Influence of Starch Polysaccharide on the Remolded Properties of 2 Indian clay Samples

The reported presence in marine clays and the recognized role of polysaccharide as a bonding agent provided the motivation to examine the role of starch polysaccharide in the remoulded properties of nonswelling (kaolinite) and swelling (bentonite) groups of clays. The starch polysaccharide belongs to a group of naturally occurring, large-sized organic molecules (termed polymers) and is built up by extensive repetition of simple chemical units called repeat units. The results of the study indicate that the impact of the starch polysaccharide on the remoulded properties of clays is dependent on the mineralogy of the clays. On addition to bentonite clay, the immensely large number of segments (repeat units) of the starch polysaccharide create several polymer segment - clay surface bonds that cause extensive aggregation of the bentonite units layers. The aggregation of the bentonite unit layers greatly curtails the available surface area of the clay mineral for diffuse ion layer formation. The reduction in diffuse ion layer thickness markedly lowers the consistency limits and vane shear strength of the bentonite clay. On addition to kaolinite, the numerous polymer segment - clay surface bonds enhance the tendency of the kaolinite particles to flocculate. The enhanced particle flocculation is responsible apparently for a small to moderate increase in the liquid limit and remoulded undrained strength of the nonswelling clay.

Spectrally broadened excitonic absorption and enhanced optical nonlinearities in Dy3+-doped ZnO nanoparticles

We have synthesized Dy3+-doped ZnO nanoparticles at room temperature through the sol-gel method. X-ray diffraction and Scanning electron microscopic studies confirm the crystalline nature of the particles. Excitonic absorption of ZnO shows three different bands, and we observe that incorporation of Dy3+ results in the shifting and broadening of the n=1 absorption band of ZnO. Photoluminescence studies done at the excitation wavelength of 335 nm show broad emission containing five different bands. Open-aperture z-scan studies done at 532 nm using 5 ns laser pulses show an optical limiting behavior, which numerically fits to a three-photon type absorption process. The nonlinearity is essentially resonant, as it is found to increase consistently with Dy3+ concentration. This feature makes Dy3+-doped ZnO a flexible optical limiter for potential device applications.

Highly dispersed ultrafine Pt and PtRu nanoparticles on graphene: formation mechanism and electrocatalytic activity

We demonstrate a robust strategy for obtaining a high dispersion of ultrafine Pt and PtRu nanoparticles on graphene by exploiting the nucleation of a metal precursor phase on graphite oxide surfaces. Our method opens up new possibilities to engineer graphene-based hybrids for applications in multifunctional nanoscale devices.

Self-assembled composite nano-materials exploiting a thermo reversible n-acene fibrillar scaffold and organic-capped ZnO nanoparticles

An organic-inorganic composite material is obtained by self-assembly of 2,3-didecyloxy-anthracene (DDOA), an organogelator of butanol, and organic-capped ZnO nanoparticles (NPs). The ligand 3, 2,3-di(6-oxy-n-hexanoic acid)-anthracene, designed to cap ZnO and interact with the DDOA nanofibers by structural similarity, improves the dispersion of the NPs into the organogel. The composite material displays mechanical properties similar to those of the pristine DDOA organogel, but gelates at a lower critical concentration and emits significantly less, even in the presence of very small amounts of ZnO NPs. The ligand 3 could also act as a relay to promote the photo-induced quenching process.

Preparation and Characterization of MWCNT/ZnO nanoparticles Hybrid

ZnO nanoparticles (ZnO NPs) were grown on the surface of multiwall carbon nanotubes (MWCNTs) by a wet chemical synthesis route. The anchoring of ZnO NPs on acid-treated MWCNTs was achieved under remarkably mild reaction conditions (low temperature, atmospheric pressure, without any capping agents and no need for subsequent thermal annealing). MWCNT/ZnO NPs hybrid samples with varying loading of ZnO NPs are prepared. A very high degree of dispersion of ZnO NPs over the surface of MWCNT was achieved by suitably controlling the ratio of ZnO NPs and MWCNTs in the solution. The hybrid sample was characterized by electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). Transmission electron microscope images of the as-prepared MWCNT/ZnO NPs hybrid reveal that mono-dispersed ZnO NPs are anchored stably on functionalized MWCNTs. The interaction of ZnO NPs with MWCNT surface was interpreted through XPS analysis.

Iron, cobalt and nickel nanoparticles encapsulated in carbon obtained by the arc evaporation of graphite with the metals

Are evaporation of graphite with Fe, Co and Ni yields two distinct types of metal nanoparticles, wrapped in graphitic layers and highly resistant to oxidation. Electron microscopy shows that the metal particles (10-40 nm) in the stub region are encapsulated in carbon onions, the particles in the soot being considerably smaller (2-15 nm). The metal particles in the soot are either ferromagnetic with lowered Curie temperatures or superparamagnetic.

Kinetic evolution studies of silver nanoparticles in a bio-based green synthesis process

Silver nanoparticles are being extensively studied due to their widespread applications and unique properties. In the present study, the growth kinetics of silver nanoparticles as synthesized on reduction of silver nitrate solution by aqueous extract of Azadirachta indica leaves was investigated. The formation of silver nanoparticles was preliminarily monitored by measuring the absorption maxima at different time intervals after adding the reducing agent to the silver salt solution (0.5, 1, 1.5, 2, 2.5, 3, 3.5 and 4 h). At different time points characterization studies were conducted using X-ray diffraction studies, FT-IR techniques, zeta potential studies and transmission electron microscopy. The total available silver in the reaction medium was determined at different durations using ICP-OES. The changes in reduction potential in the medium were also monitored using potentiometric analysis. The results confirm a definite change in the medium pertaining to formation of the stable nanoparticles after 2 h, and a significant increase in the agglomeration tendency after 4 h of interaction. The growth kinetic data of the nanoparticles till 3.5 h was found to fit the LSW model confirming diffusion limited growth. (C) 2011 Elsevier B.V. All rights reserved.

Interaction of Inorganic Nanoparticles with Graphene

The changes in the electronic and magnetic properties of graphene induced by interaction with semiconducting oxide nanoparticles such as ZnO and TiO2 and with magnetic nanoparticles such as Fe3O4, CoFe2O4, and Ni are investigated by using Raman spectroscopy, magnetic measurements, and first-principles calculations. Significant electronic and magnetic interactions between the nanoparticles and graphene are found. The findings suggest that changes in magnetization as well as the Raman shifts are directly linked to charge transfer between the deposited nanoparticles and graphene. The study thus demonstrates significant effects in tailoring the electronic structure of graphene for applications in futuristic electronic devices.

Chemical Synthesis of Metal Nanoparticles Using Amine-Boranes

The development of new synthetic strategies to obtain mono-disperse metal nanoparticles on large scales is an attractive prospect in the context of sustainability. Recently, amine-boranes, the classical Lewis acid-base adducts, have been employed as reducing agents for the synthesis of metal nanoparticles. They offer several advantages over the traditional reducing agents like the borohydrides; for example, a much better control of the rate of reduction and, hence, the particle size distribution of metal nanoparticles; diversity in their reducing abilities by varying the substituents on the nitrogen atom; and solubility in various protic and aprotic solvents. Amine-boranes have not only been used successfully as reducing agents in solution but also in solventless conditions, in which along with the reduction of the metal precursor, they undergo in situ transformation to afford the stabilizing agent for the generated metal nanoparticles, thereby bringing about atom economy as well. The use of amine boranes for the synthesis of metal nanoparticles has experienced an explosive growth in a very short period of time. In this Minireview, recent progress on the use of amine boranes for the synthesis of metal nanoparticles, with a focus towards the development of pathways for sustainability, is discussed.

Microwave assisted synthesis and UV-Vis spectroscopic studies of silver nanoparticles synthesized using vanillin as a reducing agent

The present investigation explores the adaptability of a microwave assisted route to obtain silver nanoparticles by the reduction of AgNO3 with vanillin, an environmentally benign material. Anionic surfactants such as AOT and SDS were used separately for encapsulating AgNPs and their role was compared. The UV-Visible absorption spectra present a broad SPR band consisting of two peaks suggesting the formation of silver nanoparticle with bimodal size distribution. The TEM image shows particles with spherical and hexagonal morphologies which confirms the results of UV-Vis studies. The anisotropy in the particle morphology can be attributed to the surface oxidation which in turn produces Ag@Ag2O core-shell nanostructures. Thus an intriguing feature of this system is that the obtained colloid is a mixture of AgNPs with and without Ag2O layers. Studies on the influence of pH on the stability of the synthesized nanoparticles revealed that the presence of excess Ag2O layers has a profound influence on it. Ag2O layers can be removed from AgNPs' surface by changing the solution pH to the acidic regime. The present study attests the enhanced ability of AOT in stabilizing the AgNPs in aqueous media. (C) 2011 Elsevier B.V. All rights reserved.

Dissolution properties of BaTiO3 nanoparticles in aqueous suspensions

Dissolution of barium ion from aqueous suspensions of commercial nano-sized barium titanate powders (BaTiO3) has been studied at various pH values, solids loading, different time intervals and different electrolyte concentrations. Zeta potential measurements at various pH values and Fourier transform infrared spectroscopy study were also carried out to know the surface behaviour. Dissolution of Ba2+ depends on the suspension pH and stirring time period. The iso-electric points were found at 3.4 and 12.2 for as-received BaTiO3 powder and 2.3 for the leached BaTiO3. The Ba2+-leached BaTiO3 suspension retards further leaching of Ba2+ ions at different pH values, which favours the achievement of stable suspension.

Insertion of nickel nanoparticles in the interlayers of alpha-zirconium phosphate by the decomposition of the intercalated nickel acetate

By employing EXAFS and magnetic measurements, it is shown that nanoparticles of nickel along with those of NiO are incorporated between the layers of a-zirconium phosphate (ZrP) by the thermal decomposition of nickel acetate intercalated in ZrP. The nickel nanoparticles are superparamagnetic. Hydrogen reduction produces small ferromagnetic nickel particles, most of which appear to be outside the interlayer space of ZrP.

A facile route to synthesize silver nanoparticles in polyelectrolyte capsules

We are reporting a novel green approach to incorporate silver nanoparticles (NPs) selectively in the polyelectrolyte capsule shell for remote opening of polyelectrolyte capsules. This approach involves in situ reduction of silver nitrate to silver NPs using PEG as a reducing agent (polyol reduction method). These nanostructured capsules were prepared via layer by layer (LbL) assembly of poly(allylamine hydrochloride) (PAH) and dextran sulfate (DS) on silica template followed by the synthesis of silver NPs and subsequently the dissolution of the silica core. The size of silver nanoparticles synthesized was 60 +/- 20 nm which increased to 100 +/- 20 nm when the concentration of AgNO3 increased from 25 mM to 50 mM. The incorporated silver NPs induced rupture and deformation of the capsules under laser irradiation. This method has advantages over other conventional methods involving chemical agents that are associated with cytotoxicity in biological applications such as drug delivery and catalysis. (C) 2011 Elsevier B.V. All rights reserved.

Nanoparticles of SrTiO3 prepared by gel to crystallite conversion and their photocatalytic activity in the mineralization of phenol

Nanometre-sized powders of SrTiO3 were prepared at 70-100 degrees C by the wet-chemical method of gel to crystallite (G-C) conversion. The crystallite sizes obtained were in the range 5-13 nm, as estimated by transmission electron microscopy (TEM) studies. The photocatalytic activities of these powders in the mineralization of phenol were evaluated in comparison with Degussa P25 (TiO2). The maximum photocatalytic activity was observed for powders annealed in the range 1100-1300 degrees C. The optical spectra of the particle suspensions in water showed broadened absorption around the band gap region, together with the appearance of an absorption maximum in the UV region. The effect of inorganic oxidizing species as electron scavengers on the rate of the photocatalytic degradation of phenol was studied. The influence of bulk and surface defects, which participate in the charge transfer process during photocatalysis, was investigated systematically.

Potential-distance relationships of clay-water systems considering the Stern theory

This paper deals with the use of Stem theory as applied to a clay-water electrolyte system, which is more realistic to understand the force system at micro level man the Gouy-Chapman theory. The influence of the Stern layer on potential-distance relationship has been presented quantitatively for certain specified clay-water systems and the results are compared with the Gouy-Chapman model. A detailed parametric study concerning the number of adsorption spots on the clay platelet, the thickness of the Stern layer, specific adsorption potential and the value of dielectric constant of the pore fluid in the Stern layer, was carried out. This study investigates that the potential obtained at any distance using the Stern theory is higher than that obtained by the Gouy-Chapman theory. The hydrated size of the ion is found to have a significant influence on the potential-distance relationship for a given clay, pore fluid characteristics and valence of the exchangeable ion.