Determination of ultratrace levels of lead (II) in water samples using a modified carbon paste electrode based on a new podand

A new podand of 1,1′-thiobis(naphthalene-2,1-diyl)bis(2-aminobenzoate) (TNBA) was synthesized and used as a suitable carrier for construction of Pb²⁺ modified carbon paste electrode (CPE). The effects of various plasticizers; 2-nitrophenyloctylether (o-NPOE), dioctyl pththalate (DOP), dibutyl phthalate (DBP) and paraffin oil were studied. The best performance was obtained with a matrix composition of CPE with a DOP/graphite powder/TNBA weight percent ratio of 35/60.5/4.5. The sensor exhibits significantly enhanced selectivity toward Pb²⁺ ion over the concentration range 8.0 × 10^? 8 to 1.0 × 10^? 2 mol L^? 1 with a lower detection limit of 5.0 × 10^? 8 mol L^? 1 and a Nernstian slope of 29.0 ± 0.2 mV decade^? 1 of lead activity. It has a fast response time of 8 s with a working pH range from 3.5 to 7. The interaction between TNBA and Pb²⁺ was studied spectrophotometrically and it exhibits that the stoichiometry of the complex is 1:1 in acetonitrile solution. Finally, the electrode was satisfactorily used as an indicator electrode in complexometric titration of Pb²⁺ with EDTA and in direct determination of lead in various water samples.     

La-doped ZnO nanoparticles: Simple solution-combusting preparation and applications in the wastewater treatment

La-doped ZnO nanoparticles have been successfully synthesized by a simple solution combustion method via employing a mixture of ethanol and ethyleneglycol (v/v = 60/40) as the solvent. Zinc acetate and oxygen gas in the atmosphere were used as zinc and oxygen sources, and La(NO₃)₃ as the doping reagent. The as-obtained product was characterized by means of powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectrometry and X-ray photoelectron spectroscopy. Experiments showed that La-doped ZnO nanoparticles exhibited the higher capacities for the removal of Pb²⁺ and Cu²⁺ ions in water resource than undoped ZnO nanoparticles.     

Poly(hydroxyethyl methacrylate) nanobeads containing imidazole groups for removal of Cu(II) ions

Poly(hydroxyethyl methacrylate) (PHEMA) nanobeads with an average size of 300 nm in diameter and with a polydispersity index of 1.156 were produced by a surfactant free emulsion polymerization. Specific surface area of the PHEMA nanobeads was found to be 996 m²/g. Imidazole containing 3-(2-imidazoline-1-yl)propyl(triethoxysilane) (IMEO) was used as a metal-chelating ligand. IMEO was covalently attached to the nanobeads. PHEMA-IMEO nanobeads were used for the removal of copper(II) ions from aqueous solutions. To evaluate the degree of IMEO loading, the PHEMA nanobeads were subjected to Si analysis by using flame atomizer atomic absorption spectrometer and it was estimated as 973 µmol IMEO/g of polymer. The PHEMA nanobeads were characterized by transmission electron microscopy and fourier transform infrared spectroscopy. Adsorption equilibrium was achieved in about 8 min. The adsorption of Cu²⁺ ions onto the PHEMA nanobeads was negligible (0.2 mg/g). The IMEO attachment into the PHEMA nanobeads significantly increased the Cu²⁺ adsorption capacity (58 mg/g). Adsorption capacity of the PHEMA-IMEO nanobeads increased significantly with increasing concentration. The adsorption of Cu²⁺ ions increased with increasing pH and reached a plateau value at around pH 5.0. Competitive heavy metal adsorption from aqueous solutions containing Cu⁺, Cd²⁺, Pb²⁺ and Hg²⁺ was also investigated. The adsorption capacities are 61.4 mg/g (966.9 µmol/g) for Cu²⁺; 180.5 mg/g (899.8 µmol/g) for Hg²⁺; 34.9 mg/g (310.5 µmol/g) for Cd²⁺ and 14.3 mg/g (69 µmol/g) for Pb²⁺. The affinity order in molar basis is observed as Cu²⁺ > Hg²⁺ > Cd²⁺ > Pb²⁺. These results may be considered as an indication of higher specificity of the PHEMA-IMEO nanobeads for the Cu²⁺ comparing to other ions. Consecutive adsorption and elution operations showed the feasibility of repeated use for PHEMA-IMEO nanobeads.     

Characterization of an azo-calix[4]arene-based optical sensor for Europium (III) ions

Selective and sensitive optical sensor membranes (optodes) were elaborated to detect cations in aqueous solutions. The sensing films are based on chromogenic calix[4]arene derivatives. The optode membranes were studied using UV/Vis absorption spectroscopy measurements. The sensitivity of the optode has been tested for Pb^2 +, Cd^2 +, Mg^2 + and Eu^3 + ions at pH 6.8. The results showed a good selectivity response towards Eu^3 +. Low selectivity coefficients were observed for Cd^2 + and Mg^2 + where Pb^2 + can be considered as interfering ions. The characteristics of this optode such as response time, regeneration, reproducibility and lifetime are discussed.     

Hydrothermal synthesis of nitrogen-containing carbon nanodots as the high-efficient sensor for copper(II) ions

Preparing high photoluminescent carbon nanodots (CNDs) by facile and low-cost processes have received considerable research interest. In this paper, high photoluminescent nitrogen-containing CNDs have been synthesized by one-step hydrothermal treatment of the pipe tobacco. The dispersion of these CNDs shows a strong blue luminescent emission with a max peak at 450 nm when it is excited at 369 nm. The as-made CNDs can sensitively and selectively detect Cu²⁺ ions compared with Ca²⁺, Mn²⁺, Zn²⁺, Cd²⁺, Pb²⁺ ions, which offers a novel sensing platform for the detection of Cu²⁺ ions.     

Modified carbon paste electrodes for Cu(II) determination

A new Cu²⁺ carbon paste electrode (CPE) using 2,2′-(1E,1′E)-1,1′-(2,2′-azanediylbis (ethane-2,1-diyl)bis(azan-1-yl-1-ylidene))bis(ethan-1-yl-1-ylidene)diphenol (ADEZEDP) has been prepared. The influence of variables including sodium tetraphenylborate (NaTPB), ionophore, and amount of multiwalled carbon nanotubes (MWCNT), CdO nanowires, CdS nanoparticles and palladium nanoparticles loaded on ADEZEDP and Nujol on the electrodes response were studied and optimized. At optimum values of all variables, for each nanomaterial the electrode response was linear in concentration range of 1.0 × 10^? 8 to 1.0 × 10^? 1 mol L^? 1 for ADEZEDP with Nernstian slope. The good performance of electrode viz. Wide applicable pH range (2.0–5.0), fast response time (≈ 6 s), and adequate life time (3 months) indicate the utility of the proposed electrodes for evaluation of Cu²⁺ ion content in various situations. Finally, these electrodes have been successfully applied for the determination of Cu²⁺ ions content in various real samples. The selectivity of proposed electrode was evaluated by separation solution method and fixed interference method.     

Adsorption intrinsic kinetics and isotherms of lead ions on steel slag

Batch experiments were carried out to investigate the kinetics of adsorption of lead ions by steel slag on the basis of the external diffusion, intra-particle diffusion and adsorption reaction model (pseudo-first-order, pseudo-second-order). The results showed that the controlling step for the adsorption kinetics changed with the varying experimental parameters. When the particle size of steel slag was larger than 120 mesh, intra-particle diffusion of Pb²⁺ was the controlling step, and when the initial concentration of Pb²⁺ was less than 150 mg L^?1 or the shaking rate was lower than 150 rpm, external diffusion of Pb²⁺ was promoted. Contrary to the former experimental conditions the adsorption reaction was the controlling step, and the adsorption followed second-order kinetics, with an adsorption rate constant of 13.26 g mg^?1 min^?1. The adsorption isotherm of Pb²⁺ with steel slag followed the Langmuir model, with a correlation coefficient of 0.99.     

Bioactivity of calcium phosphate coatings prepared by electrodeposition in a modified simulated body fluid

The purpose of this study was to investigate bioactivity of calcium phosphate coatings prepared by electrodeposition in a modified simulated body fluid (SBF). Calcium phosphates were electrodeposited on commercially pure titanium substrates in the modified SBF at 60 °C for 1 h maintaining the cathodic potentials of − 1.5 V, − 2 V, and − 2.5 V (vs. SCE). Subsequently, the calcium phosphate coatings were transformed into apatites during immersion in the SBF at 36.5 °C for 5 days. The apatites consisted of needle-shaped crystallites distributed irregularly with different grain sizes. As the coatings were electrodeposited at higher cathodic potential, the crystallite of the apatites got denser and the grain sizes of the apatites became bigger during subsequent immersion in the SBF. However, as the coatings were electrodeposited at higher cathodic potential, the coatings were transformed into apatites with lower crystallinity and the Ca/P atomic ratio of the apatites got higher than 1.67, that of stoichiometric hydroxyapatite, after subsequent immersion in the SBF. In addition, CO₃²⁻ ions contained in the modified SBF were incorporated in the calcium phosphate coating during electrodeposition and had an influence on transforming the calcium phosphate into bonelike apatite during subsequent immersion in the SBF showing that CO₃²⁻ incorporated in the apatites disturbed crystallization of the apatites. These results revealed that the coating electrodeposited at − 2.0 V (vs. SCE) in the modified SBF containing CO₃²⁻ ions was the most bioactive showing transformation into carbonate apatite similar to bone apatite.     

Microwave-polyol controlled synthesis and magnetic properties of monodisperse CoxNi1−xFe2O4/MWCNT nanocomposites

Monodisperse Co_xNi_1−xFe₂O₄ nanoparticles (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1) with controllable composition attached on the multi-walled carbon nanotubes (MWCNTs) were prepared by microwave-polyol method. The composition of Co_xNi_1−xFe₂O₄ nanoparticles can be controlled through adjusting the atomic ratios of cobalt and nickel nitrate in the mixed solution. The influence of the microwave power and microwave irradiation time on the monodispersion of nanoparticles was also investigated. The results show quasi-spherical Co_xNi_1−xFe₂O₄ nanoparticles with the face-centered cubic structure and average crystallite size (6 nm) are uniformly dispersed on MWCNTs. The saturation magnetization of Co_xNi_1−xFe₂O₄/MWCNT nanocomposites increases gradually from 12.90 to 20.03 emu/g with increasing Co²⁺ concentration. The coercivity is almost zero at room temperature, which indicates the superparamagnetic behavior.     

Cadmium-sensitive electrode based on tetracetone derivatives of p-tert-butylcalix[8]arene

The performance of a cadmium-sensitive electrode based on the tetracetone derivatives of p-tert butylcalix[8]arene was investigated. The ion-sensitivity of the calix[8]arene was examined via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectrometry, UV/Vis spectroscopy and FT-IR spectroscopy. The sensitive membrane containing the active ionophore was cast onto the surface of a gold electrode. The electrode exhibited a linear relationship between the charge transfer resistance (R_ct) and the logarithm of the detected ion concentration. The cathodic peak at a potential of 0.56 V increased linearly as the Cd^2 + ion concentration increased. The detection limit of the device reached 10^? 7 M with high sensitivity toward cadmium.     

Determination of Pb2+ ions by a modified carbon paste electrode based on multi-walled carbon nanotubes (MWCNTs) and nanosilica

A novel carbon paste ion selective electrode for determination of trace amount of lead was prepared. Multi-walled carbon nanotubes (MWCNTs) and nanosilica were used for improvement of a lead carbon paste sensor response. MWCNTs have a good conductivity which helps the transduction of the signal in carbon paste electrode. The electrode composition of 20 wt% paraffin oil, 57% graphite powder, 15% ionophore (thiram), 5% MWCNTs, and 3% nanosilica showed the stable potential response to Pb²⁺ ions with the Nernstian slope of 29.8 (±0.2) mV decade^?1 over a wide linear concentration range of 10^?7–10^?2 mol L^?1. The electrode has fast response time, and long term stability (more than 2 months). The proposed electrode was used to determine the concentration of lead ions in waste water and black tea samples.     

Photoluminescence properties of novel KBaBP2O8:M (M = Pb2+ and Bi3+) phosphors

A series of novel inorganic phosphors KBa_1−xPb_xBP₂O₈ and K_1+xBa_1−2xBi_xBP₂O₈ (0.01 ⩽ x ⩽ 0.08) were synthesized by using a solid-state reaction technique at high-temperature and their photoluminescence properties were investigated. The dependence of the emission intensity on the Pb²⁺ and Bi³⁺ concentration for the KBa_1−xPb_xBP₂O₈ and K_1+xBa_1−2xBi_xBP₂O₈ was studied, in which the optimal concentration as well as the critical transfer distance R_c for Pb²⁺ and Bi³⁺ was obtained and determined. The as-prepared phosphors can be effectively excited with ultraviolet (UV), and exhibit UV − blue emission with large Stokes shift. The above work indicates these phosphors could be potential candidates for application in UV lamps industry.     

Characterization of carbon nanotubes decorated with NiFe2O4 magnetic nanoparticles as a novel electrochemical sensor: Application for highly selective determination of sotalol using voltammetry

A magnetic nano‐composite of multiwall carbon nanotube, decorated with NiFe₂O₄ nanoparticles, was synthesized with citrate sol–gel method. The multiwall carbon nanotubes decorated with NiFe₂O₄ nanoparticles (NiFe₂O₄–MWCNTs) were characterized with different methods such as Fourier transform infrared spectroscopy (FT‐IR), transmission electron microscopy (TEM), atomic force microscopy (AFM), vibrating sample magnetometer (VSM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The new nano-composite acts as a suitable electrocatalyst for the oxidation of sotalol at a potential of 500 mV at the surface of the modified electrode. Linear sweep voltammetry exhibited two wide linear dynamic ranges of 0.5–1000 μmol L^? 1 sotalol with a detection limit of 0.09 μmol L^? 1. The modified electrode was used as a novel electrochemical sensor for the determination of sotalol in real samples such as pharmaceutical, patient and safe human urine.     

The super-hydrophilicities of Bi–TiO2, V–TiO2, and Bi–V–TiO2 nano-sized particles and their benzene photodecompositions with H2O addition

This study focused on the super-hydrophilicities of metal-TiO₂ photocatalysts, including metals with three-oxidation and five-oxidation states, and their benzene photodecompositions with or without H₂O addition. The nanometer-sized metal-TiO₂s, including Bi³⁺, V⁵⁺, and Bi³⁺–V⁵⁺ ions, were prepared using a solvothermal method. The XRD result identified these to have pure anatase structures after solvothermal treatment at 200 °C for 10 h, without any treatment. The spherical particle sizes were distributed within the range of 10–50 nm after 500 °C calcinations, and the particle sizes decreased with an increase of the Bi component, while it increased with the V component compared with that of pure TiO₂. The XPS result showed that the peaks for O1s (Ti–O) shifted to the larger binding energy in Bi–TiO₂; on the other hand, it shifted to the smaller binding energy in V–TiO₂. In particular, the Ti–OH peak, which means to hydrophilicity, decreased with an increase of the Bi component; it increased, however, with the V component. The contact angle expressed about 3° on the Bi–TiO₂ nano-sized film (200-nm thickness) after irradiation for 2 h; otherwise, it approached 0° on the V–TiO₂ nano-sized film after 30 min. In particular, the decreased angle was continued under dark condition on the Bi–V–TiO₂ nano-sized film. The benzene photodecomposition in the batch system increased in the order of Bi (3.3)–V (6.7)–TiO₂ > V–TiO₂ > pure TiO₂ > Bi–TiO₂, and the maximum benzene conversion was 35% after 60 min. The conversion remarkably increased, however, in almost all catalysts with H₂O addition during the benzene photo-decomposed reaction, and in particular, the conversion reached up to 80% after 180 min in Bi–V–TiO₂. In the continuous system for Bi–V–TiO₂ with H₂O addition, the photodecomposition rate of 50% was maintained for 168 h, without catalytic deactivation. After photoreaction, there were minimal deposited cokes in the photocatalyst in both reaction conditions, with and without H₂O addition. The deposited amounts were smaller, however, in the reaction with H₂O addition. This result is a proof that photocatalytic deactivation can be retarded by an H₂O supplement during VOC decomposition.     

Low-temperature synthesis,structural and magnetic properties of self-dopant LaMnO3+δ nanoparticles from a metal-organic polymeric precursor

Self-dopant LaMnO_3+δ nanoparticles have been successfully synthesized by metal citrate complex method based on Pechini-type reaction route, at low temperature (773 K). Powder X-ray diffraction and transmission electron microscope revealed pure and nanostructured phase of LaMnO_3+δ (δ = 0.125) with an average grain size of ∼72 nm (773 K) and ∼80 nm (1173 K). DC-magnetization measurements under an applied magnetic field of H = ±60 kOe showed an increase in the magnetization with the increase of calcination temperature. Ferromagnetic nature shown by non-stoichiometric LaMnO_3+δ was verified by well-defined hysteresis loop with large remanent magnetization (M_r) and coercive field (H_c). Surface areas of LaMnO_3+δ nanoparticles were found to be 157.4 and 153 m² g⁻¹ for the samples annealed at 773 K and 1173 K, respectively.     

Potentiometric studies of N,N′-Bis(2-dimethylaminoethyl)-N,N′-dimethyl-9,10 anthracenedimethanamine as a chemical sensing material for Zn(II) ions

A liquid membrane based Zn²⁺ ion selective electrode containing N,N′-Bis(2-dimethylaminoethyl)-N,N′-dimethyl-9,10 anthracenedimethanamine (Bis(TMEDA) anthracene) (I) as ionophore has been prepared and characterized. The membrane comprises of PVC, ionophore and plasticizer in the ratio of 33:2:65, respectively. It showed the best response in terms of detection limit (1.5 × 10^− 6 M) and working concentration range (1.0 × 10^− 5 M to 1.0 × 10^− 1 M) with Nernstian response towards Zn²⁺ ions. The electrode responds within 15 s of coming in contact with the solution. The potential response remains almost unchanged over a pH range of 3.0 to 7.5. The electrode can be used for at least 3 months without any considerable alteration in its response behavior. The proposed electrode revealed good selectivity towards Zn²⁺ ions over a number of alkali, alkaline earth, transition metals and some other heavy metal ions. The electrode has been used as an indicator electrode in the potentiometric titration of Zn²⁺ with EDTA. The proposed electrode also detected Zn²⁺ ions from real life samples.     

Voltammetric sensor based on carbon paste electrode modified with molecular imprinted polymer for determination of sulfadiazine in milk and human serum

A new sensitive voltammetric sensor for determination of sulfadiazine is described. The developed sensor is based on carbon paste electrode modified with sulfadiazine imprinted polymer (MIP) as a recognition element. For comparison, a non-imprinted polymer (NIP) modified carbon paste electrode was prepared. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods were performed to study the binding event and electrochemical behavior of sulfadiazine at the modified carbon paste electrodes. The determination of sulfadiazine after its extraction onto the electrode surface was carried out by DPV at 0.92 V vs. Ag/AgCl owing to oxidation of sulfadiazine. Under the optimized operational conditions, the peak current obtained at the MIP modified carbon paste electrode was proportional to the sulfadiazine concentration within the range of 2.0 × 10^? 7–1.0 × 10^? 4 mol L^? 1 with a detection limit and sensitivity of 1.4 × 10^? 7 mol L^? 1 and 4.2 × 10⁵ μA L mol^? 1, respectively. The reproducibility of the developed sensor in terms of relative standard deviation was 2.6%. The sensor was successfully applied for determination of sulfadiazine in spiked cow milk and human serum samples with recovery values in the range of 96.7–100.9%.     

A highly sensitive and selective electrochemical sensor for determination of Cr(VI) in the presence of Cr(III) using modified multi-walled carbon nanotubes/quercetin screen-printed electrode

A novel screen-printed carbon electrode modified with quercetin/multi-walled carbon nanotubes was fabricated for determination of Cr(VI) in the presence of excess of Cr(III) without any pretreatment. The method is based on accumulation of the quercetin–Cr(III) complex generated in situ from Cr(VI) at the modified electrode surface in an open circuit followed by differential pulse voltammetry detection. The new method allowed selective determination of Cr(VI) in the presence of Cr(III). The influence of various parameters affecting the adsorptive stripping voltammetry performance was investigated. Under the optimum conditions, the calibration plot was found to be linear in the Cr(VI) concentration range from 1.0 to 200 μmol^? 1 with a limit of detection(S/N = 3) of 0.3 μmol L^– 1. The relative standard deviation (RSD%) of seven replicates of the current measurements for a 50 μmol^? 1 of Cr(VI) solution was 3.0%. The developed electrode displayed a very low or no sensitivity to alkali, alkali-earth and transition metal cations and was successfully applied for the determination of Cr(VI) in drinking water samples.     

Microstructure and transport properties of Bi1.6Pb0.5Sr2−xLuxCa1.1Cu2.1O8+δ superconductor

The microstructure and electrical properties of the rare-earth Lu doped (Bi, Pb)-2212 superconductor have been investigated. The Lu concentration is varied from x = 0.000 to 0.150 in a general stoichiometry of Bi_1.6Pb_0.5Sr_2?xLu_xCa_1.1Cu_2.1O_8+δ. The X-ray diffractometer and energy dispersive X-ray spectroscopy analyses show that Lu atoms are successfully substituted into the (Bi, Pb)-2212 system and they induce significant changes in the microstructure, hole concentration, critical temperature, self- and in-field critical current density of the system. The flux pinning force (F_P) calculated from the field dependant J_C values shows that the irreversibility lines (IL) of the Lu substituted (Bi, Pb)-2212 shift towards higher fields to different extents depending on the Lu stoichiometry. The samples with x = 0.100 show a maximum F_P of 1395 ± 1 × 10³ N m^?3 as against 30 ± 1 × 10³ N m^?3 for the pure sample. The changes in hole concentration followed by very high enhancement of critical temperature (T_C), self-field J_C, J_C(B) characteristics and F_P due to Lu substitution are of great scientific and technological significance and the results are explained on the basis of microstructural variation with respect to Lu stoichiometry, hole optimization and formation of point defects due to the doping of Lu atoms in Bi_1.6Pb_0.5Sr_2?xLu_xCa_1.1Cu_2.1O_8+δ system.     

Ascorbic acid sensor based on molecularly imprinted polymer-modified hanging mercury drop electrode

Ascorbic acid sensor based on molecularly imprinted polymer (MIP) is reported for sensitive and selective analysis, without any cross-reactivity or matrix effect, in aqueous, blood serum and pharmaceutical samples. The sensor was developed by the direct coating of ascorbic acid-imprinted polymer, prepared from melamine and chloranil, on the surface of a hanging mercury drop electrode (HMDE) at + 0.4 V (vs. Ag/AgCl). The molecular recognition of ascorbic acid was highly specific using non-covalent (hydrophobically driven hydrogen-bonding and electrostatic) interactions. The analyte was preconcentrated and oxidised instantaneously in the imprinted polymer layer giving voltammetric signal on cathodic stripping at optimised operational conditions: accumulation potential + 0.4 V (vs. Ag/AgCl), polymer deposition time 120 s, template accumulation time 120 s, pH 7.0, scan rate 10 mV s^? 1, pulse amplitude 25 mV. The proposed MIP sensor is able to enhance sensitivity substantially so as to detect serum ascorbic acid level as low as 0.26 ng mL^? 1 (R.S.D. 0.5%, S/N 3) for the diagnosis of hypovitaminosis C (Vitamin C deficiency).