Sulfide Surface Research Articles

A novel activation approach for promoting chrysocolla flotation: Performance and mechanism

Chrysocolla is an important copper oxide mineral. However, owing to the unique structure of chrysocolla, effective recovery of chrysocolla using conventional sulfidization xanthate flotation methods proves challenging. In this work, the effects of Pb2+ on the surface properties, sulfidization, activation, hydrophobicity, and floatability of chrysocolla were systematically investigated in a sulfidization xanthate system. Compared to the direct sulfidization flotation results, the flotation recovery of chrysocolla significantly increased from 7.84% to 69.46% after Pb2+ stepwise activation. The results of X-ray photoelectron spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) analyses indicated that Pb species and sulfidization products on chrysocolla surfaces obviously increased in the Pb2+ stepwise activation system, the content of highly reactive PbS components on the surface of chrysocolla was higher, and the stability of sulfidization products on the chrysocolla surface was stronger than that in a single Pb2+ activation system. The results of contact angle, Fourier-transform Infrared (FTIR), and adsorption amount characterizations showed that more xanthate components were adsorbed on the surface of chrysocolla after Pb2+ stepwise activation, and the hydrophobicity of chrysocolla surface was significantly enhanced. Therefore, Pb2+ stepwise activation not only enhanced the sulfidization of chrysocolla surface but also improved the reactivity and hydrophobicity of mineral surfaces, thus realizing the effective recovery of silicic copper oxide minerals, which are extremely difficult to float.

Alkaline pretreatment of a polymetallic sulfide (Fe-Pb-Mn) ore containing silver increases the efficiency of cyanidation by decreasing elemental sulfur content and by exposing sulfide surfaces

Polymetallic sulfide ores are often not amenable to cyanide leaching due to the presence of several elements and minerals capable of interfering with this process. Thus, various strategies, such as chemical pretreatments, are often studied to improve the efficiency of cyanidation. Beyond the results of such strategies, it is important to understand the changes occurring on the mineral samples during these pretreatments. Herein, an alkaline pretreatment was applied to a silver concentrate (∼8 kg Ag/t) composed of polymetallic sulfides (Fe-Pb-Mn), which increased the silver extraction during subsequent cyanidation from 40% to 80% and decreased the cyanide consumption in half (from approximately 60 to 30 kg NaCN/t). X-ray diffraction (XRD) and ICP-MS indicated that the pretreatment could remove significant amounts of elemental sulfur, which is a known cyanicidal agent. The dissolution of significant amounts of sulfur was confirmed by chemical analysis, which also demonstrated that the dissolution of iron, lead, manganese, and silver were negligible during pretreatment. At surface level, X-ray photoelectron spectroscopy (XPS) demonstrated that the pretreatment exposes fresh sulfide surfaces (e. g. pyrite). In addition, the XPS spectra indicated that the pretreatment facilitated the exposure of clean mineral surfaces. The presence of cleaner surfaces suggested a more uniform and less hindered diffusion of leaching agents through the mineral. Indeed, fitting the extraction data to the shrinking core model showed that pretreated samples featured a nearly ideal diffusion-controlled process, while in the case of untreated samples this fitting was less adequate. During cyanidation of both untreated and pretreated samples, lead build-up was detected on the surface (readsorption), which suggested that this phenomenon does not affect the efficiency of a leaching process. This study highlights the importance of combining bulk analytical methods with surface-sensitive techniques to obtain a more complete understanding of leaching processes.

Improvement of hydrogen permeation barrier performance by iron sulphide surface films

Improvement of hydrogen permeation barrier performance by iron sulphide surface films

Sedimentary molybdenum and uranium cycling under seasonally contrasting redox conditions on the Namibian Shelf

Sedimentary molybdenum (Mo) and uranium (U) enrichments have been widely used as a proxy for redox conditions in oxygen-depleted marine paleo-environments. However, in a dynamic upwelling system the seasonal fluctuations from oxic to completely anoxic-sulfidic bottom waters and lateral sediment transport can modify the primary Mo and U signal of the sediment, which in turn may impact paleo-redox interpretations. In this study we present pore water and solid phase data collected at two cross shelf transects during the ‘more oxygenated’ austral winter and ‘anoxic’ austral summer to study the influence of spatially and seasonally contrasting redox conditions on the formation of authigenic Mo and U enrichments in organic carbon (TOC) rich mud belt sediments on the Namibian shelf. A mass balance was established for each element based on diffusive fluxes and element mass accumulation rates to evaluate the respective mechanisms of trace metal delivery, accumulation and recycling.Mo is delivered to the sediment in its dissolved form via diffusion across the sediment–water interface, especially during austral summer when bottom waters are anoxic and surface sediments are highly sulfidic. In the center of the inner shelf mud belt, the benthic Mo fluxes of up to 37 nmol cm−2 yr−1 into sulfidic surface sediments are the highest ever reported for reducing sulfidic systems and agree with the rate of Mo accumulation in the solid phase. Concurrently, high sedimentation rates and low terrigenous input limit solid phase Mo accumulation on the Namibian shelf. In ancient marine sediments, this mode of Mo cycling can be identified by low Mo/TOC ratios of ∼2 similar to those found in sediments deposited below the perennial oxygen minimum zone on the Peruvian shelf and to those found in deposits of the Cretaceous Oceanic Anoxic Event 2. Diffusive U fluxes into the sediment are generally too low to account for the sedimentary enrichment leading to the conclusion that U is delivered mainly in particulate form. In areas with anoxic bottom water, shallow dissolved U maxima directly below the sediment water interface and rather low sedimentary U content indicate that particulate U is recycled and largely released back into the bottom water. At sites where bottom water oxygen concentrations vary from anoxic to completely oxic on seasonal timescales, the depth at which Mo and U are removed from pore waters moves vertically within the sediment column thus defining a layer between the sediment surface and ∼20 cm depth, in which Mo and U accumulate in the solid phase. Our results emphasize the importance of short-term redox fluctuations in the bottom waters and underlying sediments, as well as lateral sediment transport for the authigenic enrichment of redox-sensitive trace metals in reducing shelf sediments. The relative enrichment patterns identified might be useful for the reconstruction of open marine anoxia in the geological past.

Sulfuric acid pretreatment of oxidized pyrrhotite in flotation desulphurization of magnetite concentrate

The impact of sulfuric acid pretreatment on the surface property of oxidized pyrrhotite (OX-pyrrhotite) and its application in flotation desulphurization of magnetite concentrate were investigated in this study. OX-pyrrhotite using sodium butyl xanthate (BX) collector performed a poor floatability. After sulfuric acid pretreatment, OX-pyrrhotite exposed a new sulphide surface similar to raw pyrrhotite. XPS analysis indicated that the oxidized species such as sulphate were dissolved away from the OX-pyrrhotite surface. This conversion made the natural hydrophobicity and isoelectric point of OX-pyrrhotite proximity to pyrrhotite. Contact angle and zeta potential measurements showed that the sulfuric acid pretreatment increased the adsorption of BX collector and the hydrophobicity of OX-pyrrhotite surface. FTIR and XPS analyses inferred that there existed weak adsorption of BX collector on OX-pyrrhotite surfaces. After sulfuric acid pretreatment, the interaction between BX collector and OX-pyrrhotite surfaces was strengthened, generating dixanthogen species. Therefore, the sulfuric acid pretreatment improved the floatability of OX-pyrrhotite within a wide pH region. When sulfuric acid pretreatment was adopted, the flotation desulfurization could decrease the sulfur content of magnetite concentrate from 4.50% to 0.18%.

Dual Cu and S vacancies boost CO2 photomethanation on Cu1.95S1-x: Vacancy-regulated selective photocatalysis

Tuning product selectivity and improving activity are significant in CO2 photoreduction. Herein, we demonstrate that introducing Cu and S dual vacancies on copper sulfide surfaces can improve the CO2 photoreduction activity and completely switch the selectivity from CO to CH4. Experimental results reveal that Cu and S vacancies can attain a favorable CH4 production of 12.42 μmol g−1 h−1 with 100 % selectivity. Meanwhile, the single S vacancies also exhibit an approx. 4-fold CO yield (13.63 μmol g−1 h−1) compared with vacancy-free Cu2S (3.48 μmol g−1 h−1). Mechanism research indicates that the single S vacancies could promote the CO2 → COOH* → CO* pathway to improve the CO yield, while the simultaneously introducing of Cu and S dual vacancies can further lower the energy barriers of CO2 → COOH* → HCOOH* → CHO* pathway to promote the stepwise protonation of CO2, which in turn strengthen the selectivity of CO2-to-CH4 photoreduction.

Field investigation of temporal variation and diffusion of hydrogen sulfide on waste working face and intermediate landfill cover

This paper presents the study on the variation, influencing factors and diffusion regularity of hydrogen sulfide (H2S) concentration and surface flux on the working face and intermediate geomembrane cover of a landfill. Field investigations were conducted using static chambers at a large-scale municipal solid waste landfill in Hangzhou, China, from January 2019 to June 2021. The analytical models of H2S transport in the working face and intermediate cover were developed to investigate the surface flux under various conditions. The CALPUFF model was used to demonstrate the diffusion path. The H2S surface flux on the working face ranged from 7.1 × 10−3 to 1.7 mg/m2/h, whereas the range was found to be 1.5 × 10−4 to 0.9 mg/m2/h on the intermediate geomembrane cover. This observation indicated that the geomembrane can reduce H2S emissions. In addition, the H2S surface fluxes at the HDPE GMB seams and near the gas collecting wells were generally 1–2 orders of magnitude larger than that in the intact GMB. The analytical model estimates that the intact GMB exhibits a diffusion coefficient of H2S ranging from 2.7 × 10−11 to 2.2 × 10−10 m2/s. However, the diffusion coefficient increases significantly to a range of 3.3 × 10−11–9.8 × 10−7 m2/s on the GMB seams. According to CALPUFF results, only the H2S diffusion from the working face had areas exceeding the standard concentration.

Degradation mechanism of surface sulfidization and hydrophobicity by Fe(III) in the flotation of cerussite

Unavoidable metal ions commonly exist in the pulp during flotation. These ions can affect the floatability of minerals, and they can also result in the differences in the surface features between different minerals. In this study, how Fe3+ affected the flotation behavior of cerussite was investigated by micro-flotation tests. The corresponding adsorption characteristics of the sulfidizing agent and collector on the surfaces of cerussite were investigated by surface-analysis techniques. The results of micro-flotation tests showed that the floatability of cerussite significantly decreased when Fe3+ was added before Na2S and xanthate. The flotation recovery of cerussite decreased compared with that obtained without participation of Fe3+. Additionally, the results of xanthate and Na2S adsorption tests, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and zeta potential measurements verified that Fe3+ and its hydrophilic hydroxyl derivatives (Fe-OH compounds) resulted in reduced amounts and reactive activities of S-bearing species adsorbed on the surfaces of cerussite. This decreased the adsorption capacity of subsequently added xanthate, resulting in the difficulty in effectively recovering cerussite in the sulfidization-xanthate system.

Remediation and resource utilization of petroleum-contaminated soil by pyrite-assisted pyrolysis as bifunctional materials to adsorb heavy metal and activate peroxymonosulfate oxidation

Petroleum-contaminated soil (PCS) requires not only efficient remediation technology but also economically viable reuse strategy of remediated soil with vast volume. This study developed a pyrite-assisted pyrolysis to convert PCS into a bifunctional material for the adsorption of heavy metal and the activation of peroxymonosulfate (PMS) oxidation. Adsorption isotherm and kinetic model fitting by Langmuir and pseudo-second-order well clarified the adsorption capacity and behavior of carbonized soil (CS) loaded with sulfur and iron (FeS@CS) for heavy metals. The theoretic maximum adsorption capacities of Pb2+, Cu2+, Cd2+, and Zn2+ by Langmuir model were 415.40, 80.25, 61.55, and 30.90 mg/g, respectively. The main adsorption mechanism includes sulfide precipitation, co-precipitation and surface complexation by iron oxides, and complexation by oxygen-containing functional groups. When the dosage of FeS@CS and PMS were both 3 g/L, the removal rate of aniline reached 99.64 % in 6 h. After five cycles of reuse, the aniline degradation rate was still as high as 93.14 %. The non-free radical pathway dominated in CS/PMS and FeS@CS/PMS systems. The electron hole was the primary active species in the CS/PMS system, which promoted aniline degradation by accelerating direct electron transfer. In comparison with CS, the surface of FeS@CS contained more iron oxides, oxygen-containing functional groups, and oxygen vacancies, making 1O2 the primary active species in the FeS@CS/PMS system. This study proposed a new integrated strategy for the efficient remediation of PCS and value-added reutilization of remediated soil.

Multifunctional nanocomposites induce mitochondrial dysfunction and glucose deprivation to boost immunogenic ferroptosis for cancer therapy

Ferroptosis is a type of regulated cell death that has attracted much attention owing to its ability to trigger immunogenic cell death (ICD) and enhance immunotherapy. However, ferroptosis can be greatly limited by glutathione peroxidase 4 (GPX4) and ferroptosis suppressor protein 1 (FSP1) antioxidant mechanisms. Herein, to inhibit these antioxidant effects, therapeutic nanocomposites (Cu2−XS-GOx@CaCO3) were developed by attaching glucose oxidase (GOx) and mineralized calcium carbonate to the surface of hollow mesoporous copper sulfide (Cu2−XS, 0 < x < 1). Via GOx-mediated catalysis, intracellular glucose is oxidized to gluconic acid (GA) and hydrogen peroxide (H2O2). Notably, the generated GA stimulates the release of Ca2+ to damage mitochondrial function, while the produced H2O2 enhances the Fenton-like reaction triggered by Cu2−XS, and finally results in the accumulation of reactive oxygen species. Further, the depletion of glucose could damage the pentose phosphate pathway and hinder the synthesis of reduced glutathione (GSH) and the recycling of coenzyme Q10 (CoQ10) into reduced coenzyme Q10 (CoQ10H2), suggesting simultaneous inhibition of the GPX4/GSH and FSP1/CoQ10H2 pathways. Moreover, the accumulation of reactive oxygen species and the inhibition of antioxidant mechanisms could induce ferroptosis and ICD, followed by the recruitment of cytotoxic T lymphocytes, which synergistically provide an excellent anti-tumour effect. These findings provide a strong rationale for the application of ferroptosis-mediated immunotherapy.

Surface characteristic and sulfidization-xanthate flotation behaviours of malachite as influenced by ferric ions

During the sulfidization–xanthate flotation of malachite in industrial production, Fe3+ in the pulp may affect mineral enrichment. In this study, we examined the adsorption of Fe3+ on the malachite surface and sulfidized surface to investigate the effect of Fe3+ on malachite sulfidization, sulfidization products, and mineral floatability. The results of experiments indicated that Fe3+ formed an adsorption layer on the samples surface and sulfidized samples surface, and adsorption of Fe–hydroxyl species led to hydroxylation of the samples. The proportion of Cu (I) species decreased during sulfidization, which indicated that the existence of Fe3+ had a negative effect on the sulfidization of the sample. Sulfidization products were identified, which revealed that the proportion of SO2–n increased significantly after treatment with Fe3+, suggesting that the reaction activity of the sulfidized surface was reduced. Moreover, the hydrophobicity of the mineral surface reduced after interaction with Fe3+ species, and led to reduced flotation recovery.

Effect of the hydration film on the surface sulfidization of different oxide ores: A DFT study

Sulfidization is a commonly used pretreatment process to improve the flotation of oxide ores. However, not all oxide minerals can be sulfidized. The huge sulfidization differences between smithsonite and quartz are a typical example. In this paper, DFT calculations were used to simulate the sulfidization of different oxide ores with smithsonite and quartz as an example. The calculation results showed that the hydration film plays a decisive role in whether the oxide ore can be sulfidized or not. For the smithsonite, HS can break the barrier of its surface hydration film and it can be sulfidized. However, for the quartz, due to the powerful obstacle of its surface hydration film to HS, its sulfidization failed. To find out the internal mechanism, the overlap population, PDOS, and electronic configurations were further analyzed, and their relationship with sulfidization behaviors was established. The analysis results demonstrated that Zn-O bond was more vulnerable than Zn-S bond while Si-O was much more intense than Si-S bond. Moreover, a mechanism model was also proposed to elucidate the different impacts of hydration film on the sulfidization of these two representative minerals. This work is helpful to enhance the understanding of different oxide ore sulfidization.

Understanding the sulphur-oxygen exchange process of metal sulphides prior to oxygen evolution reaction

Dynamic reconstruction of metal sulphides during electrocatalytic oxygen evolution reaction (OER) has hampered the acquisition of legible evidence for comprehensively understanding the phase-transition mechanism and electrocatalytic activity origin. Herein, modelling on a series of cobalt-nickel bimetallic sulphides, we for the first time establish an explicit and comprehensive picture of their dynamic phase evaluation pathway at the pre-catalytic stage before OER process. By utilizing the in-situ electrochemical transmission electron microscopy and electron energy loss spectroscopy, the lattice sulphur atoms of (NiCo)S1.33 particles are revealed to be partially substituted by oxygen from electrolyte to form a lattice oxygen-sulphur coexisting shell surface before the generation of reconstituted active species. Such S-O exchange process is benefitted from the subtle modulation of metal-sulphur coordination form caused by the specific Ni and Co occupation. This unique oxygen-substitution behaviour produces an (NiCo)OxS1.33-x surface to reduce the energy barrier of surface reconstruction for converting sulphides into active oxy/hydroxide derivative, therefore significantly increasing the proportion of lattice oxygen-mediated mechanism compared to the pure sulphide surface. We anticipate this direct observation can provide an explicit picture of catalysts’ structural and compositional evolution during the electrocatalytic process.

S modified manganese oxide for high efficiency of peroxydisulfate activation: Critical role of S and mechanism

Mn2O3 as a typical Mn based semiconductor has attracted growing attention due to its peculiar 3d electron structure and stability, and the multi-valence Mn on the surface is the key to peroxydisulfate activation. Herein, an octahedral structure of Mn2O3 with (111) exposed facet was synthesized by a hydrothermal method, which was further sulfureted to obtained a variable-valent Mn oxide for the high activation efficiency of peroxydisulfate under the light emitting diode irradiation. The degradation experiments showed that under the irradiation of 420 nm light, S modified manganese oxide showed an excellent removal for tetracycline within 90 min, which is about 40.4% higher than that of pure Mn2O3. In addition, the degradation rate constant k of S modified sample increased 2.17 times. Surface sulfidation not only increased the active sites and oxygen vacancies on the pristine Mn2O3 surface, but also changed the electronic structure of Mn due to the introduce of surface S2−. This modification accelerated the electronic transmission during the degradation process. Meanwhile, the utilization efficiency of photogenerated electrons was greatly improved under light. Besides, the S modified manganese oxide had an excellent reuse performance after four cycles. The scavenging experiments and EPR analyses showed that •OH and 1O2 were the main reactive oxygen species. This study therefore provides a new avenue for further developing manganese-based catalysts towards high activation efficiency for peroxydisulfate.

Synergistic activation of smithsonite with copper-ammonium species for enhancing surface reactivity and xanthate adsorption

Copper ions (Cu2+) are usually added to activate the sulfidized surface of zinc oxide minerals to enhance xanthate attachment using sulfidization xanthate flotation technology. The adsorption of Cu2+ and xanthate on the sulfidized surface was investigated in various systems, and its effect on the surface hydrophobicity and flotation performance was revealed by multiple analytical methods and experiments. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) characterization demonstrated that the adsorption of Cu2+ on sulfidized smithsonite surfaces increased the active Cu—S content, regardless of treatment in any activation system. The sulfidized surface pretreated with NH4+–Cu2+ created favorable conditions for the adsorption of more Cu2+, significantly enhancing the smithsonite reactivity. Zeta potential determination, ultraviolet (UV)-visible spectroscopy, Fourier transform-infrared (FT-IR) measurements, and contact angle detection showed that xanthate was chemically adsorbed on the sulfidized surface, and its adsorption capacity in various systems was illustrated from qualitative and quantitative aspects. In comparison to the Na2S–Cu2+ and Cu2+–Na2S–Cu2+ systems, xanthate exhibited a higher adsorption capacity on sulfidized smithsonite surfaces in NH4+–Cu2+–Na2S–Cu2+ system. Hence, activation with Cu2+–NH4+ synergistic species prior to sulfidization significantly enhanced the mineral surface hydrophobicity, thereby increasing its flotation recovery.

Enhancement of Xanthate Adsorption on Cerussite Surfaces by Pb(II) Activation and Its Effect on Floatability

Cerussite is a lead oxide mineral resource that is typically enriched through sulfidization flotation. The surface sulfidation degree and the high solubility of cerussite strongly affect the flotation ability of cerussite. In the current work, lead ions were used to pretreat cerussite to intensify its sulfidization flotation. The sulfidization mechanism regulating the lead ions pretreatment on cerussite was investigated by the micro-flotation test, ToF-SIMS, zeta potential measurement, adsorption test, and XPS. The results from the micro-flotation test demonstrated that the floatability of cerussite could be improved by adding an appropriate amount of lead ions. Compared with the treatment involving only Na2S, the maximum recovery increased by 17.57%. Adsorption experiments showed that lead modification improved the stability of xanthate products on the surface of cerussite. According to the measurement of zeta potential and the results of ToF-SIMS, the addition of lead ion Pb pretreatment increased the number of active Pb sites adsorbed by xanthate, thereby improving the formation of hydrophobic Pb-dilute precipitate. Therefore, the interaction between lead ions and the surface of cerussite enhances the strength and stability of the hydrophobic layer, resulting in enhanced hydrophobicity of cerussite.

Tracking surface ionic movement of Ni3S2@CuS electrode materials with high electrochemical performance

Supercapacitors have overwhelming advantages in cycle life, charging time and power density. Metal sulfides involve reversible Faraday redox reactions, and chemical reactions occur during charge and discharge, resulting in high specific capacity of the electrode. Different from the traditional nickel foam as a current collector, in this work, vulcanized nickel foam (Ni3S2) is used to further grow CuS nanosheets by hydrothermal reaction to produce new cathode material. The results show that the electrochemical properties of the electrode material Ni3S2@CuS obtained at 190 °C for 4 h reach a mass specific capacity of 967.7F/g. When assembled as a supercapacitor device, it has an energy density of 103.7 Wh/kg and a power density of 15050.3 W/kg. The coulomb efficiency of the device remains 97.4 % after 10,000 cycles of constant current charge and discharge. To deeply understand the mechanism of the capacitance increase, we carry out a molecular dynamics (MD) simulation on pure Ni3S2 electrode and Ni3S2@CuS to investigate the influence of this unique structure on capacitance for the first time. We discover that the CuS tunnel on the Ni3S2 electrode surface will restrict the deintercalation of K+ ions and promote the intercalation of OH–, and this phenomenon will promote the reversible redox reaction on the surface of the metal sulfides and enhance the capacitance of this pseudocapacitor.

Research on resistance of CuxNiyFez-LDHs derived catalysts to poisoning components and insight into the complex role of SO2 on C3H6-SCR performance

The resistance to poisoning components, like H2O, alkalies metals, and SO2, was investigated over Cu0.18Ni0.49Fe0.33-C catalyst. Thereinto, H2O, and K+ led to a slight decrease in catalytic activity, while SO2 caused a distinct drop at low temperatures (<250 °C) and a dramatic rise at medium (250–350 °C) and high (>350 °C) temperatures for C3H6-SCR performance. Moreover, long-term resistance to H2O and SO2 indicated that H2O induced reversible inactivation while SO2 enhanced the activity. Note that H2O and SO2 jointly affected the C3H6-SCR performance when they coexisted. According to N2 adsorption-desorption, XRD, XPS, and H2-TPR results, H2O and K+ give rise to the blockage of some small pores or the creation of large pores, the attenuation of the potent synergy between Cu and Ni, and drop of reducibility for catalysts, leading to the fall in activity. Further aided by SO2-TPD, Py-FTIR, and In situ DRIFTS techniques, the impact mechanism of SO2 on C3H6-SCR performance can be deduced. Aside from sulfites and sulfates, surface sulfides as the primary sulfide generate after SO2 adsorption at 30 °C, introducing the inert Lewis acid sites and even masking the active sites. As a result, low-temperature activity suffers from inhibition due to minor active nitrates and inert formate. The high-temperature activity is enhanced, profiting from the release of active sites following surface sulfides breakdown, suppression of C3H6 combustion, activation of C3H6 on extra Brønsted acid sites, plentiful R-NCO, and new active -CN species. Eventually, a possible C3H6-SCR mechanism in the presence of SO2 was postulated.

Influence of air exposure on structural isomers of silver nanoparticles

Up to date, the influence of ambient air exposure on the energetics and stability of silver clusters has rarely been investigated and compared to clusters in vacuum. Silver clusters up to 3000 atoms in size, on an amorphous carbon film, have been exposed to ambient air and investigated by atomic-resolution imaging in the aberration-corrected Scanning Transmission Electron Microscope. Ordered structures comprise more than half the population, the rest are amorphous. Here, we show that the most common ordered isomer structures is the icosahedron. These results contrast with the published behaviour of silver clusters protected from atmospheric exposure, where the predominant ordered isomer is face-centred cubic. We propose that the formation of surface oxide or sulphide species resulting from air exposure can account for this deviation in stable isomer. This interpretation is consistent with density functional theory calculations based on silver nanoclusters, in the size range 147-201 atoms, on which methanethiol molecules are adsorbed. An understanding of the effects of ambient exposure on the atomic structure and therefore functional properties of nanoparticles is highly relevant to their real-world performance and applications.

Adsorption characteristics of Pb(II) ions on sulfidized hemimorphite surface under ammonium sulfate system

In this work, the effect of ammonium sulfate on the adsorption characteristics of low-concentration Pb(II) ions on the sulfidized hemimorphite surface was comprehensively investigated. The results showed that ammonium sulfate could increase the maximum recovery of hemimorphite from 69.42% to 88.24% under a low concentration of Pb(II) ions. On the hemimorphite surface pretreated with ammonium sulfate, the adsorption of Pb(II) ions was enhanced and the main species of Pb adsorbed was changed from Pb―O/OH to PbS. This was due to the larger amount of ZnS providing more effective adsorption sites for Pb components to generate PbS. Meanwhile, the intensity of ZnS decreased with the formation of PbS, demonstrating that ZnS was covered by PbS which formed later on the mineral surface. It was beneficial for the adsorption of butyl xanthate on the hemimorphite surface to form more hydrophobic substances. As a result, ammonium sulfate played a crucial role in realizing the efficient recovery of hemimorphite.