NaCl pH Research Articles

Corrosion Resistance of Stainless Steel Containing Mo-Rich Areas

Stainless steels are widely used because of their high corrosion resistance. It is well known that Mo improves the pitting corrosion resistance of stainless steels1, 2), and the transpassive dissolution of pure Mo occurs in the passive region of stainless steels. In this study, a stainless steel that releases Mo-species in chloride solutions and exhibits self-healing properties was fabricated by spark plasma sintering (SPS) of type 304L gas atomized powder and 2.5 mass% of Mo powder. Sintering temperature was 1100℃ and it kept for 20 min. The specimen surface was polished down to 1 μm using a diamond paste.The as-polished and etched surfaces of the samples were observed by an optical microscope. A field emission scanning electron microscope equipped with an energy-dispersive X-ray spectroscopy system was also used to observe the surface of the specimens. From the observations, the formation of Mo-rich areas was confirmed, and the Mo-rich area was found to be consisted of three phases: inner, middle, and outer phases. Inner phase was rich in Mo, and middle and outer phases contains other elements such as Cr, Ni, and Fe.To assess the corrosion resistance, potentiodynamic polarization curves were measured in 0.1 M NaCl (pH 6.0). The size of electrode area was 300 µm × 300 µm or 5 mm × 5 mm. The stainless steel with Mo-rich areas showed higher pitting corrosion resistance compared with sintered type 316L stainless steel fabricated by SPS. After polarization, inner phase of Mo-rich area dissolved, while middle and outer phase did not dissolve. Pitting corrosion resistance was concluded to be improved by dissolved Mo-species from Mo-rich areas.References; Saito, I. Muto, and Y. Sugawara, Mater. Trans., 61 (2020), 2248-2251. Saito, I. Muto, M. Nishimoto, and Y. Sugawara, Mater. Today Commun., 33 (2022) 104211.

The Effect of Cu and Zn Addition on the Intergranular Corrosion Resistance of Al-Mg-Si Alloy

Aluminum alloys are widely used for automobile and aircraft industries because of their good strength-to-weight ratio. In general, Cu improves the strength of Al alloys but reduces localized corrosion resistance. For Al-Mg-Si alloys, it has been reported that Cu decreases intergranular corrosion resistance. In this study, the effect of Cu and Zn on intergranular corrosion resistance was analyzed by electrochemical measurements.As specimens, Cu-free alloy, Cu-added alloy, and Cu- and Zn-added alloy were prepared based on AA6061 composition. The extruded specimens were subjected to T6 heat treatment. Intermetallic compounds were characterized by SEM-EDS and TEM. Open-circuit potentials (OCPs) was measured in 0.1 M NaCl (pH 6.0). To assess the distribution density of the initiation sites of localized corrosion, the size of electrode area was 100 mm2, 9 mm2, or 1 mm2. In the electrochemical measurements, Ag/AgCl (3.33 M KCl) was used as the reference electrode.At the beginning of immersion, OCP was −1.2 V (vs. SHE) for all specimens, and OCP increased with time. After 4000 s, the OCP of Cu-free alloy became −0.5 V, the OCPs of Cu-added alloy and Cu- and Zn-added alloy became −0.4 V. After 3 h immersion, intergranular corrosion was generated on Cu-added alloy and Cu- and Zn-added alloy. In contrast, no intergranular corrosion was observed on Cu-free alloy. Based on intergranular corrosion length, it was shown that intergranular corrosion resistance of Cu- and Zn-added alloy is low compared with the others. This result suggested that Zn promotes the growth of intergranular corrosion. Moreover, the number of intergranular corrosion damages was assessed and found to be less on Cu- and Zn-added alloy than on Cu-added alloy. This result suggested that Zn decrease the number of initiation sites of intergranular corrosion. Additionally, 3-h immersion of Cu-added alloy and Cu- and Zn-added alloy was conducted with the electrode area of 9 mm2 and 1 mm2. For both alloys, intergranular corrosion occurred at 10 sites in 100 mm2 and 1 site in 9 mm2. And no intergranular corrosion occurred in the case of 1 mm2 electrode area. The distribution density of the initiation sites for intergranular corrosion on Cu-added alloy and Cu- and Zn-added alloy was estimated to be approximately 1 site per 9 mm2.

Self-assembly of oat proteins into various colloidal states as function of the NaCl concentration and pH

Oats are increasingly used in a range of liquid and semi-solid foods. Insights into the behavior of native oat proteins in aqueous media are crucially important to understand their functionality, but are sorely lacking. Here, for the first time, the impact of varying NaCl concentration and pH on the colloidal state of native oat proteins was systematically studied. Non heat-treated oat groats were used as raw material to produce oat protein isolates (OPI). Upon addition of varying concentrations of NaCl to a native OPI solution, oat proteins self-assembled into different colloidal states. Most notably, at <50 mM NaCl, oat proteins formed protein aggregates with a fractal dimension of 1.8, while at 50–300 mM NaCl, oat proteins microphase-separated to form concentrated protein droplets of ≥1 μm. To allow assessing the impact of pH systematically, titration experiments were performed to establish the relation between pH and protein charge density (α). Upon changing the charge density of a native OPI solution, protein microphase separation was found to occur in the region α = −155 (pH 8.2) to α = −118 (pH 7.1). At lower charge densities (and thus pH values), this phenomenon was no longer observed, but protein aggregation occurred, and pronouncedly so at the protein iso-ionic point (α = 0, pH 5.0). In conclusion, oat proteins self-assemble into different types of colloidal structures at varying NaCl concentration and pH. This could have important implications for the properties of oat proteins in a variety of foods and should be investigated further.

Time-Dependent Retention of a Mixture of Cs(I), Sm(III), Eu(III) and U(VI) as Waste Cocktail by Calcium Silicate Hydrate (C-S-H) Phases

In the context of the safe storage of high-level radioactive waste, the time-dependent retention of a waste cocktail (WC) consisting of Zr(IV), Mo(VI), Ru(III), Pd(II), Cs(I), Sm(III), Eu(III) and U(VI) was studied on the commercially available C-S-H phase Circosil®. The herein presented results focus on Cs(I), Sm(III), Eu(III) and U(VI). Precipitation and wall adsorption studies in the absence of the solid phase show only a small amount of precipitation for Sm(III) and Eu(III) (34 ± 18%) in the high-saline diluted Gipshut solution (DGS, pH 10.6, I = 2.6 M). For Cs(I) and U(VI), no precipitation was observed. In 0.1 M NaCl (pH 10.9), the measured retention could completely be attributed to wall adsorption for all four elements. The obtained Rd values for the time-dependent retention of Sm(III), Eu(III) and U(VI) on Circosil® of 105 to 106 L·kg−1 are in good agreement with the literature. For Cs(I) in the strongly saline background electrolytes, slightly higher Rd values of up to 8·102 L·kg−1 were determined for the crystalline Circosil® compared to the wet chemical C-S-H phases. Overall, the commercial product Circosil® is suitable as an alternative to synthesised C-S-H phases to observe trends in the retention behaviour of these elements. Comparison between both background electrolytes shows an increase in the amount and velocity of retention for all four elements with decreasing salinity. This confirms adsorption processes as the fastest and initial retention mechanism. Precipitation or incorporation of Eu(III), Sm(III) and U(VI) cannot be ruled out in the long term. Comparing the kinetic of this WC study to single-element studies in the literature, a longer uptake time to reach a steady state of 7 d in 0.1 M NaCl and 28 d in DGS instead of &lt;1 d was observed for Eu(III) and Sm(III). The situation for Cs(I) is similar. This indicates competing effects between the different WC elements for adsorption sites on the C-S-H phases.

A study on bioactive potential of Serratia marcescens from marine environment

Marine microorganisms are diverse and excessively incompatible from the terrestrial counterparts, making them a great promising tool for biotechnological applications in the area of agriculture, health, and environment. This research study mainly focused on a novel strain Serratia marcescens MBBTBC9 from marine environment. The characterization of Serratia marcescens MBBTBC9 revealed its tolerance profile against various abiotic stresses like temperature in the range of 4–50 °C, 0.5 %- 7 % NaCl concentration and pH between 7 and –13 and heavy metals with a maximum resistance level of 500 ppm against lead and copper. Atomic absorption spectroscopy elucidated the ability of S. marcescens in the removal of heavy metals. Plant growth promoting ability of S. marcescens MBBTBC9 assessed using Vigna unguiculata, the common crop cultivated in different states of India, it significantly enhanced seed germination, seedling vigour, seedling emergence and growth enhancement in both plate and pot assay. Thus, this study discloses the biological potential of S. marcescens MBBTBC9 to be a promising stress tolerant plant growth promoting marine bacterium.

Design of CoSbyOx/Ti electrocatalyst via facile thermal decomposition method for durable and high temperature chlorine evolution reaction in acidic media

Developing stable and cost-effective electrodes for the anode compartment of chlor-alkali process to drive the chlorine evolution reaction (CER) has remained as a challenge. This study introduces CoSbyOx/Ti as a durable and non-precious anode electrocatalyst synthesized via facile and scalable thermal decomposition method. This novel electrode permanently conducts CER for 240 h under 100 mA.cm−2 at 70 °C in 4 M NaCl (pH=2) with an overpotential of only 498 mV and a high selectivity of 92.2 % toward CER. From XRD results, crystalline CoSb2O6 forms above 600 °C and acts as active and stable phase during CER. From XPS analysis, a combination of Co3+ and Co2+ forms on the surface of the electrode; the content of Co3+ species increases after CER which can reduce structural defects and hence improve the stability of the structure. We further shed more light on the degradation mechanism of this type of electrodes by performing additional 240 h durability test under accelerated condition of 1000 mA.cm−2. Observations indicate a failure mechanism that is probably a combination of deactivation of the electrode and catalyst detachment in accelerated conditions.

The effect of NaCl, pH, and phosphate on biofilm formation and exopolysaccharide production by high biofilm producers of Bacillus strains.

Biofilm formation is an effective survival strategy of plant-associated microorganisms in hostile environments, so the application of biofilm-forming and exopolysaccharide (EPS)-producing beneficial microbes to plants has received more attention in recent years. This study examined the ability of biofilm and EPS production of Bacillus subtilis and Bacillus thuringiensis strains under different NaCl concentrations (0, 50, 100, 200, and 400mmol/L), pH values (5.5, 6.5, 7.5, and 8.5), and phosphate levels (0, 25, 50, and 100mmol/L at 0 and 400mmol/L NaCl). B. subtilis BS2 and B. thuringiensis BS6/BS7 strains significantly increased biofilm formation in a similar pattern to EPS production under salt stress. B. subtilis BS2/BS3 enhanced biofilm production at slightly acidic pH with a lower EPS production but the other strains formed considerably more amount of biofilm and EPS at alkaline pH. Interestingly, higher levels of phosphate substantially decreased biofilm and EPS production at 0mmol/L NaCl but increased biofilm formation at 400mmol/L salt concentration. Overall, contrary to phosphate, salt and pH differently influenced biofilm and EPS production by Bacillus strains. EPS production contributed to biofilm formation to some extent under all the conditions tested. Some Bacillus strains produced more abundant biofilm under salt and pH stress, indicating their potential to form in vivo biofilms in rhizosphere and on plants, particularly under unfavorable conditions.

Experimental investigation on the bio-tribocorrosive behavior of Ti6Al4V alloy and 316 L stainless steel in two biological solutions

In this manuscript the tribocorrosive behavior of two common biomaterials adopted in dentistry such as Titanium Grade V and Steel 316 L was investigated by a tribometer equipped with a three electrodes potentiostat and a confocal interferometric apparatus for a deep worn surface analysis. The experiments underlined that the pH and higher concentration of NaCl induced greater material loss, especially in terms of mechanical-chemical combined action which, estimated by synergistic approach, had a significant impact on the total wear. In addition, Titanium Grade V alloy showed a superior tribocorrosive wear resistance respect to Steel 316 L because of its higher hardness. Lastly, a linear correlation between tribocorrosive current and synergistic factor was found out which could be adopted in future analytical wear models.

A comprehensive investigation of protein expression profiles in L. monocytogenes exposed to thermal abuse, mild acid, and salt stress conditions.

Preventing L. monocytogenes infection is crucial for food safety, considering its widespread presence in the environment and its association with contaminated RTE foods. The pathogen's ability to persist under adverse conditions, for example, in food processing facilities, is linked to virulence and resistance mechanisms, including biofilm formation. In this study, the protein expression patterns of two L. monocytogenes 1/2a strains, grown under environmental stressors (mild acidic pH, thermal abuse, and high concentration of NaCl), were investigated. Protein identification and prediction were performed by nLC-ESI-MS/MS and nine different bioinformatic software programs, respectively. Gene enrichment analysis was carried out by STRING v11.05. A total of 1,215 proteins were identified, of which 335 were non-cytosolic proteins and 265 were immunogenic proteins. Proteomic analysis revealed differences in protein expression between L. monocytogenes strains in stressful conditions. The two strains exhibited unique protein expression profiles linked to stress response, virulence, and pathogenesis. Studying the proteomic profiles of such microorganisms provides information about adaptation and potential treatments, highlighting their genetic diversity and demonstrating the utility of bioinformatics and proteomics for a broader analysis of pathogens.

Facilitating Electrochemical Ozone Production and Chlorine Evolution Reaction by Synergistic Effect of Multicomponent Metal Oxides

AbstractThe concomitant degradation of organic contaminants using green oxidants, NaClO and O3, exhibits great potential to mitigate the deleterious impact of organic pollutants. In this work, the electrochemical ozone production (EOP) and chlorine evolution reaction (CER) performed by highly active electrocatalysts composed of Ce‐Ni‐Sb‐SnO2 and Ru‐Ir‐Ce‐Ni‐Sb‐SnO2, respectively, are presented. Ce‐Ni‐Sb‐SnO2 exhibits high selectivity with a 43.9% Faraday efficiency in EOP. Incorporating Ru and Ir in Ru‐Ir‐Ce‐Ni‐Sb‐SnO2 improves CER performance, achieving outstanding Faraday efficiency of up to 98.3%. Additionally, it achieves a low overpotential of ≈80 mV at 10 mA cm−2 with 0.3 m NaCl (pH = 6). Theoretical calculations reveal the significant impact of multicomponent oxides on reaction intermediate adsorption. Ce, Ni, Sb doping on SnO2 enhances O2 and O3 adsorption for optimal EOP performance, while Ru and Ir doping on Ce‐Ni‐Sb‐SnO2 enhances Cl adsorption, boosting CER performance. Further investigations into the decomposition of pesticides and antibiotics demonstrate that the collaborative impact of O3 and NaClO elicits a significantly more robust kinetic degradation rate in comparison to their individual influences. This work aims to shed light on the synthesis of multicomponent metal oxides as potential precursors for the cost‐effective preparation of O3 and NaClO for electrochemical advanced oxidation processes.

Expression, purification, and enzymatic characterization of an extracellular protease from Halococcus salifodinae.

Extracellular proteases from halophilic archaea displays increased enzymatic activities in hypersaline environment. In this study, an extracellular protease-coding gene, hly34, from the haloarchaeal strain Halococcus salifodinae PRR34, was obtained through homologous search. The protease activity produced by this strain at 20% NaCl, 42 °C, and pH 7.0 was 32.5 ± 0.5 (U·mL-1). The codon-optimized hly34 which is specific for Escherichia coli can be expressed in E. coli instead of native hly34. It exhibits proteolytic activity under a wide range of low- or high-salt concentrations, slightly acidic or alkaline conditions, and slightly higher temperatures. The Hly34 presented the highest proteolytic activity at 50 °C, pH 9.0, and 0-1 M NaCl. It was found that the Hly34 showed a higher enzyme activity under low-salt conditions. Hly34 has good stability at different NaCl concentrations (1-4 M) and pH (6.0-10.0), as well as good tolerance to some metal ions. However, at 60 °C, the stability is reduced. It has a good tolerance to some metal ions. The proteolytic activity was completely inhibited by phenylmethanesulfonyl fluoride, suggesting that the Hly34 is a serine protease. This study further deepens our understanding of haloarchaeal extracellular protease, most of which found in halophilic archaea are classified as serine proteases. These proteases exhibit a certain level of alkaline resistance and moderate heat resistance, and they may emerge with higher activity under low-salt conditions than high-salt conditions. The protease Hly34 is capable of degrading a number of proteins, including substrate proteins, such as azocasein, whey protein and casein. It has promising applications in industrial production.

Protein carbonylation and structural changes in porcine myofibrillar protein exposed to metal ion-H2O2-ascorbate and linoleic acid-lipoxidase oxidizing systems

The present study aimed to compare two oxidizing systems commonly present in meat for their influence on protein oxidation patterns, with emphasis on the specific lysine-derived markers for protein carbonylation (α-aminoadipic semialdehyde, AAS; lysinonorlucine, LNL) and their relationships with the common markers for protein oxidation. For this purpose, pork myofibrillar proteins (MFP, 5 mg/mL) were suspended in 0.6 M NaCl (pH 7.5) and incubated at 4 ℃ for 24 h with two oxidizing systems: (1) a metal-catalyzed oxidizing system (MOS: 10 µM FeCl3, 100 µM ascorbic acid, and 0–10 mmol/L H2O2), (2) a linoleic acid – lipoxidase oxidizing system (LOS: 7500 units of lipoxidase/mL, and 0–10 mM linoleic acid). Results showed that the amounts of AAS and LNL in both MOS- and LOS-oxidized MFP was proportional to the oxidant concentrations (H2O2 or linoleic acid), while the formation of total carbonyl and total thiol also exhibited similar oxidant-dose-dependent patterns. Meanwhile, the α-helix contents of MFP declined with oxidant concentrations irrespective of the oxidizing systems. The reducing SDS-PAGE revealed that the myosin heavy chain band started to diminish at high H2O2 concentration (5 and 10 mM) in MOS whereas at low level of linoleic acid (0.5 mM) in LOS. Overall, these results demonstrated both oxidizing systems could be involved in the formation of AAS and LNL, and that the generation of AAS and LNL can be used as reliable markers for protein oxidation, but also might be directly involved in protein structural changes and then contribute to the alternations of protein functionality.

Branched DNA-Based Electrochemical Biosensor for Sensitive Nucleic Acids Analysis with Gold Nanoparticles as Amplifier.

A branched DNA-based electrochemical biosensor was designed to sensitively detect specific nucleic acids. On this platform, novel a branched DNA with three sticky ends could be used as a biosensor to sensitively and specifically detect nucleic acids. Meanwhile, we also employed branched DNA-modified AuNPs as a signal amplifier to further improve the sensitivity. Branched DNA sensors, target DNA, and DNA-modified AuNPs formed a sandwich structure to produce an electronic signal for target DNA detection. The reaction primarily involved DNA hybridization without bulky thermal cyclers and enzymes. We proved that the hybridization reaction easily occurred under different conditions, such as the NaCl concentration, reaction time, pH, and temperature, except for a pH lower than 4. The limit of detection could go as low as 0.09 pM (S/N = 3) with excellent specificity and selectivity. There was a correlation curve relationship between the peak current and the logarithm of the target DNA concentration (0.10 pM to 10 nM). The correlation coefficient reached 0.987. The electrochemical platform enables a branched DNA nanostructure to determine nucleic acids for disease diagnosis.

Ecotoxicological response surface analysis of salt and pH in textile effluent on Bacillus subtilis and Lactuca sativa.

Textile effluents, although their composition can vary considerably, typically contain high levels of dissolved salts and exhibit wide variations in pH. Ecotoxicological studies regarding the effects of these parameters, however, have been limited owing to the need for sensitive and easy-to-handle bioindicators that require low amounts of sampling, are cost-effective, time-efficient, and ethically endorsed. This kind of study, additionally, demands robust multi-factorial statistical designs that can accurately characterize the individual and combined relationship between variables. In this research, Response Surface Methodology (RSM) was used to calculate the individual and interaction effects of NaCl concentration and pH value of a Simulated Textile Effluent (STE) on the development rate (DR) of the bioindicators: Bacillus subtilis bacteria and Lactuca sativa lettuce. The results demonstrated that the bioindicators were sensitive to both NaCl and pH factors, where the relative sensitivity relationship was B. subtilis > L. sativa. The quadratic equations generated in the experiments indicated that increased concentrations of 50-250 mg L-1 of NaCl caused a perturbance of 1.40%-34.40% on the DR of B. subtilis and 0.50%-12.30% on L. sativa. The pH factor at values of 3-11 caused an alteration of 27.00%-64.78% on the DR of the B. subtilis and 51.37%-37.37% on the L. sativa. These findings suggest that the selected bioindicators could serve as effective tools to assess the ecotoxicological effects of textile effluents on different ecological systems, and the RSM was an excellent tool to consider the ecotoxicological effects of the parameters and to describe the behavior of the results. In conclusion, the NaCl and pH factors may be responsible for disrupting different ecosystems, causing imbalances in their biodiversity and biomass. Before discharge or reuse, it is suggested to remove salts and neutralize pH from textile effluents and, mostly, develop novel, eco-friendlier textile processing techniques.

Characterization of trehalolipid biosurfactant produced by the novel marine strain Rhodococcus sp. SP1d and its potential for environmental applications

BackgroundBiosurfactants are surface-active compounds with environmental and industrial applications. These molecules show higher biocompatibility, stability and efficiency compared to synthetic surfactants. On the other hand, biosurfactants are not cost-competitive to their chemical counterparts. Cost effective technology such as the use of low-cost substrates is a promising approach aimed at reducing the production cost. This study aimed to evaluate the biosurfactant production and activity by the novel strain Rhodococcus sp. SP1d by using different growth substrates. Therefore, to exploit the biosurfactant synthesized by SP1d for environmental applications, the effect of this compound on the bacteria biofilm formation was evaluated. Eventually, for a possible bioremediation application, the biosurfactant properties and its chemical characteristics were investigated using diesel as source of carbon.ResultsRhodococcus sp. SP1d evidence the highest similarity to Rhodococcus globerulus DSM 43954T and the ability to biosynthesize surfactants using a wide range of substrates such as exhausted vegetable oil, mineral oil, butter, n-hexadecane, and diesel. The maximum production of crude biosurfactant after 10 days of incubation was reached on n-hexadecane and diesel with a final yield of 2.38 ± 0.51 and 1.86 ± 0.31 g L− 1 respectively. Biosurfactants produced by SP1d enhanced the biofilm production of P. protegens MP12. Moreover, the results showed the ability of SP1d to produce biosurfactants on diesel even when grown at 10 and 18 °C. The biosurfactant activity was maintained over a wide range of NaCl concentration, pH, and temperature. A concentration of 1000 mg L− 1 of the crude biosurfactant showed an emulsification activity of 55% towards both xylene and olive oil and a reduction of 25.0 mN m− 1 of surface tension of water. Eventually, nuclear magnetic resonance spectroscopy indicated that the biosurfactant is formed by trehalolipids.ConclusionsThe use of low-cost substrates such as exhausted oils and waste butter reduce both the costs of biosurfactant synthesis and the environmental pollution due to the inappropriate disposal of these residues. High production yields, stability and emulsification properties using diesel and n-hexadecane as substrates, make the biosurfactant produced by SP1d a sustainable biocompound for bioremediation purpose. Eventually, the purified biosurfactant improved the biofilm formation of the fungal antagonistic strain P. protegens MP12, and thus seem to be exploitable to increase the adherence and colonization of plant surfaces by this antagonistic strain and possibly enhance antifungal activity.

Isolation and Identification of Moderately Halophilic Bacteria from Soak Liquor Samples Collected of Leather Tanneries

Isolation and identification of protease and lipase producing moderately halophilic bacteria from soak liquor samples and studying their adverse effects to the sheepskin using scanning electron microscopy may provide critical data on decomposition of raw hide/skin materials during soaking process. Moreover, enzyme-production properties of the moderately halophilic isolates (such as catalase, oxidase, lipase, protease, urease, caseinase, amylase, cellulase, pullulanase, xylanase) were determined. The effects of different NaCl concentrations, pH and temperature values on the growth of moderately halophilic bacterial isolates were tested. In the present study, four moderately halophilic bacterial isolates were isolated and selected for further experiments. The isolated species designated as SLMHB5, SLMHB10, SLMHB12, SLMHB13 were similar to Vibrio alginolyticus, Terribacillus halophilus, Vibrio alginolyticus, and Vibrio parahaemolyticus species, respectively. Scanning electron micrographs of sheepskin samples demonstrated that enzymatic activities of moderately halophilic bacteria isolated from soak liquor samples which decomposed the skin structure. After 35-days storage period, the sheepskin sample showed bad odor, sticky appearance and hair slip. Hence, it is recommended to control these microorganisms during the soaking process with an effective antimicrobial agent.

Structured LDH/Bentonite Composites for Chromium Removal and Recovery from Aqueous Solutions.

This study focuses on chromium removal through adsorption and ion exchange using structured calcined layered double hydroxide (LDH) (MgAl)-bentonite composites. Firstly, the powders were structured into granulates to study the effect on Cr sorption kinetics to circumvent the limitations of working with powders in real-life applications. Secondly, the regeneration of the structured composites was optimized to enable multi-cycling operation, which is the key for their applicability beyond laboratory scale. Firstly, the LDH/bentonite ratio was optimized to obtain the best performance for the removal of Cr3+ and Cr6+ species. In powder form, the calcined adsorbent containing 80 wt% LDH and 20 wt% bentonite performed best with an adsorption capacity of 48 and 40 mg/g for Cr3+ and Cr6+, respectively. The desorption was optimized by studying the effect of the NaCl concentration and pH, with a 2 M NaCl solution without pH modification being optimal. The kinetic data of the adsorption and desorption steps were modelled, revealing a pseudo-second order model for both. This was also demonstrated using XRD and Raman measurements after the Cr3+ and Cr6+ adsorption tests, indicating successful uptake and revealing the adsorption mechanism. Finally, five consecutive adsorption-desorption cycles were performed, each showing nearly 100% adsorption and desorption.

Zeta potential prediction of dominant sandstone minerals via surface complexation modelling

Numerous injection water compositions have been developed by various researchers to optimize the oil recovery via wettability alteration. The ionic composition of the injected brine plays a profound role in the rock/brine and crude-oil/brine interfacial charge thereby its role is pivotal in oil recovery. Numerous experimental techniques have been used to assess the potential of injected brines to optimize wettability via wettability alteration. Notably among them are the spontaneous imbibition, contact angle and core flooding techniques. Zeta potential (ζ-potential) has been used by some researcher to evaluate the wettability alteration during crude oil/brine/rock interactions. However, ζ-potential measurement is relatively expensive and time consuming. Hence, the need for relatively cheap and easy approach of ζ-potential measurements. This was accomplished using Surface Complexation Modelling (SCM) via PHREEQ-C. The focus of this study was to predict ζ-potential using SCM. The qualities and quantities of the materials used during the existing experiment from literature were also used as input in the SCM. Dominant minerals in sandstone reservoir rock notably quartz, calcite, dolomite, kaolinite, illite, montmorillonite, chlorites, ilmenite, muscovite, biotite and anorthoclase were considered in this study. The SCM technique could capture the trend during the ζ-potential measurements. However, out of the 39 mineral-brine ζ-potential measured, the SCM approach could not capture the trend in 5 of these samples namely; dolomite/0.5wt% NaCl (pH = 9.5), microcline/SW (pH = 7.8), muscovite/SW (pH = 7.8), chlorite/SW (pH = 7.8) and ilmenite/20% Dil-SW (pH = 7.6). This was attributed to the effect of atmospheric CO2 on the pH of the brine during the ζ-potential measurement. The ζ-potential of carbonates (calcite and dolomite) were predominantly positive while that of tectosilicates (Quartz, Anorthoclase and Microcline), phyllosilicates (Montmorillonite, Kaolinite, Biotite, Illite, Muscovite and Chlorites) and oxides (Ilmenite) were also predominantly negative. For instance, at the calcite-SW (pH = 7.9) interface, the predicted a ζ-potential value was 20.5 mV while its measured value was observed to be 12.9 mV. The dolomite-SW (pH = 7.9) also predicted 16.7 mV and 19.7 mV for the predicted and the measured ζ-potential value respectively. Considering quartz, anorthoclase and microcline with 0.5wt% NaCl (pH = 7.9), the predicted ζ-potential values were observed to be -11.65 mV, -24.21 mV and -43.00 mV while the measured values were also observed to be -16.9 mV, -33.8 mV and -36.5 mV respectively.

Co-infections of Klebsiella pneumoniae and Elizabethkingia miricola in black-spotted frogs (Pelophylax nigromaculatus)

Pelophylax nigromaculatus is a common commercial specie of frogs that generally cultured throughout China. With the application of high-density culture, P. nigromaculatus can be co-infected by two or more pathogens, which thereby induce synergistic influence on the virulence of the infection. In this study, two bacterial strains were simultaneously isolated from diseased frogs by incubating on Luria-Bertani (LB) agar. Isolates were identified as Klebsiella pneumoniae and Elizabethkingia miricola by morphological, physiological and biochemical features, as well as 16S rRNA sequencing and phylogenetic analysis. The whole genome of K. pneumoniae and E. miricola isolates consist single circular chromosome of 5,419,557 bp and 4,215,349 bp, respectively. The genomic sequence analysis further indicated that K. pneumoniae isolate conserved 172 virulent and 349 antibiotic-resistance genes, whereas E. miricola contained 24 virulent and 168 antibiotic resistance genes. In LB broth, both isolates could grow well at 0%-1% NaCl concentration and pH 5–7. Antibiotic susceptibility testing revealed that both K. pneumoniae and E. miricola were resistant to kanamycin, neomycin, ampicillin, piperacillin, carbenicillin, enrofloxacin, norfloxacin and sulfisoxazole. Histopathological studies showed that co-infection caused considerable lesions in the tissues of brain, eye, muscle, spleen, kidney and liver, including cell degeneration, necrosis, hemorrhage and inflammatory cell infiltration. The LD50 of K. pneumoniae and E. miricola isolates were 6.31 × 105 CFU/g and 3.98 × 105 CFU/g frog weight, respectively. Moreover, experimentally infected frogs exhibited quick and higher mortality under coinfection with K. pneumoniae and E. miricola than those single challenge of each bacterium. To date, no natural co-infection by these two bacteria has been reported from frogs and even amphibians. The results will not only shed light on the feature and pathogenesis of K. pneumoniae and E. miricola, but also highlight that co-infection of these two pathogen is a potential threat to black-spotted frog farming.

On the Use of Polymer Inclusion Membranes for the Selective Separation of Pb(II), Cd(II), and Zn(II) from Seawater.

The synthesis and optimization of polymeric inclusion membranes (PIMs) for the transport of Cd(II) and Pb(II) and their separation from Zn(II) in aqueous saline media are presented. The effects of NaCl concentrations, pH, matrix nature, and metal ion concentrations in the feed phase are additionally analyzed. Experimental design strategies were used for the optimization of PIM composition and evaluating competitive transport. Synthetic seawater with 35% salinity, commercial seawater collected from the Gulf of California (Panakos®), and seawater collected from the beach of Tecolutla, Veracruz, Mexico, were employed. The results show an excellent separation behavior in a three-compartment setup using two different PIMs (Aliquat 336 and D2EHPA as carriers, respectively), with the feed phase placed in the central compartment and two different stripping phases placed on both sides: one solution with 0.1 mol/dm3 HCl + 0.1 mol/dm3 NaCl and the other with 0.1 mol/dm3 HNO3. The selective separation of Pb(II), Cd(II), and Zn(II) from seawater shows separation factors whose values depend on the composition of the seawater media (metal ion concentrations and matrix composition). The PIM system allows S(Cd) and S(Pb)~1000 and 10 < S(Zn) < 1000, depending on the nature of the sample. However, values as high as 10,000 were observed in some experiments, allowing an adequate separation of the metal ions. Analyses of the separation factors in the different compartments in terms of the pertraction mechanism of the metal ions, PIMs stabilities, and preconcentration characteristics of the system are performed as well. A satisfactory preconcentration of the metal ions was observed after each recycling cycle.