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High surface area nanoparticles of antimony doped tin oxide are synthesized for the first time by one step solution combustion method using tin oxalate and antimony chloride as precursors. The synthesis method is rapid and gives particles of sizes 9–13 nm. The material has a specific surface area of 84 m2/g as estimated by Brunaure-Emmett-Teller (BET) model. The structural properties, surface morphologies, electrical and electrochemical properties are studied as a function of the dopant concentration. Effect of dopant concentration on X-ray diffraction (XRD) patterns shows some noticeable changes in particle size. Solid state UV spectroscopy demonstrates that due to the antimony doping, the band gap of SnO2 decreases significantly. Scanning tunneling spectroscopy (STS) and Hall Effect measurement are employed to characterize the electrical properties. The comparative study of Sn1-xSbxO2 (0.01 ≤ x ≤ 0.05) indicates that the composition of Sn0.95Sb0.05O2 has the lowest resistance with the highest carrier concentration. Electrochemical properties of the material were analyzed by cyclic voltammetry in both acidic and neutral media showing the Sn0.95Sb0.05O2 with high electron transfer properties.

We herein report a series of nanocrystalline Ni-doped Co3O4: Co3−xNixO4 (0.0075 ≤ x ≤ 0.30) with a nickel doping percentage from 0.25 to 10 atomic percent synthesized using solution combustion method. These oxides are characterized by XRD and show pure nanocrystalline phase of Co3O4 with no separated peaks related to Ni/NiOx and confirms that Ni has been substituted in the lattice. TEM results indicate that the morphology and size of all the compounds are similar. Electrochemical measurements indicate that Co3O4 and Co3−xNixO4 are active for oxygen evolution reaction (OER) and also shows that low amount of nickel doping in Co3O4 can remarkably enhance OER activity in neutral, alkaline and buffer (pH-7) electrolytes. Out of all compositions, 0.5% Ni-doped Co3O4 (Co2.985Ni0.015O4) seems to be more active than Co3O4 in terms of both current density and onset potential in K2SO4 medium. The enhancement in terms of OER activity, however, decreases until the doping concentration reaches beyond 0.5%. Phosphate buffer solution (PBS) studies reveal that Co3O4 and 0.5% Ni-doped Co3O4 show OER at near thermodynamic potential. Detailed x-ray photoelectron spectroscopy (XPS) studies have indicated that surface oxygen (lattice oxygen) concentration is an important factor in deciding the OER activity which is highest for 0.5% Ni doped Co3O4 (Co2.985Ni0.015O4) and hence gives the highest OER activity.

Nanoporous geopolymer was synthesized with and without using Cetyl trimethylammonium bromide (CTAB) by condensing the mixture of metakaolin and alkali solution at a fixed ratio at room temperature. The surface area of CTAB-geopolymer was found to be more (216 m2/g) as compared to without CTAB added geopolymer (137 m2/g). The experimental results verified that the geopolymer could adsorb copper ions completely at lower concentrations and partially at higher concentrations. Pseudo second order model fits well at all the concentration from 55 to 1700 ppm as the values of the correlation coefficient lies between 0.96 and 0.99. Intraparticle diffusion model at the concentration 55 ppm explains that there is only boundary layer diffusion (instantaneous) and after this step, all the Cu ions are exchanged by the nanoporous geopolymer. At 120 ppm, intraparticle diffusion model shows multilinearity. Different adsorption models - Langmuir, Freundlich and Tempkin were also tested to evaluate the most appropriate model and it was found that adsorption follows Langmuir model. The adsorption capacity and pseudo second order rate constant is estimated to be 1.65 meq/g which is significantly higher than the fly ash based nonporous geopolymer.

Nano-crystalline Co3O4 is synthesized using solution combustion method. Characterization is done using XRD, TEM and BET surface area analysis. XRD shows pure nano-crystalline phase of Co3O4. Crystallinity of as prepared material improves by calcining the compound at 900 °C for 10 h while no effect is seen at 600 °C. TEM studies show that particles of around 50 nm size are formed at 400 °C. At 600 °C a well-defined hexagonal morphology could be seen both by TEM and SEM and the particle size is around 70 nm. However, TEM of the sample at 900 °C shows big agglomerates of cobalt oxide and no specific geometry could be obtained. Estimated BET surface area for the sample calcined at 600 °C is 10 m2/g. Detailed electrochemical studies are carried out in neutral and basic electrolytes where Ag/AgCl is used as the reference electrode. It is found that Co3O4 is active for oxygen evolution reaction in basic medium as well as in neutral medium. KOH is used as the basic medium while KNO3, K2SO4 and phosphate buffer is used for neutral medium. However, it is not active for hydrogen evolution reaction in any of the medium even at − 1.0 V. This is confirmed by gas analysis of the output gas in the cell by using a mass spectrometer. When compared with the buffer medium, it is observed that local pH changes in KNO3 and K2SO4 medium are possibly affecting the oxygen evolution reaction.

Because of microbial resistance to conventional antibiotics, there is increasing interest in silver, including silver nanoparticles (nano-Ag), in antimicrobial applications. However, questions remain regarding the relative roles of nano-Ag particles, versus Ag(+) ions released from nano-Ag dissolution, in imparting bacterial toxicity. Here, we developed a novel nano-Ag that, based on its cysteine cap, was expected to dissolve slowly and thus potentially allow for differentiating nanoparticle, versus ionic, effects of Ag. The nano-Ag was systematically tested for its differential toxicity to Escherichia coli and Pseudomonas aeruginosa. Bacterial growth, reactive oxygen species (ROS) generation, particle dissolution, cellular electron transfer activity, and cell membrane damage and potential were evaluated. In minimal growth medium, E. coli and P. aeruginosa growth were slowed at 100 mg L(-1) (0.93 mM) and 5 mg L(-1) (0.046 mM), respectively; P. aeruginosa was completely inhibited at and above 10 mg L(-1) (0.093 mM). For both strains, toxicity was associated with ROS and cell membrane damage. Based on comparisons to AgNO3 exposures, toxicity from nano-Ag was due to Ag(+) ions and not intact nano-Ag, even though nanoparticle dissolution was less than 2% in minimal growth medium. Because of their stability and slow Ag(+) ion release, the cysteine-capped nano-Ag particles here are useful to antimicrobial applications. Additionally, our systematic approach to evaluating toxicity, membrane damage, and ROS generation can be applied with other nanomaterials and bacteria.

This paper reports the synthesis of silver encapsulated β-Fe 2 O 3 core–shell hollow nanotubes soluble in aqueous medium. Colloidal β-Fe 2 O 3 nanoparticles produced by the hydrolysis of FeCl 3 are grown on Ag nanoparticles in N 2 environment to produce core–shell hollow tubular structure. A variation in the amount of silver (0.23 × 10 −4 mol dm −3 – 0.76 × 10 −4 mol dm −3 ) regularly blue shifts the excitonic band due to β-Fe 2 O 3 , and reduces the thickness of β-Fe 2 O 3 in the shell besides changing the morphology of the nanostructures. A typical amount of silver (0.58 × 10 −4 mol dm −3 ) leads to the development of core–shell hollow tubes (SC) in which the core consists of Ag nanoparticles with an average diameter of 3.5 nm and the shell is made of β-Fe 2 O 3 hollow nanotubes consisting of Cl − and NO 3 − ions with an average thickness and the inner diameter of 3 nm and 9 nm, respectively. Unlike pure β-Fe 2 O 3 nanorods, SC at 7 T exhibits superparamagnetic behavior at a relatively higher temperature (100 K), whereas β-Fe 2 O 3 under these conditions depicted paramagnetic behavior. However, at 7 T and 5 K both of the samples exhibited superparamagnetic behavior, but the magnetization for SC (0.4 emu cm −2 ) was about 5.6 times higher compared to that of pure β-Fe 2 O 3 . The presence of specific amount of Ag in SC possibly results in the observed change in morphology, decrease in dimension and the orientation of β-Fe 2 O 3 nanorods in a particular direction, which contributes to the transformation in magnetic behavior associated with enhanced saturation magnetization.

Silver iron oxide nanoparticles of fairly small size (average diameter approximately 1 nm) with narrow size distribution have been synthesized by the interaction of colloidal beta- Fe2O3 and silver nanoparticles. The surface morphology and size of these particles have been analyzed by using atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Their structural analysis has been carried out by employing x-ray diffraction (XRD), selected-area electron diffraction (SAED), optical and infrared (IR) spectroscopic techniques. The ageing of these particles exhibits the formation of self-assembly, possibly involving weak supramolecular interactions between Ag(I)O4 and Fe(III)O4 species. These particles display the onset of absorption in the near-infrared region and have higher absorption coefficient in the visible range compared to that of its precursors. Magnetic measurements reveal an interesting transition in their magnetic behavior from diamagnetic to superparamagnetic. The magnetic moment of these particles attains a limiting value of about 0.19 emu cm(-2), which is more than two times higher than that of colloidal beta- Fe2O3. With enhanced optical and magnetic properties, this system is suggested to have possible applications in optoelectronic and magnetic devices.