Stoichiometric Coefficients Research Articles

Challenges in Understanding the Mole Concept Among Level 200 Students in Science Colleges of Education in Ghana

This study investigates challenges in understanding the mole concept among pre-service teachers in Ghanaian Colleges of Education. Chemistry education is fundamental for fields such as medicine and engineering, yet students often face difficulties due to inadequate foundational knowledge and ineffective teaching methods. The mole concept is crucial for grasping various chemical phenomena, but its complexity frequently results in significant learning challenges. This study employs a mixed-method explanatory design, combining quantitative diagnostic tests and qualitative interviews with 1,211 pre-service teachers from six selected colleges. The study identifies key challenges in learning the mole concept, including difficulties in translating word problems into equations, determining mole ratios, deriving empirical and molecular formulae, and understanding the relationship between stoichiometric coefficients and moles. The analysis categorizes these challenges into comprehension, transformation, process skills, and encoding errors, with process skills and transformation challenges being the most prevalent. Findings reveal that many students struggle to solve problems without formulae, highlighting a lack of conceptual understanding. Interviews with pre-service teachers confirm quantitative data, indicating that students often rely on rote memorization rather than conceptual grasp. The study concludes that improvements in teaching methods are needed, emphasizing the importance of understanding over memorization and recommending small group collaborative learning. Contributions include filling empirical gaps in the literature regarding pre-service teachers’ challenges and suggesting practical recommendations for enhancing chemistry education.

Optimizing integrated energy systems at park level: A cooperative game approach with exergy economics

This study presents a comprehensive framework for optimizing energy systems by integrating exergy analysis, energy economics, and game theory. The concept of exergy, which quantifies the usable energy within a system, is employed to evaluate energy efficiency and losses across various energy sources, including thermal, cooling, chemical, and electrical systems. Stoichiometric coefficients, denoted by the factor λ, are utilized to simplify exergy calculations for different energy types and processes. The economic evaluation of energy flows is conducted through energy economics principles, incorporating cost allocation and balance equations. The integration of game theory into the optimization model ensures strategic interactions among energy components, leading to a Nash equilibrium that balances economic performance, efficiency, and environmental sustainability. The model also accounts for emissions and the required proportion of renewable energy. To solve the complex optimization problem, a modified Particle Swarm Optimization (PSO) algorithm is employed, featuring adaptive mechanisms for velocity and inertia updates, enhancing the search process for the optimal solution. The proposed framework is designed to optimize the Integrated Energy System (IES) efficiently, ensuring sustainable and economically viable energy management. The analysis of optimization strategies highlights a trade-off between cost and efficiency. Strategy 1, focused on minimizing cost, achieves the lowest cost at 4069.37 CNY, 25.79 % less than Strategy 2, but with a reduced exergy efficiency of 59.82 %, which is 10.14 % lower than Strategy 2′s 68.47 %. Strategy 3 offers a balanced approach, with a cost of 4970.89 CNY, 9.43 % higher than Strategy 1 but 9.43 % lower than Strategy 2. It achieves an exergy efficiency of 67.87 %, only 0.60 % lower than Strategy 2, thus providing a practical compromise between economic performance and efficiency.

Characterisation of Pseudomonas mosselii H6 for aerobic denitrification: stoichiometry and reaction kinetics

The application of aerobic denitrifying bacteria in biological nitrogen removal has been of great interest. However, the mechanism of nitrogen conversion by aerobic denitrifying bacteria is unclear due to the lack of stoichiometry and kinetic studies. Therefore, this study aimed to investigate the stoichiometry and kinetics of aerobic denitrification using Pseudomonas mosselii H6 as a model strain. The results showed that the stoichiometric equations of strain H6 under different nitrogen source conditions were obtained by nitrogen balance analysis; the concentrations of different limiting substrates were set and combined with the multi-substrate Monod kinetic equation to fit the half-saturation constants of COD, ammonia, nitrate and nitrite nitrogen for strain H6, which were 230.1008, 25.3435, 4.1009 and 23.4601 mg/L, respectively; based on the model of “two-step denitrification”, the numerical simulation of the growth and aerobic denitrification of strain H6 under different limiting substrate concentrations was carried out by using AQUASIM software to test the validity of stoichiometric coefficients and kinetic constants and perfect fitting results were obtained. These parameters will help to simulate the growth and denitrification performance of aerobic denitrifying bacteria and provide an experimental basis for further quantitatively elucidating the mechanism of action in the aerobic denitrification process.

Effect of alumina on formation mechanism and structure characteristic of sodium calcium silicate compounds with different stoichiometric coefficients

In order to illustrate the effects of Al2O3 on silicate structure for synthesizing sodium calcium silicate compounds, the formation characteristics, lattice parameters, molecular structure and element chemical state of sodium calcium silicates with different Al2O3 proportions through solid-state reaction were investigated using XRD, SEM-EDS, Raman spectroscopy and XPS analyses. Increasing the Al2O3 content facilitates the formation of Na2CaSiO4 and converts the polymorph of Na2Ca6Si4O15 from γ-type into β-type. The product particles aggregate to form clumps by increasing the Al2O3 content when the molar ratios of Na2O and CaO to SiO2 are 0.5 and 1.5, and the network orderliness of silicates deteriorates to form glassy phase at the low CaO and Na2O contents. Al2O3 can engage in the bonding process with silicate crystals to produce a finite solid solution. Increasing the Al2O3 porportion is advantageous for facilitating the participation of [AlO6] in the Si-O-Al bonding reaction, which leads to the depolymerization of [Si2O7]6-, [Si3O10]8- and [Si6O18]12− and promotes the formation of silicate chains of [SiO4]4- and [Si2O7]6-. Moreover, increasing the contents of Na2O and CaO promote the formation of [AlO4] and the depolymerization within silicate chains, which increases the bonding number of Si-Oter and Al-Oter and then reduces the binding energies of Si2p and Al2p orbits.

An unconventional approach to evaluating the environmental role of a productive system: An environmental assessment of beef farms in North-West Italy

The environmental impact of livestock is often evaluated separately from the other agricultural activities involved in an integrated system, such as that of the rearing of Piemontese cattle in the area of origin of the breed. The most frequently used assessment methods (e.g. Footprint approaches or a Life Cycle Assessment) are in fact often used, through a product-based approach, to analyse a single productive process, but such methods do not consider the production of agro-ecological services, and they neglect the interactions that characterise complex systems. Moreover, such methods often only consider the negative aspects of the environmental impact and misrepresent less intensive agriculture practices. However the current gaps in knowledge about the carbon sequestration of agricultural ecosystems, which are complex and integrated systems, require further investigation and other types of analysis tools. A carbon (C) balance of 1223 Piemontese breed beef farms, located in North-West Italy, has been calculated to evaluate whether such a method could be applied to overcome the aforementioned limitations, to evaluate whether it could be used to describe a complex and integrated system, to highlight the relationships that exist between rearing and agricultural activities and to characterise their environmental roles. Conducting a mass balance involves considering the input and output material flows and their accumulation within a system. Thus, the data necessary to quantify the C input, output and internal fluxes of a system at the farm gate, pertaining to the vegetable and animal production processes (productive factors, crop yields, animal performances, productions and sales, reuses), were collected from official documentation, and were then completed and verified through site visits. The mass balance of the system was transformed into C fluxes using stoichiometric coefficients. The fluxes evaluated for the balance were then used to estimate the changes in the C stocks to highlight not only the C emissions or losses from the system, but also their contributions towards reducing environmental hazards. A sensitivity analysis was carried out to evaluate the uncertainty and the robustness of the obtained results. The net C exchange from plants was the flux that contributed the most, amounting to 94.3 % of the inputs, and this was followed by soil losses and animal gases released through respiration and enteric fermentation, which amounted to 42.8 and 36.2 % of the outputs, respectively. The C stored and released by the considered system was calculated considering the C fluxes. Plant, animal and soil storage sites were included in the system, whereas the air site was left out. A constant C content was assumed for the soil. The productive activities of the selected group of beef farms in the Consortium were calculated to remove 96.1 103 t of C from the atmosphere (air site) over a period of one year, and that this amount of C was transferred to plant growth and agricultural products (plant site) and to an increase in live weight (LW) of the animals (animal site). The rates of the stored C to agricultural and wooded areas and to the LW of the animals slaughtered in one year were 1.18 t ha−1 and 2.24 t C t−1 LW, respectively. The sensitivity analysis demonstrated that the C balance was always positive, even for the worst scenario. This study has shown that the examined beef production system, when analysed as an integrated and complex system, can be considered an important C sink and that it is necessary to reconsider the role that livestock, and ruminants in particular, play in the global greenhouse effect.

Modeling of Physical-Chemical and Electronic Properties of Lithium-Containing 4H—SiC and Binary Phases of the Si—C–Li System

In the equilibrium model of the solid surface–adatom system, including a three-dimensional interfacial surface, changes in surface properties are considered, taking into account the chemical potential due to the action of surface tension. The relationship between chemical potential and electrochemical potential of the ith component in an electrochemical cell is analyzed. Using the density functional theory (DFT), the adsorption, electronic, and thermodynamic properties of 2 × 2 × 1 and 3 × 3 × 1 supercells of crystalline compounds AmBn, (, where n and m are stoichiometric coefficients) of the boundary binary systems of the ternary phase diagram of Si–C–Li are studied. The stability of phases AmBn and property calculations are carried out with the exchange-correlation functional within the framework of the generalized gradient approximation (GGA PBE). The parameters of the crystal structures of the compounds AmBn, the adsorption energy of the lithium adatom on a 4H–SiC substrate, the electronic structure, and the thermodynamic properties of supercells are calculated. The thermodynamically stable configurations of the 4H–SiC–Liads supercells having different locations Liads are determined. The DFT GGA PBE calculations of the enthalpy of formation of compounds AmBn are carried out in the ternary Si–C–Li system. Taking into account the changes in the Gibbs free energy in the solid-phase exchange reactions between binary compounds, equilibrium sections (connodes) in the concentration triangle of the Si–C–Li phase diagram are established. An isothermal section of the Si–C–Li phase diagram at 298 K is constructed. The patterns of diffusion processes that are related to the movement of particles on the surface layer of the 6H–SiC sample are analyzed. The activation energy of lithium diffusion in 6H–SiC is calculated from the Arrhenius type relation in two temperature ranges (769–973 K) and (1873–2673 K).

Novel eco-friendly spectrophotometric determination of lercanidipine hydrochloride in tablets using methyl red

The aim of the work was to develop a simple, eco-friendly, quick, affordable and alternative spectrophotometric procedure that uses the azodye methyl red (MR) for the determination of lercanidipine in its dosage form considering the “green” chemistry principles. Materials and methods. Analytical equipment: Shimadzu UV-1800 double beam UV-visible spectrophotometer (Japan) with included UV-Probe 2.70 software, RAD WAG AS 200/C precise analytical balance (Poland), Elmasonic EASY 40H ultrasonic bath. Lercanidipine hydrochloride (purity 99 %) was purchased from Jiyan Chemicals (India). Lercanidipine tablets 10 mg and 20 mg were used in our experiments. Results and discussion. To determine the amount of lercanidipine in tablets, a spectrophotometric method has been developed. To select the best dye for the method development, we tested a variety of dyes, including MR, bromocresol purple, bromophenol blue, cresol red, bromocresol green and bromothymol blue. We selected MR as the reagent based on the experimental studies' outcomes, and the solvent was an acetonitrile and ethanol mixture with a ratio of 95 to 5. The optimal parameters were determined for the quantitation of lercanidipine in tablets utilizing MR with 5×10-5 mol/L of dye concentration, 0.5 ml of MR solution, at a temperature of 25 °C without heating; detection wavelength was 498 nm and reaction time of 5 min. By using the molar ratios (saturation) method and Job's (continuous variations) approach, the stoichiometric coefficients of reacting components involving lercanidipine and dye were established to be 1:1. The proposed spectrophotometric procedure was linear within the concentration ranging from 6.48 – 32.41 μg/mL. Using the least squares method, a regression equation was generated: y = 0.0208x – 0.0318. The correlation coefficient was higher than 0.999, indicating that the analytical procedures' linearity is acceptable; the limit of detection and limit of quantitation were 1.19 μg/mL and 3.62 μg/mL, respectively. The robustness, accuracy and precision of the study results fell within acceptable limits. The proposed method was successfully applied to determine the content of lercanidipine in its tablet dosage forms. The analysis of the method's "greenness" using AGREE and GAPI tools yielded excellent results. Conclusions. The method that has been developed can serve as an alternative approach for the routine control of lercanidipine content in its tablets

Chemically reactive and aging macromolecular mixtures. I. Phase diagrams, spinodals, and gelation

Multicomponent macromolecular mixtures often form higher-order structures, which may display non-ideal mixing and aging behaviors. In this work, we first propose a minimal model of a quaternary system that takes into account the formation of a complex via a chemical reaction involving two macromolecular species; the complex may then phase separate from the buffer and undergo a further transition into a gel-like state. We subsequently investigate how physical parameters such as molecular size, stoichiometric coefficients, equilibrium constants, and interaction parameters affect the phase behavior of the mixture and its propensity to undergo aging via gelation. In addition, we analyze the thermodynamic stability of the system and identify the spinodal regions and their overlap with gelation boundaries. The approach developed in this work can be readily generalized to study systems with an arbitrary number of components. More broadly, it provides a physically based starting point for the investigation of the kinetics of the coupled complex formation, phase separation, and gelation processes in spatially extended systems.

Characterization of New Minimum Signature Solid Propellant Based on Ammonium Perchlorate Synergetic with Sorbitol and Magnesium Metal

Since the introduction of the concept of insensitive weapons, rocket motor designers must now ensure that their vulnerability is as low as possible. One of the inherent characteristics of a sugar-based propellant is the obvious plume coming out from the nozzle as a result of chemical reactions. The present work characterises a novel minimum signature composite solid propellant based on Ammonium perchlorate/Sorbitol with magnesium metal as a fuel and chlorine scavenger. The elemental stoichiometric coefficient and oxygen balance for the propellant mixture were calculated to find the optimum ratio between the oxidizer and fuel. The solid propellant of AP was prepared by mixing it with melted sorbitol and casting it into the cylindrical hollow tube using the freestanding method. The burning rate for five samples was measured at atmospheric pressure. The morphology was characterized by a scanning electron microscope. Calculation results reveal that ammonium perchlorate at 0.77% weight produced the best elemental stoichiometric coefficient and oxygen balance. The sample with the additive metal showed a significant increase in the burning rate. In all formulation samples of magnesium and ferrous oxide, the maximum burning rate at 0.126 cm/s showed that the metal additive and the propellant worked synergistically with each other. Results from SEM indicate that ammonium perchlorate spherical particles were uniformly dispersed within sorbitol. The addition of ferrousoxide increases the interaction between the component, and at the same time it gives the oxidizer the ability to interact more efficiently with the fuel and improve the physical strength of the solid propellant. This research is a minor step for Malaysia to become a top competitor in the aerospace industry in the future.

Information geometric bound on general chemical reaction networks.

We investigate the convergence of chemical reaction networks (CRNs), aiming to establish an upper bound on their reaction rates. The nonlinear characteristics and discrete composition of CRNs pose significant challenges in this endeavor. To circumvent these complexities, we adopt an information geometric perspective, utilizing the natural gradient to formulate a nonlinear system. This system effectively determines an upper bound for the dynamics of CRNs. We corroborate our methodology through numerical simulations, which reveal that our constructed system converges more rapidly than CRNs within a particular class of reactions. This class is defined by the count of chemicals, the highest stoichiometric coefficients in the reactions, and the total number of reactions involved. Further, we juxtapose our approach with traditional methods, illustrating that the latter falls short in providing an upper bound for CRN reaction rates. Although our investigation centers on CRNs, the widespread presence of hypergraphs across various disciplines, ranging from natural sciences to engineering, indicates potential wider applications of our method, including in the realm of information science.

Mathematical Model of Closed Microecosystem “Algae – Heterotrophic Bacteria”

Model of closed microecosystem “algae - heterotrophic bacteria” is proposed in this paper. Mathematical model is the Cauchy problem for system of nonlinear ordinary differential equations. To develop the model the Liebig’s law of the minimum is consistently used for both specific rate of biomass growth and specific death rate of algae and bacteria cells. To describe the specific rate of substrate utilization by algae and bacteria the Andrew’s model (substrate inhibition) is used. It is assumed that specific death rate of algae and bacteria cells increases with decreasing substrate concentration. It is also assumed that carbon and nitrogen are main biogenic elements, and in the system they are in the form of mineral substrate (CO2, NO2, NO3, NH4) and biological substrate (proteins, lipids and carbohydrates). Mathematical model describing time variations in concentration of elements of microecosystem is formulated under the following assumptions: 1) stoichiometric coefficients of algae and bacteria cells are constant in the development of microecosystem; 2) utilization of carbon and nitrogen by algae and bacteria occurs independently; 3) oxygen produced by algae cells during photosynthesis completely covers the demand for oxygen for algae and bacteria cells. To verify the proposed model experimental data for microecosystems «Clorella vulgaris – Pseudomonas sp.» и «Scenedesmus obliquus – Pseudomonas sp.» are used. These systems were studied in laboratory conditions, and concentrations of elements of microecosystems in stationary state were obtained. Parameters of functions describing specific rate of utilization of biogenic elements were derived from experimental data for growth kinetics of algae and bacteria. Concentration of the biomass in stationary state obtained with the use of the proposed model is in reasonable agreement with experimental data.

Experimental melting of phlogopite websterite in the upper mantle between 1.5 and 4.5 GPa

Abstract Reaction experiments have confirmed that phlogopite websterite can be formed by interaction of peridotite with hydrous alkaline or silica-rich melts. Phlogopite websterites commonly occur as xenoliths in orogenic and intraplate volcanism but do not receive much attention. We have experimentally investigated the melting behaviour of a phlogopite websterite at 1.5 GPa (1050–1300 °C), 3.0 GPa (1100–1500 °C), and 4.5 GPa (1200–1500 °C) to contribute to understanding the sources of ultrapotassic rocks that occur in different settings. The solidus temperature rises with increasing pressure, bracketed between 1050 and 1100 °C at 1.5 GPa, 1100 and 1150 °C at 3.0 GPa and between 1200 and 1250 °C at 4.5 GPa. At 1.5 GPa, phlogopite websterite melts incongruently to form olivine and melt, whereas orthopyroxene, garnet and melt are formed at 3.0 and 4.5 GPa. The transition of orthopyroxene from reactant to product with increasing pressure results in changes in the SiO2-content of melts. The experimental melts reach a maximum K2O content when phlogopite is consumed completely at temperatures ~150 °C above the solidus. The melting reactions are similar to those of phlogopite lherzolite, but the low-Al2O3 starting materials result in lower Al2O3 in the melt than in melts of phlogopite lherzolite. Comparison with natural ultrapotassic rock compositions reveals that the sources of ultrapotassic rocks in convergent settings may be dominated by phlogopite websterite, phlogopite lherzolite and phlogopite harzburgite. Sources of ultrapotassic rocks in intraplate settings are more likely to include phlogopite clinopyroxenite ± CO2 and K-richterite. In all melting experiments on phlogopite-bearing rocks, K2O from phlogopite passes into the melt, and hence the highest K2O contents in ultrapotassic rocks must be an indication of the minimum stoichiometric coefficient of phlogopite in the reaction. In cases where phlogopite websterite or phlogopite lherzolite is identified as the source, the minimum modal percentage of phlogopite in the source can be inferred from the highest K2O content. When applied to the Milk River minettes and New South Wales leucitites, the estimated modal proportion of phlogopite in the sources is greater than 20 wt.%. Phlogopite can survive the subduction process and melt later in the post-collisional environment, whereas thermal perturbations are necessary to trigger melting of phlogopite-bearing assemblages at the base of the lithosphere in intraplate settings.

Multiphase reactions of proteins in the air: Oligomerization, nitration and degradation of bovine serum albumin upon ambient exposure

Proteins in atmospheric aerosol can react with atmospheric pollutants such as ozone (O3) and nitrogen dioxide (NO2) in the atmosphere via the reactions of oxidation, nitration, and cross-linking etc. Currently, the reactions have been more thoroughly studied in the laboratory but rarely investigated in the ambient environment. In this study, we used bovine serum albumin (BSA) as the model protein to conduct the exposure experiment in the ambient environment in southern China, an area with increasing oxidative capacity, to investigate the reactions of proteins in the atmosphere. We observed the occurrence of oligomerization, nitration and degradation of BSA upon exposure. The mass fraction of BSA monomer decreased by 5.86 ± 1.61% after exposure and those of dimers, trimers and higher oligomers increased by 1.04 ± 0.49%, 1.37 ± 0.74% and 3.40 ± 1.06%, respectively. Simultaneously, the nitration degrees of monomers, dimers, trimers and higher oligomers increased by 0.42 ± 0.15%, 0.53 ± 0.15%, 0.55 ± 0.28% and 2.15 ± 1.01%, respectively. The results show that oligomerization was significantly affected by O3 and temperature and nitration was jointly affected by O3, temperature and relative humidity, indicating the important role of atmospheric oxidants in the atmospheric reactions of protein. Atmospheric degradation of BSA was observed with the release of free amino acids (FAAs) such as glycine, alanine, serine and methionine. Glycine was the dominant FAA with a molar yield ranging from ∼8% to 33% for BSA. The estimated stoichiometric coefficient (α) of glycine is 10−7–10−6 for the degradation of BSA upon O3. Our observation suggests the occurrence of protein reactions in the oxidative ambient environment, leading to the production of nitrated products, oligomers and low molecular weight products such as peptides and FAAs. This study may deepen the current understanding of the atmospheric reaction mechanisms and reveal the influence of environmental factors in the atmosphere.

Recovery of excess sulfuric acid in the lithium-ion batteries recycling process

Excess sulfuric acid which is needed for the leaching process of spent lithium-ion batteries is commonly neutralized generating significant waste streams. This research aims to extract and recover sulfuric acid using tri-n-octylamine as an extraction agent. 1-octanol, 2-ethylhexanol, and tributyl phosphate are investigated as synergetic extractants and phase modifiers. An equilibrium study is carried out on both, sulfuric acid and leachate. The equilibrium constant and the stoichiometric coefficient for the overall equilibrium reaction are determined by slope analysis. The enthalpy and Gibb’s enthalpy are studied by investigation of the effect of temperature. Regarding the experiments using leachate, the co-extraction of aluminum, cobalt, copper, iron, lithium, manganese, and nickel is studied, too. Moreover, the co-extraction of water is investigated as a significant increase in metal concentration in the raffinate is observed.

Machine Learning for Quantitative Structural Information from Infrared Spectra: The Case of Palladium Hydride.

Infrared spectroscopy (IR) is a widely used technique enabling to identify specific functional groups in the molecule of interest based on their characteristic vibrational modes or the presence of a specific adsorption site based on the characteristic vibrational mode of an adsorbed probe molecule. The interpretation of an IR spectrum is generally carried out within a fingerprint paradigm by comparing the observed spectral features with the features of known references or theoretical calculations. This work demonstrates a method for extracting quantitative structural information beyond this approach by application of machine learning (ML) algorithms. Taking palladium hydride formation as an example, Pd-H pressure-composition isotherms are reconstructed using IR data collected in situ in diffuse reflectance using CO molecule as a probe. To the best of the knowledge, this is the first example of the determination of continuous structural descriptors (such as interatomic distance and stoichiometric coefficient) from the fine structure of vibrational spectra, which opens new possibilities of using IR spectra for structural analysis.

Rapid measurement of trace periodate concentration with bromide ion–catalyzed periodate for oxidation colorization of DPD

In the study, the Br−–DPD method for the determination of IO4− concentration was established. The method facilitated the DPD indicator reaction by adding Br− and DPD at pH 5.5 (50 mM phosphate buffer) to complete the measurement of the IO4− concentration. DPD+ could be detected by UV–visible spectrophotometer at 510 nm and 551 nm. The experimental results showed a strong linear relationship between the absorbance of DPD+ and the concentrations of IO4−. The slopes of the calibration standard curves for absorption wavelengths at 510 nm and 551 nm are 1.92 × 104 M−1 cm−1 (R2 > 0.999) and 2.06 × 104 M−1 cm−1 (R2 > 0.999). The stoichiometric coefficient of the Br−–DPD method for IO4− and DPD was 1:2, and pH in the range 3.0–7.0 had no significant different on the calibration curve of the Br−–DPD method. The absorbance in experimental water remained stable within 600 s. The Br−–DPD method accurately measured trace concentration of IO4− in ultrapure water at the range of 0.05 μM–10 μM. In addition, metal ions (Fe3+, Cu2+ and Co2+) and common anions (SO42−, NO3− and Cl−) showed little interference on the Br−–DPD method. The results suggested that the Br−–DPD method is a precise and versatile approach for measuring IO4− concentration.

Treatment of Antihypertensive and Cardiovascular Drugs in Supercritical Water: An Experimental and Modeled Approach

Pharmaceutical pollutants are considered emerging contaminants, representing a significant concern to the ecosystem. Thus, this study reports on the degradation of antihypertensive and cardiovascular drugs (atenolol, captopril, propranolol hydrochloride, diosmin, hesperidin, losartan potassium, hydrochlorothiazide, and trimetazidine) present in simulated wastewater through applying the technology of oxidation using supercritical water (SCW). The operational parameters of the treatment process, particularly the feed flow rate, temperature, and concentration of H2O2, were assessed. A central composite design of experiments associated with differential evolution was employed in the optimization. Both liquid and gaseous phase products were submitted to physical–chemical characterization. As a result, the optimized conditions for the treatment were discovered to be a feed flow rate of 13.3 mL/min, a temperature of 600 °C, and a H2O2 oxidation coefficient of 0.65, corresponding to the oxygen stoichiometric coefficient in the carbon oxidation chemical reaction. Under optimal conditions, the total organic carbon (TOC) decreased from 332 to 25 mg/L (92.1%), and the pharmaceutical molecules underwent near-complete degradation. The physical–chemical parameters also met with the main environmental regulations for wastewater disposal. The compounds determined in the gaseous phase were CO2 (97.9%), H2 (1.3%), CH4 (0.3%), and CO (0.5%.). Additionally, a modeling thermodynamic equilibrium of the system was performed, based on the experimental data. The results revealed that SCW technology has a great potential to oxidize/degrade organic matter and can be applied to treat pharmaceutical pollutants.

Simple and rapid photometry for measuring low dosage of periodate with bromide ion-catalyzed oxidation of ABTS

A new method for the quantification of trace periodate (PI) concentration was developed. The Br--ABTS method was based on the oxidation coloration reaction. Under Br- catalysis, the PI rapidly oxidized ABTS to the green ABTS•+, which could be accurately determined by UV-Vis spectrophotometer. The absorbance of ABTS•+ was remarkably correlated linearly with the concentration of PI at 415 nm, and the slope of standard curve was (3.77 ± 0.01)× 104 M−1·cm−1. The proposed method had high sensitivity and the slope at different optical paths showed a good multiplicative relationship for concentration values as low as 0.02 μM to be measured. The existence of different solutes in river and lake water did not affect the accuracy of Br--ABTS method, the generated ABTS•+ could maintain good stability within 30 min, and the recovery of PI was between 95%− 105%. The stoichiometric coefficient between PI and ABTS•+ was 1.12 at pH 3.0. In addition, a common reductant (hydroxylamine), transition metal ions and inorganic anions (Cl-, SO42- and HCO3-) did not affect the Br--catalyzed oxidation of ABTS for the measurement of PI concentration. Consequently, Br--ABTS is a feasible method to determine the concentration of PI.

Insights into the Structure-Capacity of Food Antioxidant Compounds Assessed Using Coulometry.

CDAC (coulometrically determined antioxidant capacity) involves the determination of the antioxidant capacity of individual compounds or their mixtures using constant-current coulometry, with electrogenerated Br2 as the titrant, and biamperometric detection of the endpoint via Br2 excess. CDAC is an accurate, sensitive, rapid, and cheap measurement of the mol electrons (mol e-) transferred in a redox process. In this study, the CDAC of 48 individual antioxidants commonly found in foods has been determined. The molar ratio CDAC (CDACχ, mol e- mol-1) of representative antioxidants is ranked as follows: tannic acid > malvidin-3-O-glucoside ≃ curcumin > quercetin > catechin ≃ ellagic acid > gallic acid > tyrosol > BHT ≃ hydroxytyrosol > chlorogenic acid ≃ ascorbic acid ≃ Trolox®. In many cases, the CDACχ ranking of the flavonoids did not comply with the structural motifs that promote electron or hydrogen atom transfers, known as the Bors criteria. As an accurate esteem of the stoichiometric coefficients for reactions of antioxidants with Br2, the CDACχ provides insights into the structure-activity relationships underlying (electro)chemical reactions. The electrochemical ratio (ER), defined as the antioxidant capacity of individual compounds relative to ascorbic acid, represents a dimensionless nutritional index that can be used to estimate the antioxidant power of any foods on an additive basis.

Influence of sulfate ion on fluoride removal from flue gas scrubbing wastewater using lanthanum salts

Batch experiments were conducted to remove fluoride from simulated flue-gas scrubbing wastewater using La(NO3)3·6H2O. The effects of SO42− concentration and addition sequence on residual fluoride concentration and precipitates properties (mass, morphology, phase structure and composition) were investigated using fluorine ion-selective electrode, SEM, EDS and XRD. The results show that precipitates obtained in the presence of SO42− mainly consisted of LaF3 in irregular bulk shape with high crystallinity. However, amorphous particles were observed in the precipitates, which were speculated to be La[SO4]F. Due to the smaller stoichiometric coefficient of F/La in La[SO4]F compared to that in LaF3, the residual fluoride concentration increased as the SO42− concentration ascended. Subsequent addition of SO42− after lanthanum salt could inhibit the formation of amorphous particles, and further reduce the residual fluoride concentration. At a La/F molar ratio of 1:3.0, the subsequent addition of SO42− (0.02 mol/L) after La(NO3)3∙6H2O could obtain a residual fluoride concentration of 6.9 mg/L, lower than the required fluoride emission level. Further increasing the La/F molar ratio could reduce residual fluoride concentration to below 2 mg/L, while the risk of retaining La3+ would emerge.