Selective detection of toxic Pb(II) ions based on wet-chemically prepared nanosheets integrated CuO–ZnO nanocomposites

The present study describes a selective detection methodology for hazardous metal ions based on low-dimensional nanosheets (NSs) integrated CuO–ZnO composite materials. A large-scale synthesis of NSs by wet-chemical process is performed using alkaline reducing agents at higher pH medium. The prepared NSs are characterized in terms of their morphological, structural and optical properties, and efficiently applied for the toxic metal ions detection. The detailed structural, compositional, and optical characterization of NSs are evaluated by XRD, FT-IR, XPS, EDS, and UV–vis spectroscopy, which confirmed that the obtained NSs are well-crystalline CuO–ZnO and possessed good optical properties. The CuO–ZnO NS morphology is investigated by FE-SEM, which confirmed that the NS possesses microstructure shape and growth in large-quantity. The analytical application of CuO–ZnO NSs is studied for a selective extraction of toxic lead-divalent [Pb(II)] ions prior to its determination by inductively coupled plasma-optical emission spectrometry (ICP-OES). The selectivity of doped NSs phase is investigated for eight different metal ions, including Cd(II), Cu(II), Hg(II), La(III), Mn(II), Pb(II), Pd(II), and Y(III) under similar experimental conditions. From the selectivity study, it is confirmed that the composite CuO–ZnO NS phase is the most toward Pb(II) ions according to the magnitude of distribution coefficient (K_d) values, such as Pb(II) > Y(III) > Cd(II) > La(III) > Hg(II) > Cu(II) > Mn(II) > Pd(II). The uptake capacity for Pb(II) is experimentally calculated to be ∼82.66 mg g⁻¹.     

Adsorption of copper (II), chromium (III), nickel (II) and lead (II) ions from aqueous solutions by meranti sawdust

The present study proposed the use of meranti sawdust in the removal of Cu(II), Cr(III), Ni(II) and Pb(II) ions from synthetic aqueous solutions. Batch adsorption studies showed that meranti sawdust was able to adsorb Cu(II), Cr(III), Ni(II) and Pb(II) ions from aqueous solutions in the concentration range 1–200 mg/L. The adsorption was favoured with maximum adsorption at pH 6, whereas the adsorption starts at pH 1 for all metal ions. The effects of contact time, initial concentration of metal ions, adsorbent dosage and temperature have been reported. The applicability of Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherm was tried for the system to completely understand the adsorption isotherm processes. The adsorption kinetics tested with pseudo-first-order and pseudo-second-order models yielded high R² values from 0.850 to 0.932 and from 0.991 to 0.999, respectively. The meranti sawdust was found to be cost effective and has good efficiency to remove these toxic metal ions from aqueous solution.     

Separation,preconcentration and inductively coupled plasma-mass spectrometric (ICP-MS) determination of thorium(IV), titanium(IV), iron(III), lead(II) and chromium(III) on 2-nitroso-1-naphthol impregnated MCI GEL CHP20P resin

A simple and effective method is presented for the separation and preconcentration of Th(IV), Ti(IV), Fe(III), Pb(II) and Cr(III) by solid phase extraction on 2-nitroso-1-naphthol impregnated MCI GEL CHP20P resin prior to their inductively coupled plasma-mass spectrometric determinations. The influence of analytical parameters including pH of the aqueous solution, flow rates of sample and eluent solutions and sample volume on the quantitative recoveries of analyte ions was investigated. Matrix effects caused by the presence of alkali, earth alkali and some metal ions in the analyzed solutions were investigated. The presented solid phase extraction method was applied to BCR-144R Sewage Sludge (domestic origin), BCR-141R Calcareous Loam Soil, NIST 1568a Rice Flour and NIST 1577b Bovine Liver certified reference materials (CRMs) for the determination of analyte ions and the results were in good agreement with the certified values. The separation procedure presented was also applied to the various natural water samples collected from Turkey with satisfactory results.     

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.     

Preparation of chitosan/magnetite composite beads and their application for removal of Pb(II) and Ni(II) from aqueous solution

A simple and effective process has been proposed to prepare chitosan/magnetite nanocomposite beads with saturation magnetization value as high as uncoated Fe₃O₄ nanoparticles (ca. 54 emu/g). The reason was that the coating chitosan layer was so thin that it did not affect magnetic properties of these composite beads. Especially, chitosan on the surface of the magnetic Fe₃O₄ nanoparticles is available for coordinating with heavy metal ions, making those ions removed with the assistance of external magnets. Maximum adsorption capacities for Pb(II) and Ni(II), occurred at pH 6 and under room temperature were as high as 63.33 and 52.55 mg/g respectively, according to Langmuir isotherm model. These results permitted to conclude that chitosan/magnetite nanocomposite beads could serve as a promising adsorbent not only for Pb(II) and Ni(II) (pH = 4–6) but also for other heavy metal ions in wastewater treatment technology.     

Extraction and separation of Co(II) and Ni(II) from acidic sulfate solutions using Aliquat 336

Extraction and separation of Co(II) and Ni(II) from acidic sulfate solutions by solvent extraction technique were studied using different forms of Aliquat 336 diluted with kerosene. The extraction percent of each metal ion was found to increase with increasing pH and extractant concentration. Co(II) was preferentially extracted by different forms of Aliquat 336 over Ni(II) under the same extraction conditions. From analysis of the experimental results, the extraction mechanism of R₄N-forms was proposed with Co(II). It was found that the highest separation factor (S_Co/Ni) value of 606.7 was obtained with 0.36 M R₄N–SCN in kerosene from 2.0 M H₂SO₄ solution at pH 4.8 and shaking time of 20 min. Stripping of the two metal ions from the organic phase was also investigated. Based on the experimental results, a separation method was developed and tested to separate high purity Co(II), Ni(II) and Ln(III) from Ni–MH batteries leached by 2.0 M H₂SO₄. Based on the experimental results, a flow sheet was developed and tested and 0.34 g Co, 1.39 g Ln and 5.2 g Ni were obtained from the leaching process.     

Competitive adsorption of Cu(II) and Cd(II) ions on spray-dried chitosan loaded with Reactive Orange 16

Chitosan microspheres cross-linked with glutaraldehyde and containing the reactive dye Orange 16 (RO 16) as a chelating agent were obtained by spray drying technique. These microspheres (CHS-RO 16) were characterized by FTIR, TGA, DSC, SEM and EDX analyses, and tested for metal adsorption. The new adsorbent was used in batch experiments to evaluate the adsorption of Cu(II) and Cd(II) ions in single and binary metal solutions. In single metal solutions, the maximum adsorption capacity for Cu(II), obtained by Langmuir model, was close to 1.69 mmol Cu g^? 1; this means the double of the adsorption capacity for Cd(II) (i.e. 0.80 mmol Cd g^? 1). Adsorption isotherms for binary solutions showed that the presence of Cu(II) decreased Cd(II) adsorption due to a significant competition effect. On the other hand, Cu(II) adsorption hardly changed when the initial concentration of Cd(II) increased: the new adsorbent was selective to Cu(II) against Cd(II). The metal ions were efficiently desorbed from chitosan-RO 16 with aqueous solutions of H₂SO₄.     

Removal of Pb(II) ions from aqueous solution by adsorption using bael leaves (Aegle marmelos)

Biosorption of Pb(II) on bael leaves (Aegle marmelos) was investigated for the removal of Pb(II) from aqueous solution using different doses of adsorbent, initial pH, and contact time. The maximum Pb loading capacity of the bael leaves was 104 mg g^?1 at 50 mg L^?1 initial Pb(II) concentration at pH 5.1. SEM and FT-IR studies indicated that the adsorption of Pb(II) occurs inside the wall of the hollow tubes present in the bael leaves and carboxylic acid, thioester and sulphonamide groups are involved in the process. The sorption process was best described by pseudo second order kinetics. Among Freundlich and Langmuir isotherms, the latter had a better fit with the experimental data. The activation energy E_a confirmed that the nature of adsorption was physisorption. Bael leaves can selectively remove Pb(II) in the presence of other metal ions. This was demonstrated by removing Pb from the effluent of exhausted batteries.     

Synthesis,structural characterization and photophysical properties of highly photoluminescent crystals of Eu(III), Tb(III) and Dy(III) with 2,5-thiophenedicarboxylate

Lanthanide compounds of general formula [Ln₂(2,5-tdc)₃(dmf)₂(H₂O)₂]·2dmf·H₂O (Ln = Eu(III) (1), Tb(III) (2), Gd(III) (3) and Dy(III) (4), dmf = N,N′-dimethylformamide and 2,5-tdc²⁻ = 2,5-thiophedicarboxylate anion) were synthesized and characterized by elemental analysis, X-ray powder diffraction patterns, thermogravimetric analysis and infrared spectroscopy. Phosphorescence data of Gd(III) complex showed that the triplet states (T₁) of 2,5-tdc²⁻ ligand have higher energy than the main emitting states of Eu(III), Tb(III) and Dy(III), indicating that 2,5-tdc²⁻ ligand can act as intramolecular energy donor for these metal ions. An energy level diagram was used to establish the most relevant channels involved in the ligand-to-metal energy transfer. The high value of experimental intensity parameter Ω₂ for the Eu(III) complex indicate that the europium ion is in a highly polarizable chemical environment. The emission quantum efficiency (η) of the ⁵D₀ emitting level of Eu(III) was also determined. The complexes act as possible light conversion molecular devices (LCMDs).     

Enhancement strategies for Cu(II), Cr(III) and Cr(VI) remediation by a variety of seaweed species

Various chemical treatments have been applied to six brown, red and green seaweed species with a view to enhancing their metal removal for Cu(II), Cr(III) and Cr(VI). Treatment with acetone resulted in the greatest enhancement for both cationic and anionic species with relatively low mass losses (15–35%), indicating its low risk to biomass operational stability. Cation binding was increased by 69%, while the total Cr removal was augmented by 15%. Cr(VI) binding was shown to be an adsorption-coupled reduction, whereby Cr(VI) was bound to the biomass surface at pH 2 and subsequently reduced to Cr(III). Acetone treatment also resulted in biomasses that were capable of converting up to 83% of Cr(VI) in solution to Cr(III). Blocking of carboxyl and amino functionalities had significant negative effects both on total Cr removal as well as percentage conversion of Cr(VI) to Cr(III). Results therefore indicated the significant role played by these moieties in metal binding to these seaweeds. Potentiometric titrations displayed agreement between the degree of esterification and the decrease in Cu(II) removal for Ulva spp. and Polysiphonia lanosa. FTIR analysis identified changes in biomass functionality and availability after chemical modification, the results of which were in agreement with metal removal studies. In conclusion, these biosorbents represent suitable candidates to replace conventional removal technologies for metal bearing wastewaters, in particular for the detoxification of hazardous Cr(VI) waste streams.     

SP70-alpha-benzoin oxime chelating resin for preconcentration-separation of Pb(II), Cd(II), Co(II) and Cr(III) in environmental samples

In the presented work, alpha-benzoin oxime immobilized SP70 chelating resin was synthesized for separation and preconcentration of Pb(II), Cd(II), Co(II) and Cr(III). The optimization procedure for analytical parameters including pH, eluent type, flow rate, etc. was examined in order to gain quantitative recoveries of analyte ions. The effects of foreign ions on the recoveries of studied metal ions were also investigated. The detection limits (3sigma) were found to be 16.0, 4.2, 1.3, 2.4microgL(-1) for Pb, Cd, Co and Cr, respectively. The preconcentration factor was 75 for Pb, 100 for Cd, Co and Cr. The optimized method was validated with certified reference materials and successfully applied to the waters, crops and pharmaceutical samples with good results (recoveries greater than 95%, R.S.D. lower than 10%).     

In situ synthesis and luminescence characteristics of complexes of europium(III) with 4,6-diacetylresorcinol

The complexes of europium(III) with 4,6-diacetylresorcinol (H₂DAR) and a co-ligand (phen, bpy or 2,2′-bipyridine N,N′-dioxide (2,2′-bpyO₂)) were in situ synthesized in silica matrix via a two-step gel process. The formation of complexes in silica gel was confirmed by the luminescence excitation spectra. The silica gels that contain in situ synthesized europium complexes exhibit the characteristic emission bands of the Eu(III). The results show that there are two ways to enhance the emission intensity of the Eu(III): (i) synthesize the complex in silica matrix and (ii) synthesize the complex with a co-ligand, which coordinates with Eu(III) in the composite system and can efficiently transfer the energy from 4,6-diacetylresorcinol to the Eu(III). The order of the luminescence intensities of the complexes is: Eu₂(DAR)₃(phen)₂-(sol–gel) > Eu₂(DAR)₃(2,2′-bpyO₂)₂-(sol–gel) > Eu₂(DAR)₃ (bpy)₂-(sol–gel) > Eu₂(DAR)₃-(sol–gel) > pure Eu₂(DAR)₃·4H₂O.     

Adsorption of chromium(III), mercury(II) and lead(II) ions onto 4-aminoantipyrine immobilized bentonite

In this work, the immobilization of 4-aminoantipyrine onto bentonite was carried out and it was then used to investigate the adsorption behavior of Cr(III), Hg(II) and Pb(II) ions from aqueous solutions. The separation and preconcentration conditions of analytes were investigated, including effects of pH, the shaking time, the sample flow rate and volume, the elution condition and the interfering ions. Under optimum pH value (pH 4.0), the maximum static adsorption capacity of the sorbent was found to be 38.8, 52.9 and 55.5 mg g(-1) for Cr(III), Hg(II) and Pb(II), respectively. 2.0 mL of 2% thiourea in 1.0 M HCl solution effectively eluted the adsorbed metal ions. The detection limit (3σ) of this method defined by IUPAC was found to be 0.12, 0.09 and 0.23 ng mL(-1) for Cr(III), Hg(II) and Pb(II), respectively. The relative standard deviation (RSD) was lower 3.0% (n=8). The developed method has been validated by analyzing certified reference materials and successfully applied to the determination of trace Cr(III), Hg(II) and Pb(II) in water samples with satisfactory results.     

Surface-functionalized pomelo peel-derived biochar with mercapto-1,2,4-triazloe for selective elimination of toxic Pb (II) in aqueous solutions

A novel biochar adsorbent (GP-AMT) is prepared by functionalizing biochar derived from pomelo peel to eliminate Pb (II) from water. GP-AMT was characterized by FTIR, SEM, BET, TGA and XPS. GP-AMT has a large specific area and is multiaperture. The adsorption performance was studied. At the pH = 5, the maximum uptake amount of Pb(II) on GP-AMT reached 420 mg/g. The sorption behavior of GP-AMT obeys with Langmuir and pseudo second-order formula, which shows that the adsorbing property of GP-AMT is uniform chemical sorption. Thermodynamic studies attested that the sorption was an irreversible endothermic course. GP-AMT demonstrated excellent selectivity and reproducibility. After 5 cycles, it still has an excellent sorption property. XPS and zeta potential analysis revealed that the adsorbing nature of GP-AMT for heavy metal ions was coordination and ion exchange. In conclusion, surface modification of biochar can significantly improve its sorption capacity, selectivity and regenerative ability for Pb(II), and reduce the pomelo peel waste pollution.     

Chemically modified activated carbon with 1-acylthiosemicarbazide for selective solid-phase extraction and preconcentration of trace Cu(II), Hg(II) and Pb(II) from water samples

A new sorbent 1-acylthiosemicarbazide-modified activated carbon (AC-ATSC) was prepared as a solid-phase extractant and applied for removing of trace Cu(II), Hg(II) and Pb(II) prior to their determination by inductively coupled plasma optical emission spectrometry (ICP-OES). The separation/preconcentration conditions of analytes were investigated, including effects of pH, the shaking time, the sample flow rate and volume, the elution condition and the interfering ions. At pH 3, the maximum static adsorption capacity of Cu(II), Hg(II) and Pb(II) onto the AC-ATSC were 78.20, 67.80 and 48.56 mg g⁻¹, respectively. The adsorbed metal ions were quantitatively eluted by 3.0 mL of 2% CS(NH₂)₂ and 2.0 mol L⁻¹ HCl solution. Common coexisting ions did not interfere with the separation. According to the definition of IUPAC, the detection limits (3σ) of this method for Cu(II), Hg(II) and Pb(II) were 0.20, 0.12 and 0.45 ng mL⁻¹, respectively. The relative standard deviation under optimum conditions is less than 4.0% (n = 8). The prepared sorbent was applied for the preconcentration of trace Cu(II), Hg(II) and Pb(II) in certified and water samples with satisfactory results.     

Tris(2-aminoethyl) amine functionalized silica gel for solid-phase extraction and preconcentration of Cr(III), Cd(II) and Pb(II) from waters

A new tris(2-aminoethyl) amine (TREN) functionalized silica gel (SG-TREN) was prepared and investigated for selective solid-phase extraction (SPE) of trace Cr(III), Cd(II) and Pb(II) prior to its determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Identification of the surface modification was characterized and performed on the basis of FT-IR. The separation/preconcentration conditions of analytes were investigated, including effects of pH, the shaking time, the sample flow rate and volume, the elution condition and the interfering ions. At pH 4, the maximum adsorption capacity of Cr(III), Cd(II) and Pb(II) onto the SG-TREN were 32.72, 36.42 and 64.61 mg g(-1), respectively. The adsorbed metal ions were quantitatively eluted by 5 mL of 0.1 mol L(-1) HCl. Common coexisting ions did not interfere with the separation. According to the definition of International Union of Pure and Applied Chemistry, the detection limits (3sigma) of this method for Cr(III), Cd(II) and Pb(II) were 0.61, 0.14 and 0.55 ng mL(-1), respectively. The relative standard deviation under optimum conditions is less than 4.0% (n=11). The application of this modified silica gel to preconcentration trace Cr(III), Cd(II) and Pb(II) of two water samples gave high accurate and precise results.     

Copper foams in water treatment technology: Removal of hexavalent chromium

Open-cell copper foams were prepared using a space holder technique and tested as filter-beds for the uptake and reduction of Cr(VI) in drinking water. The use of raw cane sugar as a space holder provides an environmentally friendly method for the production of foams with controllable porous network characteristics. Specifically, by applying a sugar volume of 70–80% with particle sizes in the range of 0.35–0.70 mm, it was possible to obtain final porosity of 65%, high structural stability, and enhanced interconnectivity of macropores required for the free flow of treated water. Smaller sugar particles ensure a smaller pore size and a higher specific surface area, favoring the interaction of water with the effective copper surface. Column tests indicated that a realistic filtering system using the Cu-foam can operate with complete Cr(VI) removal and minimum Cu leaching in the pH 7 ± 0.2 range, capturing chromium in the form of Cr(III) and Cr(VI) oxides. Chromium is homogeneously distributed and incorporated into the copper porous network allowing an almost unlimited lifetime of effective use compared to common adsorbents.     

Tannin-immobilized mesoporous silica bead (BT–SiO2) as an effective adsorbent of Cr(III) in aqueous solutions

This study describes a new approach for the preparation of tannin-immobilized adsorbent by using mesoporous silica bead as the supporting matrix. Bayberry tannin-immobilized mesoporous silica bead (BT–SiO₂) was characterized by powder X-ray diffraction to verify the crystallinity, field-emission scanning electron microscopy to observe the surface morphology, and surface area and porosity analyzer to measure the mesoporous porous structure. Subsequently, the adsorption experiments to Cr(III) were applied to evaluate the adsorption performances of BT–SiO₂. It was found that the adsorption of Cr(III) onto BT–SiO₂ was pH-dependent, and the maximum adsorption capacity was obtained in the pH range of 5.0–5.5. The adsorption capacity was 1.30 mmol g^?1 at 303 K and pH 5.5 when the initial concentration of Cr(III) was 2.0 mmol L^?1. Based on proton nuclear magnetic resonance (HNMR) analyses, the adsorption mechanism of Cr(III) on BT–SiO₂ was proved to be a chelating interaction. The adsorption kinetic data can be well described using pseudo-first-order model and the equilibrium data can be well fitted by the Langmuir isothermal model. Importantly, no bayberry tannin was leached out during the adsorption process and BT–SiO₂ can simultaneously remove coexisting metal ions from aqueous solutions. In conclusion, this study provides a new strategy for the preparation of tannin-immobilized adsorbents that are highly effective in removal of heavy metals from aqueous solutions.     

A novel iron (III)-PVC membrane potentiomeric sensor based on N-(2-hydroxyethyl)ethylenediamine-N,N',N"-triacetic acid

This work introduces a unique ionophore for the selective determination of Fe(III) ions. This ionophore was N-(2-hydroxyethyl)ethylenediamine-N,N′,N″-triacetic acid (NTA), presenting a high affinity towards the trivalent iron cations. The designed sensor exhibited a wide linear response with a slope of 19.5 ± 0.4 mV per decade over the concentration range of 1.0 × 10^− 9–1.0 × 10^− 2 mol L^− 1, while the illustrated detection limit was 3.0 × 10^− 10 mol L^− 1 of the Fe(III) ions concentration. It was concluded that the sensor response was pH independent in the range of 1.8–4.5. The sensor possessed the advantages of short conditioning time, fast response time (10 s) and, especially, good selectivity towards the transition and heavy metal ions as well as some mono, di and trivalent cations. Concerning the electrode lifetime, no considerable potential divergence was noticed for at least 10 weeks. The sensor accuracy was investigated in the potentiometric titration of a Fe(III) solution with EDTA.     

Characterization of ordered Cu2O nanowire arrays prepared by heat treated Cu/PAM composite

Cu nanowire arrays were synthesized via a porous alumina membrane (PAM) template with a high aspect ratio, uniform pore size (120–140 nm), and ordered pore arrangement. The Cu₂O nanowire arrays were prepared from the oxidization of Cu metal nanowire arrays. The electrochemical deposition potential of Cu metal nanowires (?180 mV vs. SCE) was determined from X-ray diffraction (XRD) patterns. The microstructure and chemical composition of Cu nanowire arrays were characterized using field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD). Results indicate that the Cu/Cu₂O nanowire arrays assembled into the nanochannel of the porous alumina template with diameters of 120–140 nm. The valence of copper was controlled by the porous alumina template during the annealing process. Copper nanowires transformed to the Cu₂O phase with the space limitation of the PAM template. Single-crystal Cu₂O nanowire arrays were also obtained under the template embedded.