Aqueous Nitrate Research Articles

Thermodynamics of Aqueous Lithium Nitrate Solutions at 298.15 to 398.15 K and 0.1 to 60 MPa

Thermodynamics of Aqueous Lithium Nitrate Solutions at 298.15 to 398.15 K and 0.1 to 60 MPa

Laser printing of silver and silver oxide

We show that direct laser writing in aqueous silver nitrate with a λ = 1030 nm femtosecond laser results in the deposition of a mixture of silver oxide and silver, in contrast to the pure silver deposition previously reported with 780 nm femtosecond direct laser writing. However, adding photoinitiator prevents silver oxide formation in a concentration-dependent manner. As a result, the resistivity of the material can also be controlled by photoinitiator concentration with resistivity being reduced from approximately 9e-3 Ωm to 3e-7 Ωm. Silver oxide peaks dominate the X-ray diffraction spectra when no photoinitiator is present, while the peaks disappear with photoinitiator concentrations above 0.05 wt%. A THz polarizer and metamaterial are printed as a demonstration of silver oxide printing.

Development of Technology for the Synthesis of Nanocrystalline Cerium Oxide Under Production Conditions with the Best Regenerative Activity and Biocompatibility for Further Creation of Wound-Healing Agents

Background/Objectives: The issue of effective wound healing remains highly relevant. The objective of the study is to develop an optimal method for the synthesis of nanosized cerium oxide powder obtained via the thermal decomposition of cerium carbonate precipitated from aqueous nitrate solution for the technical creation of new drugs in production conditions; the select modification of synthesis under different conditions based on the evaluation of the physicochemical characteristics of the obtained material and its biological activity, and an evaluation of the broad-spectrum effect on cells involved in the regeneration of skin structure as well as antimicrobial properties. Methods: Several modes of the industrial synthesis of cerium dioxide nanoparticles (NPs) were carried out. The synthesis stages and the chemical and physical parameters of the obtained NPs were described using transmission electron microscopy (TEM), X-ray diffraction, Raman spectroscopy, and mass spectrometry. The cell cultures of human fibroblasts and keratinocytes were cultured with different concentrations of different nanoceria variations, and the cytotoxicity and the metabolic and proliferative activity were investigated. An MTT test and cell counting were performed. The antimicrobial activity of CeO2 variations at a concentration of 0.1–0.0001 M against Pseudomonas aeruginosa was studied. Results: The purity of the synthesized nanoceria powders in all the batches was >99.99%. According to TEM data, the size of the NPs varied from 1 nm to 70 nm under different conditions and methodologies. The most optimal technology for the synthesis of the nanoceria with the maximum biological effect was selected. A method for obtaining the most bioactive NPs of optimal size (up to 10 nm) was proposed. The repeatability of the results of the proposed method of nanoceria synthesis in terms of particle size was confirmed. It was proven that the more structural defects on the surface of the CeO2 crystal lattice, the higher the efficiency of the NPs due to oxygen vacancies. The strain provided the best redox activity and antioxidant properties of the nanoceria, which was demonstrated by better regenerative potential on various cell lines. The beneficial effect of synthesized nanoceria on the proliferative and metabolic activity of the cell lines involved in skin regeneration (human fibroblasts, human keratinocytes) was demonstrated. The antimicrobial effect of synthesized nanoceria on the culture of the most-resistant-to-modern-antibiotics microorganism Pseudomonas aeruginosa was confirmed. The optimal concentrations of the nanoceria to achieve the maximum biological effect were determined (10−3 M). Conclusions: It was possible to develop a method for the industrial synthesis of nanoceria, which can be used to produce drugs and medical devices containing CeO2 NPs.

Simultaneous Measurement of Gaseous HONO and NO2− in Solutions from Aqueous Nitrate Photolysis Mediated by Organics

Field studies suggest that NO3− photolysis may play a more significant role than previously thought. In this study, we concurrently measured HONO, NO2, and NO2− in situ to gain a deeper understanding of the photogenerated HONO transfer to air and to better constrain the rate constants of NO3− photolysis. The presence of fatty acids (e.g., nonanoic acid, NA), which are naturally present in the environment, significantly increases the production of photogenerated HONO and NO2. With an increase in oxygen percentage, the release rate of photoinduced HONO slowed, while the release rate of NO2 accelerated. The measured JNO3− value averaged 1.65 × 10−5 s−1, which is two orders of magnitude higher than values reported in similar systems. The HONO transfer rate from the solutions increased from 2.3 × 10−4 s−1 to 5.6 × 10−4 s−1 as the NA concentration increased from 0.1 to 20 mM. This can be attributed to the accumulation of NO2− induced by NA at the interface. Within this interfacial region, NO2− in the solutions becomes more prone to transfer into gaseous HONO, suggesting that photogenerated NO2− hosted in atmospheric droplets may serve as a temporary reservoir of atmospheric HONO without illumination, influencing the atmospheric oxidizing capacity in the region for hours. Therefore, simultaneous measurements of both gas and particle phase photoproducts are recommended to better constrain the rate constants of NO3− photolysis, thereby enhancing the accuracy of predicting the photochemical production of HONO in the atmosphere.

The influence of pH electrolyte on the electrochemical deposition and properties of cerium oxide thin films

Thin cerium oxide layers cathodically deposited on zinc were studied. These electrochemically deposited coatings provide effective corrosion protection and require less deposition time compared to chemical conversion coatings. The kinetics of their formation depend on various factors, such as temperature, applied current density, electrolyte composition, pH, and agitation. In this study, the effect of bath solution pH was investigated, with coatings produced at room temperature from aqueous cerium nitrate solutions. Chronopotentiometry, linear sweep voltammetry, and electrochemical impedance spectroscopy (EIS) were used to monitor the deposition process, while scanning electron microscopy and energy-dispersive spectroscopy were performed to characterize the deposits. Corrosion resistance was evaluated through potentiodynamic tests in a 3.5% NaCl solution. The results indicate that the electrolyte pH significantly influences the cerium electrodeposition process. Based on the findings, the cerium oxide coating obtained from a pH 4 solution exhibited lower corrosion current density, higher polarization resistance, and superior anti-corrosion performance.

Phytochemical fabrication of ZnO nanoparticles and their antibacterial and anti-biofilm activity

The synthesis of metal nanoparticles through bio-reduction is environmentally benign and devoid of impurities, which is very important for biological applications. This method aims to improve ZnO nanoparticle's antibacterial and anti-biofilm activity while reducing the amount of hazardous chemicals used in nanoparticle production. The assembly of zinc oxide nanoparticles (ZnO NPs) is presented via bio-reduction of an aqueous zinc nitrate solution using Echinochloacolona (E. colona) plant aqueous leaf extract comprising various phytochemical components such as phenols, flavonoids, proteins, and sugars. The synthesized nano ZnO NPs are characterized by UV–visible spectrophotometer (UV–vis), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (X-RD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and elemental composition by energy-dispersive x-ray spectroscopy (EDX). The formation of biosynthesized ZnO nanoparticles was confirmed by the absorbance at 360–370 nm in the UV–vis spectrum. The average crystal size of the particles was found to be 15.8 nm, as calculated from XRD. SEM and TEM analysis of prepared ZnO NPs confirmed the spherical and hexagonal shaped nanoparticles. ZnO NPs showed antibacterial activity against Escherichia coli and Klebsiella pneumoniae with the largest zone of inhibition (ZOI) of 17 and 18 mm, respectively, from the disc diffusion method. Furthermore, ZnO NPs exhibited significant anti-biofilm activity in a dose-dependent manner against selected bacterial strains, thus suggesting that ZnO NPs can be deployed in the prevention of infectious diseases and also used in food preservation.

Influence of silver nanoparticles synthesized from Chaenomeles leaf extracts on pathogenic microorganisms Klebsiella pneumoniae, Staphylococcus aureus, and Fusarium culmorum

Herein, we report for the first time the biosynthesis of silver nanoparticles (AgNPs) using leaf extracts of Chaenomeles Lindl. (Rosaceae) plants and its spectral characteristics, as well as antifungal and antibacterial activity. Phytosynthesis of silver nanoparticles on the base of aqueous plant extracts and silver nitrate solution was carried out by an ecofriendly and cost-effective approach. UV-Vis spectroscopy was applied to validate the plant-mediated biosynthesis of AgNPs colloidal solutions by the Surface Plasmon Resonance (SPR) bands in the region of 450–500 nm, characteristic of polycrystalline silver nanoparticles. Scanning microscopy (SEM) revealed a wide variation in range 5–58 nm and a close to spherical shape of plant-derived AgNPs. Raman scattering spectroscopy revealed the suitability of biosynthesized silver nanoparticles as the substrates for surface-enhanced Raman scattering (SERS) spectroscopy with the highest efficiency of AgNPs, biosynthesized from leaf extract of Ch. × superba, which enhanced the Rhodamine 6G dye applied at a concentration of 10–7 M. Assay of antifungal activity performed by well diffusion method revealed the dose-dependent effect of all AgNPs against the phytopathogenic fungus Fusarium culmorum. The most effective AgNPs (Ch. speciosa-AgNPs, Ch. cathayensis-AgNPs, and Ch. japonica-AgNPs) achieved a 1.42–1.63 times greater zone of inhibition of the F. culmorum colonies’ growth compared to the corresponding doses of the known chemical fungicide "Quadris". Micro preparations of the zones of incomplete growth inhibition presented changes in the mycelium morphology of F. culmorum due to the action of nanoparticles, such as deformation (curvature, expansion), and a decrease in the hyphae length and density compared to the control sample. Disc-diffusion assay showed notable species-specific antibacterial activity of AgNPs both against Gram-negative (Klebsiella pneumoniae) and Gram-positive (Staphylococcus aureus) strains. Summarizing, the results indicate the undeniable suitability of aqueous leaf extracts of the genus Chaenomeles species for the successful biosynthesis of silver nanoparticles with many useful properties, whose diverse applications require further research.

Fabrication of nickel aluminate based electrochemical sensor for dopamine detection

Nickel aluminate nanoparticles (NiAl2O4 NPs) spinel structure is synthesized via a simple solution combustion method using aqueous nickel nitrate, aluminum nitrate and citric acid. The crystal structure and microstructure of the prepared NiAl2O4 NPs are confirmed by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectrum, scanning and transmission electron microscopy (SEM/TEM). The characterized NiAl2O4 NPs are applied on a glassy carbon electrode (GCE) to design electrochemical sensor for the detection of dopamine (DA) using cyclic voltammograms (CV) and differential pulse anodic stripping voltammograms. The proposed electrochemical sensor exhibits excellent sensing activity with a low detection limit of 1.78 μM and applicable for a wide linear concentration range of 10 μM–140 μM. Further, the proposed electrode exhibits well resolved differential pulse voltammogram for the dopamine in presence of interfering uric acid and ascorbic acid.

A novel green reducing agent for the synthesis of chromium oxide nanoparticles (Cr2O3 NPs) based on saffron by-products: Characterization and antioxidant activity

The production of nanomaterials using safe, biological and environmentally friendly methods is attracting increasing attention. In the present study, aqueous extracts of Moroccan saffron (Crocus sativus L) by-products were used for the first time as a green stabilizer and reductant agent to synthesize chromium oxide nanoparticles (Cr2O3NPs). The aqueous extract of saffron by-products was analyzed for phytochemical screening, while the green synthesized Cr2O3NPs were analyzed using high-resolution scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The antioxidant activity of Cr2O3NPs, aqueous chromium nitrate solution (Cr (NO3)), and aqueous extract of saffron by-products have been also investigated using 1,1-Diphenyl-2-picrylhydrazyl (DPPH) method. The results showed that the aqueous extract of saffron by-products used for the synthesis of Cr2O3NPs appeared to be rich in phenolic (2.32 mg GA / g dry weight), flavonoid (2.28 mg RE / g dry weight), and anthocyanin compounds (33.67 mg Delphinidin / L extract). The XRD analysis confirmed that the Cr2O3NPs have a particle size of 31 nm with a hexagonal crystal structure. SEM micrographs of Cr2O3NPs showed a homogenous distribution and spherical shape, while the EDX spectrum confirmed that Cr2O3NPs contain significant amount of Chromium (61,90 %), and oxygen atoms (36,55 %). Moreover, the presence of absorption bands characteristic of the alcohol group (3451 cm−1) and the aromatic rings (1639 cm−1) in the infrared spectrum of Cr2O3NPs, indicates that the secondary metabolites of the saffron plant were successfully active in reducing chromium ions to Cr2O3NPs. Besides, the antioxidant activity results showed that the biosynthesized Cr2O3NPs exhibited strong inhibition percentages (63 %) compared to the aqueous extract of saffron by-products (74 %), and the aqueous solution of chromium nitrate (30 %) at 1,30 mg/mL. The study suggests that saffron by-products extract can be used as a natural reducing agent in the synthesis of Cr2O3NPs. Furthermore, the environmentally friendly synthesis process for Cr2O3NPs and their antioxidant effect make them suitable for use in various fields.

التخليق الحيوي لجسيمات الفضة النانوية باستخدام مستخلصات الشاي الأخضر

اصبح تركيب جسيمات الفضة النانوية بالطرق الخضراء بواسطة النباتات شائعًا بشكل متزايد بسبب ملاءمته للبيئة ، وتوفره ، وفعاليته وكلفته القليلة ، ويمكن التعامل معه بأمان ويمتلك تنوعًا واسعًا من المركبات الفعالة ، مثل مضادات الأكسدة و ومركبات مضادة للميكروبات. في الدراسة الحالية ، تم تصنيع جسيمات الفضة النانوية AgNPs باستخدام المستخلصات المائية والميثانولية لأوراق الشاي الاخضر التي اختزلت نترات الفضة, والتي تم توصيفها باستخدام العديد من التقنيات التحليلية مثل القياس الطيفي المرئي فوق البنفسجي (UV-Vis) ، والتحويل الطيفي بالأشعة تحت الحمراء (FTIR) ، والفحص المجهري الذري (AFM) ، وتشتت الأشعة السينية (XRD) وفحص جهد زيتا. أشارت الملاحظة البصرية إلى أن لون نترات الفضة المائية قد تحول بعد المعاملة بمستخلصات الأوراق وتأكد ذلك بواسطة أطياف UV-Vis. فضلا عن ذلك ، أظهر تحليل AFM أن الجسيمات كانت كروية الشكل ، مفردة أو في مجاميع بمتوسط ​​أحجام 108.3 و 84.76 نانومتر للمستخلصات المائية والميثانولية على التوالي. كذلك, أكدت تقنية XRD الطبيعة البلورية للجسيمات النانوية, وتم تقدير متوسط ​​الحجم وفقًا لمعادلة شيرير اذ بلغت 61.24 و 99.66 نانومتر للمستخلصات المائية والميثانولية (CANPs) على التوالي. بالإضافة إلى قيم زيتا المحتملة كانت-30.31 و -32.33 مللي فولت للمستخلصات المائية والميثانولية CANPs على التوالي.

Enhanced HONO Formation from Aqueous Nitrate Photochemistry in the Presence of Marine Relevant Organics: Impact of Marine-Dissolved Organic Matter (m-DOM) Concentration on HONO Yields and Potential Synergistic Effects of Compounds within m-DOM.

Nitrous acid (HONO) is a key molecule in the reactive nitrogen cycle. However, sources and sinks for HONO are not fully understood. Particulate nitrate photochemistry has been suggested to play a role in the formation of HONO in the marine boundary layer (MBL). Here we investigate the impact of marine relevant organic compounds on HONO formation from aqueous nitrate photochemistry. In particular, steady-state, gas-phase HONO yields were measured from irradiated nitrate solutions at low pH containing marine-dissolved organic matter (m-DOM). m-DOM induces a nonlinear increase in HONO yield across all concentrations compared to that for pure nitrate solutions, with rates of HONO formation increasing by up to 3-fold when m-DOM is present. Furthermore, to understand the potential synergistic effects that may occur within complex samples such as m-DOM, mixtures of chromophoric (light-absorbing) and aliphatic (non-light-absorbing) molecular proxies were utilized. In particular, mixtures of 4-benzoylbenzoic acid (4-BBA) and ethylene glycol (EG) in acidic aqueous solutions containing nitrate showed more HONO upon irradiation compared to solutions containing only one of the molecular proxies. This suggests that synergistic effects in the HONO formation can occur in complex organic samples. Atmospheric implications of the results presented here are discussed.

The effect of carbonized zeolitic imidazolate framework-67 (ZIF-67) support on the reactivity and selectivity of bimetal-catalytic aqueous NO3− reduction

A metallic catalyst, Cobalt N-doped Carbon (Co@NC), was obtained from Zeolitic-Imidazolate Framework-67 (ZIF-67) for efficient aqueous nitrate (NO3−) removal. This advanced catalyst indicated remarkable efficiency by generating valuable ammonium (NH3/NH4+) via an environmentally friendly production technique during the nitrate treatment. Among various metals (Cu, Pt, Pd, Sn, Ru, and Ni), 3.6%Pt–Co@NC exhibited an exceptional nitrate removal, demonstrating a complete removal of 60 mg/L NO3−-N (265 mg/L NO3−) in 30 min with the fastest removal kinetics (11.4 × 10−2 min−1) and 99.5% NH4+ selectivity. The synergistic effect of bimetallic Pt–Co@NC led to 100% aqueous NO3− removal, outperforming the reactivity by bare ZIF-67 (3.67%). The XPS analysis illustrated Co's promotor role for NO3− reduction to less oxidized nitrogen species and Pt's hydrogenation role for further reduction to NH4+. The durability test revealed a slight decrease in NO3− removal, which started from the third cycle (95%) and slowly proceeded to the sixth cycle (80.2%), while NH4+ selectivity exceeded 82% with no notable Co or Pt leaching throughout seven consecutive cycles. This research shed light on the significance of the impregnated Pt metal and Co exposed on the Co@NC surface for the catalytic nitrate treatment, leading to a sustainable approach for the effective removal of nitrate and economical NH4+ production.

Nitrate Uptake from Water Using Amine‐Functionalized Meso‐ and Macroporous Carbons

AbstractMeso‐ and macroporous carbon materials modified with protonated amino groups (−NH3+Cl−) for aqueous nitrate (NO3−) uptake were prepared by surface functionalization with aminopropylsilane. Although the silane coupling treatment decreased the specific surface area of the carbons, surface modification with the −NH3+Cl− group improved the NO3− uptake capacity of both meso‐ and macroporous carbons. The amount of NO3− adsorbed depends on the specific surface area of the adsorbent; an adsorbent with a larger specific surface area exhibits a larger uptake capacity. Enhanced NO3− adsorption onto the NH3+Cl−‐modified surface occurred through an ion‐exchange mechanism. Changes in the pH of the sample solutions before and after NO3− uptake revealed the competitive exchange of NO3− and OH−. NO3− uptake is inhibited by the coexistence of anions other than NO3− (excess Cl−, SO42−, CO32− and HCO3−) and/or OH− at high pH. In particular, the influence of excess Cl− reveals that NO3− uptake through ion exchange is not irreversible, and the adsorption capacity is determined based on the ion exchange equilibrium.

A unique choline nitrate-based organo-aqueous electrolyte enables carbon/carbon supercapacitor operation in a wide temperature window (-40°C to 60°C).

Some drawbacks of aqueous electrolytes, such as freezing at low temperatures and extensive evaporation at high temperatures, restrict their industrial viability. This article introduces a stabilized neutral aqueous choline nitrate electrolyte with a 10 vol.% methanol additive that improves the temperature stability of the electrolyte via enhanced hydrogen bonding with the choline cation and water and maintains the good state of health of the supercapacitor cells under extreme operating conditions. The symmetric carbon/carbon supercapacitor in 5mol/kg choline nitrate + 10 vol.% methanol (σ = 76ms/cm at 25°C) exhibits 103F/g at room temperature during galvanostatic charge/discharge up to 1.5V, which decreases to 78F/g at -40°C due to the suppressed Faradaic reactions occurring at the carbon electrode. However, under similar charge/discharge conditions, the capacitance increases to 112F/g when the supercapacitor operates at 60°C. This capacitance increase at high temperatures is due to the Faradaic reactions related to enhanced hydrogen adsorption and desorption. The most remarkable aspect of the proposed supercapacitor is its ability to maintain capacitance and power performance during high voltage floating at 1.5V at three tested temperatures (-40°C, 24°C, and 60°C).

Gibbsite- and kuzelite-based matrix for the preservation of radioactive aqueous sodium nitrate concentrates

Gibbsite- and kuzelite-based matrix for the preservation of radioactive aqueous sodium nitrate concentrates

The Chemistry of Spinel Ferrite Nanoparticle Nucleation, Crystallization, and Growth.

The nucleation, crystallization, and growth mechanisms of MnFe2O4, CoFe2O4, NiFe2O4, and ZnFe2O4 nanocrystallites prepared from coprecipitated transition metal (TM) hydroxide precursors treated at sub-, near-, and supercritical hydrothermal conditions have been studied by in situ X-ray total scattering (TS) with pair distribution function (PDF) analysis, and in situ synchrotron powder X-ray diffraction (PXRD) with Rietveld analysis. The in situ TS experiments were carried out on 0.6 M TM hydroxide precursors prepared from aqueous metal chloride solutions using 24.5% NH4OH as the precipitating base. The PDF analysis reveals equivalent nucleation processes for the four spinel ferrite compounds under the studied hydrothermal conditions, where the TMs form edge-sharing octahedrally coordinated hydroxide units (monomers/dimers and in some cases trimers) in the aqueous precursor, which upon hydrothermal treatment nucleate through linking by tetrahedrally coordinated TMs. The in situ PXRD experiments were carried out on 1.2 M TM hydroxide precursors prepared from aqueous metal nitrate solutions using 16 M NaOH as the precipitating base. The crystallization and growth of the nanocrystallites were found to progress via different processes depending on the specific TMs and synthesis temperatures. The PXRD data show that MnFe2O4 and CoFe2O4 nanocrystallites rapidly grow (typically <1 min) to equilibrium sizes of 20-25 nm and 10-12 nm, respectively, regardless of applied temperature in the 170-420 °C range, indicating limited possibility of targeted size control. However, varying the reaction time (0-30 min) and temperature (150-400 °C) allows different sizes to be obtained for NiFe2O4 (3-30 nm) and ZnFe2O4 (3-12 nm) nanocrystallites. The mechanisms controlling the crystallization and growth (nucleation, growth by diffusion, Ostwald ripening, etc.) were examined by qualitative analysis of the evolution in refined scale factor (proportional to extent of crystallization) and mean crystallite volume (proportional to extent of growth). Interestingly, lower kinetic barriers are observed for the formation of the mixed spinels (MnFe2O4 and CoFe2O4) compared to the inverse (NiFe2O4) and normal (ZnFe2O4) spinel structured compounds, suggesting that the energy barrier for formation may be lowered when the TMs have no site preference.

Indirect mineral carbonation of recycled concrete aggregate: Enhancing calcium extraction using a packed bed reactor

Mineral carbonation of industrial residues is gaining increasing interest, with the first pilot and industrial-scale applications being implemented. The process offers a low-risk, easily available solution for permanent carbon dioxide storage while concurrently valorising industrial wastes. This work investigates the indirect mineral carbonation of recycled concrete aggregate (RCA), in which calcium is first leached from the RCA into an aqueous ammonium nitrate (AN) solution, followed by carbonation to yield high-purity precipitated calcium carbonate. The study focuses on the first step, calcium dissolution, which traditionally takes place in a stirred batch reactor (SBR). However, SBRs often encounter solubility constraints, leading to low calcium extraction yields. In this investigation, we explore the application of a packed bed reactor (PBR) and demonstrate its superior performance, resulting in a calcium extraction enhancement of 27% to 55% relative to SBRs, across AN concentrations ranging from 0.25 to 2.0 mol/kg, at 25 °C and atmospheric pressure. The PBR’s superior performance can be attributed to the more compact design, enabling longer dissolution times, and to the continuous supply of fresh solvent, effectively reducing solubility limitations. The impact of key operating parameters (AN concentration, liquid flow rate and extraction time) are systemically assessed experimentally, accurately modelled using a shrinking-core model, and illustrated in process performance maps. Furthermore, this research highlights the significance of ammonium nitrate recovery from the wet solids after filtration to ensure the process’s environmental viability. The packed bed reactor (PBR) functions as an integrated filter, facilitating the straightforward recovery of 80% of the trapped ammonium nitrate solution through simple water flushing. In conclusion, the utilisation of PBRs in indirect mineral carbonation presents an innovative and efficient approach for enhancing calcium extraction while addressing environmental concerns through ammonium nitrate recovery. The applicability of PBRs extends beyond recycled concrete aggregates, and could also be successfully applied for other coarse industrial residues such as steel slags.

Selective Reduction of Aqueous Nitrate to Ammonium with an Electropolymerized Chromium Molecular Catalyst.

Nitrate (NO3-) is a common nitrogen-containing contaminant in agricultural, industrial, and low-level nuclear wastewater that causes significant environmental damage. In this work, we report a bioinspired Cr-based molecular catalyst incorporated into a redox polymer that selectively and efficiently reduces aqueous NO3- to ammonium (NH4+), a desirable value-added fertilizer component and industrial precursor, at rates of ∼0.36 mmol NH4+ mgcat-1 h-1 with >90% Faradaic efficiency for NH4+. The NO3- reduction reaction occurs through a cascade catalysis mechanism involving the stepwise reduction of NO3- to NH4+ via observed NO2- and NH2OH intermediates. To our knowledge, this is one of the first examples of a molecular catalyst, homogeneous or heterogenized, that is reported to reduce aqueous NO3- to NH4+ with rates and Faradaic efficiencies comparable to those of state-of-the-art solid-state electrocatalysts. This work highlights a promising and previously unexplored area of electrocatalyst research using polymer-catalyst composites containing complexes with oxophilic transition metal active sites for electrochemical nitrate remediation with nutrient recovery.

Isothermal compressibility, internal pressure studies of aqueous rare earth nitrate solutions at 298.15 K: An attempt to estimate ionic radii and understand inner– and outer–sphere exchange water structural interactions

In this communication, we report our analysis and results concerning the determination of ionic radii in aqueous solution phase for Lanthanum (La+3), Neodymium (Nd+3), Erbium (Er+3) and Ytterbium (Yb+3) ions in presence of nitrate (NO3-) anion at 298.15 K. The literature data for density, adiabatic compressibility, and specific heat capacity of solutions at constant pressure have been used to compute isothermal compressibility, internal pressure of solutions in limiting concentration range. The apparent molar isothermal compressibility of electrolytes and hydration numbers have been obtained. The electrostriction for rare earth cations and intrinsic volumes have been calculated using thermodynamic equations. The ionic radii of cations have been obtained using the ionic partial molar volume data of NO3- ions and the results are compared with those obtained for rare earth chlorides. The two series affect is also observed for ionic radii and internal pressure. The results have been explained on the basis of water structural effects due to electrostatic field and water dipole interaction between the inner– and outer–sphere water exchange reaction.

Cerium Nanophases from Cerium Ammonium Nitrate.

Ceria nanomaterials with facile CeIII/IV redox behavior are used in sensing, catalytic, and therapeutic applications, where inclusion of CeIII has been correlated with reactivity. Understanding assembly pathways of CeO2 nanoparticles (NC-CeO2) in water has been challenged by "blind" synthesis, including rapid assembly/precipitation promoted by heat or strong base. Here, we identify a layered phase denoted Ce-I with a proposed formula CeIV(OH)3(NO3)·xH2O (x ≈ 2.5), obtained by adding electrolytes to aqueous cerium ammonium nitrate (CAN) to force precipitation. Ce-I represents intermediate hydrolysis species between dissolved CAN and NC-CeO2, where CAN is a commonly used CeIV compound that exhibits unusual aqueous and organic solubility. Ce-I features Ce-(OH)2-Ce units, representing the first step of hydrolysis toward NC-CeO2 formation, challenging prior assertions about CeIV hydrolysis. Structure/composition of poorly crystalline Ce-I was corroborated by a pair distribution function, Ce-L3 XAS (X-ray absorption spectroscopy), compositional analysis, and 17O nuclear magnetic resonance spectroscopy. Formation of Ce-I and its transformation to NC-CeO2 is documented in solution by small-angle X-ray scattering (SAXS) and in the solid-state by transmission electron microscopy (TEM) and powder X-ray diffraction. Morphologies identified by TEM support form factor models for SAXS analysis, evidencing the incipient assembly of Ce-I. Finally, two morphologies of NC-CeO2 are identified. Sequentially, spherical NC-CeO2 particles coexist with Ce-I, and asymmetric NC-CeO2 with up to 35% CeIII forms at the expense of Ce-I, suggesting direct replacement.