I. Sinha

Solvothermal synthesis of CuO–MgO nanocomposite particles and their catalytic applications

CuO–MgO nanocomposites were prepared by a solvothermal procedure. Analysis of the X-ray diffraction patterns of the nanoparticle samples showed the formation of minor second phase CuO in addition to MgO as a major phase. On the other hand, TEM images showed CuO minor phase nanoparticles embedded in the MgO matrix. The catalytic properties of these nanomaterials were then investigated with respect to increase in CuO component in the nanocomposite. Three different catalytic reactions for the treatment of model pollutants were selected for this purpose. These were the catalytic reduction of p-nitrophenol, and catalytic degradation of methyl orange and methylene blue. In all cases the catalytic activity was found to increase with the amount of CuO in the nanocomposite. The catalytic efficiencies of all three reactions were high and followed zero-order kinetics.

Kinetics of p-Nitrophenol Reduction Catalyzed by PVP Stabilized Copper Nanoparticles

Copper nanoparticles (CuNPs) in aqueous medium were prepared with alkaline hydrazine hydrate as the reductant and PVP as the stabilizing agent without any inert gas protection. Careful variation in the amount of reductant resulted in formation of two stable CuNPs dispersions with different average sizes and consequently different localized surface plasmon resonance absorbances. These two as-synthesized CuNPs dispersions were used to catalyze the model p-nitrophenol reduction reaction. The kinetics of reduction was monitored as a function of concentration and temperature of reactants. Using this we determined the activation energy, pre-exponential factor and the entropy of activation for the two types of CuNPs samples. Catalytic activities of the CuNPs were found to be affected mainly by their activation energies.Graphical Abstract

Glycerol as green hydrogen source for catalytic reduction over anisotropic silver nanoparticles

The search for nanomaterials for catalysis of transfer hydrogenation reactions with green hydrogen sources is an important topical issue. In this work we show that anisotropic silver nanoparticles act as efficient catalysts for p-nitrophenol (Nip) reduction with glycerol, a renewable biomass byproduct, as the green hydrogen source. Anisotropic silver nanoparticles (AgNPs) were prepared using polyol method in presence of Cu2+ salt as an etchant. These AgNPs are found to be a combination of mixture of anisotropic shapes and spherical faceted nanoparticles. The percentage of anisotropic shapes in the distribution changes with amount of etchant used. Effect of shape and size of AgNPs on the catalytic kinetics of Nip reduction using glycerol as a hydrogen source was investigated. The AgNPs sample having more nanoparticles with anisotropy and finer average particle size exhibits better kinetics, lower activation energy and better turnover frequency (TOF).

Green synthesis and catalytic application of curcumin stabilized silver nanoparticles

AbstractAn ultrasonication based green synthesis approach was used to prepare curcumin-stabilized silver nanoparticles (c-AgNPs). Nanoparticles thus obtained were characterized by UV-Visible spectroscopy, X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). Two different size distributions of c-AgNPs were obtained by changing the ratio of curcumin to silver salt precursor. These c-AgNPs were used as catalysts in the catalytic reduction of p-nitrophenol to p-aminophenol. The c-AgNPs with narrower size distribution exhibited better catalytic activity as well as lower activation energy. Variation of apparent rate constant with the reactant concentration agreed with the Langmuir-Hinshelwood (LH) model. Consequently, the surface rate constant related to the rate-determining step and the respective adsorption constants of p-nitrophenol and of borohydride were determined as per this model. Graphical AbstractAn ultrasonication based green synthesis approach was used to prepare curcumin stabilized silver nanoparticles (c-AgNPs). These c-AgNPs were used as catalysts in the model reaction of catalytic reduction of p-nitrophenol to p-aminophenol. The c-AgNPs with narrower size distribution exhibited better catalytic activity as well as lower activation energy.

Chromium removal from aqueous media by superparamagnetic starch functionalized maghemite nanoparticles

AbstractSuperparamagnetic starch functionalized maghemite nanoparticles (SMhNPs) were synthesised by a co-precipitation method viain situ functionalization and used as nano-adsorbents for the removal of Cr(VI) from aqueous waste. The characterization of the prepared nanoparticles was done by XRD, FTIR, TEM and VSM techniques. Adsorption of Cr(VI) on the surface of superparamagnetic starch functionalized maghemite nano-adsorbents was investigated and the removal was higher in acidic pH as compared to that exhibited in basic medium. The adsorption of Cr(VI) by the SMhNPs followed pseudo-second order kinetics and the adsorption isotherm data fits well the Freundlich adsorption isotherm. The KF value for Cr(VI) removal by SMhNPs is found to be 24.76 mg.g−1, which is significantly better than the adsorption capacities reported in literature for maghemite nanoparticles. Thermodynamic studies revealed that the adsorption of Cr(VI) onto the superparamagnetic starch functionalized maghemite nano-adsorbents is spontaneous and endothermic in nature. Graphical AbstractThe low activation energy for the adsorption of Cr (VI) (31.54 kJ.mol−1) suggests that it was physically adsorbed on starch functionalized maghemite nanoparticles. Given the reversible nature of such adsorption, the adsorbent was found to demonstrate very good recovery and recyclability, making it a relatively cheap eco-friendly alternative.

Curcumin Functionalized Ag/Ag O Nanocomposites: Efficient Visible Light Z-scheme Photocatalysts.

Curcumin‐functionalized Ag/Ag2O (c‐Ag/Ag2O) nanocomposites with varying proportions of curcumin and Ag/Ag2O were prepared by a simple one pot green synthesis protocol in aqueous medium. The plasmonic band undergoes slight redshift, broadening and decrease in intensity with increase in the proportion of Ag2O formed. These composite nanoparticles were found to be efficient visible‐light photocatalysts for aerobic oxidation of methyl orange and rhodamine B (RhB). Functionalization by curcumin significantly enhanced the photocatalytic activity with good reusability. The photocatalytic oxidation rate showed super linear increase with light intensity because of localized surface plasmon resonance (LSPR)‐induced strong near field. The trapping experiments confirmed that superoxide radicals were the main active species responsible for the degradation reaction. A plasmonic Z‐scheme photocatalytic mechanism is proposed to explain the possible charge transfer and separation behavior of electron–hole pairs among Ag, Ag2O and curcumin under visible‐light irradiation.