Coloration of cotton fibers with anisotropic silver nanoparticles

Anisotropic silver nanoparticles were assembled on cotton fibers to realize the coloration of cotton. The assembly of silver nanoparticles on fibers was achieved by linking of poly(diallyldimethylammonium chloride) (PDDA) at room temperature. The silver nanoparticle treated cotton showed different colors because of localized surface plasmon resonance (LSPR) property of silver nanoparticles. The coloration was completed through electrostatic interaction between the PDDA treated cotton surface and the anisotropic silver nanoparticles in the reaction system. Scanning electron microscopy (SEM) characterization demonstrated that the morphologies of silver nanoparticles remained unchanged during the coloration process, so the treated cotton inherited the LSPR optical features of silver nanoparticles. Moreover, the cotton colorated with silver nanoparticles showed reasonably good color fastness to washing, which will facilitate the practical application of this coloration process.

Silver nanoparticles prepared by gamma irradiation across metal-organic framework templates

In this study, we demonstrate for the first time the successful fabrication of well-dispersed ultrafine silver nanoparticles inside metal-organic frameworks through a single step gamma irradiation at room temperature. HKUST-1 crystals are soaked in silver nitrate aqueous solution and irradiated with a Cobalt 60 source across a range of irradiation doses to synthesize highly uniformly distributed silver nano-particles. The average size of the silver nanoparticles across the Ag@HKUST-1 materials is found to vary between 1.4 and 3 nm for dose exposures between 1 and 200 kGy, respectively. The Ag@HKUST-1 hybrid crystals exhibit strong surface plasmon resonance and are highly durable and efficient catalytic materials for the reduction of 4-nitrophenol to 4-aminophenol (up to 14.46 × 10-3 s-1 for 1 kGy Ag@HKUST-1). The crystals can be easily recycled for at least five successive cycles of reaction with a conversion efficiency higher than 99.9%. The gamma irradiation is demonstrated to be an effective and environmental friendly process for the synthesis of nano-particles across confined metal-organic frameworks at room temperature with potential applications in environmental science.

Comparative study of materials-binding peptide interactions with gold and silver surfaces and nanostructures : A thermodynamic basis for biological selectivity of inorganic materials

Controllable 3D assembly of multicomponent inorganic nanomaterials by precisely positioning two or more types of nanoparticles to modulate their interactions and achieve multifunctionality remains a major challenge. The diverse chemical and structural features of biomolecules can generate the compositionally specific organic/inorganic interactions needed to create such assemblies. Toward this aim, we studied the materials-specific binding of peptides selected based upon affinity for Ag (AgBP1 and AgBP2) and Au (AuBP1 and AuBP2) surfaces, combining experimental binding measurements, advanced molecular simulation, and nanomaterial synthesis. This reveals, for the first time, different modes of binding on the chemically similar Au and Ag surfaces. Molecular simulations showed flatter configurations on Au and a greater variety of 3D adsorbed conformations on Ag, reflecting primarily enthalpically driven binding on Au and entropically driven binding on Ag. This may arise from differences in the interfacial solvent structure. On Au, direct interaction of peptide residues with the metal surface is dominant, while on Ag, solvent-mediated interactions are more important. Experimentally, AgBP1 is found to be selective for Ag over Au, while the other sequences have strong and comparable affinities for both surfaces, despite differences in binding modes. Finally, we show for the first time the impact of these differences on peptide mediated synthesis of nanoparticles, leading to significant variation in particle morphology, size, and aggregation state. Because the degree of contact with the metal surface affects the peptide's ability to cap the nanoparticles and thereby control growth and aggregation, the peptides with the least direct contact (AgBP1 and AgBP2 on Ag) produced relatively polydispersed and aggregated nanoparticles. Overall, we show that thermodynamically different binding modes at metallic interfaces can enable selective binding on very similar inorganic surfaces and can provide control over nanoparticle nucleation and growth. This supports the promise of bionanocombinatoric approaches that rely upon materials recognition.

Optical actuation of inorganic/organic interfaces: comparing peptide-azobenzene ligand reconfiguration on gold and silver nanoparticles

Photoresponsive molecules that incorporate peptides capable of material-specific recognition provide a basis for biomolecule-mediated control of the nucleation, growth, organization, and activation of hybrid inorganic/organic nanostructures. These hybrid molecules interact with the inorganic surface through multiple noncovalent interactions which allow reconfiguration in response to optical stimuli. Here, we quantify the binding of azobenzene-peptide conjugates that exhibit optically triggered cis-trans isomerization on Ag surfaces and compare to their behavior on Au. These results demonstrate differences in binding and switching behavior between the Au and Ag surfaces. These molecules can also produce and stabilize Au and Ag nanoparticles in aqueous media where the biointerface can be reproducibly and reversibly switched by optically triggered azobenzene isomerization. Comparisons of switching rates and reversibility on the nanoparticles reveal differences that depend upon whether the azobenzene is attached at the peptide N- or C-terminus, its isomerization state, and the nanoparticle composition. Our integrated experimental and computational investigation shows that the number of ligand anchor sites strongly influences the nanoparticle size. As predicted by our molecular simulations, weaker contact between the hybrid biomolecules and the Ag surface, with fewer anchor residues compared with Au, gives rise to differences in switching kinetics on Ag versus Au. Our findings provide a pathway toward achieving new remotely actuatable nanomaterials for multiple applications from a single system, which remains difficult to achieve using conventional approaches.

Optical actuation of inorganic/organic interfaces: comparing peptide-azobenzene ligand reconfiguration on gold and silver nanoparticles

Photoresponsive molecules that incorporate peptides capable of material-specific recognition provide a basis for biomolecule-mediated control of the nucleation, growth, organization, and activation of hybrid inorganic/organic nanostructures. These hybrid molecules interact with the inorganic surface through multiple noncovalent interactions which allow reconfiguration in response to optical stimuli. Here, we quantify the binding of azobenzene-peptide conjugates that exhibit optically triggered cis-trans isomerization on Ag surfaces and compare to their behavior on Au. These results demonstrate differences in binding and switching behavior between the Au and Ag surfaces. These molecules can also produce and stabilize Au and Ag nanoparticles in aqueous media where the biointerface can be reproducibly and reversibly switched by optically triggered azobenzene isomerization. Comparisons of switching rates and reversibility on the nanoparticles reveal differences that depend upon whether the azobenzene is attached at the peptide N- or C-terminus, its isomerization state, and the nanoparticle composition. Our integrated experimental and computational investigation shows that the number of ligand anchor sites strongly influences the nanoparticle size. As predicted by our molecular simulations, weaker contact between the hybrid biomolecules and the Ag surface, with fewer anchor residues compared with Au, gives rise to differences in switching kinetics on Ag versus Au. Our findings provide a pathway toward achieving new remotely actuatable nanomaterials for multiple applications from a single system, which remains difficult to achieve using conventional approaches.

Selective oxidation synthesis of MnCr2O4 spinel nanowires from Commercial stainless steel foil

For the first time, MnCr₂O₄ spinel single-crystalline nanowires were simply synthesized by heating commercial stainless steel foil (Cr_0.19Fe_0.70Ni_0.11) under a reducing atmosphere. The nanowires have an average diameter of 50 nm and a length of about 10 μm. Some nanowires are sheathed with a thin layer of amorphous silicon oxide. Photoluminescence measurements revealed that the nanowires exhibit an emission band at 435 nm, which resulted from the oxygen-related defects in the silicon oxide sheath. It was found that the reducing atmosphere plays a key role for the nanowire growth. In the reducing atmosphere, the Mn and Cr elements in the stainless steel could be selectively oxidized because of their higher affinity for oxygen than the Fe and Ni elements. The Fe and Ni elements in the stainless steel, however, acted as the catalyst for the vapor–liquid–solid (VLS) growth of the MnCr₂O₄ nanowires.

Catalytic properties of nanofibrous carbon in selective oxidation of hydrogen sulphide

Nanofibrous carbonaceous materials (NFC) as a new class of materials having many applications, can catalyze the selective oxidation of H2S to sulfur. The correlation between NFC structure and its activity and selectivity in H2S oxidation was determined. It is demonstrated that selectivity can be improved if NFC with more ordered structure be synthesized and the portion of the original catalyst in carbon be reduced by increasing the carbon accumulated in the catalyst.

New effective catalysts based on mesoporous nanofibrous carbon for selective oxidation of hydrogen sulfide

The systems based on granular mesoporous nanofibrous carbonaceous (NFC) materials synthesized by decomposition of hydrocarbons over nickel- containing catalysts are promising catalysts for selective oxidation of hydrogen sulfide. Sample series of nanofibrous carbon with three main types of their fiber structures and different contents of metal catalysts inherited from the catalysts for their synthesis were studied in this reaction. The correlation between NFC structure and its activity and selectivity in hydrogen sulfide oxidation was determined. The metal inherited from the initial catalysts for the synthesis of NFC influences the activity and selectivity of the resulting carbon catalysts. A particular influence is observed in the case of the catalyst withdrawn from the synthesis reactor at the stage of stationary operation of the metal catalyst (low specific carbon yields per unit weight of the catalyst). The presence of the metal phase results in an increase in the carbon catalyst activity and in a decrease in the selectivity to sulfur. NFC samples with the highest activity and selectivity are nanotubes and those with graphite planes perpendicular to the axis of the fibers. Carbon nanotubes have high selectivity, while samples obtained on copper–nickel catalysts also possess high activity. The promising NFC catalysts provide high conversion and selectivity (almost independent of the molar oxygen/hydrogen sulfide ratio) when a large excess of oxygen is contained in the reaction mixture.

A resonance tunable and durable LSPR nano-particle sensor : AL2O3 capped silver nano-disks

Localized surface plasmon resonance (LSPR) biosensors are employed to detect target biomolecules which have particular resonance wavelengths. Accordingly, tunability of the LSPR wavelength is essential in designing LSPR devices. LSPR devices employing silver nano-particles present better efficiencies than those using other noble metals such as gold; however, silver nano-particles are easily oxidized when they come in contact with liquids, which is inevitable in biosensing applications. To attain both durability and tunabilty in a LSPR biosensor, this paper proposes alumina (AL₂O₃) capped silver nano-disks. It is shown that through controlling the thickness of the cap, the LSPR resonance frequency can be finely tuned over a wide range; and moreover, the cap protects silver nano-particles from oxidation and high temperature.

Structure of the electrical double layer at aqueous gold and silver interfaces for saline solutions

We report the structure of the electrical double layer, determined from molecular dynamics simulations, for a range of saline solutions (NaCl, KCl, MgCl2 and CaCl2) at both 0.16 and 0.60molkg(-1) on different facets of the gold and silver aqueous interfaces. We consider the Au/Ag(111), native Au/Ag(100) and reconstructed Au(100)(5×1) facets. For a given combination of metallic surface and facet, some variations in density profile are apparent across the different cations in solution, with the corresponding chloride counterion profiles remaining broadly invariant. All density profiles at the higher concentration are predicted to be very similar to their low-concentration counterparts. We find that each electrolyte responds differently to the different metallic surface and facets, particularly those of the divalent metal ions. Our findings reveal marked differences in density profiles between facets for a given metallic interface for both Mg(2+) and Ca(2+), with Na(+) and K(+) showing much less distinction. Mg(2+) was the only ion for which we find evidence of materials-dependent differences in interfacial solution structuring between the Ag and Au.

Gold and silver mining in the 16th and 17th centuries, land titles and agricultural productivity

Although agricultural productivity is critical for economic development very little is known about the causes of the large dispersion in agricultural productivity across the world. Microeconomic studies increasingly stress the lack of land rights in many poor countries as an important source of low productivity. This paper examines the role played by land titles in explaining differences in agricultural productivity for 93 countries. Using the per capita accumulated value of gold and silver production in the 16th and 17th centuries as instruments for land rights it is shown that enforcement of land titles is a significant source of agricultural productivity inequality across the world.

Plasmon-enhanced two-photon-induced isomerization for highly-localized light-based actuation of inorganic/organic interfaces

Two-photon initiated photo-isomerization of an azobenzene moiety adsorbed on silver nanoparticles (Ag NPs) is demonstrated. The azobenzene is linked to a materials-binding peptide that brings it into intimate contact with the Ag NP surface, producing a dramatic enhancement of its two-photon absorbance. An integrated modeling approach, combining advanced conformational sampling with Quantum Mechanics/Capacitance Molecular Mechanics and response theory, shows that charge transfer and image charges in the Ag NP generate local fields that enhance two-photon absorption of the cis isomer, but not the trans isomer, of adsorbed molecules. Moreover, dramatic local field enhancement is expected near the localized surface plasmon resonance (LSPR) wavelength, and the LSPR band of the Ag NPs overlaps the azobenzene absorbance that triggers cis to trans switching. As a result, the Ag NPs enable two-photon initiated cis to trans isomerization, but not trans to cis isomerization. Confocal anti-Stokes fluorescence imaging shows that this effect is not due to local heating, while the quadratic dependence of switching rate on laser intensity is consistent with a two-photon process. Highly localized two-photon initiated switching could allow local manipulation near the focal point of a laser within a 3D nanoparticle assembly, which cannot be achieved using linear optical processes.

Photoinduced reversible shape conversion of silver nanoparticles assisted by TiO₂.

Silver nanoprisms were transformed into nanodecahedra through photoinduction of ultraviolet (UV) light in the presence of titanium dioxide (TiO2) quantum dots (QDs). Subsequently, the silver nanodecahedra were reconverted to silver nanoprisms under sodium lamp if there was sufficient citrate in the reaction system. The localized surface plasmon resonance (LSPR) optical properties of silver nanoparticles were tuned during photoinduced shape conversion. The photocatalytic activity of TiO2 QDs assisted the conversion of prisms to decahedra upon UV light irradiation. Nevertheless, the presence of TiO2 did not inhibit the photoinduced reconversion from decahedra to prisms by sodium light. It was demonstrated that citrate was indispensable in the photoinduction process. In addition, oxygen in solution played a vital role in the reversible shape conversion of silver nanoparticles. Moreover, simulated sunlight can convert silver nanoprisms to nanodecahedra instead of UV light with assistance of TiO2 QDs, which would promote the photoinduced reaction of silver nanoparticles based on a natural light source.