Molar Ratio Values Research Articles

Impact of nanosilver surface electronic distributions on serum protein interaction and hemocompatibility.

Translation of silver-based nanotechnology "from bench to bedside" requires a deep understanding of the molecular aspects of its biological action, which remains controversial at low concentrations and non-spherical morphologies. Here, we present a hemocompatibility approach based on the effect of the distinctive electronic charge distribution in silver nanoparticles (nanosilver) on blood components. On basis of spectroscopic, volumetric, microscopic, dynamic light scattering measurements, pro-coagulant activity tests and cellular inspection we determine that, at extremely low nanosilver concentrations (0.125 - 2.5 μg mL-1) there is a relevant interaction effect on serum albumin and on red blood cells. The explanation has its origin in the surface charge distribution of nanosilver and their electron-mediated energy transfer mechanism. Prism-shaped nanoparticles, with anisotropic charge distributions, act at the surface level generating a compaction of the native protein molecule, while the spherical nanosilver, by exhibiting isotropic surface charge, generates a polar environment comparable to the solvent. Both morphologies induce aggregation at NPs / BSA ≅ 0.044 molar ratio values without altering the coagulation cascade tests, although the spherical-shaped nanosilver has a negative impact on red blood cells. Overall, our results suggest that the electron distributions of nanosilver, even at extremely low concentrations, are a critical factor influencing the molecular structure of blood proteins and red blood cells' membranes. Isotropic forms of nanosilver should be considered with caution, as they are not always the least harmful.

Se and Hg in processed fish-derived products and their fish raw materials: Occurrence, Se:Hg molar ratio, HBVSe index, bioaccessibility and Caco-2 cells toxicity

Processing conditions applied during food production could affect food component contents and bioaccessibility. Here, possible changes in Hg and Se total and species contents and bioaccessibility have been tracked in each stage of the production chain of processed fish-derived products. Therefore, Se:Hg molar ratio and Selenium Health Benefit Value (HBVSe) were calculated for final products and raw materials, resulting favorable in all cases, suggesting the safety of surimi-based products regarding mercury. Speciation studies revealed the presence of SeMeSeCys and SeMet in all samples. Thus, the integrity of the selenium species seems to be maintained. Moreover, in vitro gastrointestinal digestion model evidenced that Se bioaccessibility ranged between 20–39 % for all samples, while in case of Hg was between 8–37 %. Additionaly, SeMeSeCys and SeMet were also identified in the gastrointestinal extracts. Finally, no cytotoxicity was observed after exposure of Caco-2 cells to the gastrointestinal extracts.

Investigation on Microstructural and Mechanical Properties of FeNiMnCrCoTi0.1 High Entropy Alloy with B Addition

High-entropy alloys (HEAs) are alloys with high potential for use in defense, aircraft, and aerospace industries due to their properties such as high strength, hardness, wear resistance, corrosion resistance, and ability to operate at high temperatures. Therefore, in this study, FeNiMnCrCoTi0.1BX (x values in molar ratio, x = 0-1) high entropy alloys were produced by arc melting technique under protective gas atmosphere using a reverse vacuum method. The microstructural properties of the produced HEAs were examined by scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) analysis was also performed. The crystal lattice structure of the produced HEAs was determined by X-ray diffraction (XRD) analysis. Microhardness and compression tests were conducted to determine the mechanical properties of the produced HEAs. It is observed that the hardness of the FeNiMnCrCoTi0.1BX high-entropy alloy increases as the boron content increases. The highest microhardness obtained was 593.8 HV in the FeNiMnCrCoTi0.1B alloy. As the boron content increases, the yield stress has also increased in compression testing. The highest yield stress was determined to be 1329 MPa in the FeNiMnCrCoTi0.1B alloy.

Effect of the mixed micelles of zwitterionic-anionic surfactant on efficiency of antibiotic azithromycin dihydrate

The study highlights the importance of mixed micelles in enhancing the binding and solubilization properties of partially water-soluble medications, using zwitterionic cocoamidopropyl betaine (CAPB) and anionic sodium tetradecyl sulfate surfactants. Surface tension and fluorescence spectroscopy evaluated the critical micelle concentration (CMC) of CAPB-STS mixed micelle. The thermodynamic parameters were assessed using Clint, Rubingh, and Motomura’s approach, which showed a synergistic interaction between the CAPB and STS. UV spectroscopy technique was used to evaluate the applicability of mixed micelle to enhance the solubility and binding constant (Kb) of antibiotic azithromycin dihydrate (AZI). Kb values of AZI were increased from 2.301 to 3.415 and molar solubilization ratio (MSR) values of AZI were increased from 0.228 to 0.801 by decreasing αCAPB from 0.9 to 0.1. The result indicated that zwitterionic CAPB was an electrostatic interaction consisting of both attractive (−CH2COO¯ group) and repulsive (−N+ group) interactions with AZI (−NH+ group), causing AZI molecules to reside in the Stern layer. While STS consisted of a negative −SO4¯ head group, it caused increased electrostatic interaction, and AZI penetrated the palisade layer of mixed micelles. At 7.00 mmolL-1 concentration of αCAPB 0.1, the solubility of AZI in water was increased to 2.77 mmol/L from 0.0032 mmol/L. Additionally, after 8 h, the controlled release of AZI in PBS at pH 7.4 was 95.58 % and decreased up to 30.77 % at αCAPB 0.1 mixed micelles. The observation of controlled AZI release from αCAPB 0.9 to 0.1 indicates that AZI molecules were strongly bound to mixed micelles by both hydrophobic and electrostatic interactions. In the end, a mixed micelle of CAPB-STS could serve as a useful drug-solubilizing agent in pharmaceutical applications.

Trace element concentrations in common dolphins (Delphinus delphis) in the Celtic Seas ecoregion: Interelement relationships and effects of life history and health status

Given the increased extraction of trace elements for use by new and emerging technologies, monitoring the environmental fate and potential effects of these compounds within the aquatic environment has never been more critical. Here, hepatic trace element concentrations were assessed in a key sentinel predator, the common dolphin (Delphinus delphis), using a long-term dataset. Variation in concentrations were assessed in relation to other elements, time period, decomposition state, sex, age, total body length, sexual maturity and nutritional status, and cause of death. Additionally, mercury toxicity thresholds for evaluating risk were reviewed and employed. Concentrations of elements which bioaccumulate, THg, MeHg, Cd, and Pb, in addition to Se and V, were strongly correlated with age, and/or body length. An association was observed between Zn concentrations and disease status, with significantly higher concentrations measured in individuals that died from infectious disease, compared to other causes. Strong inter-elemental relationships were detected, namely between Hg and Se, MeHg and Se, Cd and Se, and Cu and Zn. While THg:Se molar ratio values were observed to increase with age and body length, approaching equimolarity. THg was largely comprised of inorganic Hg in older individuals, potentially bound to Se, therefore the effects from THg toxicity may possibly be less important than originally assumed. In contrast, higher MeHg:Hg ratio values were reported in juveniles, suggesting a poorer efficiency in demethylation and a higher sensitivity. The generation of data on proportions of hepatic MeHg and inorganic Hg is highly informative to both future toxicity threshold assessments within pollutant indicator assessments, and to understanding the ultimate fate of mercury in the marine web.

Controls on riverine magnesium isotopic composition: Evidence from mono-lithological catchments

The magnesium isotopic composition (δ26Mg) of river water could provide evidence for continental weathering and the global Mg cycle. However, constraining the lithological and isotope fractionation controls on river δ26Mg is still a challenge. Here, we investigated δ26Mg of various compartments in granitic and basaltic catchments, and δ26Mg of river water in sandstone catchments in the Southeastern Tibetan Plateau. Rivers draining sandstone have the lowest δ26Mg values (−1.86‰ to −1.42‰) due to weathering of carbonate which may exhibit as a matrix, cement morphology, and layers crystallized around silicate. The δ26Mg values of river water in granitic and basaltic catchments are −0.72‰ to −0.54‰ and −0.52‰ to −0.30‰, respectively, lower than the soil and plant in the corresponding catchments. Sequestration of isotopically heavy Mg into clays during silicate weathering is predominant and produces a fractionated source of river water with isotopically light Mg. Such Mg isotope fractionation could be affected by denudation rate which changes mineral residence time in these catchments. The strong correlations between Ca/Mg molar ratio, 1/Mg, and δ26Mg value in rivers draining silicate indicate that Mg re-distribution between secondary clays and solutions is proportional to Mg isotope fractionation, the decrease of riverine Mg from silicate weathering will be accompanied by the decrease of riverine δ26Mg. Based on this, a limited impact of Mg isotope fractionation on river δ26Mg is inferred at the continental scale.

Effect of Nb Addition on the Corrosion and Wear Resistance of Laser Clad AlCr2FeCoNi High-Entropy Alloy Coatings

Laser clad AlCr2FeCoNiNbx (x = 0, 0.5, 1.0, 1.5, 2.0, with x values in molar ratio) high-entropy alloy (HEA) coatings were fabricated on Q345 carbon steel. This study delves into the impact of Nb incorporation on the reciprocating sliding wear resistance of these laser clad coatings against a Φ6 mm silicon nitride ball. The microstructure of the as-clad AlCr2FeCoNiNbx coatings transformed from a single Face-Centered Cubic (FCC) solid solution (when x = 0) to the hypoeutectic state (when x = 0.5) and progressed to the hypereutectic state (when x ≥ 1.0). This evolution was marked by an increase in the Laves phase and a decrease in FCC. Consequently, the HEA coatings exhibited a gradually increasing Vickers hardness, reaching a peak at HV 820. Despite a decline in corrosion resistance, there was a notable enhancement in wear resistance, and the friction of the HEA coating could be reduced by Nb addition. The phase evolution induced by Nb addition led to a shift in the predominant wear mechanism from delamination wear to abrasive wear. The wear rate of Nb0.5 was impressively low, at 6.2 × 10−6 mm N−1 m−1 when reciprocating sliding under 20 N in air. In comparison to Nb0, Nb0.5 showcased 3.6, 7.2, and 6.5 times higher wear resistance at 5 N, 10 N, and 20 N, respectively. Under all applied loads, Nb1.5 has the lowest wear rate among all HEA coatings. This substantiates that the subtle introduction of Laves phase-forming elements to modulate hardness and oxidation ability proves to be an effective strategy for improving the wear resistance of HEA coatings.

Facile fabrication of ZIF-8 MOF through varied molar ratio: A novel antibacterial agent against multidrug resistance bacteria

Public health officials are now concerned about the rise in harmful bacterial strains that are resistant to antibiotic prophylaxis. As a result, there is an urgent need for the creation of efficient antibacterial agents. For which, numerous materials with nanoscale dimensions showing exceptional antibacterial capacity were planned and created to combat these multidrug resistant bacteria. Furthermore, bacteria cannot build immune responses within the nanomaterial bactericidal system because of special antimicrobial mechanism. Metal/metal oxide nanoparticulate systems, MOFs (metal organic frameworks) have received attention for their potent antibacterial properties and potential role as antibiotic replicants. In this study different molar ratio was taken to create for ZIF-8 MOF with rich mesoporous structure through solgel technique. PXRD, FTIR and SEM method were used to characterise the MOF. Due to the interaction of Zn2+ ions and imidazole, the as-synthesised ZIF-8C of (3:1); Zinc: HMIM molar ratio values exhibits better antibacterial efficacy than ZIF-8A (1:1) and B (1:3). It was discovered that the MIC and inhibition zone against S. aureus and E. coli were excellent. In addition to offering a viable option for biomedical implants, this discovery offers a promising pathway for suppressing drug resistance bacteria.

Conversion mechanism of thermal plasma-enhanced CH4-CO2 reforming system to syngas under the non-catalytic conditions

Thermal plasma activation of CH4-CO2 reforming (CRM) to syngas under non-catalytic conditions is an efficient and clean technology for the large-scale utilization of hydrocarbon resources and the conversion of greenhouse gases. This study investigates the equilibrium state and transformation mechanism of a CRM reaction system activated by thermal plasma through experimental, thermodynamic, and kinetic analyses. The experimental results illustrated that the CO2 conversion rate and H2 selectivity showed a downward trend with an increase in the CO2/CH4 molar ratio, whereas the CH4 conversion rate and CO selectivity showed the opposite trend. When CO2/CH4 molar ratio was 6/4, the selectivity for CO and H2 increased to 87.0 % and 80.8 %, respectively. Excess CO2 promotes the partial oxidation of CH4 to eliminate carbon deposition, resulting in an H2/CO molar ratio value closer to 1. Thermodynamic results show that the thermal-plasma-initiated CRM reaction can reach thermodynamic equilibrium more easily than the conventional catalyzed reactions, achieving much higher feedstock gas conversion without carbon deposition. The kinetic results obtained from the PSR model revealed that CH4 and CO2 were cleaved to form free radicals at the instant of contact with the plasma flame. O, H, and other particles generated in the form of free radicals rapidly collided with each other and transformed into CO and H2, accelerating the reaction process. The results presented in this study will help reveal the transformation mechanism of the CRM reaction activated by thermal plasma under non-catalytic conditions and provide a new perspective for studying CRM reactions.

Simulation of Dry Reforming of Methane Catalyzed by Iron Hexagonal Mesoporous Silicates (Fe-HMS) Using Aspen HYSYS

This paper deals with the theoretical study of mesoporous silicates applied to the dry reforming of methane. In order to enhance natural gas and reduce the concentration of carbon dioxide, which is a greenhouse gas in the atmosphere in the same way as methane, the catalytic properties of silicate of the Fe-HMS-n type were used in the simulation of the methane dry reforming reaction on HYSYS. The dry reforming of methane aims to produce syngas, which is an important raw material in the production of fertilizers and resins. Among the Fe-HMS-n silicates used, Fe-HMS-15 provided good catalytic performance for methane dry reforming. A study of the influence of the quantity of iron incorporated in the silicates on the activity was carried out. This led to the conclusion that increasing the iron content improves the catalytic performance of silicates. On the other hand, this performance decreases for high porous volumes. By varying the relative quantity of reactants, the results proved that a molar ratio value greater than unity favors a majority production of dihydrogen due to the decomposition of methane. Conversely, the excess of carbon dioxide leads to the formation of carbon monoxide in a preponderant manner.

Lean methane catalytic combustion over the mesoporous MnOx-Ni/MgAl2O4 catalysts: Effects of Mn loading

In the current investigation, the textural features and catalytic efficiency of the Mn-promoted Ni/MgAl2O4 catalysts were evaluated in the catalytic combustion of lean methane. The results demonstrated that adding manganese oxide up to 5 wt.% to the catalyst improved the structural features and light-off temperatures due to the increase of the reduction degree and oxygen vacancies. The role of the Tcalcination and processing factors on the methane conversion of the 5%Mn-20%Ni/MgAl2O4 catalyst was also studied. The results indicated that the CH4 conversion decreased with the increment of O2/CH4 molar ratio and GHSV value. The stability test revealed that the prepared sample exhibited high stability during 10 h time on stream. Furthermore, the obtained results indicated that the BET area, reduction degree, oxygen mobility, and catalytic performance increased with decreasing the calcination temperature from 700 to 500 °C.

Controlled synthesis of gemini surfactant-capped gold nanoparticles. Gemini structure-nanoparticle properties relationship study

Gold nanoparticles were prepared by the method of chemical reduction utilising sodium borohydride as reducing agent and stabilised with bisammonium gemini surfactants with variable length of polymethylene spacer. Physico-chemical investigations indicated the presence of plasmon resonance peaks in the wavelength range 507–544 nm for all investigated Au nanodispersions. The nanoparticle size analysis shows the relationship between the size of gold nanoparticles and the spacer length of stabilising gemini molecules. The strong aggregation tendency of gemini surfactants with short polymethylene spacer composed of 2–4 methylene units in aqueous solutions may be responsible for the formation of clusters of gold nanoparticles which results in the observed large hydrodynamic size of nanoparticle clusters at the surfactants concentrations below the CMC. At higher surfactant-to-gold molar ratio values, clusters disintegration occurs and the decrease in size of the nanoparticles is observed. The shape of gold nanoparticles was found to be spherical and polyhedral, as evidenced by the SEM images. The size values varied between 30–60 nm and 10–15 nm for AuNPs capped with gemini molecules with short and medium/long spacer, respectively. Gold nanoparticles are strongly positively charged, with positive zeta potential values being in the interval +44 to +90 mV in the whole analysed region of molar ratio values and surfactant spacer length. The biological experiments indicate a dependence of biological activity of gold nanoparticles on the structural parameter (spacer length) of stabilising gemini molecules. Both cytotoxicity and anti-inflammatory activity of gold nanoparticles were found to increase with the increasing gemini spacer length up to 12 methylene groups in the spacer.

INFLUENCE OF TiC CONTENT ON MICROSTRUCTURE AND PROPERTIES OF AlCoCrFeNi HIGH-ENTROPY ALLOY COATINGS PREPARED BY LASER CLADDING

In this study, AlCoCrFeNi-TiCx (x values in molar ratio, x = 0, 0.1, 0.2, 0.3) high-entropy alloy coatings (HEAcs) were prepared on the surface of H13 steel by laser cladding (LC). The microhardness, corrosion resistance, and wear resistance of the HEAcs were analyzed using a microhardness tester, electrochemical workstation, and friction and wear tester, respectively. The results showed that with an increase in the TiC content of the coatings, the interior of the coatings mainly consisted of disordered body-centered cubic (BCC), ordered BCC (B2), and TiC phases, and lattice distortion occurred inside the coatings. TiC was distributed as white particles at the grain boundaries, and the internal microstructure was mainly composed of equiaxed crystals (EC) and petal-like dendrites. The EC were gradually refined owing to the pinning effect. The spinodal decomposition causes a large number of reticulated microstructures inside the grains, and nanoscale TiC precipitation appears in the reticulated microstructures. Owing to lattice distortion and solid solution strengthening, the microhardness of the TiC[Formula: see text] coating was up to 966 HV[Formula: see text], which was approximately 3.2 times that of the substrate. As the TiC content increases, the friction coefficient and mass loss of the coatings gradually decreased, the self-corrosion current ([Formula: see text] gradually decreased and the self-corrosion potential ([Formula: see text] gradually increased. The coatings exhibited good wear and corrosion resistance.

Research on Optimization of Process Parameters of Electroless Nickel Plating Based on Orthogonal Test

As a widely used surface strengthening technology, electroless plating can be applied to various materials such as metals and non-metals, but its process parameters are numerous and difficult to optimize. For this reason, this study designed a three-factor and four-level orthogonal experimental scheme with the main salt/reducing agent molar ratio, lactic acid and PH value as the factors, and the plating speed and microhardness as the evaluation indicators. The range analysis was carried out on the experimental results, the best process parameters were selected, and the influence rules and reasons of the three factors on the evaluation indexes were discussed.

Boosting the VOCs purification over high-performance α-MnO2 separated from spent lithium-ion battery: Synergistic effect of metal doping and acid treatment

Spent lithium-ion batteries and VOCs both pose a significant threat to the environment and human health. In this work, a series of high-performance α-MnO2 catalysts with metal dopant and acid treatment are synthesized from acid leaching solution of cathode materials, which were separated from spent lithium-ion manganese battery (SLMB). Compared with pure α-MnO2, all SLMB-MnO2 (α-MnO2 prepared from SLMB) exhibit better catalytic activities of VOCs oxidation. Among them, SLMB-MnO2-2, with a molar ratio value of KMnO4 to Mn2+ of 2, exhibits the best catalytic activity (T90 = 224 °C and 297 °C for toluene and chlorobenzene oxidation, respectively). By comparison of their physicochemical properties, it can be found that SLMB-MnO2-2 possesses a larger specific surface and abundant mesopores, better redox ability at low temperature, much more generation of oxygen vacancies, and abundant adsorbed oxygen species. Moreover, the suitable dopant of copper and appropriate concentration of acid treatment play a synergistic role in enhancing the catalytic performance of VOCs oxidation on SLMB-MnO2-2. Furthermore, combined with in-situ DRIFTS and TD/GC–MS, the catalytic mechanism of toluene oxidation is explored on SLMB-MnO2-2.

Mercury and selenium bioaccumulation in wild commercial fish in the coastal East China Sea: Selenium benefits versus mercury risks

This study investigated the contents of total mercury (THg), methylmercury (MeHg) and selenium (Se) in 22 fish species and 10 invertebrate species from the coastal East China Sea. The THg and MeHg contents were significantly higher in benthic fishes. Both Hg and Se biomagnified in the food webs, with evidences of associations during trophic transfer. In addition, Se:Hg molar ratio and Se health benefit value (HBVSe) were used as novel criteria for Hg exposure risk assessments, showing that Se presented in molar excess of Hg in all samples, which would negate the risks of Hg toxicity. HBVSe provided more informative results than Se:Hg molar ratio, pointing to possibly lower health risks for some fishes containing high levels of Hg and Se. Although the HBVSe results challenge the traditional Hg health risk assessment, its future application still requires worldwide comprehensive investigations.

The salinity origin and hydrogeochemical evolution of groundwater in the Oued Kert basin, north‐eastern of Morocco

Water scarcity in the Rif region of northwestern Morocco, particularly in the Kert plain, has resulted in significant groundwater exploitation to achieve human and socioeconomic objectives. These methods helped in identification of the source of dissolved elements and the mechanism that increased groundwater salinization. Current study is the part of groundwater's salinity sources and hydrogeochemical development in the Oued Kert basin (Mediterranean zone, Driouch province, eastern Morocco); 46 samples (45 wells and one spring) were collected in June 2021. Using the Cl-/Br- ratio, which appears to be a good tracer for detecting non-atmospheric Cl- contributions to groundwater provided chemical analyses are accurate since its variability is limited. To achieve this goal, processes that increase groundwater salinization was studied. The results indicate that the groundwater samples studied had medium to high conductivity electric, which can attain 9500 S/cm. The regional distribution of physicochemical parameters is consistent with the distribution of alluvial and evaporate rocks. The high molar ratio values of Sr2+/SO42− and Sr2+/Ca2+ imply an extra input of strontium, likely through carbonate precipitation/dissolution processes as well as adsorption reactions. The varied Bromide concentrations (1-7 mg/L) detected in groundwater samples were evaluated against the binary mixing model to determine the salinization mechanisms responsible for the analyzed system. It suggests that evaporate rocks dissolution was the predominant source of groundwater mineralization in the studied region. However, irrigation of water inflows and local saltwater intrusion seems to alter aquifer quality dramatically.

Deciphering Mn modulated structure-activity interplay and rational statistical analysis for CO2 rich syngas hydrogenation to clean methanol

Methanol produced from chemical transformation of coal derived CO2 rich syngas can be a sustainable replacement for conventional crude oil based fuels with an impressive feature of reducing greenhouse gas emissions. Mostly industrial catalysts are promoted, however, lack of detailed insight into the mechanism of promotion has so far restricted the identification of non-precious promoter. In this work, a series of Cu–Zn–Mn oxide catalysts were synthesized by varying Mn loading from 0 to 30 mol% at pH near 7 and 70 °C via co-precipitation technique to elucidate the role of Mn-promoted malachite precursors in micro structural properties of catalyst. Investigation revealed that incorporating 20 mol% Mn (CuZn:Mn[0.2]) in malachite lattice resulted in better stabilization and dispersion of CuO domains owing to maximum dilution of Cu2+ ions as compared to other three analogous catalysts. Consequently, CuZn:Mn[0.2] catalyst unveiled ∼1.4-fold and ∼1.2-fold increase in CO conversion and methanol selectivity respectively as compared to the unpromoted catalyst. However, Mn loading beyond 20 mol% showed a detrimental effect on the catalytic efficiency due to dominant presence of an additional aurichalcite by-phase which revokes dilution of Cu2+ ions. Co-feeding CO2 in syngas improves dual active sites synergy (Cu0/Cu+) which helps in understanding catalytic mechanism of methanol synthesis. For best performing catalyst, statistically validated non-linear mathematical models were derived using response surface methodology along with central composite design. These models forecasted the correlations between process parameters as well as identified the relative contribution of each parameter. For maximising both methanol selectivity and CO conversion, desirability function predicted the optimum values of reaction temperature, pressure, and feed gas molar ratio (CO/CO2/H2) as 242 °C, 49 bar and 3 respectively. Under these conditions, 46% CO conversion and 93% methanol selectivity were obtained. Thus, the formulated coal to methanol process originating from catalyst design to optimization of process parameters paves the way for sustainable solutions referring to global “3E” issues, viz. energy, environment, and economic challenges.

Synthesis and Characterization of Nitrogen Doped Reduced Graphene Oxide Based Cobalt-ZIF-8 Catalysts for Oxygen Reduction Reaction

Non-Platinum Group Metal (non-PGM) catalysts have recently attracted huge attention for use in the Polymer Electrolyte Membrane Fuel Cell (PEMFC) vehicles, as the demand for alternative and sustainable transportation is increasing exponentially. Carbon-based catalysts have advantages such as relative ease of manufacturing, low cost of synthesis, high electrochemical durability, and high electrical conductivity which makes them a potential alternative. While there are several ways to improve the catalytic activity of carbon catalysts, one promising technique is doping heteroatoms into the lattices of the sp2 carbon structure. The most commonly used doping is by nitrogen (N-doping) where a nitrogen precursor is used to incorporate N atoms to help improve electrochemical performances. Transition Cobalt-Nitrogen-Carbon (Co-N-C) catalysts show promising catalytic performance and durability due to their fast electron transfer rates leading to increased kinetic reaction rates. In this paper, we report the synthesis and characterization of Nitrogen-doped Graphene/Graphene oxide with Metal-Organic Framework (MOF) material using wet chemical and pyrolysis techniques for the development of an efficient catalytic material to tackle the sluggish cathodic Oxygen Reduction Reaction (ORR) in fuel cells (FCs). Transition metal, Cobalt is doped into Zeolite Imidazole Frameworks (ZIF-8) using Cobalt Nitrate as precursor to enhance the mass and kinetic rates of the ORR reaction at the cathode. The synthesized metal-doped MOF catalysts (Co-ZIFx) are further pyrolyzed by one-step pyrolysis in an argon atmosphere at 600oC for 2 hours. These catalysts are produced with varying amounts of precursor metals (different molar ratios of metal precursor to ZIF-8 such as 0.6, 0.9 and 1.2 respectively; x denotes molar ratio values) to analyze the effects of each element proportion on the electrochemical performance. The pyrolyzed electrocatalysts (named Co-ZIFx-600 respectively) were further synthesized chemically using nitrogen-doped graphene (N-Gr) catalysts through wet chemical synthesis procedure and are named as N-Gr-Co-ZIFx and N-Gr-Co-ZIFx-600 (x changes with the molar ratios of metal precursor). Doping of graphene carbon lattice with nitrogen heteroatoms has proven to influence charge densities and adsorption mechanism which further enhances the catalytic activity. Nitrogen loading effects were also analyzed to study the electronic and electrochemical behavior of individually varied graphene materials. Various characterization techniques, viz., FTIR, Raman spectroscopy, XRD, SEM and EDS were performed to analyze various physical and chemical properties affecting the electrochemical performances. FTIR of N-Gr-Co-ZIF-600 catalysts showed the presence of cobalt-doped ZIF-8 peaks around 420 cm-1 and the presence of nitrogen bonds at a stretching frequency of around 3000 cm-1. XRD results showed the formation of crystalline phases of the Cobalt-doped ZIF-8 with a (100) orientation. Further, it was observed that the crystallinity was affected with an increase in the metal loading. SEM examination of the Cobalt-doped ZIF-8 samples showed an increase in grain size from around 100 nm to 2 μm with an increase in cobalt composition. EDS results of the catalysts indicated uniform distribution of the various elements such as carbon, nitrogen, cobalt, oxygen, and zinc (from ZIF-8) in varying proportions as we alter the metal precursor doping in ZIF-8. Cyclic Voltammetry is performed in 0.1M HClO4 aqueous solution to evaluate the electrochemical performances of the synthesized catalysts. It is found that the addition of the transition metal plays a major role in the enhancement of electrochemical performance compared to that of non-transition metal carbon-based catalysts. the N-Gr-Co-ZIFx-600 catalyst showed relatively better ORR activity in acidic media with onset and half-wave potentials only 24 and 51 mV lower than those of the Pt/C catalyst. Overall, the synthesized N-Gr-Co-ZIFx-600 is a potential candidate as a high activity, stable, and low-cost ORR catalyst for FCs. All the results of the characterizations will be discussed in detail for different metal precursor loadings (0.6, 0.9 and1.2 molar ratios) of different MOF derived carbon-based electrocatalysts.

The role of phosphate on non-skeletal carbonate production in a Cretaceous alkaline lake

Alkaline carbonate-rich systems may, under some circumstances, result in significant accumulation of aqueous phosphorus. Additionally, the geochemistry of modern alkaline lakes, combined with current understanding of CaCO3 precipitation kinetics, indicates that the establishment of high alkalinity, high dissolved inorganic carbon (DIC), and CaCO3 supersaturation require compounds that inhibit or interfere with CaCO3 precipitation. Furthermore, the interplay between these factors may potentially affect fabric development in non-skeletal carbonates. In order to understand how these interlinked processes may have regulated PO4 concentrations and the processes and products of non-skeletal CaCO3 precipitation in the distant past, we conducted a detailed geological and geochemical study in two cores drilled in different portions of the Santos Basin, offshore southeastern Brazil, consisting of lacustrine carbonate rocks from the Lower Cretaceous Barra Velha Formation. We find that phosphorus in the sediments comes from two main products, phosphatic bioclasts and authigenic phosphate (of both primary and diagenetic origins). We also find that phosphorus occurs in concentrations of up to several thousand ppm in some intervals and is preferentially associated with some calcite textures potentially reflecting the primary sedimentary depositional conditions (e.g., upward-radiating aggregates of fibrous calcite, or “shrubs” and spherulitic aggregates of fibrous calcite, or “spherulites”). Microanalytical data from selected samples and high-Mg CaCO3 textures show median P values can be particularly high in crusts, shrubs and spherulitic calcite minerals interpreted here to have formed as primary to early diagenetic deposits, and roughly vary between 1000 and 2000 ppm (10.5–21.1 mmol/kg). The average P/(Ca + Mg) molar ratio values based on the same data for these three calcite textures are 1.45 ± 0.98, 1.13 ± 0.97 and 1.09 ± 0.90 mmol/mol, respectively, being as high as 4.80 mmol/mol in specific spots in “shrubby” textures. Although multiple source-to-sink mechanisms were likely involved in the P budget in lake waters and in the sediments, such as recycling and remobilisation of skeletal- and organic-bound phosphate, high alkalinity may have enhanced its accumulation in the lake’s waters. In light of current understanding of CaCO3 precipitation kinetics, we hypothesise that phosphate may have played a central role in maintaining high calcium carbonate saturation (14–45 < Ωcalcite ≤ 100–180). These conditions would have favoured growth of calcite crystals on pre-existing substrates over nucleation of finely particulate carbonate sediment. By combining these observations with theoretical geochemical considerations, we propose that phosphate inhibition of calcium carbonate precipitation was enhanced by high alkalinity, further sustaining CaCO3 supersaturation and favouring distinctive carbonate growth textures. This unique and relatively well-preserved example of non-skeletal carbonate production implies that similar regulation of CaCO3 precipitation kinetics and PO4 concentrations may have operated across other intervals of time in Earth’s history, both in non-marine and marine environments that pre-date the emergence of skeletal calcification.