N.K. Renuka

Supercharged ceria quantum dots with exceptionally high oxygen buffer action

Herein we present the exceptionally high oxygen buffer action of ceria quantum dots of size 3.7 nm. Ceria nanoparticles were obtained via a facile ammonia precipitation route, and were characterized using TEM, XRD, BET surface area analysis, XPS analysis and TPR study using H2 as the probe molecule. A supercharging effect that leads to low temperature oxygen release is observed in these ultra-fine ceria particles. Existence of under stoichiometry in the ceria nanostructures with practically no oxygen vacancies has been substantiated with experimental proof.

Facile synthesis of γ-Fe2O3 nanoparticles integrated H2Ti3O7 nanotubes structure as a magnetically recyclable dye-removal catalyst

Nanocomposites consisting of γ-Fe2O3 nanoparticles incorporated in hydrogen titanate (H2Ti3O7 or lepidocrocite-type or H2Ti2O4(OH)-type structures) nanotubes (HTNF) have been synthesized through a simple strategy involving the combination of hydrothermal treatment followed by an ion-exchange process both conducted in aqueous media. The resulting nanocomposites reveal high efficiency in dye-adsorption capacity, magnetic separability from an aqueous solution, and recyclability. The unique nanostructures of HTNF composites are composed of γ-Fe2O3 nanoparticles typically attached to the ends of HTN bundles rather than along the surface and exhibit high magnetic separability in an aqueous medium using a moderate external magnetic field. The methylene blue (MB) dye-adsorption characteristics of HTNF nanocomposites have been investigated by varying the amount of γ-Fe2O3 (0–25 wt%) and the initial MB concentration (∼7.5–250 μM) at the initial solution-pH of ∼10. The HTNF nanocomposite with 5 wt% γ-Fe2O3 shows relatively higher MB dye adsorption capacity (99 mg g−1) along with reasonable magnetic separability (2 min) from an aqueous solution. The MB adsorption on the surface of the HTNF nanocomposites follows a pseudo-second-order kinetics model and the equilibrium adsorption isotherm follows both the Langmuir and Dubinin–Kaganer–Radushkevich (DKR) models. The recyclability of the HTNF magnetic nanocomposite in dye-removal application has been demonstrated by decomposing the previously adsorbed MB dye via surface-cleaning treatment conducted in H2O2 solution.

A novel template free synthetic strategy to graphene–iron oxide nanotube hybrid

A magnetically separable graphene–iron oxide nanotube composite was synthesised for the first time via an adept template free hydrothermal route. The physical characterization of the material was done using XRD, FTIR, SEM, TEM and VSM analysis. A mechanism analogous to the Kirkendall effect, involving the diffusion of Fe2+ ions and consequent expansion of voids leading to the formation of hollow iron oxide nanotubes has been proposed in accordance with the results obtained from XRD and TEM analysis. The composite turned out to be an excellent adsorbent for the removal of toxic Cr(VI) ions. Adsorptive removal and magnetic separation was achieved quickly within 60 seconds which highlights the efficiency of the prepared hybrid. The isotherm analysis indicated that the adsorption data can be represented by the Langmuir isotherm model. The superior adsorptive removal efficiency of the composite can be attributed to the synergistic effect between graphene and the iron oxide nanotubes. Through this report, we have demonstrated the first attempt of a template free synthesis of iron oxide nanotubes and their incorporation on graphene sheets. Subsequently the composites ability as an adsorbent was evaluated in its efficiency for Cr(VI) removal.

Redox properties and catalytic activity of CuO/γ-Al2O3 meso phase

Copper oxide based systems are well appreciated for their oxidation activity. The present piece of work discusses the redox properties and catalytic activity of CuO impregnated on mesoporous alumina support. A series of catalysts with copper loading varying from 2.0 to 14 wt% were prepared by deposition precipitation method on meso alumina obtained via surfactant assisted route using dodecylamine. CO oxidation has been taken as the test reaction for investigating the catalytic activity of these systems. The catalysts are characterised by TEM, SEM, XRD, FTIR spectroscopy, DR UV spectroscopy, N2 adsorption-desorption study, ESR spectroscopy and TPR using H2. The characterisations indicated CuO in highly dispersed amorphous state at copper loadings <14 wt% in the samples, and as crystalline phase at higher loadings. Easily reducible well dispersed CuO species favoured the reaction, indicating the decisive role of reducibility of the catalysts in CO oxidation. Almost complete oxidation of CO was affected over the system under the prescribed reaction conditions, and practically nil deactivation was recorded when the reaction was performed over a period of 50h.

An elegant and handy selective sensor for ppt level determination of mercury ions

We project a reduced graphene oxide-fluorescein sensor moiety that offers a quick, selective and sensitive optical response to the presence of a noxious heavy metal ion, mercury (Hg2+) in aqueous solution. A turn off and turn on optical response is envisaged by the unit on competitive adsorption of fluorescein and mercury ions on reduced graphene oxide sheets. The crux behind the sensing of Hg2+ ion by the reduced graphene oxide-fluorescein unit lies behind the decrease in absorbance/fluorescence intensity of the dye on complexing with reduced graphene oxide and the corresponding restoration of the optical response upon highly selective competitive adsorption of Hg2+ ions by reduced graphene oxide sheets. Quantification of these optical responses was attained by colorimetric and fluorimetric measurements, which yielded ppb level and ppt level mercury ion assay. The LOD values were 240 ppb and 780 ppt respectively for these analytical methods. The moiety is highly selective and specific for mercury ions over alkali, alkaline earth metals and its congeners. The significant advance in this investigation is the fabrication of a reduced graphene oxide-fluorescein unit as a qualitative read out tool for naked eye detection of Hg2+ ions in ppm levels noting the colour and for the visual detection of ppt levels of Hg2+ through fluorescence in UV light. A highly efficient GFU immobilized filter paper strip was developed which could sense Hg2+ under UV light in a concentration as low as ppb level. Moreover, investigations on tap water samples spiked with Hg2+ ions underlines that the reduced graphene oxide-fluorescein moiety can swiftly monitor Hg2+ levels in complex solutions and demonstrates its potential utility in practical applications.

P123 and solvent-assisted synthesis of titania nanocuboids with co-exposed {101} and {001} planes

A surfactant-assisted method is reported here for the successful synthesis of mesoporous assembled titania nanostructures. The surfactant used here is a non-ionic triblock copolymer, P123, which plays a dual role: controls the oriented growth assembly of nanostructures and acts as templates for the formation of a mesoporous structure. The coexistence of active exposed planes on the mesoporous anatase titania is noticed, which is a result of a dual solvent-assisted mechanism, the very first observation in this direction. The mesoporous nature of the sample is confirmed by low angle XRD and the nitrogen adsorption–desorption isotherm. The obtained mesopores possess a uniform pore size and the average pore diameter of 17.4 nm. Such a large pore width for mesoporous titania using the P123 template is reported rarely in the literature. The photocatalytic activity of the structure is commendable as proved by the decomposition of methylene blue dye. The activity is seen far higher than that of similar works reported previously under identical experimental conditions.

Novel template free synthetic strategy to single crystalline multishelled hollow nanospheroids of titania with boosted application potential

Hollow nanostructures have inspired curiosity for their fascinating properties that originate from the unique structure, combining their free inner nanospace and chemical functionality of boundary materials. Herein, we provide the first account on the fabrication of single crystalline multishelled titania hollow nanospheroids under mild conditions through a template free solvothermal method. Judicious control over the reaction time revealed that the synthetic stages pass through hollow spheres of various interiors, all of which are single crystalline in nature, which makes a significant advance in this field. The formation mechanism is explained by Ostwald ripening based dissolution and the recrystallization process. Evidence for secondary Ostwald ripening that leads to a multishelled metal oxide structure is presented for the first time. Another highlight of the report is the enhanced application potential of the material that the multishelled structure offers. The material was observed to be an outstanding photocatalyst than all of the titania structures previously reported under identical experimental conditions, which arises due to the multiple reflection of light from the complex interiors.

Synthesis, characterisation and activity of SBA-16 supported oxidation catalysts for CO conversion

Abstract V 2 O 5 , CeO 2 , and CuO were dispersed on rice husk derived SBA-16, and the CO oxidation activities of these systems were examined. The catalysts were characterised using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, temperature-programmed reduction, and diffuse reflectance ultraviolet spectroscopy. The CuO doped mesoporous silica was identified as a promising catalyst. More than 98% of CO conversion was achieved over the system.

Acid base properties and catalytic activity of vanadium pentoxide supported on cerium oxide

The surface acidity and basicity of vanadium pentoxide supported on CeO2 were determined using a set of Hammett indicators. The data have been correlated with the catalytic activity of these oxides towards liquid phase acylation of phenol.

Electron donor properties and catalytic activity of manganese ferrospinels

The electron donating properties of manganese ferrospinels of various compositions (MnFe2O4, Mn1.2Fe1.8O4, Mn2FeO4 and Mn2.5Fe0.5O4) were studied from the adsorption of electron acceptors of various electron affinity values from acetonitrile as solvent. The limit of electron transfer from the oxide surface is from 1.77 to 2.40 eV in terms of the electron affinity of the electron acceptor. The data have been correlated with the catalytic activity of these oxides towards autoxidation of sulfites. Both weak and strong electron donor sites catalyze the reaction.