We describe the degradation of chlorocarbons (CCl<inf>4</inf>, C <inf>6</inf>H<inf>5</inf>CH<inf>2</inf>Cl and CHCl<inf>3</inf>) in solution at room temperature (27 ± 4 °C) by the monolayer-protected silver quantum cluster, Ag<inf>9</inf>MSA<inf>7</inf> (MSA: mercaptosuccinic acid) in the presence of isopropyl alcohol (IPA). The main degradation products were silver chloride and amorphous carbon. Benzyl chloride was less reactive towards clusters than CCl<inf>4</inf> and CHCl<inf>3</inf>. Materials used in the reactions and the reaction products were characterized using several spectroscopic and microscopic tools such as ultraviolet-visible (UV/Vis) absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), photoluminescence spectroscopy, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), energy dispersive analysis of X-rays (EDAX) and scanning electron microscopy (SEM). We have shown that clusters are more efficient for the degradation of halocarbons than the corresponding monolayer-protected nanoparticles (Ag@MSA, particle diameter 15 ± 5 nm) at a given time and temperature. The higher reactivity of clusters is attributed to their small size and large surface area. Clusters and nanoparticles were used for reactions in supported (on neutral alumina) and unsupported forms. A possible mechanism for the reaction has been postulated on the basis of experimental results. © 2013 The Royal Society of Chemistry.

Pradeep Thalappil

Department Of Chemistry

Alumina

Amorphous carbon

Degradation

Fourier transform infrared spectroscopy

HALOCARBONS

Monolayers

Nanoparticles

Photoelectrons

Photoluminescence spectroscopy

Raman spectroscopy

Scanning electron microscopy

Silver

Silver halides

X ray diffraction

X ray photoelectron spectroscopy

Degradation products

ENERGY DISPERSIVE ANALYSIS OF X-RAYS

Isopropyl alcohols

Large surface area

MERCAPTOSUCCINIC ACIDS

MICROSCOPIC TOOLS

Particle diameters

Possible mechanisms

Chlorine compounds

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Journal of Materials Chemistry A

We present the first example of intercluster reactions between atomically precise, monolayer protected noble metal clusters using Au25(SR)18 and Ag44(SR)30 (RS- = alkyl/aryl thiolate) as model compounds. These clusters undergo spontaneous reaction in solution at ambient conditions. Mass spectrometric measurements both by electrospray ionization and matrix assisted laser desorption ionization show that the reaction occurs through the exchange of metal atoms and protecting ligands of the clusters. Intercluster alloying is demonstrated to be a much more facile method for heteroatom doping into Au25(SR)18, as observed by doping up to 20 Ag atoms. We investigated the thermodynamic feasibility of the reaction using DFT calculations and a tentative mechanism has been presented. Metal core-thiolate interfaces in these clusters play a crucial role in inducing these reactions and also affect rates of these reactions. We hope that our work will help accelerate activities in this area to establish chemistry of monolayer protected clusters. © 2015 American Chemical Society.

Journal of the American Chemical Society

Intercluster Reactions between Au25(SR)18 and Ag44(SR)30

This paper describes an unusual chemical reaction that takes place on a graphene composite in a concerted fashion. The reaction shows the conversion of a persistent organochlorine pesticide, lindane (C<inf>6</inf>H<inf>6</inf>Cl<inf>6</inf>), present in water, to different isomers of trichlorobenzenes (TCBs, C<inf>6</inf>H<inf>3</inf>Cl<inf>3</inf>) on the surface of reduced graphene oxide-silver composites (RGO@Ag). The reaction is unique to the composite and does not occur on RGO and nanoparticles of Ag separately. The products of the reaction were isolated and extensively characterized using analytical techniques such as gas chromatography-mass spectrometry, electrospray ionization mass spectrometry, infrared and NMR, which unequivocally confirmed their identity. The as-formed TCBs were removed from the aqueous medium by adsorption on the same composite. Adsorption of lindane is physical in nature, but that of TCBs is through - interactions. The study reveals the unusual chemical reactivity of graphene-metal composites and their potential for water treatment. The uniqueness of the reaction on RGO@Ag is due to the simultaneous removal of three HCl molecules, leading to the formation of aromatic compounds and concomitant formation of silver chloride. Recycling capacity and effect of diverse species present in natural waters were tested for potential applications in sustainable water treatment. © 2015 American Chemical Society.

ACS Sustainable Chemistry and Engineering

Simultaneous dehalogenation and removal of persistent halocarbon pesticides from water using graphene nanocomposites: A case study of lindane

Noble metal nanostructures are widely explored as they have unusual size- and shape-dependent physical, chemical, and optical properties. Silver and gold nanosystems were synthesized in a variety of forms-including spherical, rod, wire, triangle, star, and flower shapes. These systems were used for applications in catalysis, sensing, surface-enhanced Raman scattering, and many others. When the size of the particles of noble metal nanosystems (NMNs) reaches in-between molecules and nanoparticles (NPs), they exhibit molecular properties such as discrete optical absorption and photoluminescence. Use of bulk noble metals in water treatment and medicine is very well documented since ancient times. In recent history, water pollution has become one of the major problems throughout the world. The intensity of water contamination is becoming more complex with time because of the addition of a large number of chemicals and biological species, mainly because of anthropogenic activities. Permissible limits for most of the contaminants have decreased as time progressed. Technologies to be developed must be able to detect ultralow concentrations and remove large amounts of pollutants. NMNs promise to be efficient adsorbents for the treatment of polluted water as they exhibit high absorption and scattering cross-sections. In the recent past, noble metal clusters, a new category of materials, were employed in selective and sensitive detection of heavy metals and anions using their optical properties, efficient adsorption capacities, and high reactivity. Some of them were demonstrated as practical devices for these purposes. NMNs were found to exhibit affinity toward pesticides and novel mineralization reactions were seen with halocarbons. NPs of silver, palladium, and gold were also used for the removal of other organic molecules such as pharmaceuticals, dyes, explosives, and for the catalytic degradation of chlorinated solvents. Silver NPs and clusters have been shown to be useful as antimicrobial agents. In all the above applications, NMNs were used alone or as a component of the composite. In some cases, NMNs were supported onto metal oxide surfaces such as Fe2O3, TiO2, MgO, Al2O3, and Mn2O3 as the separation of materials and purified water is easy after treatment. Alloy NPs, alloy clusters, and composites are emerging materials, and they need to be explored as they provide new opportunities in comparison to the known materials. © 2014 Elsevier Inc. All rights reserved.

Water Reclamation and Sustainability

Noble Metal Nanosystems for the Detection and Removal of Pollutants in Drinking Water

Luminescent AgAu alloy quantum clusters are synthesized by a simple method that utilizes the galvanic reduction of polydisperse plasmonic silver nanoparticles. The clusters are characterized by ultraviolet-visible (UV/Vis) absorption spectroscopy, photoluminescence (PL) spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and matrix-assisted laser desorption ionization mass spectrometry (MALDI MS). Selective and tunable quenching of cluster luminescence by CuII ions is observed and depends highly on the solvent as well as the protecting ligands. Metal-ion selectivity is exclusively caused by metallophilic interactions with the cluster core, and the tunability depends on the nature of the protecting ligands as well as solvent effects. Detailed XPS and time-resolved luminescence measurements reveal that the tunability of luminescence quenching is achieved by the systematic variation of the metallophilic interactions between the Au I ions of the alloy cluster and CuI ions formed by the reduction of CuII ions by the cluster core. This is the first report of tunable metallophilic interactions between monolayer-protected quantum clusters and a closed-shell metal ion. We hope that these results will draw more attention to the field of quantum cluster-metal ion interactions and provide useful insights into the stability of these clusters, origin of their intense luminescence, mechanisms of metal-ion sensing, and also help in the development of methods for tuning their properties. Luminescent AgAu alloy quantum clusters are synthesized by the galvanic reduction of polydisperse plasmonic silver nanoparticles. Selective and tunable luminescence quenching by CuII ions depends on the solvent and protecting ligands. The tunability is achieved by variation of the metallophilic interactions between the AuI ions of the cluster and CuI ions formed by reduction by the cluster core. Copyright © 2014 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

European Journal of Inorganic Chemistry

Luminescent AgAu alloy clusters derived from ag nanoparticles- Manifestations of tunable AuI-CuI metallophilic interactions

Sub-nanometer-sized metal clusters, having dimensions between metal atoms and nanoparticles, have attracted tremendous attention in the recent past due to their unique physical and chemical properties. As properties of such materials depend strongly on size, development of synthetic routes that allows precise tuning of the cluster cores with high monodispersity and purity is an area of intense research. Such materials are also interesting owing to their wide variety of applications. Novel sensing strategies based on these materials are emerging. Owing to their extremely small size, low toxicity, and biocompatibility, they are widely studied for biomedical applications. Primary focus of this review is to provide an account of the recent advances in their applications in areas such as environment, energy, and biology. With further experimental and theoretical advances aimed at understanding their novel properties and solving challenges in their synthesis, an almost unlimited field of applications can be foreseen. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Particle and Particle Systems Characterization

Noble metal clusters: Applications in energy, environment, and biology

We describe the application of a recently discovered family of materials called quantum clusters, which are sub-nanometer particles composed of a few atoms with well-defined molecular formulae, exhibiting intense absorption and emission in the visible region in metal ion sensing, taking Ag 25 as an example. The changes in the optical properties of the cluster, in both absorption and emission upon exposure to various metal ions in aqueous medium are explored. The cluster can detect Hg 2+ down to ppb levels. It can also detect 5d block ions (Pt 2+, Au 3+ and Hg 2+) down to ppm limits. Hg 2+ interacts with the metal core as well as the functional groups of the capping agents and the interaction is concentration-dependent. To understand the mechanism behind this type of specific interaction, we have used spectroscopic and microscopic techniques such as UV-vis spectroscopy, luminescence spectroscopy, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). Specific reasons responsible for the interaction of Hg 2+ have been proposed. © 2011 Elsevier B.V.

Journal of Hazardous Materials

Luminescent sub-nanometer clusters for metal ion sensing: A new direction in nanosensors

An alloy cluster containing a 13-atom core, with a composition Ag 7Au 6(H 2MSA) 10 (H 2MSA= mercaptosuccinic acid) was synthesized from silver clusters by a galvanic exchange reaction. The clusters were characterized by several spectroscopic and microscopic methods. The alloy cluster shows luminescence with a quantum yield of 3.5 × 10 -2 at room temperature. Theoretical calculations for Ag 7Au 6(SCH 3) 10 suggest a distorted icosahedral core. Copyright © 2012 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Angewandte Chemie - International Edition

Ag 7Au 6: A 13-atom alloy quantum cluster

Application of nanoparticles (NPs) in environmental remediation such as water purification requires a detailed understanding of the mechanistic aspects of the interaction between the species involved. Here, an attempt was made to understand the chemistry of noble metal nanoparticle-pesticide interaction, as these nanosystems are being used extensively for water purification. Our model pesticide, chlorpyrifos (CP), belonging to the organophosphorothioate group, is shown to decompose to 3,5,6-trichloro-2-pyridinol (TCP) and diethyl thiophosphate at room temperature over Ag and Au NPs, in supported and unsupported forms. The degradation products were characterized by absorption spectroscopy and electrospray ionization mass spectrometry (ESI MS). These were further confirmed by ESI tandem mass spectrometry. The interaction of CP with NP surfaces was investigated using transmission electron microscopy, energy dispersive analysis of X-rays, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). XPS reveals no change in the oxidation state of silver after the degradation of CP. It is proposed that the degradation of CP proceeds through the formation of AgNP-S surface complex, which is confirmed by Raman spectroscopy. In this complex, the P-O bond cleaves to yield a stable aromatic species, TCP. The rate of degradation of CP increases with increase of temperature and pH. Complete degradation of 10 mL of 2 ppm CP solution is achieved in 3 h using 100 mg of supported Ag@citrate NPs on neutral alumina at room temperature at a loading of ∼0.5 wt %. The effect of alumina and monolayer protection of NPs on the degradation of CP is also investigated. The rate of degradation of CP by Ag NPs is greater than that of Au NPs. The results have implications to the application of noble metal NPs for drinking water purification, as pesticide contamination is prevalent in many parts of the world. Study shows that supported Ag and Au NPs may be employed in sustainable environmental remediation, as they can be used at room temperature in aqueous solutions without the use of additional stimulus such as UV light. © 2012 American Chemical Society.

Langmuir

Understanding the degradation pathway of the pesticide, chlorpyrifos by noble metal nanoparticles

A highly luminescent freestanding film composed of the quantum cluster, Au 15, was prepared. We studied the utility of the material for specific metal ion detection. The sensitivity of the red emission of the cluster in the composite to Cu 2+ has been used to make a freestanding metal ion sensor, similar to pH paper. The luminescence of the film was stable when exposed to several other metal ions such as Hg 2+, As 3+, and As 5+. The composite film exhibited visual sensitivity to Cu 2+ up to 1 ppm, which is below the permissible limit (1.3 ppm) in drinking water set by the U.S. environmental protection agency (EPA). The specificity of the film for Cu 2+ sensing may be due to the reduction of Cu 2+ to Cu 1+/Cu 0 by the glutathione ligand or the Au 15 core. Extended stability of the luminescence of the film makes it useful for practical applications. © 2012 American Chemical Society.

ACS Applied Materials and Interfaces

Luminescent, freestanding composite films of Au 15 for specific metal ion sensing

Nanotechnologies for the treatment of water, air and soil

Atomically precise silver clusters for efficient chlorocarbon degradation

Journal	Data powered by TypesetJournal of Materials Chemistry A
Publisher	Data powered by TypesetRoyal Society of Chemistry
ISSN	20507488
Open Access	No