and Redox Gradient-Insights from a Mofette Site

Mofettes (natural geogenic CO₂ exhalations) represent excellent sites to study the behavior of Cu in soils and the co-occurrence of different mobilization and immobilization processes since they exhibit both a gradient in redox conditions (oxic to permanently anoxic) and in soil organic matter (SOM; low to high contents). Soil and pore water samples from an 18 m-transect over a mofette showed a complex behavior of Cu, with highest mobility in the transition between oxic and anoxic conditions. Cu(II) sorption experiments on SOM-rich topsoil revealed that Cu mobility under oxic conditions was confined by adsorption to SOM while in the oxygen-free mofette center reduction and precipitation of sulfides was the dominating Cu-sequestering process. In transition areas with low amounts of oxygen (<10%), there was no mineral precipitation, instead high dissolved-to-soil organic carbon ratios strongly increased Cu mobility. Our results show that low stability of SOM formed under oxygen-limited conditions leads to increased Cu mobility unless sulfur-reducing conditions cause Cu sequestration by sulfide precipitation. The interplay of these (im)mobilization processes and especially the unexpectedly high mobility under suboxic conditions have to be considered when assessing Cu mobility along spatial or temporal redox gradients, e.g., at contamination sites or periodically flooded soils.

Temporal Evolution of Copper Distribution and Speciation in Roots of Triticum aestivum Exposed to CuO, Cu(OH)2, and CuS Nanoparticles

Utilization of nanoparticles (NP) in agriculture as fertilizers or pesticides requires an understanding of the NP properties influencing their interactions with plant roots. To evaluate the influence of the solubility of Cu-based NP on Cu uptake and NP association with plant roots, wheat seedlings were hydroponically exposed to 1 mg/L of Cu NPs with different solubilities [CuO, CuS, and Cu(OH)₂] for 1 h then transferred to a Cu-free medium for 48 h. Fresh, hydrated roots were analyzed using micro X-ray fluorescence (μ-XRF) and imaging fluorescence X-ray absorption near edge spectroscopy (XANES imaging) to provide laterally resolved distribution and speciation of Cu in roots. Higher solubility Cu(OH)₂ NPs provided more uptake of Cu after 1 h of exposure, but the lower solubility materials (CuO and CuS) were more persistent on the roots and continued to deliver Cu to plant leaves over the 48 h depuration period. These results demonstrate that NPs, by associating to the roots, have the potential to play a role in slowly providing micronutrients to plants. Thus, tuning the solubility of NPs may provide a long-term slow delivery of micronutrients to plants and provide important information for understanding mechanisms responsible for plant uptake, transformation, and translocation of NPs.

Multiform Sulfur Adsorption Centers and Copper-Terminated Active Sites of Nano-CuS for Efficient Elemental Mercury Capture from Coal Combustion Flue Gas

Nanostructured copper sulfide synthesized with the assistance of surfactant with nanoscale particle size and high Brunauer-Emmett-Teller surface area was for the first time applied for the capture of elemental mercury (Hg⁰) from coal combustion flue gas. The optimal operation temperature of nano-CuS for Hg⁰ adsorption is 75 °C, which indicates that injection of the sorbent between the wet flue gas desulfurization and the wet electrostatic precipitator systems is feasible. This assures that the sorbent is free of the adverse influence of nitrogen oxides. Oxygen (O₂) and sulfur dioxide exerted a slight influence on Hg⁰ adsorption over the nano-CuS. Water vapor was shown to moderately suppress Hg⁰ capture efficiency via competitive adsorption. The simulated adsorption capacities of nano-CuS for Hg⁰ under pure nitrogen (N₂), N₂ + 4% O₂, and simulated flue gas reached 122.40, 112.06, and 89.43 mgHg⁰/g nano-CuS, respectively. Compared to those of traditional commercial activated carbons and metal sulfides, the simulated adsorption capacities of Hg⁰ over the nano-CuS are at least an order of magnitude higher. Moreover, with only 5 mg loaded in a fixed-bed reactor, the Hg⁰ adsorption rate reached 11.93-13.56 μg/g min over nano-CuS. This extremely speedy rate makes nano-CuS promising for a future sorbent injection technique. The anisotropic growth of nano-CuS was confirmed by X-ray diffraction analysis and provided a fundamental aspect for nano-CuS surface reconstruction and polysulfide formation. Further X-ray photoelectron spectroscopy and Hg⁰ temperature-programmed desorption tests showed that the active polysulfide, S-S dimers, and copper-terminated sites contributed primarily to the extremely high Hg⁰ adsorption capacity and rate. With these advantages, nano-CuS appears to be a highly promising alternative to traditional sorbents for Hg⁰ capture from coal combustion flue gas.

Biochar affects the dissolved and colloidal concentrations of Cd, Cu, Ni, and Zn and their phytoavailability and potential mobility in a mining soil under dynamic redox-conditions

There is a lack of knowledge on the effects of biochar (BC) on the release dynamics of potentially toxic elements (PTEs) in different phases of soil under systematic change of redox potential (E_H). We aimed to elucidate the impact of pre-definite E_H on the release dynamics of dissolved and colloidal concentrations of Cd, Cu, Ni, and Zn as well as their phytoavailability and potential mobility in the solid-phase of a mining soil treated with rice hull biochar (S+BC) compared to non-treated soil (S). The influence of E_H-dependent changes of soil pH, dissolved organic carbon (DOC), dissolved aromatic carbon (DAC), Fe, Mn, SO₄^2-, and Cl^- on the elements release was also determined. The experiment was conducted stepwise from reducing (-30mV in S and -12mV in S+BC) to oxidizing (+218mV in S and +333mV in S+BC) conditions using an automated biogeochemical microcosm system. Biochar-treated soil exhibited a wider range of E_H and a lower pH than the non-treated soil. Dissolved concentrations of Cd, Cu, Ni, Zn, Fe, Mn, SO₄^2-, and DAC increased under oxic conditions in the non-treated and biochar-treated-soils, which might be due to the decline of pH, and/or sulfide oxidation. Cadmium was more abundant in the colloidal fraction, while Cu, Mn, and DOC were more abundant in the dissolved fraction. Nickel, Zn, and Fe distributed almost equally in both fractions. Biochar increased the dissolved concentration of Cd, Ni, Zn and in particular Cu under oxic conditions. However, the biochar did not significantly affect the colloidal fraction of Cd, Cu, Ni, and Zn. The phytoavailability of the studied elements was higher than the potential mobility. We conclude that increasing the dissolved concentrations of the elements under oxic conditions might increase their release and transfer into the groundwater and the food chain which should be harmful for the environment.

Elusive Chemistry of Hydrogen Sulfide and Mercaptans in Wine

This paper summarizes, discusses, and complements recent findings about the fate of H₂S and methanethiol (MeSH) during wine storage. Analytical assays to determine free volatile sulfur compounds (VSCs) and brine-releasable (BR-) VSCs in combination with accelerated reductive (AR) aging and micro-oxygenation (MOX) assays allow characterizing the different categories of species able to produce H₂S and MeSH and the processes of interconversion. Each wine seems to contain a specific total amount of H₂S and MeSH distributed into free, metal-complexed, and oxidized forms (di and polysulfides) interconnected through reversible redox equilibria whose external expression is wine redox potential. Oxidation transforms all mercaptans likely into nonvolatile disulfides and hydrodisulfides. In anoxia, these molecules are spontaneously and quantitatively reduced back. The concomitant accumulation of major wine thiols would provoke complex dissociation and the release of free H₂S and MeSH. Additionally, total amounts can increase due to the metal-catalyzed desulfhydration of cysteine and methionine.

Compound Copper Chalcogenide Nanocrystals

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

The effects of copper fining on the wine content in sulfur off-odors and on their evolution during accelerated anoxic storage

Three different red wines with reductive character have been treated with two different doses of copper sulfate (0.06 and 0.5mg/L) and with a commercial copper-containing product at the recommended dose (0.6mg/L). Wines were in contact with copper one week, centrifuged and stored at 50°C in strict anoxia for 2weeks (up to 7 in one case). Brine-releasable (BR-) and free fractions of Volatile Sulfur Compounds were determined throughout the process. Relevant increases of BR-H₂S suggest that those wines contained other H₂S precursors non-detectable by the brine dilution method. Copper treatments had two major effects: 1) immediate decrease the levels of free H₂S and methanethiol (MeSH); 2) slow the rate at which free H₂S (not MeSH) increases during anoxic storage. After 7weeks of anoxia levels of free H₂S and MeSH were high and similar regardless of the copper treatment. Higher copper doses could induce the accumulation of BR-H₂S.

Redox-induced mobilization of copper, selenium, and zinc in deltaic soils originating from Mississippi (U.S.A.) and Nile (Egypt) River Deltas: A better understanding of biogeochemical processes for safe environmental management

Studies about the mobilization of potentially toxic elements (PTEs) in deltaic soils can be challenging, provide critical information on assessing the potential risk and fate of these elements and for sustainable management of these soils. The impact of redox potential (E_H), pH, iron (Fe), manganese (Mn), sulfate (SO₄^2-), chloride (Cl^-), aliphatic dissolved organic carbon (DOC), and aromatic dissolved organic carbon (DAC) on the mobilization of copper (Cu), selenium (Se), and zinc (Zn) was studied in two soils collected from the Nile and Mississippi Rivers deltaic plains focused on increasing our understanding of the fate of these toxic elements. Soils were exposed to a range of redox conditions stepwise from reducing to oxidizing soil conditions using an automated biogeochemical microcosm apparatus. Concentrations of DOC and Fe were high under reducing conditions as compared to oxidizing conditions in both soils. The proportion of DAC in relation to DOC in solution (aromaticity) was high in the Nile Delta soil (NDS) and low in the Mississippi Delta soil (MDS) under oxidizing conditions. Mobilization of Cu was low under reducing conditions in both soils which was likely caused by sulfide precipitation and as a result of reduction of Cu²⁺ to Cu¹⁺. Mobilization of Se was high under low E_H in both soils. Release of Se was positively correlated with DOC, Fe, Mn, and SO₄^2- in the NDS, and with Fe in the MDS. Mobilization of Zn showed negative correlations with E_H and pH in the NDS while these correlations were non-significant in the MDS. The release dynamics of dissolved Zn could be governed mainly by the chemistry of Fe and Mn in the NDS and by the chemistry of Mn in the MDS. Our findings suggest that a release of Se and Zn occurs under anaerobic conditions, while aerobic conditions favor the release of Cu in both soils. In conclusion, the release of Cu, Se, and Zn under different reducing and oxidizing conditions in deltaic wetland soils should be taken into account due to increased mobilization and the potential environmental risks associated with food security in utilizing these soils for flooded agricultural and fisheries systems.

Microfluidic Synthesis and Biological Evaluation of Photothermal Biodegradable Copper Sulfide Nanoparticles

The continuous synthesis of biodegradable photothermal copper sulfide nanoparticles has been carried out with the aid of a microfluidic platform. A comparative physicochemical characterization of the resulting products from the microreactor and from a conventional batch reactor has been performed. The microreactor is able to operate in a continuous manner and with a 4-fold reduction in the synthesis times compared to that of the conventional batch reactor producing nanoparticles with the same physicochemical requirements. Biodegradation subproducts obtained under simulated physiological conditions have been identified, and a complete cytotoxicological analysis on different cell lines was performed. The photothermal effect of those nanomaterials has been demonstrated in vitro as well as their ability to generate reactive oxygen species.

Formation and Release of H2S, Methanethiol, and Dimethylsulfide during the Anoxic Storage of Wines at Room Temperature

A total of 21 different wines (13 reds, 5 whites, and 3 rosés) were kept at 25 °C in anoxia for 379 days. Free and total forms of H2S and methanethiol (MeSH) and dimethylsulfide (DMS) were measured initially and after 117, 221, and 379 days of storage. Levels of free H2S, free and total MeSH, and DMS continuously increased during storage, while levels of total H2S remained essentially unchanged. Average increases of free H2S amount to 6.2 μg/L (from 1.1 to 12.9 μg/L), those of free MeSH to 1.6 μg/L (from 0.7 to 3.5 μg/L), and those of total MeSH to 1.9 μg/L (from 1.1 to 3.0 μg/L), whereas those of DMS were 27.8 μg/L (from 11 to 69 μg/L). The fraction of H2S under free forms significantly increased, suggesting that release is a major factor explaining H2S increases. All increases can be satisfactorily predicted from data obtained at 50 °C.

Reaction Mechanisms of Metals with Hydrogen Sulfide and Thiols in Model Wine. Part 1: Copper-Catalyzed Oxidation

Sulfidic off-odors as a result of hydrogen sulfide (H2S) and low-molecular-weight thiols are commonly encountered in wine production. These odors are usually removed by the process of Cu(II) fining, a process that remains poorly understood. The present study aims to elucidate the underlying mechanisms by which Cu(II) interacts with H2S and thiol compounds (RSH) under wine-like conditions. Copper complex formation was monitored along with H2S, thiol, oxygen, and acetaldehyde concentrations after the addition of Cu(II) (50 or 100 μM) to air-saturated model wine solutions containing H2S, cysteine, 6-sulfanylhexan-1-ol, or 3-sulfanylhexan-1-ol (300 μM each). The presence of H2S and thiols in excess to Cu(II) led to the rapid formation of ∼1.4:1 H2S/Cu and ∼2:1 thiol/Cu complexes, resulting in the oxidation of H2S and thiols and reduction of Cu(II) to Cu(I), which reacted with oxygen. H2S was observed to initially oxidize rather than form insoluble copper sulfide. The proposed reaction mechanisms provide insight into the extent to which H2S can be selectively removed in the presence of thiols in wine.

Reaction Mechanisms of Metals with Hydrogen Sulfide and Thiols in Model Wine. Part 2: Iron- and Copper-Catalyzed Oxidation

Sulfidic off-odors arising during wine production are frequently removed by Cu(II) fining. In part 1 of this study ( 10.1021/acs.jafc.6b00641 ), the reaction of H2S and thiols with Cu(II) was examined; however, the interaction of iron and copper is also known to play an important synergistic role in mediating non-enzymatic wine oxidation. The interaction of these two metals in the oxidation of H2S and thiols (cysteine, 3-sulfanylhexan-1-ol, and 6-sulfanylhexan-1-ol) was therefore examined under wine-like conditions. H2S and thiols (300 μM) were reacted with Fe(III) (100 or 200 μM) alone and in combination with Cu(II) (25 or 50 μM), and concentrations of H2S and thiols, oxygen, and acetaldehyde were monitored over time. H2S and thiols were shown to be slowly oxidized in the presence of Fe(III) alone and were not bound to Fe(III) under model wine conditions. However, Cu(II) added to model wine containing Fe(III) was quickly reduced by H2S and thiols to form Cu(I) complexes, which then rapidly reduced Fe(III) to Fe(II). Oxidation of Fe(II) in the presence of oxygen regenerated Fe(III) and completed the iron redox cycle. In addition, sulfur-derived oxidation products were observed, and the formation of organic polysulfanes was demonstrated.

Detection of Engineered Copper Nanoparticles in Soil Using Single Particle ICP-MS

Regulatory efforts rely on nanometrology for the development and implementation of laws regarding the incorporation of engineered nanomaterials (ENMs) into industrial and consumer products. Copper is currently one of the most common metals used in the constantly developing and expanding sector of nanotechnology. The use of copper nanoparticles in products, such as agricultural biocides, cosmetics and paints, is increasing. Copper based ENMs will eventually be released to the environment through the use and disposal of nano-enabled products, however, the detection of copper ENMs in environmental samples is a challenging task. Single particle inductively coupled plasma mass spectroscopy (spICP-MS) has been suggested as a powerful tool for routine nanometrology efforts. In this work, we apply a spICP-MS method for the detection of engineered copper nanomaterials in colloidal extracts from natural soil samples. Overall, copper nanoparticles were successfully detected in the soil colloidal extracts and the importance of dwell time, background removal, and sample dilution for method optimization and recovery maximization is highlighted.

Synthesis of ultrastable copper sulfide nanoclusters via trapping the reaction intermediate: potential anticancer and antibacterial applications

Copper-based nanomaterials have broad applications in electronics, catalysts, solar energy conversion, antibiotics, tissue imaging, and photothermal cancer therapy. However, it is challenging to prepare ultrasmall and ultrastable CuS nanoclusters (NCs) at room temperature. In this article, a simple method to synthesize water-soluble, monodispersed CuS NCs is reported based on the strategy of trapping the reaction intermediate using thiol-terminated, alkyl-containing short-chain poly(ethylene glycol)s (HS-(CH2)11-(OCH2CH2)6-OH, abbreviated as MUH). The MUH-coated CuS NCs have superior stability in solutions with varied pH values and are stable in pure water for at least 10 months. The as-prepared CuS NCs were highly toxic to A549 cancer cells at a concentration of higher than 100 μM (9.6 μg/mL), making them be potentially applicable as anticancer drugs via intravenous administration by liposomal encapsulation or by direct intratumoral injection. Besides, for the first time, CuS NCs were used for antibacterial application, and 800 μM (76.8 μg/mL) CuS NCs could completely kill the E. coli cells through damaging the cell walls. Moreover, the NCs synthesized here have strong near-infrared (NIR) absorption and can be used as a candidate reagent for photothermal therapy and photoacoustic imaging. The method of trapping the reaction intermediate for simple and controlled synthesis of nanoclusters is generally applicable and can be widely used to synthesize many metal-based (such as Pt, Pd, Au, and Ag) nanoclusters and nanocrystals.

Mercury isotope fractionation during precipitation of metacinnabar (β-HgS) and montroydite (HgO)

To utilize stable Hg isotopes as a tracer for Hg cycling and pollution sources in the environment, it is imperative that fractionation factors for important biogeochemical processes involving Hg are determined. Here, we report experimental results on Hg isotope fractionation during precipitation of metacinnabar (β-HgS) and montroydite (HgO). In both systems, we observed mass-dependent enrichments of light Hg isotopes in the precipitates relative to the dissolved Hg. Precipitation of β-HgS appeared to follow equilibrium isotope fractionation with an enrichment factor ε(202)Hg(precipitate-supernatant) of -0.63‰. Precipitation of HgO resulted in kinetic isotope fractionation, which was described by a Rayleigh model with an enrichment factor of -0.32‰. Small mass-independent fractionation was observed in the HgS system, presumably related to nuclear volume fractionation. We propose that Hg isotope fractionation in the HgS system occurred in solution during the transition of O- to S-coordination of Hg(II), consistent with theoretical predictions. In the HgO system, fractionation was presumably caused by the faster precipitation of light Hg isotopes, and no isotopic exchange between solid and solution was observed on the timescale investigated. The results of this work emphasize the importance of Hg solution speciation and suggest that bonding partners of Hg in solution complexes may control the overall isotope fractionation. The determined fractionation factor and mechanistic insights will have implications for the interpretation of Hg isotope signatures and their use as an environmental tracer.

Sulfidation as a natural antidote to metallic nanoparticles is overestimated: CuO sulfidation yields CuS nanoparticles with increased toxicity in medaka (Oryzias latipes) embryos

Sulfidation is considered as a natural antidote to toxicity of metallic nanoparticles (NPs). The detoxification contribution from sulfidation, however, may vary depending on sulfidation mechanisms. Here we present the dissolution-precipitation instead of direct solid-state-shell mechanism to illustrate the process of CuO-NPs conversion to CuS-NPs in aqueous solutions. Accordingly, the CuS-NPs at environmentally relevant concentrations showed much stronger interference on Japanese medaka (Oryzias latipes) embryo hatching than CuO-NPs, which was probably due to elevated free copper ions released from CuS-NPs, leading to significant increase in oxidative stress and causing toxicity in embryos. The larval length was significantly reduced by CuS-NPs, however, no other obviously abnormal morphological features were identified in the hatched larvae. Co-introduction of a metal ion chelator [ethylene diamine tetraacetic acid (EDTA)] could abolish the hatching inhibition induced by CuS-NPs, indicating free copper ions released from CuS-NPs play an important role in hatching interference. This work documents for the first time that sulfidation as a natural antidote to metallic NPs is being overestimated, which has far reaching implications for risk assessment of metallic NPs in aquatic environment.

Biological and environmental transformations of copper-based nanomaterials

Copper-based nanoparticles are an important class of materials with applications as catalysts, conductive inks, and antimicrobial agents. Environmental and safety issues are particularly important for copper-based nanomaterials because of their potential large-scale use and their high redox activity and toxicity reported from in vitro studies. Elemental nanocopper oxidizes readily upon atmospheric exposure during storage and use, so copper oxides are highly relevant phases to consider in studies of environmental and health impacts. Here we show that copper oxide nanoparticles undergo profound chemical transformations under conditions relevant to living systems and the natural environment. Copper oxide nanoparticle (CuO-NP) dissolution occurs at lysosomal pH (4-5), but not at neutral pH in pure water. Despite the near-neutral pH of cell culture medium, CuO-NPs undergo significant dissolution in media over time scales relevant to toxicity testing because of ligand-assisted ion release, in which amino acid complexation is an important contributor. Electron paramagnetic resonance (EPR) spectroscopy shows that dissolved copper in association with CuO-NPs are the primary redox-active species. CuO-NPs also undergo sulfidation by a dissolution-reprecipitation mechanism, and the new sulfide surfaces act as catalysts for sulfide oxidation. Copper sulfide NPs are found to be much less cytotoxic than CuO-NPs, which is consistent with the very low solubility of CuS. Despite this low solubility of CuS, EPR studies show that sulfidated CuO continues to generate some ROS activity due to the release of free copper by H2O2 oxidation during the Fenton-chemistry-based EPR assay. While sulfidation can serve as a natural detoxification process for nanosilver and other chalcophile metals, our results suggest that sulfidation may not fully and permanently detoxify copper in biological or environmental compartments that contain reactive oxygen species.

Quantitative X-ray Absorption and Emission Spectroscopies: Electronic Structure Elucidation of Cu2S and CuS

The electronic structures of Cu₂S and CuS have been under intense scrutiny, with the aim of understanding the relationship between their electronic structures and commercially important physical properties. Here, X-ray absorption and emission spectroscopic data have been analyzed using a quantitative, molecular orbital (MO) based approach to understand the electronic structure of these two complex systems. Cu₂S is shown to have a significant amount of Cu²⁺ sites and therefore Cu⁰ centers. The presence of low-valent Cu is correlated with the electrical conductivity of Cu₂S, especially at high temperatures. CuS is shown to have tetrahedral Cu²⁺ and trigonal Cu¹⁺ sites, with crystal planes that have alternating high and low charge on the Cu centers. These alternating charges may contribute to internal energy transitions required for photoluminescence properties. The in-depth electronic structure solutions presented here not only solve a complicated much-debated problem, but also demonstrate the strength of quantitative MO based approach to X-ray spectroscopies.

Formation of Zn- and Fe-sulfides near hydrothermal vents at the Eastern Lau Spreading Center: implications for sulfide bioavailability to chemoautotrophs

BACKGROUND

The speciation of dissolved sulfide in the water immediately surrounding deep-ocean hydrothermal vents is critical to chemoautotrophic organisms that are the primary producers of these ecosystems. The objective of this research was to identify the role of Zn and Fe for controlling the speciation of sulfide in the hydrothermal vent fields at the Eastern Lau Spreading Center (ELSC) in the southern Pacific Ocean. Compared to other well-studied hydrothermal systems in the Pacific, the ELSC is notable for unique ridge characteristics and gradients over short distances along the north-south ridge axis.

RESULTS

In June 2005, diffuse-flow (< 50 degrees C) and high-temperature (> 250 degrees C) vent fluids were collected from four field sites along the ELSC ridge axis. Total and filtered Zn and Fe concentrations were quantified in the vent fluid samples using voltammetric and spectrometric analyses. The results indicated north-to-south variability in vent fluid composition. In the high temperature vent fluids, the ratio of total Fe to total Zn varied from 39 at Kilo Moana, the most northern site, to less than 7 at the other three sites. The concentrations of total Zn, Fe, and acid-volatile sulfide indicated that oversaturation and precipitation of sphalerite (ZnS(s)) and pyrite (FeS2(s)) were possible during cooling of the vent fluids as they mixed with the surrounding seawater. In contrast, most samples were undersaturated with respect to mackinawite (FeS(s)). The reactivity of Zn(II) in the filtered samples was tested by adding Cu(II) to the samples to induce metal-exchange reactions. In a portion of the samples, the concentration of labile Zn2+ increased after the addition of Cu(II), indicating the presence of strongly-bound Zn(II) species such as ZnS clusters and nanoparticles.

CONCLUSION

Results of this study suggest that Zn is important to sulfide speciation at ELSC vent habitats, particularly at the southern sites where Zn concentrations increase relative to Fe. As the hydrothermal fluids mix with the ambient seawater, Zn-sulfide clusters and nanoparticles are likely preventing sulfide oxidation by O2 and reducing bioavailability of S(-II) to organisms.

Low polydispersed copper-sulfide nanocrystals derived from various Cu-alkyl amine complexes

Copper-sulfides, Cu2-xS nanocrystals (NCs) have been synthesized using the reaction between a Cu-alkyl amine complex and a sulfur/1-dodecanethiol. Here, 1-dodecanthiol plays an important role to reduce the reaction temperature of sulfuration. The Cu/S composition (the Cu-defect density) of Cu2-xS NCs depends on the stability of Cu-alkyl amine complex. XPS analyses reveal that the substance of Cu-defect is attributed to an introducing of Cu+2S2-2 species. There is a good correlation between an intensity of a near IR absorption peak and a Cu-defect density estimated by XPS analyses. These results demonstrate that optical properties of Cu2-xS NCs in a near IR region are tunable.

Impact of water temperature and dissolved oxygen on copper cycling in an urban estuary

An increasing body of evidence suggests that much of the trace metal contamination observed in coastal waters is no longer derived from point-source inputs, but instead originates from diffuse, non-point sources. Previous research has shown that water temperature and dissolved oxygen regulate non-point source processes such as sediment diagenesis; however, limited information is available regarding the effect of these variables on toxic trace metal cycling and speciation in natural waters. Here, we present data on the seasonal variation of dissolved Cu cycling in the Long Island Sound, an urban estuary adjacent to New York City. An operationally defined chemical speciation technique based on kinetic lability and organic complexation has been applied to examine the most ecologically relevant metal fraction. In contrast to the decrease from spring to summer observed in the total dissolved Cu pool (average +/- SD: 15.1 +/- 4.4 nM in spring and 11.8 +/- 3.5 nM in summer), our results revealed that in the highly impacted western LIS, levels of labile Cu reached higher levels in summer (range 3.6-7.7 nM) than in spring (range 1.5-3.9 nM). Labile Cu in surface waters of the western Sound appeared to have a wastewater source during spring high flow conditions, coinciding with elevated levels of sewage-derived Ag. Labile Cu elsewhere in the LIS during spring apparently resulted from fluvial input and mixing. During summer, labile Cu increased in bottom waters (at one site, bottom water labile Cu increased from 1.5 nM in spring to 7.7 nM in summer), and covariance with tracers of diagenetic remobilization (e.g., Mn) revealed a sedimentary source. Although total dissolved Cu showed no consistent trends with water quality parameters, labile Cu in bottom waters showed an inverse correlation with dissolved oxygen and a positive, exponential correlation with water temperature. These results suggest that future increases in coastal water temperatures may cause the benthic source of labile Cu to become proportionally more significant.

Shape-controlled synthesis and self-assembly of hexagonal covellite (CuS) nanoplatelets

Single-crystalline, hexagonal covellite (CuS) nanoplatelets were successfully synthesized through a facile, inexpensive, reproducible, and improved solvothermal process in toluene at 120 degrees C for 24 h with hexadecylamine as a capping agent and copper acetate and carbon disulfide as precursors. These nanoplatelets are about 26+/-1.5 nm in diameter and 8+/-1.2 nm thick, and have a tendency to self-assemble into pillarlike nanostructures with face-to-face stacks, raftlike nanostructures with side-by-side arrays, and stratiform nanostructures with layer-by-layer self-assembly. The crystal shape, morphology, and crystallographic orientation of the covellite obtained were investigated by means of XRD, TEM, and high-resolution TEM, and a potential self-assembly mechanism was proposed.

Fundamental features of copper ion precipitation using sulfide as a precipitant in a wastewater system

We have investigated the precipitation features of copper ion using sulfide as a precipitant by varying the mole ratio of sulfide to copper ion, pH, temperature and the kind and concentration of complexing agent. In the precipitation of copper ion by sulfide, sludge is produced as cupric sulfide; thus, there is a possibility for its recycled use in photochemical and ceramic processes. When the ratio of the concentration of copper ion to sulfide was increased to more than 1.0, the extent of precipitation was very high. As the ratio was increased, nucleation time was decreased and crystal growth rate was raised. The higher the pH, the greater the amount of precipitated copper ion due to lowered solubility of cupric sulfide. When temperature changed from 25 degrees C to 55 degrees C, the precipitation of copper ion was increased a little. On the basis of estimated thermodynamic parameters such as Gibbs free energy and enthalpy, the precipitation reaction was spontaneous and endothermic. The precipitation of copper ion was lowered in the presence of complexing agent and it was affected by the stability of the copper complex. The feasibility test for the application of precipitation treatment to actual wastewater containing copper ion showed, although there was a little decrease in the removal of copper, the precipitation extent of copper was higher than 90% compared with that for artificial wastewater.

Displacement of Cu(II) by Ag(I) in Solvated Metal Sulfides. A DFT and AIM Computational Study

The substitution of Cu2+ by Ag+ in hydrated CuIIS and (CuII)3S3 was modeled computationally by density functional theory quantum theory of atoms in molecules, and solvent field methods. The coordination, first-shell and partly second-shell molecular structures, and thermochemical data for solvated Cu2+, Ag+, CuIIS, (CuII)3S3, AgCu2S3 and their reactions were obtained. The thermochemical data showed that displacement of Cu2+ and Cu+ from CuIIS and (CuII)3S3 by Ag+, while unfavorable in the gas phase, is facilitated in an aqueous environment. Several covalently bonded species were examined as intermediates in the substitution reactions.

Voltammetry of copper sulfide particles and nanoparticles: investigation of the cluster hypothesis

An association of Cu with sulfide in aerobic natural waters has been attributed to these components' coexistence in clusters of sizes intermediate between mononuclear complexes and colloidal particles. This hypothesis is investigated here. Copper sulfide solid phases display size-related voltammetric behavior at Hg electrodes. Suspensions of copper sulfide powders held at accumulation potentials of 0 to -0.2 V (vs Ag/AgCl) produce voltammetric peaks near -0.15, -0.65, and -0.95 V during subsequent cathodic scans. The first two peaks arise from electrochemically generated Cu-oxyhydroxides and HgS; the -0.95 V peak arises from reduction of sorbed copper sulfide particles. Nanoparticles of radius approximately 10(-8) m produce the third peak even without stirring or accumulation. Still smaller analytes give only the first two peaks. Published evidence alleging production of subnanometer copper sulfide clusters during titrations of Cu2+ and HS- was not reproduced when sulfide oxidation was avoided. Instead, such titrations apparently generate nanoparticles. The titration stoichiometry is 1/1, consistent with previous descriptions of this process: Cu2+ + HS- --> 1/2Cu2S x S0 (brown sol) --> CuS (green sol). Titrating Cu2+ into organic-rich (muscilaginous) Adriatic Sea water, which contains 10(-7) M natural thiols and sulfide, produces solid products. In the future, voltammetry might prove useful for studying semiconductor sulfide nanoparticles in nature.

Study of copper sulfide crystallization in PEO-SDS solutions

The crystallization of copper sulfide in aqueous supersaturated solutions in the presence of the polymer poly(ethylene oxide), PEO, and the surfactant sodium dodecyl sulfate, SDS, was investigated. In these systems, copper sulfide precipitation competes with the reaction between copper cations and dodecyl sulfate anions. The competition of the two reactions may affect the reaction products significantly; therefore it is important to study the properties of the surfactant salt, copper dodecyl sulfate (Cu(DS)2), in detail. The thermodynamic solubility constant of Cu(DS)2 was measured at 8 degrees C and was equal to (2.4 +/- 0.4) x 10(-10) M3. The Krafft point of Cu(DS)2 and its solubility curve (precipitation temperature for a range of concentrations) were also measured. The latter was found to be very close to room temperature. Temperature is thus a very significant parameter in these systems and must be carefully controlled in all experiments. The crystallization of copper sulfide in PEO-SDS solutions was investigated in solutions with compositions above and below the solubility curve. Copper sulfide nanoparticles predominate and are stabilized at temperatures above the solubility curve. Surprisingly, at temperatures below the solubility curve CuxS coexists with Cu(DS)2, which appears in the form of lamellar crystals. The system is further complicated by the presence of at least two different types of copper sulfides corresponding to different oxidation states of copper. Our results suggest that the predominance of Cu(DS)2 at lower temperatures is due to its limited solubility and is modified by the CuI/CuII redox equilibrium in combination with the solution pH.