Weak Alkaline Conditions Research Articles

Enhancing nitrate removal efficiency of micro-sized zero-valent iron by chitosan gel balls encapsulating

The activity of micro-sized zero-valent iron (MZVI) material for nitrate removal in neutral pH and low C/N ratios water needs to be improved. In this study, micro-sized zero-valent iron@chitosan (MZVI@CS) material was synthesized through embedding MZVI particles into chitosan (CS) gel by sol-gel method, and was used for deep removal of NO3−-N in the absence of organic carbon sources and neutral pH. The NO3−-N removal rate of MZVI@CS was 0.37 mg-N·L−1·d−1 (dosage of 1%, initial pH = 7, 25 °C, initial nitrate concentration = 15 mg-N·L−1), which was 11.33 times higher than that of MZVI. The apparent activation energy (Ea) of MZVI@CS with nitrate was 38.23 kJ·mol−1. MZVI@CS can remove nitrate effectively at a low concentration (15 mg-N·L−1). A stable denitration rate (0.37–2.28 mg-N·L−1·d−1) could be maintained under weak acidic, neutral and alkaline conditions (pH = 5–9). More than 80% of reduced nitrate was converted to N2, and only a small amount was converted to NH4+ or NO2−. The gel structure of MZVI@CS eliminated the agglomeration between MZVI particles while the forming of Fe-CS chelates reduced the formation of iron oxide and solved the problems of passivation, hence successfully strengthened the NO3−-N removal efficiency of MZVI. Therefore MZVI@CS has great application potential in NO3−-N deep removal of water bodies with neutral pH and low C/N ratios.

Aggregative Growth of Oligopeptide‐Protected Gold Nanoclusters into Plasmonic Particles

AbstractThe stimuli response of nanomaterials represents a highly appealing characteristic, whereas the practical applications (in catalysis, biosensing etc.) are largely restricted by the limited understanding on the recognition mechanism. Herein, we report a pH‐regulated size evolution from atomically precise Au nanoclusters (NCs) to plasmonic nanoparticles (NPs). The spectral monitoring demonstrates a three‐stage aggregative growth pathway. First, the non‐covalent interactions among the exterior oligopeptide ligands are gradually enhanced with the increased alkalinity, and then the Au−S bonding is partially disrupted, with the exposed Au atoms aggregating to form relatively larger, polydisperse clusters under weak alkaline conditions. Finally, size‐redistribution occurs slowly under strong alkaline conditions to form the plasmonic particles. The controllable transition sheds light on the transition characteristics from molecular state to metallic state of Au nanomaterials.

Isolated molybdenum-based microporous POMs for selective adsorption of gases.

Dodecanuclear, icosanuclear and octanuclear porous MOF-like POM materials [MoV12O12(μ2-O)4(μ3-O)12(Htrz)4(trz)4]·nH2O (n = 22, 1; n = 92, 2; Htrz = 1H-1,2,3-triazole), [MoV8O8(μ2-O)12(Htrz)8]½·[MoV12O12(μ2-O)4(μ3-O)12(Htrz)4(trz)4]·44H2O (3), and [MoV8O8(μ2-O)12(Htrz)8]·62H2O (4) have been obtained and well characterized. Higher Mo12 agglomerates have been fabricated in acidic solution, while isolated Mo8 species formed in weak alkaline conditions. Fortuitously, their additive 3 is precipitated in a neutral environment. Structural analyses indicate that there are diversiform pores present in 1-4, which are formed by polyoxometalates (POMs) themselves and intermolecular accumulations, or even induced by free disordered water molecules. Obvious downfield shifts have been found in the solid 13C NMR spectra for the coordinated 1,2,3-triazoles in 1 and 2. In particular, isolated single species of polyoxometalate-based porous framework POMOF 4 can be identified in the solution 13C NMR spectrum and further supported by solid and solution UV-vis spectroscopy. Moreover, gas adsorption tests indicate that 1 is the most promising CO2 adsorbent of these four materials, compared with other common gases O2, H2, CH4 and N2 under different pressures. The peculiarities of this sort of POMOFs, as well as the relationships and interactions with gases, have been discussed.

Determination of As species distribution and variation with time in extracted groundwater samples by on-site species separation method

It is challenging to dependably keep the native distribution of arsenic (As) species before sample analysis in the laboratory. The on-site separation method can avoid sample contamination and species change in the process of sample collection and transportation from field to laboratory. In this study, As species distribution and variation of the extracted groundwater was first analyzed by an on-site species separation method in Jianghan Plain, China. Our study illustrated that: 1) high-As groundwater generally existed under mildly reducing conditions (Eh < 200 mV), weak alkaline conditions (pH < 7.2), elevated concentrations of dissolved Fe(II) and S(-II), and high proportions of As (III); 2) As species in the groundwater changed dramatically at room temperature in 36 hours post extraction (HPE). Fe-sulfide and Fe oxides minerals, which adsorbed As (V), were the main reasons influencing the As species concentration; 3) Acidification and strong complexing agents cannot preserve As species effectively. The average proportion of As (III) in the wells, where groundwater samples from the depth of 25 m exceed 10 μg L−1 As, can be reduced by 61% and 63% after HCl and EDTA were added, respectively. Accurate assessment of concentrations and distribution variation of As species in groundwater can guide the removal of As and the safe use of water resources, especially in drought areas relying on drinking well water.

Efficient removal of hazardous benzohydroxamic acid (BHA) contaminants from the industrial beneficiation wastewaters by facile precipitation flotation process

Benzohydroxamic acid (BHA) is intensively used as collector in the mineral processing industry, and thus tremendous hazardous beneficiation wastewater containing BHA organic contaminant needs urgent treatment. In this work, an efficient removal of BHA organic contaminants from various industrial beneficiation wastewaters via the chelation, flocculation, and precipitation flotation process was studied. The removal efficiency of BHA, COD and turbidity of the purified water, and the chelation mechanism were investigated by optical microscope, SEM, FTIR, XPS, Zeta potential, and thermodynamic analyses. The results showed that organic BHA contaminant can be chelated firstly by Cu(II) to form hydrophobic BHA-Cu precipitate effectively via the “O-O” chelation and a five-membered chelation ring was formed under weak alkaline conditions. The generated precipitate was then successfully removed using CTAB as surfactant and NP-40 as frother in a microbubble flotation column. Over 94% BHA was removed under the optimal chelation, flocculation and flotation conditions: chelation with Cu(II) concentration of 30 mg/L and pH of 8 for 30 min; flocculation with CTAB concentration of 0.2 mg/L for 20 min; followed by flotation with NP-40 frother of 0.6 mg /L and air flow rate of 100 mL/min for over 40 min. Under this condition, 83.91% COD was removed, and the residuel COD and turbidity of the purified water were lower than 25 mg/L and 0.1 NTU, respectively, which met the wastewater discharge requirement. It’s demonstrated that the precipitate flotation can be employed as an effective method to purify industrial wastewater containing BHA. In addition, the interaction mechanism of Cu(II) and BHA under different pH values was also discussed in this work.

Petrological Composition of the Last Coal Seam in the Longmendong Section before the End-Permian Mass Extinction

Late Permian coal deposits are widely distributed throughout southwestern China. This paper describes the petrological composition of the last coal seam in the Longmendong section of the Emeishan area during the latest Changhsingian (Permian) and records important information regarding the evolution of the mass extinction event that occurred at the end of the Permian. The results show that the dominant coal maceral group is vitrinite, followed by liptinite and inertinite macerals, and the coal minerals include quartz, chamosite and pyrite. The pyrofusinite and carbon microparticles occurrence modes could have been formed during wildfires in the adjacent areas. The β-tridymite occurrence modes and the high proportions and occurrence modes of magmatic quartz indicate that synchronous felsic volcanic activity occurred during the peat mire accumulation period. The chamosite and quartz occurrence modes suggest that they primarily precipitated from Fe-Mg-rich siliceous solutions that was derived from the weathering of nearby Emeishan basalt. The pyritic coal balls occurrence modes in the C1 coal seam are likely the result of coal-forming plants and Fe-Mg-rich siliceous solutions in neutral to weak alkaline conditions during late syngenetic stages or early epigenetic stages within paleomires.

Synthesis, aggregation behavior of alternating copolymer emulsifier in oil solution and its application in oil-based drilling fluids

In order to solve the emulsification problem of oil-based drilling fluids under high-temperature conditions, the copolymer emulsifier with the structure of alternating tertiary amine moieties and alkyl groups was synthesized by the reaction of N,N-dimethylethylenediamine and the alternating copolymer of maleic anhydride with 1-octadene (PMAO). The structure compositions and molecular weight of copolymer emulsifiers were characterized by FT-IR spectra, 1H NMR spectra, elemental analyse and multi-angle laser light scattering. The influence of tertiary amine moieties proportion in copolymer emulsifier on aggregation, interfacial activity, pH-response and emulsion stability were studied. The abundant presence of tertiary amine makes copolymer stabilize water-in-oil emulsion under neutral and weak alkaline conditions while destabilizing the emulsion under acidic conditions. Combining the above experimental data and the stability of water-in-oil emulsions prepared by the copolymer emulsifier, it was found that the emulsifier which has a high proportion of tertiary amine was indeed better at the performance of salt resistance under high temperature. When the copolymer emulsifier (D100) was used in an oil-based drilling fluid system, the electricity stability is greater than 1000 V and the filtrate volume is only 0.6 mL after aging at 232 °C for 16 h.

Degradation of unsymmetrical dimethylhydrazine in water by hybrid mesoporous TiO2 and H2O2 under vacuum ultraviolet (VUV) irradiation

In this study, mesoporous TiO2 with various hydrolysis rates were prepared and combined with H2O2 for the photodegradation of unsymmetrical dimethylhydrazine (UDMH) under VUV irradiation. Results showed that the mesoporous TiO2 synthesized by the hydrolysis in water (MT100) exhibited a good mesoporous structure and the largest specific surface area (178.85 m2 g−1). Consequently, MT100 showed the best degradation efficiency, with the rate constant (k) for VUV/MT100 and VUV/MT100/H2O2 of 0.0185 and 0.2595 min−1, respectively, which was 1.4 and 4.0 times of that of P25. The addition of H2O2 significantly enhanced the degradation efficiency by photoactivation of H2O2 and the synergistic effect. The rate constant and the mineralization rate (after a 3-h treatment) increased by 13 and 3.8 times when 40 mM H2O2 was added into VUV/MT100. The weak alkaline condition (pH = 9) would facilitate the degradation of UDMH. The ⋅OH was the key oxidizing species in VUV/MT100/H2O2. Eight intermediates were detected during the degradation and the possible pathways of UDMH degradation in VUV/MT100/H2O2 process were proposed. VUV/MT100/H2O2 provides an efficient method to degrade UDMH.

Iron-carbon material enhanced electrokinetic remediation of PCBs-contaminated soil

The high toxicity and persistence of polychlorinated biphenyls (PCBs) in the environment demands the development of effective remediation for PCBs-contaminated soils. In this study, electrokinetic (EK) remediation integrated with iron-carbon material (Fe/C) was established and used to remediate PCB28 (1 mg kg−1) contaminated soil under a voltage gradient of 1 V cm−1. Effects of Fe/C dosage, soil type, and remediation time were investigated. The operational condition was optimized as 4 g kg−1 Fe/C, yellow soil, and 14 d-remediation, achieving PCB28 removal efficiency of 58.6 ± 8.8% and energy utilization efficiency of 146.5. Introduction of EK-Fe/C did not significantly affect soil properties except for slight soil moisture content increase and total Fe content loss. Soil electrical conductivity exhibited an increasing trend from anode to cathode attributed to EK-induced electromigration and electroosmosis. EK accelerated the corrosion and consumption of reactive Fe0/Fe3C in Fe/C by generating acid condition. Fe/C in turn effectively prevented EK-induced soil acidification and maintained soil neutral to weak alkaline condition. A synergistic effect between EK and Fe/C was revealed by the order of PCB28 removal efficiency-EK-Fe/C (58.6 ± 8.8%) > EK (37.7 ± 1.6%) > Fe/C (6.8 ± 5.0%). This could be primarily attributed to EK and Fe/C enhanced Fenton reaction, where EK promoted Fe/C dissolution and H2O2 generation. In addition to oxidation by Fenton reaction generated ·OH, EK-mediated electrochemical oxidation, Fe/C-induced reduction and migration of Fe/C adsorbed PCBs were all significant contributors to PCB28 removal in the EK-Fe/C system. These findings suggest that the combination of EK and Fe/C is a promising technology for remediation of organics-contaminated soil.

Experimental and theoretical investigation on the inhibition performance of disulfide derivatives on cobalt corrosion in alkaline medium

Cobalt, as the barrier layer material for 14 nm copper interconnection, has been widely applied owing to its superior characteristics of low resistivity, excellent adhesion performance and blocking properties for copper. Most of the preciously developed cobalt corrosion inhibitors under weak alkaline condition are toxic, low water solubility, and limited to traditional experimental research. In this work, 3,3-dithiodipropionic acid (DDA), 2,2-dibenzamidodiphenyl disulfide (DPD) as potential corrosion inhibitors for cobalt in NH4Cl and H2O2 media under alkaline environment were investigated. Electrochemical experiments, surface morphology characterization, quantum chemical calculation and molecular dynamic simulation were combined to analyze the corrosion inhibition ability and mechanism. The experimental and theoretical results present that these disulfide derivatives can inhibit the corrosion behavior of cobalt surface effectively in ammonium-based aqueous solutions. When the concentration of inhibitors was 0.5 wt%, the corrosion inhibition efficiency of DDA, DPD reach up to 92.9%, 91.41%, respectively. Their favorable capability is attributed to the dense adsorption films following the Langmuir adsorption isotherm. Besides, these two inhibitors show excellent performance of galvanic corrosion inhibition at the Co/Cu interface, which is consistent with the shift tendency simulations for binding to Co/Cu substrates. The results of water solubility and toxicity tests indicate that DDA is more suitable for industrial applications.

Flotation of cassiterite using alkyl hydroxamates with different carbon chain lengths: A theoretical and experimental study

The effects of five alkyl hydroxamates (hexyl hydroxamate (C6), octyl hydroxamate (C8), decyl hydroxamate (C10), dodecyl hydroxamate (C12) and tetra-decyl hydroxamate (C14)) with different carbon chain lengths on the flotation behaviour of cassiterite have been studied by using theoretical and experimental methods. Microflotation tests results showed that increasing the carbon chain length improved the collecting abilities of hydroxamates for cassiterite under acidic to weak alkaline conditions. Adsorption measurements suggested that the adsorption amount of hydroxamic species on the cassiterite surface increased along with carbon chain length. Density functional theory (DFT) calculation results indicated that alkyl hydroxamates with a longer carbon chain have lower electronic stabilities and larger dipole moments. In the absence of H2O molecules, hydroxamates with longer carbon chains easily absorbed on the SnO2 surface by chelating 6-membered rings.H2O molecules could spontaneously adsorb on the SnO2 surface. Hydroxamates adsorbed on the hydroxylated SnO2 surface via hydrogen bonding interaction. X-ray photoelectron spectroscopy (XPS) analysis revealed that hydroxamates adsorbed on cassiterite through physical interaction, thereby suggesting that the computational simulation results are reliable.

Construction of double dynamic covalent bond crosslinked hydrogel based on water-soluble block polymers

Functional phenylboronic-and hydrazide-containing N -isopropyl acrylamide based diblock polymer, and ketone-and glucose group-containing acrylamide based diblock polymer, were prepared by the reversible addition-fragmentation chain transfer (RAFT) polymerization. The structure and properties of the copolymers were studied, and doubly dynamic hydrogel was prepared under different conditions. The main driving force of gel formation is the acylhydrazone bond formed by the hydrazine and ketone group, and the boronate ester bond formed by the boronic acid and glucose group. Under acidic conditions, the acylhydrazone bond ensures the rapid formation kinetics and good self-healable ability of the hydrogel. Under neutral or weak alkaline conditions, the active boronate ester bond endows the hydrogel with fast gelation kinetics and maintains the gel state, while the stable acylhydrazone bond can enhance the mechanical strength of the hydrogel gradually. Under alkaline conditions, the two dynamic covalent bonds are synergistic, giving the hydrogel multiple responsiveness and macroscopically self-healable ability.

Biocatalyst and colorimetric biosensor of carcinoembryonic antigen constructed via chicken egg white-copper phosphate organic/inorganic hybrid nanoflowers

In this article, the dual-functional chicken egg white-copper phosphate organic-inorganic hybrid nanoflowers (Cu-NFs), combining the functions of signal amplification and biological recognition, were prepared through a simple one-pot method. The Cu-NFs exhibit excellent biocatalytic activity of peroxidase and polyphenol oxidase. Besides, a biotin-labeled secondary antibody encapsulated Cu-NFs-2 (Cu-NFs-2@Biotin-NHS-Ab2) capture probe was prepared by using the interaction between avidin in the egg white and biotin. Based upon this superiority, the as-prepared Cu-NFs-2 were used in labeled avidin-biotin enzyme-linked immunosorbent assay (Cu-NFs-2 based-LAB-ELISA) to construct a sensitive colorimetric biosensor for the ultrasensitive detection of carcinoembryonic antigen (CEA). Under weak alkaline (pH = 7.5) conditions, the as-developed colorimetric sensor displayed a wide linear range of 0.05–40 ng/mL with a detection limit of 3.52 pg/mL. Furthermore, this colorimetric sensor has been successfully applied to the detection of CEA in human serum samples. Therefore, the as-developed colorimetric sensor has broad application prospects in the field of medical diagnosis and portable detection.

Facile synthesis of novel tremella-like Mn0@Mn2O3 and its exceptional performance on removal of phosphate

Phosphorus is an essential nutrient for biological growth, but its excessive presence in water can lead to eutrophication. Reducing phosphorus concentrations is an important way to prevent eutrophication of surface water bodies. In this study, a novel zero-valent manganese (ZVM) Mn0@Mn2O3 sorbent was synthesized via a facile one-step reduction method at ambient temperature. The morphology and surface properties of the Mn0@Mn2O3 were analyzed by Scanning electron microscopy (SEM), X-ray diffraction (XRD), Zeta potential analyzer, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The obtained amorphous sample consists of many small tremella-like particles. The as-prepared sorbent shows exceptional phosphate removal performance and has a maximum adsorption capacity of 113.7 mg-P/g at pH 7.0, superior to many reported adsorbents. The removal of phosphate is obviously pH-dependent and is favorable under near-neutral and weak-alkaline conditions (pH 6.5–8.5). The kinetics data fit well to the pseudo-second-order model. The coexisting SO42-, CO32- and Cl- have no great influence on phosphate sorption, whereas, the SiO32- shows negative effect at high concentration. The sorbent is effective for phosphate removal from real municipal wastewater. The results of ionic strength effect experiment, SEM, XRD, FTIR and XPS analyses reveal that the phosphate was mainly removed through surface precipitation and formation of inner-sphere surface complexes. The Mn0@Mn2O3 is a promising sorbent for phosphate removal from surface water and wastewater, owning to its exceptional performance, high selectivity, environmental friendliness and easy preparation.

Natural community of macroalgae from chromium-contaminated site for effective remediation of Cr(VI)-containing leachates

The natural macroalgal community, which developed in the unique and extremely Cr(VI)-polluted aquatic reservoir situated near a historical chromium-waste landfill, was studied in order to recognize the main mechanisms of Cr(VI) detoxification by the algal species. The conducted taxonomic analysis revealed mixed composition of the filamentous forms of algae and showed that three species of Tribonema, namely T. vulgare, T. microchloron and T. viride, which have not been studied before with regard to the mechanisms of Cr(VI) removal, are likely responsible for the effective bioremediation of this highly Cr(VI)-polluted habitat. The studied algal community, with the ability to grow in extremely high concentrations of Cr(VI), i.e. up to ca. 6150 times the upper limit for surface water, exhibited hyperaccumulative properties for chromium (max 16230 mg/kg dry weight) under the given environmental conditions. We found that the main mechanism of Cr(VI) detoxification was reduction followed by Cr(III) biosorption – feasibly by ion exchange and complexation mechanisms – and that the excellent efficiency of chromium reduction under the given, unfavorable weakly alkaline conditions indicates the biological origin of this process. It was concluded that the examined reservoir inhabited by the algal community can be used, after some modifications, as a simple cost-effective “bioreactor” allowing the reduction of chromium concentration to the desired level. Moreover, the conducted studies are also essential to obtain in-depth knowledge and should also be helpful in the relevance of the community for its further application as a potential biosorbent of Cr(VI) on a global scale.

Sorptive removal of methylene blue from water by magnetic multi-walled carbon nanotube composites.

In the present study, five magnetic multi-walled carbon nanotubes (MMWCNTs) with different diameters were prepared and their performance on the sorptive removal of methylene blue (MB) from water was investigated. Transmission electron microscope, scanning electron microscope, Fourier transform infrared spectrometer, X-ray diffraction, and vibrating sample magnetometer confirm that the surface of these MMWCNTs has been decorated by Fe3O4 nanoparticles, which renders the MMWCNTs superparamagnetic. Thus, these MMWCNTs can be easily separated from water after the adsorption. During the adsorption process, pH slightly affected the removal efficiency of MB and the adsorption performed better under weak alkaline conditions. Adsorption kinetics followed the pseudo-second-order kinetic model well, and the Dubinin-Radushkevich model fitted the isotherms best. The maximum adsorption capacity for MB reached 204.2 mg/g, and the values decreased with increasing diameters of MMWCNTs due to decreasing specific surface areas. The thermodynamics parameters indicated the spontaneous and exothermic nature of the adsorption. The reusability test showed that MMWCNTs could be used for 6 cycles without significant loss of the adsorption capacity. And common ions (K+, Na+, Ca2+ and Al3+) and SDS in water did not show greatly effects on the removal efficiency of MB. Hence, MMWCNTs prepared in this study could be promising adsorbents for dyes removal from wastewater.

Homeostatic responses and growth of Leymus chinensis under incrementally increasing saline-alkali stress.

Despite considerable tolerance to salt and alkali stress, Leymus chinensis populations on the southwestern Songnen Plain in northern China are threatened by increasing soil salinity and alkalinity. To explore the species’ responses to saline-alkali stress, we grew it in substrates with varying concentrations of nitrogen (N) and phosphorus (P) while applying varying levels of saline-alkali stress (increasing in 14-, 17- or 23 -day intervals). We measured the plants’ contents of N and P, and the N:P ratio, and calculated their homeostasis indices (HN, HP and HN:P) under each nutrient and saline-alkali stress treatment. The N content was found to be more sensitive to saline-alkali stress than the P content. The N and P contents were highest and the N:P ratio was stable at pH 8.4. At both pH 8.1 and 8.4, HN:P> HN > HP, but the indices and their relations differed at other pH values. Exposure to saline-alkali stress for the 14-day incremental interval had weaker effects on the plants. Rapid changes in salinity-alkalinity weakened both the positive effects of the weakly alkaline conditions (pH 7.5–8.4) and the negative effects of more strongly alkaline conditions (pH 8.7 or 9.3) on L. chinensis. When L. chinensis plants lack N, applying N fertilizer will be extremely efficient. The optimal concentrations of N and P appeared to be 16 and 1.2 mmol/L, respectively. When the L. chinensis plants were N- and P-limited, the specific growth rate correlated positively with N:P, when limited by N it correlated positively with the environmental N concentration, and when limited by P it was weakly positively correlated with the environmental P concentration.

Bimetallic carbides embedded in heteroatom-doped carbon nanotubes for efficient electrocatalytic hydrogen evolution reaction and high-performance lithium storage

A sacrifice-template strategy combined with carbonization treatment was rationally designed to fabricate tubular-like carbon nanotubes coupled with ultrasmall Mo-W bimetallic carbides for boosting electrocatalytic hydrogen evolution and lithium ions storage. Specifically, metal chelating coordination reaction and the dissolution of template undergo simultaneously under weak alkaline condition, thus leading to the formation of the hollow Mo-W-polydopamine (MoW-PDA) hybrid nanotubes. After carbonization, ultrasmall Mo-W bimetallic carbides embedded in the heteroatom (N, P)-codoped carbon nanotubes (MoxW2-xC/N, P-codoped CNTs) endow to prevent the aggregation between nanoparticles and provide more active sites. As a proof of concept, MoxW2-xC/N, P-codoped CNTs exhibited outstanding electrocatalytic activity toward hydrogen evolution reaction with a low overpotential and steady durability in acidic and alkaline solutions. Moreover, MoxW2-xC/N, P-codoped CNTs displayed extraordinary lithium storage performance, which delivered decent reversible capacities of 560.9 mAh g−1 and 366.6 mAh g−1 at 1.0 A g−1 and 5.0 A g−1 after 1000 cycles, respectively, one of best performances for metal carbide-based anode. This work highlights a novel strategy to fabricate bifunctional carbides toward efficient electrocatalytic reaction and lithium ions storage.

Experimental investigation of the reactions between pyrite and aqueous Cu(I) chloride solution at 100–250 °C

Replacement of pyrite by copper-bearing sulfides is widespread in mineral deposits, with zonation of chalcocite, bornite, and chalcopyrite being a common result of this process. Copper occurs predominantly as Cu(I) in hydrothermal fluids, but the mechanistic details of reactions between pyrite and aqueous Cu(I) and their relevance to the zonation of Cu sulfides in hydrothermal deposits remain poorly understood, because of a lack of relevant experimental constraints. In this study, we investigated the reactions between pyrite and aqueous Cu(I) chloride solutions over a wide range of physicochemical conditions (100–250 °C; pH = 1–8; saturated vapor pressure). The experimental results show that Cu-bearing sulfides form at temperatures of >150 °C, and that pH exerts an important control on the mineralogy of the reaction products. In strongly acidic conditions (pH = 1.1), pyrite dissolution occurs; in acidic-to-neutral conditions (pH = 3.0–6.0), chalcopyrite and bornite are the main products; in weakly alkaline conditions (pH = 8.2), the replacement products are chalcocite and bornite. Chalcopyrite, bornite, and chalcocite generally occur in a zoned sequence outward from the pyrite reaction front to the bulk solution, and the replacement of pyrite by chalcopyrite is heterogeneous. In situ Raman observation and S isotope analyses suggest that pyrite replacement by chalcopyrite is a redox-coupled dissolution–precipitation reaction, with the oxidative dissolution of pyrite to form sulfate, generating the electrons that maintain the reductive replacement of pyrite by chalcopyrite. The sites of oxidative dissolution and reductive replacement can be spatially separated, but coupled by electron transfer. By contrast, the further replacement of chalcopyrite by bornite and chalcocite does not involve the oxidative dissolution of sulfur, but release of iron and H+, which could be promoted at higher pH. Notably, when the zonation of sulfides is established in a hydrothermal experiment of pyrite replacement by Cu(I) solution, gradients of H2S (or HS–), Cu(I), and Fe(II) are developed between the pyrite reaction front and bulk solution via diffusion through interstitial pore space. As such, the inner zones of chalcopyrite and bornite are not in equilibrium with the bulk solution as confirmed by thermodynamic calculations. The results imply that the zonation of Cu-bearing sulfides in mineral deposits records heterogeneous chemical environments, from the mineral interface- to the ore deposit-scale during dynamic mineralization processes.

Determination and Comparison of the Solubility, Oil-Water Partition Coefficient, Intestinal Absorption, and Biliary Excretion of Carvedilol Enantiomers.

Carvedilol is administered as a racemic mixture for the therapy of hypertension and heart failure. S-enantiomer is the dominant conformation of pharmacodynamics, but its further development was obstructed by its poor bioavailability. In this study, carvedilol and its enantiomers were compared in terms of solubility, permeability, and biliary excretion, and reasons for the poor bioavailability were discussed. Equilibrium solubility and log P were measured by a shake flask method at a wide pH range (1.2-8.0), and intestinal absorption and biliary excretion were evaluated using a single-pass rat intestinal perfusion model. According to BCS guidance, carvedilol and its R/S enantiomers are considered highly soluble at pH value less than 5.0 and low soluble at neutral or weak alkaline conditions. RS-carvedilol showed significantly lower solubilities at pH1.2-5.0 and higher solubilities at pH6.0-8.0 than its enantiomers. In addition, carvedilol and its enantiomers possessed similar log P values at pH1.2-8.0. High intestinal permeabilities of carvedilol and its enantiomers were observed, and S-carvedilol showed higher absorption than R-carvedilol and RS-carvedilol. The biliary excretion about two major metabolites, 1-hydroxycarvedilol O-glucuronide and 8-hydroxycarvedilol O-glucuronide, of RS-carvedilol, S-carvedilol, and R-carvedilol were 66.4%, 73.5%, and 54.3%, respectively. In conclusion, there are significant differences amongst carvedilol and its R/S enantiomers in terms of solubility, intestine absorption, and biliary excretion abilities. The first pass effect is the primary reasons for the low bioavailability of S-carvedilol. Therefore, pharmaceutical strategies or parenteral routes should be considered to avoid the first pass metabolism.