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This paper describes a versatile, and simple synthetic route for the preparation of a range of reduced graphene oxide (RGO)-metal/metal oxide composites and their application in water purification. The inherent reduction ability of RGO has been utilized to produce the composite structure from the respective precursor ions. Various spectroscopic and microscopic techniques were employed to characterize the as-synthesized composites. The data reveal that the RGO-composites are formed through a redox-like reaction between RGO and the metal precursor. RGO is progressively oxidized primarily to graphene oxide (GO) and the formed metal nanoparticles are anchored onto the carbon sheets. Metal ion scavenging applications of RGO-MnO2 and RGO-Ag were demonstrated by taking Hg(II) as the model pollutant. RGO and the composites give a high distribution coefficient (Kd), greater than 10Lg-1 for Hg(II) uptake. The Kd values for the composites are found to be about an order of magnitude higher compared to parent RGO and GO for this application. A methodology was developed to immobilize RGO-composites on river sand (RS) using chitosan as the binder. The as-supported composites are found to be efficient adsorbent candidates for field application. � 2010 Elsevier B.V.

Manganese dioxide nanowhiskers (MDN), prepared by the reduction of potassium permanganate by ethyl alcohol has been investigated as an adsorbent for Hg(II) removal from aqueous medium. Characterization of the as-synthesized material was carried out using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). SEM and TEM data showed that the as-synthesized MDN looks like agglomerated whiskers of 5-10nm in diameter and 100-300nm in length. XRD data revealed the formation of birnessite type layered manganese dioxide. Mn(IV) oxidation state of Mn in MDN was confirmed by XPS. Batch experiments were conducted to evaluate the Hg(II) adsorption capacity of MDN. Hg(II) adsorption on MDN is a fast process and the kinetics followed a pseudo-second-order rate equation. The Hg(II) uptake varied with pH and showed optimum performance at pH 6-9. The experimental evidence revealed that physisorption is the dominating mechanism in Hg(II) removal. Considering the practical difficulty in handling nanomaterials, MDN was supported on Al2O3 (MDN@Al2O3) and the composite was shown to be an efficient adsorbent for Hg(II) from simulated chlor-alkali industrial effluent. The results suggest that this material can be a practical solution for Hg(II) scavenging in several industrial processes. � 2010 Elsevier B.V.

We describe an innovative approach based on alloying of metals to remove metal ions from drinking water. A novel adsorbent, gold nanoparticle supported on alumina, was developed for the removal of inorganic mercury from water. The observed adsorption capacity for mercury is 4.065 gm per gm of gold nanoparticles, which is ∼10 times higher metal adsorption capacity than previously reported adsorbents. Gold nanoparticle has been supported on alumina, at a capacity of 738 mg/kg alumina, for use in practical applications. Batch and column studies were done for adsorption analysis and a practical filter has been developed. The interaction between gold and mercury was studied using UV-vis, TEM, SEM, EDAX and XRD. The chemistry of metal alloying can be utilized for sequestration of mercury from drinking water. Established separation techniques for recovery of metals from the alloy can be utilized, making this a complete solution for drinking water applications.

We report an in situ soft chemical synthesis of a novel hybrid material, cellulose-nanoscale-manganese oxide composite (C-NMOC), and its application for Pb(II) removal from aqueous solutions. For comparison, detailed Pb(II) adsorption studies were also performed with nanoscale-manganese oxide powder (NMO), prepared through a similar route. Various spectroscopic and microscopic techniques were used to characterize the as-synthesized materials. X-ray photoelectron spectroscopic (XPS) measurements confirmed the existence of Mn(IV) phase in NMO whereas C-NMOC showed largely the Mn(III) phase. The existence and uniform distribution of manganese oxide in cellulose fiber materials was confirmed by SEM and EDAX analyses. The adsorption studies reveal that the Pb(II) uptake onto C-NMOC is a fast process and >90% of the uptake occurred within the first 10min contact time. The Sips isotherm predicted the equilibrium data well and the maximum Pb(II) uptake capacity of C-NMOC (4.64% Mn loading) was estimeted to be 80.1mgg-1. The Pb(II) adsorption capacity of C-NMOC (per gram of Mn present) was several times higher than commercial manganese oxide (?-MnO2) and at least twice larger than NMO. The experimental evidence reveals that physisorption plays a dominant role in Pb(II) adsorption by both NMO and C-NMOC. � 2010 Elsevier B.V.

The presence of parts per billion (ppb) levels of chlorpyrifos (O, O-Diethyl-O-(3,5,6-trichloro-2-pyridyl) phosphorothioate) and malathion (S-1,2-bis(ethoxycarbonyl) ethyl O, O-dimethyl phosphorodithioate), two common pesticides found in the surface waters of developing countries, have been visually detected using gold nanoparticles. Visual detection of the presence of pesticide is possible when the color change occurring by the adsorption of pesticides on gold nanoparticles is enhanced by sodium sulfate. The method presented here is simple and there is no need of sample preparation or preconcentration. The response occurs within seconds and the color change is very clear. The detection is possible if chlorpyrifos and malathion are present up to a concentration of 20 and 100 ppb, respectively. Themethod shows great potential for on-site pesticide monitoring. The method is also applicable as a qualitative technique for the performance evaluation of various household water filters, which claim pesticide removal. � Taylor & Francis Group, LLC.