V.T.P. Vinod

Visible-light-driven SnO2/TiO2 nanotube nanocomposite for textile effluent degradation

Nanocomposite of SnO2/TiO2 nanotube (NT) was prepared by a simple two-step procedure, viz., hydrothermal preparation of TiO2 NT followed by chemical precipitation of SnO2 nanoparticle sensitized TiO2 NT. Transmission electron microscopy analysis revealed that the as-synthesized TiO2 NTs exhibit a diameter of 20–30 nm and a length of 1–2 μm with a wall thickness of 2–5 nm. The particle size of SnO2 nanoparticles in the composite was estimated to be 4–6 nm. Both the TiO2 NT and SnO2/TiO2 NT composite were considered for the photocatalytic degradation of textile dye effluent under UV and sunlight irradiation. The SnO2/TiO2 NT composite showed improved degradation efficiency. Photoluminescence spectra of SnO2/TiO2 NT composites showed a decrease in intensity when compared to the TiO2 NT – revealing that the rate of recombination is reduced in the SnO2/TiO2 NT composite, which is responsible for larger photocatalytic activity. Further, an effluent degradation efficiency of 85% was obtained for the SnO2/TiO2 NT composite under sunlight irradiation and this can be considered as one of the best values achieved so far.

Morphology and metal binding characteristics of a natural polymer-kondagogu (Cochlospermum gossypium) gum.

Kondagogu (Cochlospermum gossypium) gum (KG), a natural tree exudate, was investigated for its morphological, adsorption and metal interaction behavior with various toxic heavy metals (Pb, Cd, Ni, Cr and Fe). SEM, AFM and TEM techniques were used to study the morphological changes occurring after metal adsorption onto the biopolymer structure. The degree of biosorption of metals on KG biopolymer surfaces was assessed by small-angle X-ray scattering analysis. EDXA spectrum revealed that the ion-exchange mechanism plays a major role in the binding process between KG and metal ions. The higher electron density observed in the KG-Cd complex suggests that Cd is strongly bound to KG compared to the other metals. This work provides a potential platform for developing a hydrocolloid-based nanogel for bioremediation of environmental contaminants.

Large scale synthesis and formation mechanism of highly magnetic and stable iron nitride (ε-Fe3N) nanoparticles

e-Fe3N magnetic nanoparticles with an average size of 45 nm were synthesized by nitriding the zero valent iron nanoparticle precursors using ammonia gas as a reactive ambience. The technique reported in this study is found to be promising in producing highly stable e-Fe3N magnetic nanoparticles and can be extended to other forms of Fe-nitrides.

Coercivity enhancement in Mn-Al-Cu flakes produced by surfactant-assisted milling

We herein report the achievement of exceptionally high coercivity (Hc) values: 9.92 and 5.86 kOe at 5 and 300 K, respectively, for Mn55Al43Cu2 flakes produced by surfactant-assisted milling process without employing any heat-treatment. The use of surfactants such as oleic acid and oleylamine during milling yielded high-aspect ratio flakes for the Mn-Al-Cu alloy. Structural studies confirmed the presence of τ- and β-phases as the major constituents in the Mn-Al-Cu flakes. The observed Hc enhancement is due to the increase in anisotropy field and structural defects, which is hypothesized to originate from the domain-wall pinning as a consequence of precipitation of fine Cu-particles present at the grain boundaries.

A surfactant-assisted high energy ball milling technique to produce colloidal nanoparticles and nanocrystalline flakes in Mn–Al alloys

We herein exploit the advantages of surfactant assisted-high energy ball milling (SA-HEBM) for the processing of Mn–Al alloy. In this method, a combination of two surfactants, such as oleic acid and oleylamine, was used along with a solvent, n-heptane, during milling. The use of the SA-HEBM process yielded two different products: a sediment powder consisting of sub-micron sized Mn–Al flakes and a suspension in the milling medium (colloid) containing Mn–Al nanoparticles. The colloid consisted of Mn–Al nanocrystalline particles (5–16 nm) having a lamellar morphology with an average thickness of 1.5 nm and length of 16 nm. Magnetic measurements of these colloidal nanoparticles demonstrated an almost non-magnetic behavior at 300 K. The Mn–Al sediment powders obtained with the SA-HEBM process at regular milling time intervals were investigated for their structural and magnetic performance and also compared with the corresponding powders obtained from the conventional HEBM process. The phase composition of Mn–Al powders processed by both HEBM and SA-HEBM is quite similar and they adhere to the phase constituents of parent alloy: τ-, β-phases with some traces of e-phase. Nevertheless, the estimated magnetic parameters such as saturation magnetization and coercivity for the SA-HEBM powders exhibited improved values, as compared to the HEBM powders. A maximum coercivity of 4.88 kOe was obtained for the 8 h milled SA-HEBM powder and this value is 23% higher than that of HEBM processed powder. The results were explained based on the effect of surfactants on the morphology of the milled powder.