A gold nanoparticle-based colorimetric sensing ensemble for the colorimetric detection of cyanide ions in aqueous solution

A colorimetric sensing ensemble was prepared by mixing readily prepared adenosine triphosphate (ATP)-stabilized AuNPs with Cu²⁺-phenanthroline complexes. The sensing mechanism of the ensemble was examined by UV-vis spectrometry and transmission electron microscopy. The studies showed that the Cu²⁺-phenanthroline complex was converted to free phenanthroline when exposed to cyanide anions and the free phenanthroline caused the ATP-stabilized AuNPs to aggregate, which in turn, resulted in a visible color change in the AuNP solution. The ensemble could detect cyanide ions in aqueous solution at physiological pH, either spectrophotometrically or visually, with high selectivity toward cyanide anions over a range of mono- and di-anions commonly found in biological and environmental systems. This sensing ensemble also allows a quantitative assay of the analyte in a neutral aqueous solution, down to a concentration of 10⁻⁵ M.     

Functionalized CdS quantum dots-based luminescence probe for detection of heavy and transition metal ions in aqueous solution

Strong luminescence CdS quantum dots (QDs) have been prepared and modified with l-cysteine by a facile seeds-assistant technique in water. They are water-soluble and highly stable in aqueous solution. CdS QDs evaluated as a luminescence probe for heavy and transition metal (HTM) ions in aqueous solution was systematically studied. Five HTM ions such as silver(I) ion, copper(II) ion, mercury(II) ion, cobalt(II) ion, and nickel(II) ion significantly influence the photophysics of the emission from the functionalized CdS QDs. Experiment results showed that the fluorescence emission from CdS QDs was enhanced significantly by silver ion without any spectral shift, while several other bivalent HTM ions, such as Hg(2+), Cu(2+), Co(2+), and Ni(2+), exhibited effective optical quenching effect on QDs. Moreover, an obvious red-shift of emission band was observed in the quenching of CdS QDs for Hg(2+) and Cu(2+) ions. Under the optimal conditions, the response was linearly proportional to the concentration of Ag(+) ion ranging from 1.25 x 10(-7) to 5.0 x 10(-6)molL(-1) with a detection limit of 2.0 x 10(-8)molL(-1). The concentration dependence of the quenching effect on functionalized QDs for the other four HTM ions could be well described by typical Stern-Volmer equation, with the linear response of CdS QDs emission proportional to the concentration ranging from 1.50 x 10(-8) to 7.50 x 10(-7)molL(-1) for Hg(2+) ion, 3.0 x 10(-7) to 1.0 x 10(-5)molL(-1) for Ni(2+) ion, 4.59 x 10(-8) to 2.295 x 10(-6)molL(-1) for Cu(2+) ion, and 1.20 x 10(-7) to 6.0 x 10(-6)molL(-1) Co(2+) ion, respectively. Based on the distinct optical properties of CdS QDs system with the five HTM ions, and the relatively wide linear range and rapid response to HTM ions, CdS QDs can be developed as a potential identified luminescence probe for familiar HTM ions detection in aqueous solution.     

Adsorption of heavy metal ions from aqueous solution by polyrhodanine-encapsulated magnetic nanoparticles

The influence of salt concentration on the terminal velocities of gravity-driven single bubbles sliding along an inclined glass wall has been investigated, in an effort to establish whether surface forces acting between the wall and the bubble influence the latter's mobility. A simple sliding bubble apparatus was employed to measure the terminal velocities of air bubbles with radii ranging from 0.3 to 1.5 mm sliding along the interior wall of an inclined Pyrex glass cylinder with inclination angles between 0.6 and 40.1°. Experiments were performed in pure water, 10 mM and 100 mM KCl solutions. We compared our experimental results with a theory by Hodges et al. which considers hydrodynamic forces only, and with a theory developed by two of us which considers surface forces to play a significant role. Our experimental results demonstrate that the terminal velocity of the bubble not only varies with the angle of inclination and the bubble size but also with the salt concentration, particularly at low inclination angles of ～1-5°, indicating that double-layer forces between the bubble and the wall influence the sliding behavior. This is the first demonstration that terminal velocities of sliding bubbles are affected by disjoining pressure.     

Multi-element preconcentration of heavy metal ions from aqueous solution by APDC impregnated activated carbon

Ammonium pyrrolidinedithiocarbamate impregnated activated carbon (APDC-AC) has been used for the preconcentration of Cd(II), Cu(II), Ni(II), and Zn(II) from aqueous solution by column solid phase extraction (SPE) technique. Trace metal ions in aqueous solution were quantitatively sorbed onto APDC-AC packed in a SPE column at pH 5.0 with a flow rate of 1.0 mL min⁻¹. The sorbed metals were eluted with 1 M nitric acid in acetone solution at a flow rate of 0.6 mL min⁻¹ and analyzed by flame atomic absorption spectrometry. The effects of sample volume, amount of APDC-AC, volume of eluent and ionic strength of working solution on metal ion recovery have been investigated. The present methodology gave recoveries from 90 to 106% and R.S.D. from 0.6 to 5.5%.     

Phosphorylated polyacrylonitrile‐based electrospun nanofibers for removal of heavy metal ions from aqueous solution

The phosphorylated polyacrylonitrile‐based (P‐PAN) nanofibers were prepared by electrospinning technique and used for removal of Cu²⁺, Ni²⁺, Cd²⁺, and Ag⁺ from aqueous solution. The morphological and structural properties of P‐PAN nanofibers were characterized by scanning electron microscope and Fourie transform infrared spectra. The P‐PAN nanofibers were evaluated for the adsorption capacity at various pH, contact time, and reaction temperature in a batch system. The reusability of P‐PAN nanofibers for the removal of heavy metal ions was also determined. Adsorption isotherms and adsorption kinetics were also used to examine the fundamental adsorption properties. It is found that the P‐PAN nanofibers show high efficiency, and the maximal adsorption capacities of metal ions as calculated from the Langmuir model were 92.1, 68.3, 14.8, and 51.7 mg/g, respectively. The kinetics of the heavy metal ions adsorption were found to follow pseudo‐second‐order rate equation, suggesting chemical adsorption can be regarded as the major factor in the adsorption process. Sorption/desorption results reveal that the obtained P‐PAN nanofibers can remain high removal efficiency after four cycles.     

New synthesized ligands for detection of heavy metal ions

Some new chemo-sensors (4,4'-((1E,1′E)-(2,2′-dichloro-[1,1′-biphenyl]-4,4′-diyl)bis(diazene-2,1-diyl))bis(3,5-dihydroxybenzoic acid), 4-((E)-(4-(N-(4-((E)-(4-carboxy-2,6-dihydroxyphenyl)diazenyl)phenyl)sulfamoyl)phenyl)diazenyl)-3,5-dihydroxybenzoic acid, 4-((E)-(4-((4-((E)-(4-carboxy-2,6-dihydroxyphenyl)diazenyl)-2-sulfophenyl)amino)phenyl)diazenyl)-3,5-dihydroxybenzoic acid) were synthesized. These synthesized sensors were then characterized by FTIR, TLC, UV–Visible spectrophotometry, and NMR techniques. The sensors showed the best results for detection of all type of heavy metal ions simply by changing the colour of metal ion solution and by shifting in the λ_max values of sensors due to interactions.     

Detection of metal ions in aqueous solution by voltohmmetry

A new electrochemical detection principle is described for the trace analysis of dissolved species which can be deposited at polycrystalline thin-film metal electrodes and which change the surface resistance of the electrode. Because the latter parameter is measured in dependence on the applied electrode potential this method is called voltohmmetry. The preparation of the required thin-film electrodes and the experimental set-up is introduced and discussed. Typical voltohmmetric experiments are illustrated by measurements of Tl+/Tl at polycrystalline gold electrodes with a thickness of 15 nm. The analytical capabilities of this new approach are discussed. It is already possible to determine heavy metals such as Tl+, Pb2+ or Cd2+ in the range of a few microgram/L by surface resistance-potential measurements at thin-film electrodes with a simple cyclic technique. Further developments of voltohmmetry are envisaged.     

A fluorescent and colorimetric chemosensor for selective detection of aluminum in aqueous solution

We have synthesized a new Schiff base 1, which detects Al³⁺ through fluorescence and naked eye in aqueous solution. The sensor 1 exhibited selective and sensitive recognition toward Al³⁺ via significant fluorescence enhancement (31-fold). Moreover, it showed a significant color change from colorless to yellow. The complex formation was proposed to be 1:1 ratio, based on the Job plot, ESI-mass spectrometry analysis, ¹H NMR titration, and IR analysis. The detection limit was 1.00 μM, which is below the WHO acceptable limit (1.85 μM) in drinking water. In addition, the sensor 1 could be recyclable simply through treatment with a proper reagent such as EDTA.     

Ratiometric and turn-on monitoring for heavy and transition metal ions in aqueous solution with a fluorescent peptide sensor

A novel fluorescent peptide sensor containing tryptophan (donor) and dansyl fluorophore (acceptor) was synthesized for monitoring heavy and transition metal (HTM) ions on the basis of metal ion binding motif (Cys-X-X-X-Cys). The peptide probe successfully exhibited a turn on and ratiometric response for several heavy metal ions such as Hg²⁺, Cd²⁺, Pb²⁺, Zn²⁺, and Ag⁺ in aqueous solution. The enhancements of emission intensity were achieved in the presence of the HTM ions by fluorescent resonance energy transfer (FRET) and chelation enhanced fluorescence (CHEF) effects. The detection limits of the sensor for Cd²⁺, Pb²⁺, Zn²⁺, and Ag⁺ were lower than the EPA's drinking water maximum contaminant levels (MCL). We described the fluorescent enhancement, binding affinity, and detection limit of the peptide probe for HTM ions.     

A TCF-based colorimetric and fluorescent probe for palladium detection in an aqueous solution

A new fluorescent probe (TCF-AC) that contains 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) skeleton has been developed. Probe TCF-AC exhibits highly selective and sensitive detection toward Pd⁰ in EtOH/H₂O (1:1, v/v, PBS 20?mM, pH?=?7.4) solution with fluorescence “turn on” and colorimetric changes. The Pd⁰ detection by TCF-AC holds some advantages including good anti-interference ability, a relative large Stokes shift (>100?nm), and a low detection limit (7.05?×?10^?7?M). Cell imaging studies demonstrate that TCF-AC is applicable to detect Pd⁰ in living HeLa cells.     

Removal of heavy metal ions from aqueous solutions by alkaline-earth metal phosphates

The possibility of utilization of calcium or magnesium phosphates of various composition for heavy and non-ferrous metal extraction from aqueous solutions has been studied. The efficiency of the phosphates in removal of Pb(II), Cr(III) and Fe(III) ions has been shown to decrease in the following sequence: Mg₃(PO₄)₂>MgNH₄PO₄>Ca₃(PO₄)₂>CaHPO₄>Ca₁₀(PO₄)₆(OH)₂ which is inverse to their hydrolytic stability series. It has been established that phosphates of non-apatite structure are capable of binding up to 12 mmol g⁻¹ of the named heavy metals by a chemical interaction. Hydroxyapatite interacts with the polyvalent metal ions via either the above mentioned or ion-exchange mechanism, depending on preparation method used for the apatite and the nature of metal.     

Complexation of polymethacrylopiperidide with transition metal ions in aqueous solution

The interactions of polymethacrylopiperidide with Cu²⁺, Ni²⁺, Co²⁺ and Fe³⁺ ions have been investigated by potentiometric and conductometric titration, ESR and u.v. spectroscopy, viscometry and sedimentation. The average number of ligands coordinating with the central metal ions and the stability constants of polymeric metal complexes were determined. It is assumed that the polymethacrylopiperidide interacts with transition metal ions through the nitrogen atoms. The influence of spatial arrangement of donor atoms on the coordination ability of polyligand is discussed.     

Granulated sulfur-containing sorbents for recovery of heavy metal ions from aqueous solutions

Granulated sorbents that can recover zinc salts from aqueous solutions were produced by poly-condensation of organochlorine wastes from manufacture of epichlorohydrin with sodium polysulfide on the surface of ash-and-slag particles formed at thermal power plants in the system constituted by aqueous hydrazine and an alkali.     

Label-free aptamer-based colorimetric detection of mercury ions in aqueous media using unmodified gold nanoparticles as colorimetric probe

We report a simple and sensitive aptamer-based colorimetric detection of mercury ions (Hg²⁺) using unmodified gold nanoparticles as colorimetric probe. It is based on the fact that bare gold nanoparticles interact differently with short single-strand DNA and double-stranded DNA. The anti-Hg²⁺ aptamer is rich in thymine (T) and readily forms T–Hg²⁺–T configuration in the presence of Hg²⁺. By measuring color change or adsorption ratio, the bare gold nanoparticles can effectively differentiate the Hg²⁺-induced conformational change of the aptamer in the presence of a given salt with high concentration. The assay shows a linear response toward Hg²⁺ concentration through a five-decade range of 1 × 10⁻⁴ mol L⁻¹ to 1 × 10⁻⁹ mol L⁻¹. Even with the naked eye, we could identify micromolar Hg²⁺ concentrations within minutes. By using the spectrometric method, the detection limit was improved to the nanomolar range (0.6 nM). The assay shows excellent selectivity for Hg²⁺ over other metal cations including K⁺, Ba²⁺, Ni²⁺, Pb²⁺, Cu²⁺, Cd²⁺, Mg²⁺, Ca²⁺, Zn²⁺, Al³⁺, and Fe³⁺. The major advantages of this Hg²⁺ assay are its water-solubility, simplicity, low cost, visual colorimetry, and high sensitivity. This method provides a potentially useful tool for the Hg²⁺ detection.     

Interaction of a carbonate-containing reagent with heavy metal ions in aqueous solutions

Results of interaction of a carbonate-containing water-treatment waste with ions of copper(II), zinc(II), nickel(II), iron(III), and chromium(III) in aqueous solutions are compared.     

Sorption of heavy metal from aqueous solution by volcanic ash

Lava ash from Mt. Etna volcano has been tested in a series of batch experiments in order to find out its suitability to act as metal ion sorbent from wastewaters. The results show that the removal of Cd, Cu and Cr elements reaches a suitable level. Various experimental parameters have been tried to verify their influence on the metal sorption. Each ionic species in solution can be removed only in its own range of optimal pH. No competitive effects have been found. The equilibrium data are satisfactorily fitted by the Freundlich isotherm. Desorption experiments by acid aqueous solutions result in leaching of negligible amounts of metal ions.