Heavy metal: Simultaneous detection, extraction

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  • Published: Sep 15, 2011
  • Author: David Bradley
  • Channels: Atomic
thumbnail image: Heavy metal: Simultaneous detection, extraction

Picomolar test

A novel approach to detection of toxic metal ions based on amino-functionalized gold nanoparticles not only provides analytical data on contaminated aqueous samples, but at the same time allows the ions to be extracted from the sample. Atomic absorption spectroscopy verifies the detection of heavy metals down to picomolar concentrations.

Neha Chauhana, Shweta Guptaa, Nahar Singha, Sukhvir Singh, Kedar Sooda, Renu Pasricha of the National Physical Laboratory, Council of Scientific and Industrial Research and Saikh Islam of the Nanosensor Research Laboratory, in Jamia Millia Islamia, New Delhi, India, have devised a technology that exploits the ability of gold nanoparticles capped with 4-aminothiophenol to report and remove heavy metal ions, including cadmium, cobalt and mercury, from samples of processed water. They point out that although heavy metals are ubiquitous in nature, they have become of heightened environmental concern during the last quarter century as ongoing research reveals more about their toxicology and detrimental effects on ecosystems. For instance, divalent lead, mercury, nickel, lead, cobalt, and cadmium ions all pose significant public health risks, the team says, particular when present in drinking water even at concentrations as low as parts per million.

They explain that noble metal nanoparticles have been investigated for their detection potential because they exhibit an enhanced optical interaction with visible light, which is modulated by adsorption of metal ions, so generating a potentially detectable signal available to a colorimetric assay. Moreover, their chemical inertness and resistance to surface oxidation make gold the optimal choice for such sensors, the team adds. Several teams have demonstrated detection of heavy metal ions using gold nanoparticles. Chauhana and colleagues have now combined detection with extraction in their version of this technology.

Capped nanoparticles

The researchers used transmission electron microscopy (TEM) and its high-resolution form HRTEM, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and I-V (electrical) characterisation to investigate the interaction between the capped nanoparticles and the metal ions as a function of time and concentration. They used flame atomic absorption spectroscopy to determine the absorption capacity of their nanoparticles, as well as UV-vis spectroscopy. The team also accounted for factors, such as ligand concentration and pH and demonstrated that controlling the pH of the nanoparticle solution could be used to increase adsorption of metal ions.

Moreover, they were able to successfully demonstrate that no alloys formed between the gold and the heavy metal contaminants, thus allowing the heavy metal ions to be removed from the detection system. To test the removal process they coated spherical glass beads with functionalized gold nanoparticles and confirmed extraction of the metal ions using AAS. Concentrations were found to be lower than the safe thresholds suggested by the World Health Organisation, WHO. Nevertheless, they were able to show that the nanoparticles were capable of removing up to 50 micrograms per litre. The coated beads could be reused easily.



Credit: Elsevier/Chauhana et al Mopping up heavy metal ions and detecting them simultaneously

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