There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Adsorption of heavy metals on conventional and nanostructured materials for wastewater treatment purposes: A review

Role of nanomaterials in water treatment applications: a review.

This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

A Benchmark Study on the Thermal Conductivity of Nanofluids

Most of the metal ions are carcinogens and lead to serious health concerns by producing free radicals. Hence, fast and accurate detection of metal ions has become a critical issue. Among various metal ions arsenic, cadmium, lead, mercury and chromium are considered to be highly toxic. To detect these metal ions, electrochemical biosensors with interfaces such as microorganisms, enzymes, microspheres, nanomaterials like gold, silver nanoparticles, CNTs, and metal oxides have been developed. Among these, nanomaterials are considered to be most promising, owing to their strong adsorption, fast electron transfer kinetics, and biocompatibility, which are very apt for biosensing applications. The coupling of electrochemical techniques with nanomaterials has enhanced the sensitivity, limit of detection, and robustness of the sensors. In this review, toxicity mechanisms of various metal ions and their relationship towards the induction of oxidative stress have been summarized. Also, electrochemical biosensors employed in the detection of metal ions with various interfaces have been highlighted.

A review on detection of heavy metal ions in water – An electrochemical approach

Co9S8/graphene nanocomposites (Co9S8/G) at various concentrations of graphene and Co9S8 were prepared by a simple chemical route from cobalt nitrate and graphene as precursors in the presence of PVP as surfactant and thioacetamide (TAA) as sulfur source. To gain knowledge about the structural, morphological and physical properties, the composite material was analyzed by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetric Analysis (TGA). SEM measurements showed the presence of well dispersed, ∼300 nm sized Co9S8 nanoflakes. To assess the properties of the nanocomposites for their applicability in supercapacitors, electrochemical analysis was carried out in 6 M KOH electrolyte. A maximum specific capacitance of 808 F g−1 was observed for Co9S8/G-d at 5 mV s−1 scan rate. Galvanostatic charge–discharge curves showed the excellent cyclic stability of Co9S8/G-d composite with higher charge–discharge duration than pure Co9S8. The excellent electrochemical performance of the composite could be due to the better electrical conductivity behavior of graphene on Co9S8 nanoflakes.

Co9S8 nanoflakes on graphene (Co9S8/G) nanocomposites for high performance supercapacitors

Effect of reducing agent on graphene synthesis and its influence on charge storage towards supercapacitor applications

Synthesis of tin oxide/graphene (SnO 2 /G) nanocomposite and its electrochemical properties for supercapacitor applications

Magnetic cobalt and nickel ferrites (CoFe2O4 & NiFe2O4) with graphene nanocomposites (CoFe2O4–G & NiFe2O4–G) were synthesized via a solvothermal process and used as an adsorbent for the removal of lead (Pb(II)) and cadmium (Cd(II)) ions from aqueous solution. The as-prepared materials were characterized by field emission-scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), a Brunauer–Emmett–Teller (BET) surface area analyzer, transmission electron microscopy (TEM) and VSM analysis. To probe the nature of the adsorbent, various experiments were investigated like contact time, adsorbent dose, solution pH and temperature were optimized. The isotherm model fitting studies demonstrated that the data fitted the Langmuir isotherm model well. The highest adsorption equilibrium for Pb(II) is 142.8 and 111.1 mg g−1 at pH of 5 and 310 K for CoFe2O4–G & NiFe2O4–G; while for Cd(II) it was 105.26 and 74.62 mg g−1 at pH of 7 and 310 K. The results show that such type of materials could be used for the removal of heavy metal ions from water for environmental applications.

V. Velmurugan

Papers

Role of nanomaterials in water treatment applications: a review.

Co9S8 nanoflakes on graphene (Co9S8/G) nanocomposites for high performance supercapacitors

Effect of reducing agent on graphene synthesis and its influence on charge storage towards supercapacitor applications

Synthesis of tin oxide/graphene (SnO 2 /G) nanocomposite and its electrochemical properties for supercapacitor applications

CoFe2O4 and NiFe2O4@graphene adsorbents for heavy metal ions – kinetic and thermodynamic analysis