High Sulfide Research Articles

Origin and hydrochemical evolution of confined groundwater in Shanghai, China

Confined groundwater is an indispensable resource for the urban security of Shanghai, China, where multi-layer aquifer structures and human activities create a complex groundwater environment. An understanding of the hydrochemical characteristics and evolutionary mechanisms of groundwater is necessary for its protection and effective utilization and will be explored in this study. A total of 87 groundwater samples were collected from five confined aquifers. Hydrochemistry analysis methods such as Durov diagram, Gibbs model and Saturation index were used to determine the origin and hydrochemical evolution of the confined groundwater. The results show that the samples have two different origins, marine–continental and continental, which have different hydrochemical characteristics. Cl− content of 7.5 meq L−1 was used as a demarcation index for the two origins. The groundwater with a marine–continental-origin is dominated by ancient seawater from which Na+ and Cl− are derived, whereas Ca2+, Mg2+, and HCO3− are derived mainly from carbonate dissolution. Groundwater with a continental-origin is dominated by the effects of water–rock interaction, where major ions are derived mainly from silicate weathering and carbonate dissolution. In both types of groundwater, SO42− is mainly derived from insoluble sulfides that are present in low quantities, whereas SO42− in the few samples with high insoluble sulfide content is derived from human activities. Cation exchange is another controlling factor regarding the hydrochemical composition of groundwater, and water from the two origins have different reaction modes as follows: reverse cation exchange is dominant in marine–continental groundwater, whereas positive cation exchange is more common in continental groundwater. Over the past century, saline water has been flowing into the groundwater funnel region due to human activities, which has resulted in changes in the hydrochemical composition. The recent influx of fresh groundwater and artificial recharge has caused groundwater salinization and mineral re-dissolution.

Prussian Blue Analogue-Derived Fe-Doped CoS2 Nanoparticles Confined in Bayberry-like N-Doped Carbon Spheres as Anodes for Sodium-Ion Batteries.

Obvious volume change and the dissolution of polysulfide as well as sluggish kinetics are serious issues for the development of high performance metal sulfide anodes for sodium-ion batteries (SIBs), which usually result in fast capacity fading during continuous sodiation and desodiation processes. In this work, by utilizing a Prussian blue analogue as functional precursors, small Fe-doped CoS2 nanoparticles spatially confined in N-doped carbon spheres with rich porosity were synthesized through facile successive precipitation, carbonization, and sulfurization processes, leading to the formation of bayberry-like Fe-doped CoS2/N-doped carbon spheres (Fe-CoS2/NC). By introducing a suitable amount of FeCl3 in the starting materials, the optimal Fe-CoS2/NC hybrid spheres with the designed composition and pore structure exhibited superior cycling stability (621 mA h g-1 after 400 cycles at 1 A g-1) and improved the rate capability (493 mA h g-1 at 5 A g-1). This work provides a new avenue for the rational design and synthesis of high performance metal sulfide-based anode materials toward SIBs.

Au-Ag-Se-Te-S Mineralization in the Maletoyvayam High-Sulfidation Epithermal Deposit, Kamchatka Peninsula

The Maletoyvayam high-sulfidation (HS) epithermal Au-Ag deposit is one of the numerous hydrothermal deposits of the Kamchatka volcanogenic belt, consisting of two main associations: Au-rich (Ag-free) and Ag-bearing. The first one derived from acidic solutions, whereas the second assemblage crystallized from moderately dilute solutions, with both occurring at high oxygen fugacity. The Au-rich association contains the most atypical gold chalcogenides of the Au-Se-Te-S system, which are characterized by Se-S and Te-Se substitutions, e.g., a complete series from maletoyvayamite to tolstykhite Au3(Se,S)4Te6; a series of auroselenide Au(Se1.00–0.64S0.36–0.00); a combined series of gachingite Au(Te,Se) and unnamed Au(Se,Te): Au(Te0.80–0.40Se0.20–0.60). Meanwhile, in the second Ag-bearing assemblage, sulfides of the Au-Ag type prevails, e.g., petrovskaite AuAgS, miargyrite (Ag,Au)(Sb,As)S2, uytenbogaardtite Ag3AuS2, fischesserite Ag3AuSe2 with Au-Ag substitution, and tolstykhite. The Se/S ratio, of the second association, decreases while increasing the Ag concentration in the ore-forming system, including Au-Ag substitutions. The Au content in miargyrite (Au,Ag)SbS3 reaches up to 0.48 apfu, suggesting the existence of a new mineral phase of composition AgAuSb2S6. Au oxide complexes, in both associations, are represented by either a mixture of redeposited gold and Fe-Sb oxide or a homogeneous (Au,Sb,Fe)2O3 composition. These oxides are formed by replacement of calaverite. The ore mineralization of this HS deposit is considered unique due to the special conditions of the ore-forming environment, such as acidic solutions, high oxygen fugacity, and log fSe2 above −5.7; all contributed to the formation of AuSe phases.

Utilization of rice straw as an inhibitor of strength deterioration of sulfide-rich cemented paste backfill

Cemented paste backfill (CPB) has been a practical approach for mining waste management, underground goaf treatment, and green mining. Strength deterioration because of high sulfide content (SC) is a severe challenge for sulfide-rich CPB. To investigate the influence of rice straw (RS) on the strength of sulfide-rich CPB, RS was utilized as an inhibitor of strength deterioration. RS dosage (RSD), RS length (RSL), and sulfide content (SC) were chosen as the factors, and two stages of the experiment were carried out. It was found that high SC produced pores, cracks, and loose microstructure of CPB, resulting in the strength deterioration of sulfide-rich CPB. The 90-day uniaxial compressive strength (90 d-UCS) was the maximum of the UCS of sulfide-rich CPB. The hydration products and microstructural characteristics observed by XRD and scanning electron microscopy (SEM) illustrated that RS has the effect of bridging and water retention. Accordingly, adding RS improved the long-term strength of sulfide-rich CPB. The optimal RSD, RSL, and SC for 90 d-UCS of sulfide-rich CPB were obtained through the response surface methodology approach. The optimal conditions within the experimental range of this study for maximum 90 d-UCS of CPB with high SC (17 wt%) were RSD of 0.032 wt% and RSL of 0.28 cm, producing a 90 d-UCS of 5.14 MPa.

Reactivation of metal-fertilized lower continental crust: Origin of intrusion-related Asiha gold deposit in Eastern Kunlun orogenic Belt, China

Gold deposits in the East Kunlun Orogen Belt (EKOB) are generally identified as orogenic gold deposits. However, recently, a new magmatic-hydrothermal model has been proposed to explain the genesis of these deposits that show intimate spatial and temporal relationships with abundant Triassic granitic intrusions, implying an intrusion-related gold system. The petrogenesis of these granites and their relation to gold mineralization are still unclear, owing to the lack of direct evidence of the connection between gold mineralization and granitic rocks. The gold-bearing Asiha intrusions (GBAI) from the Gouli area of the eastern segment of the EKOB are not only contemporary and located with mineralization but also have abnormally high gold content and sulfide accessory mineral. The GBAI are mainly composed of quartz diorite and granite porphyry. An integrated investigation involving mineral composition, zircon U-Pb dating and Hf isotopes, whole-rock elemental (including Au) and Sr-Nd-Pb isotopic geochemistry of the GBAI, as well as the in-situ Pb isotopic geochemistry of pyrites from the Asiha gold deposit, was conducted to constrain magmatic sources and petrogenesis of the GBAI, and gold mineralization mechanism. Zircon U-Pb dating reveals that the Asiha quartz diorite was formed at 230 Ma. The mineralized granite porphyries with high SiO2 contents (71.7–74.3 wt%) are peraluminous high-K calc-alkalic rocks, while the unmineralized quartz diorite with low SiO2 contents (58.1–60.0 wt%) are metaluminous high-K calc-alkalic rocks. Both rocks are potassic, strongly enriched in LILEs and LREEs with high LILE/HFSE ratios, depleted in Nb, Ta, Ba and Sr, and have weakly negative Eu anomalies and high zircon saturation temperature. Petrographic and geochemical features suggest that the quartz diorite is typical of I-type, while the granite porphyry is highly fractionated I-type granite. Their variable concentrations of major and trace elements are due to fractional crystallization of plagioclase, hornblende, and accessory minerals (apatite, zircon and monazite). Notably, the Asiha intrusions all contain high Au contents (Au = 0.02–0.05 ppm) compared to the primitive mantle estimated from chondrite values (0.88 ppb), indicating the existence of gold enrichment. All these granites are characterized by limited ranges of initial 87Sr/86Sr (0.7087–0.7133), εNd(t) (−6.0 to −5.0), 206Pb/204Pb (18.1–19.0),207Pb/204Pb (15.6–15.7), and 208Pb/204Pb (38.2–38.9), as well as zircon εHf(t) with values of −4.4 to −1.7. Their lead isotopes are consistent with that of pyrite in the ores (206Pb/204Pb = 18.41–18.45, 207Pb/204Pb = 15.61–15.65, 208Pb/204Pb = 38.47–38.56). Based on our results, we suggest that the GBAI were originally generated by partially melting of a previously Au-fertilized juvenile lower crust, which had been formed by metasomatized SCLM-derived alkaline basaltic underplating, and underwent AFC processes during emplacement. Subsequently, the post-magmatic fluids concentrated and precipitated Au to form the Au-bearing quartz veins.

Transformations of Ferrihydrite-Extracellular Polymeric Substance Coprecipitates Driven by Dissolved Sulfide: Interrelated Effects of Carbon and Sulfur Loadings.

The association of poorly crystalline iron (hydr)oxides with organic matter (OM), such as extracellular polymeric substances (EPS), exerts a profound effect on Fe and C cycles in soils and sediments, and their behaviors under sulfate-reducing conditions involve complicated mineralogical transformations. However, how different loadings and types of EPS and water chemistry conditions affect the sulfidation still lacks quantitative and systematic investigation. We here synthesized a set of ferrihydrite-organic matter (Fh-OM) coprecipitates with various model compounds for plant and microbial exopolysaccharides (polygalacturonic acids, alginic acid, and xanthan gum) and bacteriogenic EPS (extracted from Bacillus subtilis). Combining wet chemical analysis, X-ray diffraction, and X-ray absorption spectroscopic techniques, we systematically studied the impacts of C and S loadings by tracing the temporal evolution of Fe mineralogy and speciation in aqueous and solid phases. Our results showed that the effect of added OM on sulfidation of Fh-OM coprecipitates is interrelated with the amount of loaded sulfide. Under low sulfide loadings (S(-II)/Fe < 0.5), transformation to goethite and lepidocrocite was the main pathway of ferrihydrite sulfidation, which occurs more strongly at pH 6 compared to that at pH 7.5, and it was promoted and inhibited at low and high C/Fe ratios, respectively. While under high sulfide loadings (S(-II)/Fe > 0.5), the formation of secondary Fe-S minerals such as mackinawite and pyrite dominated ferrihydrite sulfidation, and it was inhibited with increasing C/Fe ratios. Furthermore, all three synthetic EPS proxies unanimously inhibited mineral transformation, while the microbiogenic EPS has a more potent inhibitory effect than synthetic EPS proxies compared at equivalent C/Fe loadings. Collectively, our results suggest that the quantity and chemical characteristics of the associated OM have a strong and nonlinear influence on the extent and pathways of mineralogical transformations of Fh-OM sulfidation.

Application of electrochemical methods for studying steel corrosion in alkali‐activated materials

AbstractAlkali‐activated materials (AAMs) are binders that can complement and partially substitute the current use of conventional cement. However, the present knowledge about how AAMs protect steel reinforcement in concrete elements is incomplete, and uncertainties exist regarding the application of electrochemical methods to investigate this issue. The present review by EFC WP11‐Task Force ‘Corrosion of steel in alkali‐activated materials’ demonstrates that important differences exist between AAMs and Portland cement, and between different classes of AAMs, which are mainly caused by differing pore solution compositions, and which affect the outcomes of electrochemical measurements. The high sulfide concentrations in blast furnace slag‐based AAMs lead to distinct anodic polarisation curves, unusually low open circuit potentials, and low polarisation resistances, which might be incorrectly interpreted as indicating active corrosion of steel reinforcement. No systematic study of the influence of the steel–concrete interface on the susceptibility of steel to corrosion in AAMs is available. Less common electrochemical methods present an opportunity for future progress in the field.

Application of the k-Prototype Clustering Approach for the Definition of Geostatistical Estimation Domains

The definition of geostatistical domains is a stage in the estimation of mineral resources, in which a sample resulting from a mining exploration process is divided into zones that show homogeneity or minimal variation in the main element of interest or mineral grade, having geological and spatial meaning. Its importance lies in the fact that the quality of the estimation techniques, and therefore, the correct quantification of the mineral resource, will improve in geostatistically stationary areas. The present study seeks to define geostatistical domains of estimation for a mineral grade, using a non-traditional approach based on the k-prototype clustering algorithm. This algorithm is based on the k-means paradigm of unsupervised machine learning, but it is exempt from the one-time restriction on numeric data. The latter is especially convenient, as it allows the incorporation of categorical variables such as geological attributes in the grouping. The case study corresponds to a hydrothermal gold deposit of high sulfidation, located in the southern zone of Peru, where estimation domains are defined from a historical record of data recovered from 131 diamond drill holes and 37 trenches. The characteristics directly involved were the gold grade (Au), silver grade (Ag), type of hydrothermal alteration, and type of mineralization. The results obtained showed that clustering with k-prototypes is an efficient approach and can be used as an alternative or complement to the traditional methodology.

Application of 2-D Electrical Resistivity Imaging, and Induced Polarization Methods for Delineating Gold Mineralisation at Felda Chiku 3, Kelantan, Malaysia

A geophysical survey has been carried out to assess the distribution of gold minerals at the Felda Chiku 3, Gua Musang district, Kelantan, Peninsular Malaysia. A 2-D geo-electrical resistivity imaging (ERI), combined with Induced Polarization (IP) method, and Oasis Montaj modelling were applied to delineate the potential conductive zones associated with sulphide mineralization. Most Peninsular Malaysia’s gold deposits occur in hydrothermal sulphides as discrete ore formations within the host rocks. A good correlation between the ERI and the IP profiles was observed during the interpretation of the model that successfully identifying the low resistive, and high chargeable sulphide zones, which correspond to the gold mineralization zones. The correlations could be linked to the conductive features at depth ranging from about 25 m - 135 m, trending along N-S directions. The study suggests further geo-electrical investigation to be carried out towards the south-western part of the area as more potential mineralized zones with N-S trends could be found in this region. Further studies would be able to give the extent of the gold deposits in Kelantan and by extension, allow for better informed mineral exploration and drilling operations to mine the gold in the region.

Co-operative harmless treatment and neutralization utilization process research of LPG spent caustic coupled chloroaluminate ionic liquid spent catalysts

In the petrochemical industry, due to strong acids and toxic heavy metals, chloroaluminate ionic liquid spent catalysts pose a potential environmental risk. Given the strong alkalinity and high pollution load, the treatment step for liquefied petroleum gas (LPG) spent caustic requires adding acid, resulting in significant acid consumption and the risk of secondary pollution. According to the characteristics of these two types of solid waste, the coupling process of LPG spent caustic and chloraluminate ionic liquid waste catalyst is proposed with the goal of resource and harmlessness. The LPG spent caustic and the chloroaluminate ionic liquid spent catalyst are pretreated by precipitation-flocculation and hydrolysis, respectively, after which they are neutralized. The main factors in the pretreatment and neutralization process are systematically examined. Under optimum circumstances, 98 % of the sulfide from LPG spent caustic was removed, 86.8 % of the chemical oxygen requirement was removed, and the oil content in the treated solution was 10 mg/L. The hydrolysis reaction was milder when the hydrolysis media was mixed with the chloroaluminate ionic liquid spent catalyst at a volume ratio of 40:1. By changing the hydrolysis medium, it was confirmed that the neutralizing solution containing sodium chloride had an inhibitory effect on the reaction when reused in the hydrolysis reaction of the spent catalyst. The treated LPG SC and the acidic hydrolysate were neutralized at a volume ratio of 14.8:100.The pH after the reaction was 7, and the recoveries of aluminum and copper ions were 99.99 % and 93.36 %, respectively. The precipitates were calcined at high temperatures, and the characterization of the calcined products confirmed the formation of copper aluminate spinel by XRD, FT-IR, and SEM-EDS. The COD, sulfide, and oil indicators in the neutralization solution meet the tertiary effluent discharge standards of China's National Comprehensive Effluent Discharge Standard (GB 8978-1996). The process eliminates the risk of high sulfide and COD from the LPG SC and recovers the spent catalyst's metal resources. In addition, the whole process has no additional added acid or alkali. A new approach to disposing of these two hazardous wastes (LPG SC and chloroaluminate ionic liquid spent catalysts) for the petrochemical industry is offered.

Cobalt ions induced morphology control of metal-organic framework-derived indium oxide nanostructures for high performance hydrogen sulfide gas sensors

Real-time gas sensors with high response and selectivity are highly desirable for hydrogen sulfide (H2S) monitoring concentration changes in the environment, especially at the ultra-trace level. Herein, cobalt-doped indium oxide (In2O3) with shorter-length nanorings was synthesized by foreign metal cobalt ions. By controlling the morphology of the material and calcinating the indium-based metal-organic frameworks (In-MOFs), the nanostructures of the obtained materials have a larger specific surface area, which further improves the sensing performance. The sensor prepared with a suitable amount of cobalt doping materials can exhibit the best gas-sensing performance. The Co-doped In2O3 sensor shows a high response to 2 ppm H2S (∼12.6) at 225 °C, low detection limits (100 ppb), and excellent selectivity, which is 5.34 times higher than pure In2O3 at 300 °C. Moreover, the potential growth mechanism speculates that the presence of Cobalt ions leads to a change in material morphology from nanorods to nanorings. This work provides an implementable method for controlling the morphology of the materials, which could facilitate the development of high-performance gas sensors.

Experimental Study on Efficient Recovery of High-Grade Sulfide Ore

A gold mine is a typical broken zone altered rock type gold deposit, with some high grade primary sulfide ore at 20~30m from the surface, and the ore grade is about 5g/t. To understand the nature of the ore, Performed the process mineralogy testing and analysis, The occurrence state of the gold mineral is very good, Most gold is bare gold, It is conducive to the enrichment and recovery; To determine the best selection process and parameters, Conducted experimental studies including Nelson reselection and flotation, Finally determined to adopt the Nielsen reselection-heavy tail flotation process, Au grade 42.15g/t, Au recovery rate of 48.92%; Reconcentration tailings after one rough selection, two sweeps, two selection, Au grade 38.26g/t, The grade of Au of tailings is 0.16g/t; The combined Au recovery rate of reselection + flotation was 97.39%, The concentrate quality and recovery indexes are all good, The benefits are considerable.

Emerging high entropy metal sulphides and phosphides for electrochemical water splitting

This review highlights recent advances in high entropy metal sulfides and phosphides (HEMSs/Ps), their classification, synthesis approaches, crystal structures and morphologies, and applications in electrochemical water splitting.

Peroxide-mediated selective conversion of biomass polysaccharides over high entropy sulfides via solar energy catalysis

Biomass polysaccharides are converted over novel high-entropy sulfides (CdZnCuCoFe)Sx under mild reaction conditions via solar energy catalysis. A large amount of carbon monoxide (CO) was produced at 1.73 mmol g−1 h−1 with a high selectivity of 99.1% among the gas products.

Study of Physico-chemical and Bacteriological Quality of Water from Ain Mkbrta Source in Morocco

Springs water is underground water, considered purer than surface water. Its nature depends on the rocks and soils through which it flows. They can be highly charged with specific minerals, which explains why these waters do not meet drinking water standards, but they are widely used for therapeutic properties. In this current work, we investigated the physico-chemical and bacteriological analysis of a water source known for its therapeutic effects, particularly in dermatology. We also examined the geological characteristics to understand the origin of the mineralization of these waters, with the aim of making better use of them on both a medical and economical levels. Ain Mkbrta source, 60 km from Fez city. It belongs to the Rif external domains (Rif Chain), and given its chemical composition, this spring is similar to the Moulay Yacoub hydrothermal spring, with a very pronounced odor due to the presence of hydrogen sulfide. The outcome of physico-chemical analysis of Ain Mkbrta spring showed a very high conductivity, a high hydrogen sulfide content and a wide variety of minerals in significant quantities, such as calcium, magnesium, bicarbonate, sulfate, sulfide, and chloride. Furthermore, Bacteriological analysis is moderately satisfactory, with low concentrations of fecal coliforms and revivable germs.

HsGDY on Ni Foam for Loading MoS 2 /Ni 3 S 2 to Enhance the Performance on Lithium–Sulfur Batteries

Lithium–sulfur batteries are considered important devices for the power of movable equipment, but there are still some challenges that limit their applications, such as how to obtain a cathode for high sulfide adsorption and rapid conversion. Here, a new strategy is proposed to enhance the performance of lithium–sulfur batteries by growing 3-dimensional hydrogen-substituted graphdiyne (HsGDY) layers on Ni foam via Glaser cross-coupling reaction to anchor MoS 2 /Ni 3 S 2 , enhancing the conductivity of host material of S. The results show that the 3-dimensional HsGDY framework enables the fast adsorption of lithium polysulfides and the Ni 3 S 2 /MoS 2 performs as the reaction center with a low charge transfer resistance. The charge capacity of Ni@HsGDY/MoS 2 /Ni 3 S 2 cell is up to 1,234.7 mAh·g −1 at the first circle, and the specific capacity keeps 486 mAh·g −1 after 500 cycles at a current density of 2 C. The incorporation of HsGDY into the cathode promotes the adsorption and the conversion of polysulfides, paving a path to obtain lithium–sulfur batteries with high energy density.

Preparation and degradation of high air stability sulfide solid electrolyte 75Li2S·25P2S5 glass-ceramic

The development of next-generation lithium-ion batteries relies heavily on the design and manufacture of solid electrolytes with excellent ionic conductivity and air stability. 75Li2S·25P2S5 glass-ceramic is a desirable and promising solid-electrolyte material, but further research is needed to understand how certain synthesis factors affect the local structure and ionic conductivity of the material. In addition, the majority of the existing research on the air stability of solid electrolytes simply record the change in the amount of H2S released over time, which is insufficient. Herein, we highlight the impact of a range of conditions in the ball milling stage (including jar filling factor, rotation speed, ball-to-powder ratio and total milling time) and the calcination stage (including heat-treatment temperatures and heat-treatment durations) on the 75Li2S·25P2S5 glass-ceramic synthesis, through powder X-ray diffraction, Raman and electrochemical impedance spectroscopy. We have found that this material has a relatively high air stability under optimal synthesis situations, taking approximately 6.5 min to release 5 ppm H2S. In addition, we present degradation studies on 75Li2S·25P2S5 glass-ceramic by electrochemical impedance spectroscopy, scanning electron microscope, energy dispersive spectroscopy and Raman. After being exposed to air for a period of time, the ionic conductivity of 75Li2S·25P2S5 glass-ceramic significantly decreased, and its morphology and structure were severely deteriorated. It is most likely that the sample eventually generates a mixture of Li3PO4, Li2SO4 and S8.

Geology and metallogenesis of the Tiegelongnan Cu–Au–Ag deposit, Duolong ore district, Tibet

The Tiegelongnan deposit is a giant deposit (&gt;10 million tons Cu resources with an average grade of 0.53%) located in the west of the Bangong Co‐Nujiang metallogenic Belt, where typical porphyry and epithermal types of alteration and mineralization are developed. A compilation of geological features and mineralogical studies revealed that the Tiegelongnan deposit developed two stages of hydrothermal alteration. The early stage was related to porphyry emplacement, developing potassic, phyllic and propylitic alterations, telescoped by the late advanced argillic alteration in the shallow levels. Correspondingly, two stages of mineralization occurred, the early porphyry‐type mineralization being overlapped by the late high‐sulfidation epithermal mineralization. Due to differences in pH, log fO2, K+ activity and temperature of ore‐forming fluids, distinct sulfide minerals of low to extremely high sulfidation states, such as chalcopyrite, tennantite, enargite and covellite, precipitated throughout the entire hydrothermal process. The Tiegelongnan deposit is a complex porphyry metallogenetic system of ‘multiple structures’. The Early Cretaceous andesitic volcanic rocks of the Meiriqiecuo Formation exposed on the surface act as a cap for the ore body, beneath which an oxidizing‐leaching zone lies. Under the cap and the oxidizing‐leaching zone, a porphyry ore body is remoulded by high‐grade high‐sulfidation epithermal hydrothermal mineralization, which gradually transitions to continuous porphyry‐type mineralization at depth.

In situ construction of hollow Ni3S2-Co9S8 heterostructures with enhanced reaction kinetics for potassium ion storage

Owing to high theoretical capacity, nickel sulfide and cobalt sulfide were highly competitive anode materials for potassium ion batteries (PIBs). However, the slow reaction kinetics and poor structural stability during the cycle hinder its application in the anode materials of PIBs. An exquisite heterogeneous structure of bimetal sulfide Ni3S2-Co9S8 nanotube wrapped with a nitrogen-doped carbon layer is prepared by in situ growth and solvothermal strategies. Such a well-designed structural provides a channel for the rapid diffusion of potassium ions, promotes charge transfer at the heterojunction interface and effectively improves the reaction kinetics. When used as the anode for PIBs, the Ni3S2-Co9S8@NSC exhibits an excellent capacity of 419 mA h g−1 after 200 cycles at 0.1 A g−1 and an excellent rate performance of 220 mA h g−1 at 5 A g−1. And after 200 cycles at 1 A g−1 and 2 A g−1, there are 285 mA h g−1 and 238 mA h g−1 high reversible capacities, respectively. Moreover, potassium ion hybrid capacitor can provide good energy density (148 Wh kg−1), power density (6639.3 W kg−1) and excellent cycle reversibility. Based on experiments and DFT calculations, the heterojunction structure in the composite can not only optimize the electronic structure and distribution to improve the conductivity, but also improve the potassium ion adsorption energy to accelerate the reaction kinetics. The excellent electrochemical properties reveal the advantages of reasonably designing carbon coated hollow heterostructures for energy storage.

Biosorption of cadmium and cobalt by intertidal multicomponent biofilms

Intertidal sediments are sinks for heavy metals due to the anoxic condition, fine grain size, high sulphide and organic matter contents. However with changing water pH, particularly in view of the acidifying ocean water, metals are released in the overlying water making them bioavailable. The motivation of this research was to identify a natural barrier to immobilize the released metals in the sediments and thus prevent bioaccumulation. Multi-species intertidal biofilms have higher level of stress tolerance compared to single species due to their extended exposure to the dynamic environmental conditions facilitating in-situ sequestration of contaminants. The present study focuses on evaluating the potential of naturally-occurring intertidal phototropic biofilms cultured in controlled environment to absorb and adsorb Cd and Co along with the estimation of the biological parameters, such as, chlorophyll a, biomass, extracellular polymeric substances (EPS), and cell vitality. Biofilms withstood up to 1 ppm of Cd and 5 ppm of Co (threshold concentrations) beyond which they failed to proliferate. This suggests the potential application of these biofilms as bio-indicators of metal pollution. The overall percent adsorption, ranging between 5 and 17 % was insignificant compared to percent absorption, ranging between 15 and 90 %. The intracellular absorption was 66 % for Cd and 58 % for Co at threshold concentrations. With increasing metal concentration, decreasing chlorophyll a synthesis and increasing EPS production was observed demonstrating that the biofilms combat heavy metal pollution by secreting EPS as an adaptive mechanism. We found intertidal multicomponent biofilms are capable of sequestering heavy metals from the water. In the natural environment, the biofilms would get buried in the sediments with time thus sequestering the metals.