Luminescent, freestanding composite films of Au<SUB>15</SUB> for specific metal ion sensing

A highly luminescent freestanding film composed of the quantum cluster, Au15, 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 Cu2+ 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 Hg2+, As3+, and As5+. The composite film exhibited visual sensitivity to Cu2+ 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 Cu2+ sensing may be due to the reduction of Cu2+ to Cu1+/Cu0 by the glutathione ligand or the Au15 core. Extended stability of the luminescence of the film makes it useful for practical applications

Reduced graphene oxide-metal/metal oxide composites: facile synthesis and application in water purification

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-MnO<SUB>2</SUB> and RGO-Ag were demonstrated by taking Hg(II) as the model pollutant. RGO and the composites give a high distribution coefficient (K<SUB>d</SUB>), greater than 10Lg<SUP>-1</SUP> for Hg(II) uptake. The K<SUB>d</SUB> 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

Luminescent, Freestanding Composite Films of Au₁₅ for Specific Metal Ion Sensing

A highly luminescent freestanding film composed of the quantum cluster, Au₁₅, 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 Cu²⁺ 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 Hg²⁺, As³⁺, and As⁵⁺. The composite film exhibited visual sensitivity to Cu²⁺ 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 Cu²⁺ sensing may be due to the reduction of Cu²⁺ to Cu¹⁺/Cu⁰ by the glutathione ligand or the Au₁₅ core. Extended stability of the luminescence of the film makes it useful for practical applications

Transparent, luminescent, antibacterial and patternable film forming composites of graphene oxide/reduced graphene oxide

Multifunctional graphene oxide/reduced graphene oxide (GO/RGO) composites were prepared through electrostatic interaction using biocompatible ingredients. Different functionalities were added to GO/RGO by anchoring materials such as native lactoferrin (NLf), NLf protected Au clusters (designated as Au@NLf), chitosan (Ch) and combinations thereof. Anchoring of Ch and NLf enhances the antibacterial property of RGO/GO. The addition of Ch to RGO/GO not only helped in forming stable dispersions but also helped in fabricating large (cm<SUP>2</SUP>) area films through a simple solvent evaporation technique. Functionalities such as photoluminescence were added to Ch-RGO/GO composites by anchoring Au@NLf on it. The composites thus formed showed stable luminescence in presence of various metal ions in the solid state. The composite showed reasonable stability against pH and temperature variations as well. The as-prepared films were transparent and the transparency could be modulated by controlling the concentration of RGO/GO in the composite. The antibacterial property and ability to form stable thin films may provide an opportunity to use such composites for medical and environmental remediation applications as well. Erasable patterns were fabricated on the film by stamping required patterns under compressive pressure. Luminescent patterns can be inscribed on the film and can be erased by simply wetting it. Such films with erasable information may be useful for security applications