Aqueous Nitrate Research Articles

Complex extraction of rare earth elements from nitrate solutions with a tri-n-octylamine-octanoic acid bifunctional ionic liquid

In this work, a new hydrophobic bifunctional ionic liquid based on tri-n-octylamine and octanoic acid was synthesised and a physicochemical characterisation was performed on it. The extraction of a series of rare earth elements (Y, Eu, Gd, Tb) (REEs) from aqueous nitrate solutions in a system containing the resulting ionic liquid was studied. Extraction isotherms were obtained and regularities of the interphase distribution of REEs were determined as a function of extraction process time, NaNO3 concentration, the pH of the aqueous phase, the concentration of the ionic liquid in the system, the volume ratio, and temperature of the process. It was shown that the extraction of REEs nitrates by the ionic liquid based on tri-n-octylamine and octanoic acid occurred in accordance with the mechanism of binary extraction of salts with the formation of two extractable compounds in the organic phase. In addition, this IL has been shown to exhibit excellent reusability.

Electrochemical reduction of aqueous nitrate using metallic silver particles as spatially suspended catalyst

Increasing nitrate concentrations in water sources is a serious concern. The current study demonstrates the electrochemical reduction of nitrate in the presence of silver metallic particles (AgMPs). Using Ti/RuO2 anode and a Ti cathode, nitrate removal in undivided and divided cells was limited to 18% and 77%, respectively, in the absence of AgMPs. Total Nitrogen (TN) removal in undivided and divided cells was nil and 29.5%, respectively, in the absence of AgMPs. Under identical conditions, the presence of 8 mM AgMPs increased nitrate removal to 63% and 99%, respectively, with significant improvement in nitrate conversion to N2. The effect of various parameters on nitrate removal and selectivity of products was studied using a divided cell: concentration of AgMPs, inter-electrode distance, cathode material, current density, initial nitrate concentration, and reusability of AgMPs. In the presence of 8 mM AgMPs, nitrate removal using different cathodes was Ti ≈ Fe > Cu > SS > Fe/Sn. The cathode type also affected the selectivity, with the maximum conversion to N2 achieved with the Ti cathode. Nitrate removal and conversion to N2 improved with the increase in current density up to 10 mA/cm2. Overall, the presence of AgMPs substantially improved nitrate removal and conversion to N2. The production of reductive species (AgHx) by the intercalation of nascent hydrogen on metallic silver appears to promote catalytic nitrate reduction. AgMPs could be reused up to 10 times with consistent performance. This work offers a new approach to nitrate reduction using an efficient and reusable catalyst.

Industrial demonstration of indirect mineral carbonation in the cement and concrete sector

This paper reports on the successful construction, commissioning and operation of a mobile indirect mineral carbonation (IMC) pilot plant in the concrete sector. This work confirms the technical feasibility of IMC at large scale, while producing precipitated calcium carbonate (PCC) and leached recycled concrete aggregate (RCA) as useful products. The plant is capable of handling industrial flue gas or pure CO2 as carbon feedstock, while processing around 80 kg/h of RCA as calcium feedstock, and storing around 0.9 kg/hr of CO2. Good recyclability of the aqueous ammonium nitrate mother liquor is suggested, although small changes occurred over time, with only small effects on the operation. Importantly, some CaCO3 precipitates in the dissolution reactor, especially at high CO2 feed rates; this does not decrease the CO2 storage rate, but it reduces the PCC production rate. The plant may be operated at a variety of operating conditions and it responds to them as expected from thermodynamic considerations. Similarly, the trade-offs in terms of performance parameters also change as expected. The observed calcium extraction efficiency is rather low due to the thermodynamic nature of the batch dissolution step. Also, the ammonium nitrate losses are rather high due to the plant not having a solvent recovery step integrated. Potentially alternative reactor concepts for the dissolution section can improve the calcium extraction efficiency while including a washing step, thus alleviating the main limitation. Material tests with the products of the process suggest that leached RCA is as good as, or even better than fresh RCA for use as aggregate in concrete; ground PCC performs similar as ground limestone in cement, however it is not the most attractive use of fine PCC, as higher value applications exist. Although improvements to the plant design are necessary to make the process economically and environmentally viable, this work represents an important steppingstone towards industrial implementation of IMC, and confirms its technical feasibility in the concrete sector.

Particle Network Self-Assembly of Similar Size Sub-Micron Calcium Alginate and Polystyrene Particles Atop Glass.

Particle-mediated self-assembly, such as nanocomposites, microstructure formation in materials, and core-shell coating of biological particles, offers precise control over the properties of biological materials for applications in drug delivery, tissue engineering, and biosensing. The assembly of similar-sized calcium alginate (CAG) and polystyrene sub-micron particles is studied in an aqueous sodium nitrate solution as a model for particle-mediated self-assembly of biological and synthetic mixed particle species. The objective is to reinforce biological matrices by incorporating synthetic particles to form hybrid particulate networks with tailored properties. By varying the ionic strength of the suspension, the authorsalter the energy barriers for particle attachment to each other and to a glass substrate that result from colloidal surface forces. The particles do not show monotonic adsorption trend to glass with ionic strength. Hence, apart from DLVO theory-van der Waals and electrostatic interactions-the authors further consider solvation and bridging interactions in the analysis of the particulate adsorption-coagulation system. CAG particles, which support lower energy barriers to attachment relative to their counterpart polystyrene particles, accumulate as dense aggregates on the glass substrate. Polystyrene particles adsorb simultaneously as detached particles. At high electrolyte concentrations, where electrostatic repulsion is largely screened, the mixture of particles covers most of the glass substrate; the CAG particles form a continuous network throughout the glass substrate with pockets of polystyrene particles. The particulate structure is correlated with the adjustable energy barriers for particle attachment in thesuspension.

Unravelling the structural and dynamical properties of concentrated aqueous ammonium nitrate solutions: MD simulation studies

ABSTRACT In this work, we present, the concentration-dependent solvation structure and dynamics of an ammonium nitrate (AN) ion pair in aqueous media by means of classical molecular dynamics simulations. Structural properties were investigated by computing the potentials of mean force (PMFs), radial distribution functions (RDFs), cluster size distribution functions, and hydrogen bond dynamics. The change in the depth of the contact ion pair (CIP) and solvent-separated ion pair minima (SSIP) is marginal, whereas for the solvent-assisted ion pair (SAIP) is more stable at lower salt concentrations. The marginal difference in the depth of the CIP minimum of the PMF is explained based on cluster size distribution and hydrogen bonding. The solvation structure of the ions is not affected by the salt concentration. Ab-initio and classical molecular dynamics simulations (both constrained and unconstrained) give similar results for the solvation structure around the cation and the anion. The spatial density distribution functions of the anions around the cations show that the anions occupy the space around the ammonium hydrogen atoms. Profound differences in dynamical properties are found in the case of concentrated solutions as compared to dilute solutions.

Changes in nitrate binding with lanthanides in BLPhen complexes

Preorganized ligands such as bis-lactam-1,10-phenanthroline (BLPhen) offer unique selectivity trends in solvent extraction of rare-earth ions, particularly from aqueous nitrate solutions. However, due to the ligand’s lipophilicity it is experimentally challenging to obtain crystal structures of the corresponding lanthanide (Ln):ligand complexes to describe the local structure of the first coordination shell and the role of the nitrate ions in the organic phase. Herein, we report first principles molecular dynamics (FPMD) simulations of the complexation of trivalent lanthanide ions (La, Nd, and Eu) with the BLPhen ligand in the presence of nitrate ions in the dichloroethane (DCE) solvent. We find that two nitrate anions are present in the first solvation shell and the third nitrate anion is far from the first solvation shell in all three [Ln(BLPhen)2]3+ complexes examined. Moving along the lanthanide series from La to Nd to Eu, the binding pocket formed by the two BLPhen ligands shrinks in size; as a result, the two nitrate configuration changes from one-monodentate/one-bidentate binding mode for La and Nd to all monodentate for Eu. Meanwhile, the total coordination number drops from 11 for La and Nd to 10 for Eu. More interestingly, the bidentate binding in [La(BLPhen)2]3+ and [Nd(BLPhen)2]3+ complexes is highly dynamic, frequently switching to monodentate and back. The FPMD insights into the differing modes and dynamics of nitrates in the first coordination shell will be useful for further atomistic understanding of the complex structure, formation, and stability in the organic phase.

Anti-angiogenic activity of Ficus deltoidea L. Jack silver nanoparticles using chorioallantoic membrane assay

Background: Ficus deltoidea L. Jack is a folk medicinal plant known for its pharmacological properties, including anti-inflammatory, anticancer and anti-angiogenic. This study aimed to evaluate the anti-angiogenic properties of silver nanoparticles biosynthesized using F. deltoidea leaf extract (AgNPs-Fd). Methods: The AgNPs-Fd were synthesized by mixing 100 mL 1 mM aqueous silver nitrate (AgNO3) and 100 mL 0.1% F. deltoidea ethanolic leaf extract. The resulting AgNPs-Fd were observed for color change and Tyndall effects. Reaction mixture color change from pale brown to reddish brown was observed at 48 h at 37°C. The characterization of AgNPs-Fd was completed with UV–Vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. For quantitative analysis of the vascular network in the chorioallantoic membrane (CAM) assay, AngioTool open-source software was used. Results: The plasmon resonance peak for AgNPs-Fd at 430 nm was visible in the UV-Visible spectrum, indicating the formation of AgNPs-Fd. The F. deltoidea extract and nanoparticles interacted well according to FTIR analysis. The AgNPs-Fd morphology of 20 nm particle sizes was observed using TEM. The chromatographic analysis of AgNPs-Fd identified potential anti-angiogenic compounds, such as phytol, stigmasterol, lupeol and sitosterol. The angiogenic inhibition properties of AgNPs-Fd were tested using the CAM assay. The 90 mg dose AgNPs-Fd treatment in CAMs demonstrated significant anti-angiogenesis, indicating effectiveness in controlling vessel formation. Conclusions: The present study suggests that eco-friendly work and the “green” process of AgNPs-Fd is potentially applicable for nanobiotechnology in anti-angiogenic fields.

Green synthesis, characterization, and biological evaluation of gold and silver nanoparticles using Mentha spicata essential oil

Green synthesis of bioactive nanoparticles (NPs) is getting more attractive in various fields of science including the food industry. This study investigates the green synthesizing and characterization of gold NPs (AuNPs) and silver NPs (AgNPs) produced using Mentha spicata L. (M. spicata) essential oil as well as their antibacterial, antioxidant, and in vitro cytotoxic effects. The essential oil was mixed with both Chloroauric acid (HAuCl4) and aqueous silver nitrate (AgNO3) solutions separately and incubated at room temperature for 24 h. The chemical composition of the essential oil was identified by gas chromatography coupled with a mass spectrometer detector (GC–MS). Au and Ag nanoparticles were characterized using UV–Vis spectroscopy, transmission electron microscopy, scanning electron microscopy, dynamic light scattering (DLS), X-ray diffraction (XRD) and Fourier transform infrared (FTIR). The cytotoxicity of both types of nanoparticles was evaluated using MTT assay on cancerous HEPG-2cell line by exposing them to various concentrations of both NPs for 24 h. The antimicrobial effect was evaluated by the well-diffusion technique. The antioxidant effect was determined by DPPH and ABTS tests. According to the results of GC–MS analysis, 18 components were identified, including carvone (78.76%) and limonene (11.50%). UV–visible spectroscopy showed a strong absorption peak of 563 nm and 485 nm, indicating the formation of Au NPs and Ag NPs, respectively. TEM and DLS demonstrated that AuNPs and AgNPs were predominantly spherical shaped with average sizes of 19.61 nm and 24 nm, respectively. FTIR analysis showed that biologically active compounds such as monoterpenes could assist in the formation and stabilization of both types of NPs. Additionally, XRD provided more accurate results, revealing a nano-metal structure. Silver nanoparticles exhibited better antimicrobial activity against the bacteria than AuNPs. Zones of inhibition ranging 9.0–16.0 mm were recorded for the AgNPs, while zones of 8.0–10.33 mm were observed AuNPs. In the ABTS assay, the AuNPs and AgNPs showed a dose-dependent activity and synthesized nanoparticles exhibited higher antioxidant activity than MSEO in both assays. Mentha spicata essential oil can be successfully used for the green production of Au NPs and Ag NPs. Both green synthesized NPs show antibacterial, antioxidant, and in vitro cytotoxic activity.

Solubilities of Amino Acids in the Presence of Chaotropic Anions

This work addresses the effect of chaotropic anions (thiocyanate and tosylate) on the solubility of glycine, L-leucine, L-phenylalanine, and L-aspartic acid in aqueous solutions at 298.2 K. The salts used were NaSCN, KSCN, NH4SCN, and NaC7H7SO3 (sodium tosylate), with salt concentrations ranging from 0 to 2 molal. The pH of the saturated solutions was registered, and solid-phase studies were also performed. All the thiocyanate salts and sodium tosylate induced a salting-in effect, except in the systems composed of glycine in aqueous sodium tosylate solutions at 0.5 and 1 molal. For L-leucine, L-phenylalanine, and L-aspartic acid the salting effect of anions followed the order tosylate− > SCN− > NO3-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathrm{NO}}_{3}^{-}$$\\end{document} > Cl−, in good agreement with the behavior predicted by the Hofmeister series. Differently, the relative solubility of glycine in aqueous nitrate solutions was higher than in those containing thiocyanate, followed by the chloride and, closing the rank, the solutions containing the tosylate anion, suggesting that the solubility change in this case is achieved by a different mechanism.

Evaluation of extraction behaviour of techno metal neodymium from nitrate feed using Tri-n-hexylamine di-2-ethyl hexyl phosphate as extractant

The rare earths are presently considered as the critical elements by the European Union. High technological use of neodymium as neodymium-iron-boron permanent magnet resulted in more demand and dearth of supply of this rare earth. This has initiated efforts on an urgent basis to find alternative resources for potential recovery of neodymium. This present investigation focuses on study of the extraction profile of neodymium from the aqueous nitrate feed using a bifunctional ionic liquid comprised of trihexylamine di-2-ethyl hexyl phosphate in kerosene. The variations in shaking time, salt concentration, aqueous phase pH, diluting agents, Nd3+ concentration, temperature were performed in order to know their impact on the extraction were analyzed. Results indicated that the extraction percentage increases when salt concentration as well as with extractant concentration increased. Extraction becomes 99.1% with 2 M NaNO3 at pH 3 using 0.1 M of the ionic liquid. Increase in the aqueous feed pH also increased extraction percentage while temperature showed negative impact. The amine based ionic liquid has been found as a potential extractant for Nd extraction from nitrate medium.

Spectrophotometric and Spectrofluorimetric Quantification of Urea via Silver Nanoparticles Prepared by Wet Chemical Method

Silver nanoparticles have been utilized in an easy, sensitive, and effective approach through spectrophotometry and spectrofluorimetry to quantify urea in water samples. Here, 1,3-di-(1H-imidazole-1-yl) -2-propanol (DIPO) was employed to stabilize Ag NPs produced from the reduction of aqueous silver nitrate by sodium borohydride (NaBH<sub>4</sub>). Beer-Lambert's law was applied for determination using the complexation of Ag NPs with urea molecules. The results show urea can be assessed concurrently with good results and percent recoveries. The UV-visible absorbance and fluorescence emission calibration curves were plotted at 445 and 471 nm wavelengths, respectively. Beer-Lambert’s law was obeyed in the 0.1-15 mM concentration range. A linear correlation for both UV-visible spectrophotometry and spectrofluorimetry was obtained on optimum conditions using the suggested methods having a limit of detection (LOD) was found to be 0.897 and 0.048, respectively. The percent recovery ± RSD by the spectrophotometric and spectrofluorimetric method was found to be 88 ± 19.7%, 96.67 ± 21.53%, 130.8 ± 1.33% and 102.3 ± 12.7%, 97.26 ± 5.63%, 111.4 ± 3.8%, respectively. Following a comparison of the obtained data, it may be possible to identify spectroscopic approaches with greater efficacy and efficiency that may be used to determine urea's presence in actual samples of biological and non-biological fluids.

Incorporation of rare earth elements into [formula omitted

The structural effects of the incorporation of the rare earth elements (REE) La, Ce, Pr, Nd, Eu, Sm, Gd, Er, Tm, Yb and Y into a synthetic Ba–Ca carbonate have been investigated. We precipitated solutions with a composition Ba0.9Ca1.1(CO3)2 doped with REE-nitrates. The precipitate, with few exceptions, consisted of a crystalline solid, slightly depleted in Ba with respect to the expected composition, and an amorphous phase. On heating, the whole sample became crystalline and consisted of a Ba-enriched and a Ba-depleted phase. The phases are isostructural. The lattice parameters are strongly influenced by the incorporation of ≈ 6% REE. There is a linear dependence of the unit cell volume on the radius of the incorporated REE for those elements with a radius < 1.0 Å, i.e. Yb, Tm, Er, Y, Gd, Sm, Eu, Nd and Pr, while the unit cell volume of a sample doped with La (r(La) = 1.03 Å) and Ce (r(Ce) = 1.01 Å) is not well described by this dependency. Raman spectroscopy shows that the local environment of the CO3-groups does not differ substantially between the Ba-enriched and the Ba-depleted phase, but changes linearly as a function of the ionic radius of the REE. The present study clearly shows that substantial amounts of REE can be incorporated into the Ba–Ca-carbonate studied here, making it potentially useful as a matrix in nuclear waste treatments involving aqueous nitrate solutions of lanthanides and actinides.

Effects of nitrate concentrations on As(III) immobilization via new ferric arsenite hydroxynitrate precipitates

The Fe(III)-As(III)-anion precipitation as layered double hydroxide-like compounds such as tooeleite and ferric arsenite hydroxychloride (FC) has been found in As(III)-contaminated acidic mine soils. However, the question of whether As(III) is immobilized by Fe(III) in aqueous nitrate media, a common constituent in soils and metallurgical wastewater, remains unclear. Herein, we investigated the effects and mechanism of nitrate on As(III) immobilization via Fe(III)-As(III)-nitrate precipitation. Our results indicated that new ferric arsenite hydroxynitrate (FN) with variable Fe(III)/As(III)/nitrate molar ratios crystallized in an initial nitrate content range of 11,160–74,400 mg·L−1 at pH 2.3. This FN precipitation resulted in 60.3–87.9% of As(III) removal and a fall-rise immobilization trend as a function of the initial nitrate concentration. The optimal initial nitrate concentration for As(III) fixation was 44,640 mg·L−1. Although FN shared similar morphology and crystal structure with tooeleite and FC, the substitution of NO3− for SO42− and Cl− in the FeO6-AsO3 interlayers caused a significant local structural distortion due to different ionic radii. The characteristic infrared and Raman bands of the nitrate group in FN occurred at 1,363 cm−1, 1,384 cm−1 and 152 cm−1, 722 cm−1, 1,055 cm−1, respectively. The FN induced significantly enhanced As(III) immobilization relative to its tooeleite and FC counterparts at equimolar concentrations of NO3−, SO42−, and Cl− as the media.

Green Synthesis of Silver Nanoparticles: Their Characterization, Antimicrobial, Antioxidant Activity and Nanogel Formulation

This study investigates an efficient and sustainable route of preparing Ag nanoparticles (NPs) using 1–5 mmol/L aqueous silver nitrate with leaf extracts of five plants—<i>Musa balbisiana</i> (banana), <i>Azadiracta indica</i> (neem), <i>Ricinus communis</i> (castor-oil plant), <i>Tridax procumbens</i> (tridax), and <i>Cardiospermum halicacabum</i> (balloon vine) for their wide availability. These synthesized nanoparticles were characterized with the help of ultraviolet (UV)–visible (Vis) spectrophotometer. The peaks were observed in 418–493 nm. For <i>M. balbisiana</i>, <i>A. indica</i>, <i>R. communis</i>, and <i>C. halicacabum</i>, the average size of nanoparticles was in the range of 90–100 nm. For <i>T. procumbens</i>, it was 39–60 nm as determined by dynamic light scattering. Energy dispersive X-ray spectroscopy analysis showed the peak in silver region confirming presence of elemental silver. Field emission scanning electron microscopy showed that the particles were of a spherical shape in <i>M. balbisiana</i> sample with an average size of 33.87 nm as well as in <i>T. procumbents</i> sample with an average size of 28.512 nm. Ag NPs showed effective antibacterial and antifungal activity against representative pathogens of bacteria and fungi. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity of Ag NPs was found to be in the range of 8.9%–78.86%. H₂O₂ radical scavenging activity was recorded in the range of 6.036%–57.342%. The nanogel was prepared from synthesized Ag NPs, and its properties like viscosity and stability were evaluated. The results confirmed that this protocol is a simple, rapid, one-step, eco-friendly, nontoxic, and alternative conventional physical/chemical method.

Cover Feature: Gamma Radiation‐Induced Degradation of Acetohydroxamic Acid (AHA) in Aqueous Nitrate and Nitric Acid Solutions Evaluated by Multiscale Modelling (ChemPhysChem 5/2023)

The Cover Feature represents acetohydroxamic acid degradation in used nuclear fuel reprocessing cycles, where it is broken down by hydrolysis and radiation in aqueous nitric acid to form acetic acid, hydroxylamine, nitrous oxide, and hydrogen gas. Designed by Rett Longmore. More information can be found in the Research Article by Jacy K. Conrad, Gregory P. Horne and co-workers.

Synthesis of Rumex hastatus-based silver nanoparticles induced the inhibition of human pathogenic bacterial strains

The development of antibiotic resistance in pathogenic bacterial strains has drawn attention to the quest for new natural antibacterial drugs. Therefore, in the present study, extracts of Rumex hastatus leaves were obtained in methanol and water, and R. hastatus-based silver nanoparticles (AgNPs) were synthesized. Structural and functional properties of synthesized silver nanoparticles were determined by UV–vis spectroscopy, XRD, FTIR and SEM. The synthesized AgNPs and crude extracts were tested to check their antibacterial potential against human pathogenic bacterial strains of Staphylococcus aureus, Staphylococcus haemoliticus, Bacillus cereus, Escherichia coli, Salmonella typhi and Pseudomonas aeruginosa in well diffusion and broth dilution methods. The present investigation has revealed for the first time that the broth dilution method was found more reproducible than that of the well diffusion method even at lower concentrations of AgNPs and crude extracts. UV– Vis spectroscopic analysis of AgNPs revealed a peak at 367 nm. XRD pattern showed a face-centered cubical to the spherical structure of AgNP crystals. FTIR analysis revealed that flavonoids and terpenoids are responsible for the reduction of AgNO3 to Ag+. SEM analysis determined the spherical structure and 51 nm average diameter of nanoparticles. The antibacterial activity of R. hastatus-based (AgNPs) was found to be significantly higher than aqueous plant extract and silver nitrate alone. Bacterial growth was inhibited by R. hastatus-based AgNPs in a dose-dependent manner. To our knowledge, silver nanoparticles (AgNPs) of R. hastatus were synthesized and characterized for the first time in this study and, based on the findings of current research work R. hastatus extract-based silver nanoparticles are suggested to be used as an antibacterial drug instead of synthetic drugs for the treatment of various human diseases/infections caused by the tested bacterial strains.

Batchwise Leaching of Calcium from Demolition Concrete Fines in an Aqueous Ammonium Nitrate Solution: Part 2 Modeling

This article addresses the application of the indirect mineral carbonation process to recycled concrete aggregates (RCA). In such a process, calcium is first leached from the RCA feedstock into an aqueous ammonium nitrate solution and then it is carbonated to precipitate calcium carbonate. The calcium leaching step is modeled in this contribution, whereas it was investigated experimentally in part 1 of this series, where the focus was more on thermodynamic aspects than on kinetics. In this part 2 paper, kinetics aspects are also included by modeling them using two different approaches. In the first approach, the reaction–diffusion model is implemented, accounting for the congruent dissolution of the calcium hydroxide phase and the incongruent dissolution of the calcium silicate hydrate components of concrete fines. In the second approach, a double-shrinking-core model is used, which for the sake of simplicity assumes congruent dissolution of calcium silicate hydrates as well, infinitely fast reaction/dissolution kinetics, and pseudo-steady-state diffusion. The model parameters have been either determined through targeted experiments or estimated by fitting measurements obtained in experiments with two different materials, both in the size range of up to a diameter of 4 mm. Both models exhibit satisfactory accuracy in describing the experimental data; particularly for particles larger than about 0.1 mm in diameter, the two models calculate a nearly identical evolution of the calcium concentration in solution. The simplifications of the double-shrinking-core model lead to a loss of resolution in characterizing the evolution of leaching inside the particles, whereas they enable faster computations. The latter feature makes such a model a convenient tool for studying process performance, namely, productivity, calcium recovery, and solvent efficiency, through parametric analysis; this has been demonstrated as reported in the last part of the article.

Electrochemical degradation and mineralisation of organic dyes in aqueous nitrate solutions

Electrochemical treatment of organic matter for environmental remediation necessitates the development of cheap and robust electrodes that are chemically and structurally stable. To address this challenging requirement, we demonstrate a new electrochemical approach using a simple copper electrode under cathodic conditions to electrochemically generate reactive nitrosonium ions for the degradation of different classes of synthetic organic dyes. This could be achieved in an aqueous HNO3/KNO3 electrolyte at a relatively low cathodic potential of −0.5 V RHE at room temperature. UV–visible absorption spectroscopy, Raman spectroscopy, liquid chromatography – mass spectrometry and total organic carbon measurements revealed the rapid decolorisation and mineralisation of several dye types such as triarylmethane dyes (crystal violet, cresol red), an azo dye (methyl orange) as well as a sulfur containing thiazine dye (toluidine blue). The total organic carbon content of a 50 mg L−1 methyl orange solution was found to decrease by 83% after 1 h of electrolysis. Promisingly, locally sourced river and creek water samples spiked with 50 mg L−1 methyl orange were also successfully treated for up to 6 cycles at a simple Cu electrode, demonstrating potential for the remediation of polluted waterways.

Opportunities and challenges in aqueous nitrate and nitrite reduction beyond electrocatalysis

Nitrate (NO3−) and nitrite (NO2−) ions are common health-threatening contaminants in water. Thermal catalytic hydrogenation is a promising strategy to reduce nitrate and nitrite during water treatment.

Novel eco-friendly synthesis of silver nanoparticles using clove and cardamom extracts and cytotoxic and antimicrobial efficacies against oral pathogens- In vitro study

Background: Green synthesized nanoparticles are perceived as an inexpensive, safe &amp; ecologically beneficent approach to control pathogenic oral microbes compared to conventional methods. In the current study, silver nano particles (AgNPs) were effectively synthesised using clove and cardamom plant extracts. Methods: In the present study, aqueous silver nitrate was reacted with the clove, cardamom extracts and characterization was analyzed using UV-vis spectrophotometer and TEM analysis. Clove and cardamom reinforced silver nanoparticles were examined at 25 µL, 50 µL and 100 µL concentrations for their antibacterial activity against Staphylococcus aureus, Streptococcus mutans, Lactobacillus species and Candida albicans. Cytotoxicity was assessed using brine shrimp assays. Results: The formation of AgNPs was observed as shifting in color from orange-red color to dark brown at the end of the day three. Reducing silver ions to AgNPs, as shown by UV-vis spectroscopy, has produced an emission peak at 462 nm. TEM imaging showed that the particles were spherical and varied in size from 5-20 nm. Antimicrobial activity of the AgNPs at 100 µL was superior to that of antibiotics against Streptococcus mutans. Excellent antibacterial activity was shown by a zone of inhibition that was closer to that of antibiotics when examined against Lactobacillus. Staphylococcus aureus and Candida albicans were also moderately impacted. There was no evidence of cytotoxicity. Conclusion: Silver nanoparticles reinforced with clove and cardamom exhibited no cytotoxicity and showed promise as a potent antibacterial agent against oral pathogensKey words: silver nanoparticles.