Simultaneous determination of Hg(II) and Cu(II) in water samples using fluorescence quenching sensor of N-doped and N,K co-doped graphene quantum dots

The present study was aimed to use of N doped graphene quantum dots (N-GQDs) and N,K co-doped graphene quantum dots (N,K-GQDs) as a fluorescence quenching sensor to determine both mercury and copper in water sample, simultaneously using simple fluorescence protocol. Each of N-GQDs or N,K-GQDs was optimized separately with 1–5% (w/v) HNO₃ or KNO₃, respectively, and their quantum yields were determined and compared. It was found that N-GQDs, obtained from 3% (w/v) HNO₃ doped resulted higher fluorescence intensity at the maximum excitation and emission wavelengths of 370 and 460 nm, respectively, with higher quantum yield (QY = 83.42%) compared with that of undoped GQDs (QY = 16.35%). While N,K-GQDs obtained from 5%(w/v) KNO₃ gave somewhat different fluorescence spectrum, but still had the same maximum excitation and emission wavelengths with rather highest QY (94.07%). However, it is interesting that detection sensitivity expressed as slope of their calibration curve (y = 5.43x − 19.48; r² = 0.9971) of the N-GQDs is rather higher than that (y = 1.29x + 17.66; r² = 0.9977) of the N,K-GQDs for Hg²⁺ fluorescence quenching sensor, and the fluorescence intensity of N-GQDs had better selectively quenching effect only by both Hg²⁺ and Cu²⁺. Thus, their quenching effects were selected to develop the fluorescence turn-off sensor for trace level of both metal ions in real water samples. For method validation, the N-GQDs exhibited high sensitivity to detect both Hg²⁺ and Cu²⁺ with wide linear ranges of 20–100 μM and 100–500 μM, respectively. Limit of detection (LOD) and limit of quantitation (LOQ) were 0.42 μM & 1.41 μM for Hg²⁺ and 13.19 μM & 43.97 μM for Cu²⁺, respectively, with their precision expressed as an intra-day and an inter-day analysis of 6.98% & 11.35% for Hg²⁺ and 11.78% & 9.43% for Cu²⁺, respectively. Also the study of matrix analysis of the water samples (drinking water and tap water), was carried out using N-GQDs and N,K-GQDs resulted good percentage recoveries in comparison with those using undoped GQDs under the same optimum conditions.     

Fabrication of the polyethersulfone/functionalized mesoporous carbon nanocomposite nanofiltration membrane for dyes and heavy metal ions removal: Experimental and quantum mechanical simulation method

The presence of industrial pollutants, especially salts, heavy metals ions, and dyes in water and wastewater is considered a serious environmental issue. To eliminate these pollutants, a high-performing nanofiltration (NF) membrane was prepared by blending the functionalized mesoporous carbon CMK-5 (F-CMK-5) nanofiller. This membrane was synthesized by introducing the active groups of sulfonyl and amide to the surface of mesoporous carbon CMK-5 through covalent functionalization. Characterizations were conducted to study the membranes' physical properties and separation performance in terms of antifouling properties and rejection of salts, heavy metal ions, and dyes. The interactions between the active sites of the nanocomposite membrane and the studied solutes, including dyes and heavy metal ions in aqueous solutions, were studied by the density functional based tight binding method and structural optimization was carried out. Insertion of the F-CMK-5 nanofiller was eventuated in a remarkable increase in surface hydrophilicity, pure water flux, and antifouling properties. For all membranes, the lowest and the highest salt rejection was obtained for NaCl and Na₂SO₄, respectively, exhibiting the characteristics of NF membranes. Moreover, M_0.3 with 0.3 wt% nanofiller showed the highest rejection for heavy metal ions (Fe²⁺ = 99.9%, Zn²⁺ = 99.9%, Cu²⁺ = 99.7%, and Pb²⁺ = 99.2%) and dyes (RB5 = 99.21, DR16 = 98.87, and MB = 98.12%), as well as high separation performance for filtration of multipollutant solutions. The reusability and 144 h uninterrupted filtration experiments for M_0.3 confirmed the stability of the membrane. The findings suggest that the PES/F-CMK-5 nanocomposite NF membrane is a promising candidate for water and wastewater treatment.     

Rapid and sensitive spectrofluorimetric determination of enrofloxacin, levofloxacin and ofloxacin with 2,3,5,6-tetrachloro-p-benzoquinone

A highly sensitive spectrofluorimetric method was developed for the first time, for the analysis of three fluoroquinolones (FQ) antibacterials, namely enrofloxacin (ENR), levofloxacin (LEV) and ofloxacin (OFL) in pharmaceutical preparations through charge transfer (CT) complex formation with 2,3,5,6-tetrachloro-p-benzoquinone (chloranil,CLA). At the optimum reaction conditions, the FQ–CLA complexes showed excitation maxima ranging from 359 to 363 nm and emission maxima ranging from 442 to 488 nm.Rectilinear calibration graphs were obtained in the concentration range of 50–1000, 50–1000 and 25–500 ng mL⁻¹ for ENR, LEV and OFL, respectively.The detection limit was found to be 17 ng mL⁻¹ for ENR, 17 ng mL⁻¹ for LEV, 8 ng mL⁻¹ for OFL, respectively. Excipients used as additive in commercial formulations did not interfere in the analysis. The method was validated according to the ICH guidelines with respect to specificity, linearity, accuracy, precision and robustness. The proposed method was successfully applied to the analysis of pharmaceutical preparations. The results obtained were in good agreement with those obtained using the official method; no significant difference in the accuracy and precision as revealed by the accepted values of t- and F-tests, respectively.     

Cathodic stripping voltammetry of pipemidic acid and ofloxacin in pharmaceutical dosages and human urine

Sensitive cathodic stripping voltammetric methods have been developed for two quinolone antibacterial drugs, pipemidic acid (PIP) and ofloxacin (OFL) using hanging mercury drop electrode as working electrode vs. Ag/AgCl reference electrode. The methods were developed for the determination of drugs individually as well as simultaneously. 0.1 M and 0.01 M hydrochloric acid was used as medium for PIP and OFL, respectively, 0.1 M potassium chloride was used as base electrolyte. Reduction waves were observed for PIP within ?700 mV to ?800 mV and for OFL within ?1100 mV to ?1200 mV. Linear calibration ranges for PIP and OFL were observed within 10–100 μg ml^?1 with detection limits of 50 ng ml^?1 and 1 μg ml^?1, respectively. Relative standard deviations (RSD) for the analysis of 10 gµg ml^?1 of PIP and OFL (n = 6) were 0.5% and 1.4%, respectively. The presence of glucose, lactose, sorbitol, gum arabic, starch, magnesium stearate, methylparaben and propylparaben did not affect the determinations of both PIP and OFL. The methods were used for the analysis of pharmaceutical preparations and the results indicated relative deviation of 0.5–5.5% from labeled values with RSD within 0.49–2.5%. PIP and OFL could also be determined simultaneously, and were determined from spiked human urine.     

Synthesis,characterization and the electrocatalytic application of prussian blue/titanate nanotubes nanocomposite

A novel kind of nanocomposite, titanate nanotubes (TNTs) decorated by electroactive Prussian blue (PB), was fabricated by a simple chemical method. The as-prepared nanocomposite was characterized by XRD, XPS, TEM, FT-IR and Cyclic voltammetry (CV). Experimental results revealed that PB was adsorbed on the surface of TNTs, and the adsorption capacity of TNTs was stronger than that of anatase-type TiO₂ powder (TNP). The PB-TNTs nanocomposite was modified onto a glassy carbon electrode and the electrode showed excellent electroactivity. The modified electrode also exhibited outstanding electrocatalytic activity towards the reduction of hydrogen peroxide and can serve as an amperometric sensor for H₂O₂ detection. The sensor fabricated by casting Nafion (NF) above the PB-TNTs composite film (NF/PB-TNTs/GCE) showed two linear ranges of 2 × 10^?5–5 × 10^?4 M and 2 × 10^?3–7 × 10^?3 M, with a detection limit of 1 × 10^?6 M. Furthermore, PB-TNTs modified electrode with Nafion (NF/PB-TNTs/GCE) showed wider linear range and better stability compared with PB-TNTs modified electrode without Nafion (PB-TNTs/GCE) and PB modified electrode with Nafion (NF/PB/GCE).     

A comparative study on the monovalent and divalent cation separation of polymeric films and membranes from salt solutions under diffusion-dialysis

This study deals with selective separation of mono- and divalent cations from aqueous salt solutions using polymeric films based on polyethylene (PE) and polyamide6 (PA6), and two different commercial nanofiltration (NF) membranes. The diffusion rates (D) of ions (Na⁺ and Ca²⁺), separation factors (α) and ion rejections (R) of the films and NF membranes are examined comparatively as well as their surface morphology and hydrophilicity. It is observed that the diffusion rates of Na⁺ are in the range of 0.7–1.8 × 10⁻⁸cm² .s⁻¹ in the decreasing order of PE > NF90 > NF270 > PA6 while Ca²⁺ shows diffusion rates of 7.4–18.4 × 10⁻⁸ cm² .s⁻¹ in the increasing order of NF270 > NF90 ≈ PA6 > PE. Rejection values of the polymeric films and NF membranes against to Na⁺ and Ca²⁺ vary between 90% and 99.6%.The highest α(Ca²⁺/Na⁺) is found to be 20 for PA6 film. D, α, and R value of both polymeric films and NF membranes are strongly affected by the existence of osmosis during diffusion-dialysis and the sizes of hydrated sodiu and calcium ions. In conclusion, the film based on PA6 may be a good alternative for selective separation of mono- an divalent cations.     

Treatment of sugar processing industry wastewater using copper electrode by electrocoagulation: Performance and economic study

This paper demonstrates the use of copper electrode for the treatment of sugar processing industry wastewater (SPIW) in terms of chemical oxygen demand (COD) by applying electrocoagulation (EC) method. EC process was carried out in batch mode with electrode effective area of 0.0112 m², supplied current intensity (CI) of 44.64 A/m² - 223.21 A/m², electrode gap (EG) of 0.5–2.5 cm, electrolyte (NaCl) dose (ED) of 0.5–2.5 g/L to treat SPIW with initial chemical oxygen demand (COD) of 6000 mg/L. The maximum COD removal 73% of SPIW is achieved at optimized condition of SPIW pH: 7, CI: 89.28 A/m², EG: 1.5 cm & ED: 1.5 g/L. Sludge and scum generated during EC process were characterized by FTIR, TGA/DTA/DTG, proximate & ultimate analysis to find its applicability and their disposal. Additionally, economic study of EC treatment process at optimum condition suggest treatment cost was 11.2 US$/m³ and it indicate economic results as comparison to other available treatment processes.     

Analysis of ofloxacin in plasma samples by high-performance liquid chromatography

Summary A sensitive HPLC method has been developed for determination of ofloxacin (OFL) in biological fluids. Sample preparation was performed by adding phosphate buffer (pH 7.4, 0.1m) then extraction with trichloromethane. OFL and the internal standard, sarafloxacin (SAR), were separated on a reversed-phase column with aqueous phosphate solution-acetonitrile, 80∶20, as mobile phase. The fluorescence of the column effluent was monitored at λ_ex 338 and λ_em 425 nm. The retention times were 2.66 and 4.24 min for OFL and SAR, respectively, and the detection and quantitation limits were 8 and 15 ng mL⁻¹, respectively. Plots of response against ofloxacin concentration were linear in the range 8 to 2000 ng mL⁻¹. Recovery was 92.9% for OFL.     

Detection of noncovalent FKBP-FK506 and FKBP-Rapamycin complexes by capillary electrophoresis-mass spectrometry and capillary electrophoresis-tandem mass spectrometry

The well known biospecific noncovalent receptor-ligand association complexes between the immunophilin FKBP and the immunosuppressive drugs FK506 and Rapamycin (RM) were investigated by on-line capillary electrophoresis-mass spectrometry (CE-MS) under selected ion monitoring (SIM) conditions and by CE-MS with tandem mass spectrometry (CE-MS/MS) under selected reaction monitoring (SRM) conditions. Solutions of hFKBP (33.3 µM) were dissolved in 50 mM ammonium acetate at pH 7.5. Samples that contained 100 µM of FK506 or RM also were prepared under the same solution conditions. By using these aqueous pH neutral conditions, samples were analyzed by SIM CE-MS and SRM CE-MS and the target complexes were separated by CE with mass spectrometer detection of the individual complexes between FKBP and FK506 [hFKBP + FK506 + 7HJ⁷⁺ as well as FKBP and RM [hFKBP + RM + 7HJ⁷⁺. In an experiment where a mixture of FK506 and RM was analyzed in the presence of FKBP, a nine-to-one ratio of ion current abundances between the RM and FK506 complexes was observed as reported in the literature from other studies. These results suggest that CE-MS and CE-MS/MS may be yet another analytical method for studying noncovalent interactions of biologically important macromolecules under physiological conditions.     

Selective and efficient liquid membrane transport of gold as gold cyanide using an anion carrier

The facilitated transport of Au(III) from cyanide solutions through a bulk liquid membrane is reported. The organic phase consisted of a chloroform solution containing Victoria blue dye as the Au(CN)⁻₄ carrier. The effects of pH of source phase, potassium cyanide concentration in source phase, Victoria blue concentration in the organic phase and sodium hydroxide in the receiving phase on the efficiency of transport process were examined. Under optimum conditions the extent of Au(CN)⁻₄ transport across the liquid membrane was about 97% after 180 min. The carrier can selectively and efficiently transport Au(CN)⁻₄ ion from the aqueous solutions containing other cations such as alkali and alkaline earth, Zn²⁺, Pb²⁺, Cu²⁺, Cd²⁺, Hg²⁺, Ag⁺, Co²⁺, Fe²⁺, Pt²⁺, Pd²⁺ and Ni²⁺.     

Cysteine functionalized poly(hydroxyethyl methacrylate) monolith for heavy metal removal

The aim of this study was to investigate the performance of monoliths composed of hydroxyethyl methacrylate (HEMA) to which N-methacryloyl-(L)-cysteine methyl ester (MAC) was polymerized for removal of heavy metal ions. Poly(HEMA-MAC) monolith was produced by bulk polymerization. Poly(HEMA-MAC) monolith was characterized by FTIR and scanning electron microscopy (SEM). The poly(HEMA-MAC) monolith with a swelling ratio of 89%, and containing 69.4 μmol MAC/g were used in the adsorption studies. Adsorption capacity of the monolith for the metal ions, i.e., Cu²⁺, Cd²⁺, Zn²⁺, Hg²⁺, and Pb²⁺ were investigated in aqueous media containing different amounts of the ions (10–750 mg/L) and at different pH values (3.0–7.0). The maximum adsorption capacities of the poly(HEMA-MAC) monolith were 68.2 mg/g for Zn²⁺, 129.2 mg/g for Cu²⁺, 245.8 mg/g for Pb²⁺, 270.2 mg/g for Hg²⁺, and 284.0 mg/g for Cd²⁺. pH significantly affected the adsorption capacity of MAC incorporated monolith. The competitive adsorption capacities were 587 μmol/g for Zn²⁺, 1646 μmol/g for Cu²⁺, 687 μmol/g for Pb²⁺, 929 μmol/g for Hg²⁺, and 1993 μmol/g for Cd²⁺. The chelating monolith exhibited the following metal ion affinity sequence on molar basis: Cd²⁺ > Cu²⁺ > Hg²⁺ > Pb²⁺ > Zn²⁺. The formation constants of MAC–metal ion complexes have been investigated applying the method of Ruzic. The calculated values of stability constants were 5.28 × 10⁴ L/mol for Cd²⁺, 4.16 × 10⁴ L/mol for Cu²⁺, 2.27 × 10⁴ L/mol for Hg²⁺, 1.98 × 10⁴ L/mol for Pb²⁺, and 1.25 × 10⁴ L/mol for Zn²⁺. Stability constants were increased with increasing binding affinity. The chelating monoliths can be easily regenerated by 0.1 M HNO₃ with higher effectiveness. These features make poly(HEMA-MAC) monolith a potential adsorbent for heavy metal removal.     

Pharmacophore modeling, 3D-QSAR,docking, and molecular dynamics simulation on topoisomerase IV inhibitors of wild type Staphylococcus aureus

Staphylococcus aureus is a gram-positive bacterium. It is a foremost cause of skin and respiratory infections, endocarditis, osteomyelitis, Ritter’s disease, and bacteraemia. Topoisomerase enzyme is involved in preventing or correcting topological problems of overwinding or underwinding occurring in DNA before replication process. An exhaustive molecular modeling studies that includes pharmacophore modeling, ligand-based three-dimensional quantitative structure-activity relationship (3D-QSAR), molecular docking, molecular dynamics simulation, and ADME calculations were performed on isothiazoloquinolones derivatives which are reported as effective inhibitors against topoisomerase IV of wild type S. aureus. In pharmacophore modeling by using pharmacophore alignment and scoring engine (PHASE) a five-point model (AHHRR.3) was generated with existing compounds having statistical significant as correlation coefficient (R ² = 0.954), cross-validation coefficient (Q ² = 0.650), and F value of 130.5. Ligand-based 3D-QSAR study was applied using comparative molecular field analysis (CoMFA) with Q ² = 0.616, R ² = 0.989, and comparative molecular similarity indices analysis (CoMSIA) with Q ² = 0.510, R ² = 0.995. The predictive ability of this model was determined using a test set of molecules that gave acceptable predictive correlation (R ² Pred) values 0.55 and 0.56 for CoMFA and CoMSIA, respectively. Docking and molecular dynamic simulations were employed to position the inhibitors into protein active site to find out the most probable binding mode and most reliable conformations. Developed pharmacophore models and docking methods provide guidance to design enhanced activity molecules.

     

Flower-like NiCo2S4/NiFeP/NF composite material as an effective electrocatalyst with high overall water splitting performance

Rational design and building of high efficiency, secure and inexpensive electrocatalyst is a pressing demand and performance to promote sustainable improvement of hydrogen energy. The bifunctional electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution response (HER) with high catalytic performance and steadiness in the equal electrolyte are extra treasured and meaningful. Herein, a unique three-dimensional (3D) structure electrocatalyst for NiCo₂S₄ growing on the flower-like NiFeP was designed and synthesized in this study. The results show that the flower-like NiCo₂S₄/NiFeP/NF composite electrocatalyst has large specific surface area, appropriate electrical conductivity, and greater lively websites uncovered in the three-dimensional structure, and affords extraordinary electrocatalytic overall performance for the ordinary water splitting. In alkaline solution, the OER and HER overpotentials of NiCo₂S₄/NiFeP/NF only need 293 mV and 205 mV overpotential to provide the current densities of 100 mA/cm² and 50 mA/cm², respectively. This high electrocatalytic activity exceeds the catalytic activity of most nickel-iron based electrocatalysts for OER and HER process. Accordingly, the optimized NiCo₂S₄/NiFeP/NF sample has higher stability (24 h) at 1.560 and 10 mA/cm², which extensively speeds up the overall water splitting process. In view of the above performance, this work offers a fine approach for the further improvement of low fee and excessive effectivity electrocatalyst.     

Stability constants of some metal cation complexes of tetraphenyl p - tert -butylcalix[4]arene tetraketone in nitrobenzene saturated with water

Abstract  

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium \textM^{2 +} ( \textaq ) + 1 ·\textSr^{2 +} ( \textnb ) \rightleftarrows 1 ·\textM^{2 +} ( \textnb ) + \textSr^{2 +} ( \textaq ) {\text{M}}^{2 + } \left( {\text{aq}} \right) + {\mathbf{1}} \cdot {\text{Sr}}^{2 + } \left( {\text{nb}} \right) \rightleftarrows {\mathbf{1}} \cdot {\text{M}}^{2 + } \left( {\text{nb}} \right) + {\text{Sr}}^{2 + } \left( {\text{aq}} \right) taking place in the two-phase water–nitrobenzene system (M²⁺ = Ca²⁺, Ba²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, UO₂ ²⁺, Mn²⁺, Co²⁺, Ni²⁺; 1 = tetraphenyl p-tert-butylcalix[4]arene tetraketone; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the 1 · M²⁺ complexes in water-saturated nitrobenzene were calculated; they were found to increase in the cation order Ba²⁺, Mn²⁺ < Co²⁺ < Cu²⁺, Ni²⁺ < Zn²⁺, Cd²⁺, UO₂ ²⁺ < Ca²⁺ < Pb²⁺.     

Individual extraction constants of some divalent metal cations in the two-phase water-phenyltrifluoromethyl sulfone system

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium \textM ²⁺ ( \textaq ) + \textSr ²⁺ ( \textorg ) ? \textM ²⁺ ( \textorg ) + \text Sr ²⁺ ( \textaq ) {\text{M}}^{ 2+ } \left( {\text{aq}} \right) + {\text{Sr}}^{ 2+ } \left( {\text{org}} \right) \Leftrightarrow {\text{M}}^{ 2+ } \left( {\text{org}} \right) + {\text{ Sr}}^{ 2+ } \left( {\text{aq}} \right) taking place in the two-phase water–phenyltrifluoromethyl sulfone (abbrev. FS 13) system (M²⁺ = Mg²⁺, Ca²⁺, Ba²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, \textUO₂^{2 +} {\text{UO}}_{2}^{2 + } , Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺; aq = aqueous phase, org = FS 13 phase) were evaluated. Furthermore, the individual extraction constants of the M²⁺ cations in this two-phase system were calculated; they were found to increase in the series of Mg²⁺, \textUO₂^{2 +} {\text{UO}}_{2}^{2 + }  < Ca²⁺, Co²⁺ < Cd²⁺, Ni²⁺ < Zn²⁺ < Cu²⁺, Mn²⁺, Fe²⁺ < Pb²⁺ < Ba²⁺.     

Solvent extraction of some divalent metal cations into nitrobenzene by using a synergistic mixture of strontium dicarbollylcobaltate and nonactin

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M²⁺(aq) + 1 · Sr²⁺(nb) ⇔ 1 · M²⁺(nb) + Sr²⁺(aq) taking place in the two-phase water–nitrobenzene system (M²⁺ = Mg²⁺, Ca²⁺, Ba²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Mn²⁺, Ni²⁺; 1 = nonactin; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Moreover, the stability constants of the 1 · M²⁺ complexes in nitrobenzene saturated with water were calculated; they were found to increase in the following order: Mg²⁺, Mn²⁺ < Ba²⁺, Cu²⁺, Zn²⁺, Ni²⁺ < Sr²⁺ < Ca²⁺ < Pb²⁺.     

Stability constants of some metal cation complexes of tetraphenyl <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">tert</Emphasis>-butylcalix[4]arene tetraketone in nitrobenzene saturated with water

Abstract  From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium taking place in the two-phase water–nitrobenzene system (M²⁺ = Ca²⁺, Ba²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, UO₂ ²⁺, Mn²⁺, Co²⁺, Ni²⁺; 1 = tetraphenyl p-tert-butylcalix[4]arene tetraketone; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the 1 · M²⁺ complexes in water-saturated nitrobenzene were calculated; they were found to increase in the cation order Ba²⁺, Mn²⁺ < Co²⁺ < Cu²⁺, Ni²⁺ < Zn²⁺, Cd²⁺, UO₂ ²⁺ < Ca²⁺ < Pb²⁺. Graphical abstract        

Synthesis of maghemite nano-particles and its application as radionuclidic adsorbant to purify <Superscript>109</Superscript>Cd radionuclide

Maghemite nano-particles were synthesized by a solid-state chemical reaction for its highly selective use as, cyclotron-produced, ¹⁰⁹Cd (462.9 days) purification method of choice. ¹⁰⁹Cd radiochemical separation starts with Ag activities precipitated with HCl 0.0015 M followed by, on a second step, ¹⁰⁹Cd separation from Cu carrier and ⁶⁵Zn (243.8 days) using Ca (NO₃)₂ 0.01 M. Experimental parameters such, pH and sorbent concentration, on ¹⁰⁹Cd extraction efficiency were investigated. Phase morphology, nanostructure and size of nano-particles were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). A 10–20 nm average grain size was derived from XRD line broadening and SEM data. Heat treatment on Fe³⁺:Fe²⁺ ratios equal to 2:1, produced powders, resulting in tetragonal (maghemite) structure at 300 °C and rhombohedra (hematite) at 600 °C. ¹⁰⁹Cd chemical and radionuclidic purity were determined by ICP-AES and HPGe detector gamma-ray spectrometry. The overall recovery and radionuclide purity were 80.0% from obtained 129.63 kBq/C MeV (70 kBq/μAh) initial activity and 91.4%, respectively.     

Determination of thermodynamic properties of YRhO3(s) by solid-state electrochemical cell and differential scanning calorimeter

The standard molar Gibbs free energy of formation of YRhO₃(s) has been determined using a solid-state electrochemical cell wherein calcia-stabilized zirconia was used as an electrolyte. The cell can be represented by: ( - )\textPt - Rh/{ \textY₂\textO_\text3( \texts ) + \textYRh\textO₃( \texts ) + \textRh( \texts ) }//\textCSZ//\textO₂( p( \textO₂ ) = 21.21  \textkPa )/\textPt - Rh( + ) \left( - \right){\text{Pt - Rh/}}\left\{ {{{\text{Y}}_2}{{\text{O}}_{\text{3}}}\left( {\text{s}} \right) + {\text{YRh}}{{\text{O}}_3}\left( {\text{s}} \right) + {\text{Rh}}\left( {\text{s}} \right)} \right\}//{\text{CSZ//}}{{\text{O}}_2}\left( {p\left( {{{\text{O}}_2}} \right) = 21.21\;{\text{kPa}}} \right)/{\text{Pt - Rh}}\left( + \right) . The electromotive force was measured in the temperature range from 920.0 to 1,197.3 K. The standard molar Gibbs energy of the formation of YRhO₃(s) from elements in their standard state using this electrochemical cell has been calculated and can be represented by: D_\textfG^\texto{ \textYRh\textO₃( \texts ) }/\textkJ  \textmo\textl ^{- 1}( ±1.61 ) = - 1,147.4 + 0.2815  T  ( \textK ) {\Delta_{\text{f}}}{G^{\text{o}}}\left\{ {{\text{YRh}}{{\text{O}}_3}\left( {\text{s}} \right)} \right\}/{\text{kJ}}\;{\text{mo}}{{\text{l}}^{ - 1}}\left( {\pm 1.61} \right) = - 1,147.4 + 0.2815\;T\;\left( {\text{K}} \right) . Standard molar heat capacity C^o_p,m C^{o}_{{p,m}} (T) of YRhO₃(s) was measured using a heat flux-type differential scanning calorimeter in two different temperature ranges from 127 to 299 K and 305 to 646 K. The heat capacity in the higher temperature range was fitted into a polynomial expression and can be represented by: $ {*{20}{c}} {\mathop C\nolimits_{p,m}^{\text{o}} \left( {{\text{YRh}}{{\text{O}}_3},{\text{s,}}T} \right)\left( {{\text{J}}\;{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}} \right)} & { = 109.838 + 23.318 \times {{10}^{ - 3}}T\left( {\text{K}} \right)} & { - 12.5964 \times {{10}^5}/{T^2}\left( {\text{K}} \right).} \\ {} & {\left( {305 \leqslant T\left( {\text{K}} \right) \leqslant 646} \right)} & {} \\ $ \begin{array}{*{20}{c}} {\mathop C\nolimits_{p,m}^{\text{o}} \left( {{\text{YRh}}{{\text{O}}_3},{\text{s,}}T} \right)\left( {{\text{J}}\;{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}} \right)} & { = 109.838 + 23.318 \times {{10}^{ - 3}}T\left( {\text{K}} \right)} & { - 12.5964 \times {{10}^5}/{T^2}\left( {\text{K}} \right).} \\ {} & {\left( {305 \leqslant T\left( {\text{K}} \right) \leqslant 646} \right)} & {} \\ \end{array} The heat capacity of YRhO₃(s) was used along with the data obtained from the electrochemical cell to calculate the standard enthalpy and entropy of formation of the compound at 298.15 K.     

Mass-transfer in hollow-fiber modules for extraction and back-extraction of copper(II) with LIX64N carriers

The extraction of Cu²⁺ ions from sulfate solutions across a hollow-fiber membrane containing LIX64N carriers dissolved in kerosene has been studied, in which Cu(II) was then back-extracted to a stripping-phase containing HCl. Experiments were conducted as a function of the initial feed concentration of Cu²⁺ (1–10 mol/m³), feed pH (2–6), the carrier concentration (0.1–0.4 mol/dm³), and stripping acidity (0.4–4 mol/dm³). A mass-transfer model was developed to predict the extent of Cu²⁺ extraction from aqueous feed in hollow-fiber contactors. The calculated time profiles of Cu²⁺ concentrations were in reasonable agreement with the experimental data (average standard deviation 9% in both extraction and back-extraction modules). The rate-controlling step(s) of such dispersion-free extraction processes were identified. It was shown that the extraction was governed by combined interfacial reaction and aqueous diffusion under the ranges studied, whereas the back-extraction was limited by combined membrane diffusion and aqueous diffusion.