nan Anshup

A practical silver nanoparticle-based adsorbent for the removal of Hg2+ from water.

In this work, we describe the use of silver nanoparticles of 9 ± 2 and 20 ± 5 nm core diameter, protected by mercaptosuccinic acid (MSA) and supported on activated alumina for the removal of mercuric ions present in contaminated waters, at room temperature (28 ± 1 °C). These two nanoparticle samples were prepared by using two Ag:MSA ratios 1:6 and 1:3, respectively, during synthesis and were loaded on alumina at 0.5 and 0.3% by weight. The mechanism of interaction of silver nanoparticles with Hg(2+) ions was studied using various analytical techniques such as ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering (DLS), inductively coupled plasma-optical emission spectrometry (ICP-OES), energy dispersive analysis of X-rays (EDAX), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Interactions of the metal ion with the metal core, the surface head group and the monolayer functionality were investigated. A high removal ability of 0.8 g of mercury per gram of Ag@MSA was achieved in the case of 1:6 Ag@MSA. These two materials show better uptake capacity of Hg(2+) in the pH range of 5-6. The ease of synthesis of the nanomaterial by wet chemistry, capability to load on suitable substrates to create stable materials and affordable cost will make it possible to use this approach in field applications, especially for the treatment of Hg(2+) contaminated waters.

High yield combustion synthesis of nanomagnesia and its application for fluoride removal.

We describe a novel combustion synthesis for the preparation of Nanomagnesia (NM) and its application in water purification. The synthesis is based on the self-propagated combustion of the magnesium nitrate trapped in cellulose fibers. Various characterization studies confirmed that NM formed is crystalline with high phase purity, and the particle size varied in the range of 3-7nm. The fluoride scavenging potential of this material was tested as a function of pH, contact time and adsorbent dose. The result showed that fluoride adsorption by NM is highly favorable and the capacity does not vary in the pH range usually encountered in groundwater. The effects of various co-existing ions usually found in drinking water, on fluoride removal were also investigated. Phosphate was the greatest competitor for fluoride followed by bicarbonate. The presence of other ions studied did not affect the fluoride adsorption capacity of NM significantly. The adsorption kinetics followed pseudo-second-order equation and the equilibrium data are well predicted by Frendlich equation. Our experimental evidence shows that fluoride removal happened through isomorphic substitution of fluoride in brucite. A batch household defluoridation unit was developed using precipitation-sedimentation-filtration techniques, addressing the problems of high fluoride concentration as well as the problem of alkaline pH of the magnesia treated water. The method of synthesis reported here is advantageous from the perspectives of small size of the nanoparticle, cost-effective recovery of the material and improvement in the fluoride adsorption capacity.

Towards a practical solution for removing inorganic mercury from drinking water using gold nanoparticles

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.

Biopolymer-reinforced synthetic granular nanocomposites for affordable point-of-use water purification

Creation of affordable materials for constant release of silver ions in water is one of the most promising ways to provide microbially safe drinking water for all. Combining the capacity of diverse nanocomposites to scavenge toxic species such as arsenic, lead, and other contaminants along with the above capability can result in affordable, all-inclusive drinking water purifiers that can function without electricity. The critical problem in achieving this is the synthesis of stable materials that can release silver ions continuously in the presence of complex species usually present in drinking water that deposit and cause scaling on nanomaterial surfaces. Here we show that such constant release materials can be synthesized in a simple and effective fashion in water itself without the use of electrical power. The nanocomposite exhibits river sand-like properties, such as higher shear strength in loose and wet forms. These materials have been used to develop an affordable water purifier to deliver clean drinking water at US

Enhanced visual detection of pesticides using gold nanoparticles

2.5/y per family. The ability to prepare nanostructured compositions at near ambient temperature has wide relevance for adsorption-based water purification.

Antimicrobial silver: An unprecedented anion effect

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. The method 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.

Confined Metastable 2-Line Ferrihydrite for Affordable Point-of-Use Arsenic-Free Drinking Water.

Silver is an indispensable metal but its use has to be minimised for sustainable growth. Much of the silver lost during use is unrecoverable; an example being its use as an antimicrobial agent, a property known since ages. While developing methods to create an affordable drinking water purifier especially for the developing world, we discovered that 50 parts per billion (ppb) of Ag+ released continuously from silver nanoparticles confined in nanoscale cages is enough to cause antimicrobial activity in conditions of normal water. Here we show that the antibacterial and antiviral activities of Ag+ can be enhanced ~1,000 fold, selectively, in presence of carbonate ions whose concentration was maintained below the drinking water norms. The protective layers of the organisms were affected during the carbonate-assisted antimicrobial activity. It is estimated that ~1,300 tons of silver can be saved annually using this new way to enhance its antimicrobial activity.

Chapter 16 – Detection and Extraction of Pesticides from Drinking Water Using Nanotechnologies

Arsenic-free drinking water, independent of electrical power and piped water supply, is possible only through advanced and affordable materials with large uptake capacities. Confined metastable 2-line ferrihydrite, stable at ambient temperature, shows continuous arsenic uptake in the presence of other complex species in natural drinking water and an affordable water-purification device is made using the same.

Noble metal nanoparticles for water purification: a critical review

Intensive farming, rapid industrialization, and increasingly sophisticated lifestyles have added artificial chemicals into many water bodies. While pesticide residues in groundwater was unexpected years ago as soil was thought to act as a filter, it is an established fact that groundwater sources in many parts of the world are heavily contaminated with them. Although these levels are significant vis-a-vis the permissible limits, the concentrations are low in comparison to those of other commonly encountered chemicals and the purification technologies have to be efficient for them to be removed at affordable cost. For such a solution to be useful for all strata of the society, it needs to be economically attractive, requiring zero electricity and minimum maintenance. Any novel technology should solve the problem in its entirety and not result in toxic by-products or residuals. These requirements pose numerous challenges to chemistry and engineering, some of which are discussed here.