Animesh K. Ojha

Synthesis of superparamagnetic bare Fe3O4 nanostructures and core/shell (Fe3O4/alginate) nanocomposites

In this article we report about the synthesis of superparamagnetic bare Fe3O4 nanostructures and core/shell (Fe3O4/alginate) nanocomposites by simple low-temperature based method at pH values 5, 9, and 14. The structural morphology and magnetic behavior of Fe3O4 nanostructures and core/shell (Fe3O4/alginate) nanocomposites (Fe3O4/alg NCs) have been investigated by X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (RS), ultraviolet-visible (UV-vis) spectroscopy, transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and vibrating sample magnetometer (VSM). The particle size was calculated by TEM measurements and it turns out to be ∼10 nm and ∼14 nm for bare Fe3O4 nanoparticle and Fe3O4/alg NCs with core/shell structure, respectively. The magnetic properties of the synthesized products were found to be function of pH at which the synthesis has been done. The synthesized Fe3O4 nanoparticle and Fe3O4/alg NCs were found to be superparmagnetic in nature at room temperature. We observed that the value of saturation magnetization in case of Fe3O4/alg NCs decreases by increasing the pH value.

Cadmium oxide nanoparticles grown in situ on reduced graphene oxide for enhanced photocatalytic degradation of methylene blue dye under ultraviolet irradiation

Cadmium oxide (CdO) nanoparticles (NPs), reduced graphene oxide (rGO) and rGO-CdO nanocomposites have been synthesized using one step hydrothermal method. The structural and optical properties of CdO NPs, rGO, and rGO-CdO nanocomposites were investigated by X-ray diffraction (XRD), energy dispersive X-ray (EDX), high resolution transmission electron microscopy (HR-TEM), Raman spectroscopy (RS), ultraviolet-visible spectroscopy (UV-Vis.) and photoluminescence (PL) spectroscopy techniques. The rGO has a sharp 2D peak compared to GO. The sharp nature of 2D band may be due to the larger contribution from single layer sheet. The photocatalytic activity of the synthesized samples has been investigated under UV irradiation. The results of photocatalytic measurements revealed that ~80% of MB dye is degraded by adding the rGO-CdO nanocomposites as photocatalysts into the dye solution. The decrease in the intensity of emission peaks indicates that the photogenerated charge carriers have been transferred from CdO NPs to rGO sheets, which causes to increase the density of O2(-) and OH radicals in the dye solution. The CdO nanoparticles gown on the rGO sheets showed enhanced ferromagnetism (FM) at room temperature, which may be attributed to the short range magnetic interaction of magnetic moments of CdO NPs and spin units present on the rGO sheets.

pH-dependent Raman study of pyrrole and its vibrational analysis using DFT calculations.

Raman spectra of pyrrole in aqueous medium at different pH values, 2.5, 5.5, 7.5 and 10.5 were recorded in the two spectral regions, 1,040-1,160 cm(-1) and 3,300-3,360 cm(-1) and pH dependence of the linewidth, peak position and intensity of the Raman bands corresponding to the ring breathing and symmetric nu(N-H) stretching modes were examined. A linear pH dependence of the peak positions for the ring breathing mode and a maximum at nearly neutral pH (7.5) for the symmetric nu(N-H) normal mode is observed, whereas the linewidth (FWHM) shows almost no variation with the change of pH. A slight decrease in the wavenumber position of the nu(N-H) mode at pH value >7.5 indicates that the influence of deprotonation is small, which results from a weak interaction between the reference molecule and the surrounding environment. The density functional theory (DFT) calculations were made primarily to obtain the optimized geometry and vibrational spectra of pyrrole in the ground electronic state using B3LYP functional and the highest level basis set 6-311++G(d,p). The assignments of the normal modes of pyrrole were made on the basis of potential energy distribution (PED). The calculations were also performed on protonated and deprotonated structures of pyrrole.

Facile and controlled synthesis of aligned WO3 nanorods and nanosheets as an efficient photocatalyst material

In this work, we have performed a facile and controlled synthesis of WO3 nanorods and sheets in different crystal phases (triclinic, orthorhombic and monoclinic) of WO3 using the sol-gel method. The detailed structures of the synthesized materials were examined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy measurements. The shapes and crystal phases of the WO3 nanostructures were found to be highly dependent on the calcination temperature. The variation in crystalline phases and shapes is modified the electronic structure of the samples, which causes a variation in the value of optical band gap. The value of the Raman line intensity ratio I264/I320 has been successfully used to identify the structural transition from the triclinic to the orthorhombic phase of WO3. The PL spectra of the synthesized products excited at wavelengths 380, 400, and 420nm exhibit intense emission peaks that cover the complete visible range (blue-green-red). The emission peaks at ~460 and ~486nm were caused by the near band-edge and band to band transition, respectively. The peaks in spectral range 500-600nm might be originated from the presence of oxygen vacancies lying within the energy band gap. The synthesized WO3 nanostructures showed improved photocatalytic activity for the photodegradation of MB dye. The enhanced photocatalytic activity of WO3 nanosheets compared to WO3 nanorods for photodegradation of methylene blue (MB) dye could be due to the shape of the nanostructured WO3. The sheet type of structure provides more active surface for the interaction of dye molecules compared to the rods, which results in a more efficient degradation of the dye molecules.

Tailoring of enhanced interfacial polarization in WO3 nanorods grown over reduced graphene oxide synthesized by a one-step hydrothermal method

In the present report, well-defined WO3 nanorods (NRs) and a rGO–WO3 composite were successfully synthesized using a one-pot hydrothermal method. The crystal phase, structural morphology, shape, and size of the as-synthesized samples were studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. The optical properties of the synthesized samples were investigated by Raman, ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectroscopy. Raman spectroscopy and TEM results validate the formation of WO3 (NRs) on the rGO sheet. The value of the dielectric constant (e′) of WO3 NRs and rGO–WO3 composite is decreased with an increase in frequency. At low frequency (2.5 to 3.5 Hz), the value of e′ for the rGO–WO3 composite is greater than that of pure WO3 NRs. This could be due to the fact that the induced charges follow the ac signal. However, at higher frequency (3.4 to 6.0), the value of e′ for the rGO–WO3 composite is less compared to that of the pure WO3 NRs. The overall decrease in the value of e′ could be due to the occurrence of a polarization process at the interface of the rGO sheet and WO3 NRs. Enhanced interfacial polarization in the rGO–WO3 composite is observed, which may be attributed to the presence of polar functional groups on the rGO sheet. These functional groups trap charge carriers at the interface, resulting in an enhancement of the interfacial polarization. The value of the dielectric modulus is also calculated to further confirm this enhancement. The values of the ac conductivity of the WO3 NRs and rGO–WO3 composite were calculated as a function of the frequency. The greater value of the ac conductivity in the rGO–WO3 composite compared to that of the WO3 NRs confirms the restoration of the sp2 network during the in situ synthesis of the rGO–WO3 composite, which is well supported by the results obtained by Raman spectroscopy.

Synthesis, characterizations and antimicrobial activities of well dispersed ultra-long CdO nanowires

We present a simple, efficient, low cost and template free method for preparation of well dispersed ultra-long (1 μm) CdO nanowires. The CdO nanowires were characterized by x-ray diffraction (XRD), Transmission electron microscopy (TEM), UV-visible spectroscopy and Raman measurements. The direct and indirect band gaps were calculated to be 3.5 eV and 2.6 eV, respectively. In the Raman spectra only second order features were observed. The CdO nanowires were used to study antimicrobial activities against B.subtilis and E.coli microbes. It shows antimicrobial activity against B.subtilis and E.coli. However, the antimicrobial activities are better against B.subtilis than that of E.coli.

Controlled synthesis and magnetic properties of monodispersed ceria nanoparticles

In the present study, monodispersed CeO2 nanoparticles (NPs) of size 8.5 ± 1.0, 11.4 ± 1.0 and 15.4 ± 1.0 nm were synthesized using the sol-gel method. Size-dependent structural, optical and magnetic properties of as-prepared samples were investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), high resolution transmission electron microscopy (HR-TEM), ultra-violet visible (UV-VIS) spectroscopy, Raman spectroscopy and vibrating sample magnetometer (VSM) measurements. The value of optical band gap is calculated for each particle size. The decrease in the value of optical band gap with increase of particle size may be attributed to the quantum confinement, which causes to produce localized states created by the oxygen vacancies due to the conversion of Ce4+ into Ce3+ at higher calcination temperature. The Raman spectra showed a peak at ∼461 cm-1 for the particle size 8.5 nm, which is attributed to the 1LO phonon mode. The shift in the Raman peak could be due to lattice ...

Ni, Co and Ni–Co codoping induced modification in shape, optical band gap and enhanced photocatalytic activity of CeO2 nanostructures for photodegradation of methylene blue dye under visible light irradiation

A simple method has been used to synthesize uneven sizes and shapes of CeO2 nanostructures by Ni, Co and Ni–Co codoping without using any surfactant. All the samples were further characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-VIS) spectroscopy and photoluminescence (PL) spectroscopy measurements. The Ni–Co codoped CeO2 nanostructures show broad absorption in the visible range (450–800 nm) as compared to undoped, Ni and Co doped CeO2 nanostructures. The broad absorption feature (visible range) has made it a suitable material for obtaining enhanced photocatalytic activity under visible light irradiation. Further, Ni–Co codoping reduces the value of the optical band gap of CeO2 nanostructures sharply from 3.46 to 2.5 eV. The recombination rate of photo-induced electrons and holes for Ni–Co codoped CeO2 nanostructures is significantly reduced. A more realistic mechanism for superior photocatalytic activity of the Ni–Co codoped CeO2 nanostructures is also proposed. In the CeO2 matrix, the Ni and Co ion sites may act as electron and hole trap centers, which essentially improve the separation efficiency of the photo-induced electrons and holes in the Ni–Co codoped CeO2 nanostructures.

Well-controlled in-situ growth of 2D WO 3 rectangular sheets on reduced graphene oxide with strong photocatalytic and antibacterial properties

Finding the materials, which help to control the water pollution caused by organic and bacterial pollutants is one of the challenging tasks for the scientific community. 2D sheets of WO3 and composite of WO3 and reduced graphene oxide (rGO) have been synthesized in a well-controlled way using a hydrothermal method. The as synthesized 2D sheet of WO3 and rGO-WO3 composite were characterized by various techniques. The 2D sheets of WO3 and rGO-WO3 composite are efficiently utilized for the photocatalytic degradation of methylene blue (MB) and Rhodamine B (RhB) dyes under sunlight. The rGO-WO3 composite reveals excellent photocatalytic degradation of RhB dye by degrading it upto 85% under sunlight. However, the MB dye was degraded by 32%. The greater degradation of RhB dye was explained in terms of the molecular electrostatic potential. We found that RhB has a more positive potential compared to MB dye where O2- and OH̊ radicals interact more strongly, resulting in a greater degradation of the RhB dye. The antibacterial activity of the 2D sheets of WO3 and rGO-WO3composite was also investigated on gram positive (B. subtilis) and gram negative (P. aeroginosa) microbes for the first time.

A study on adsorption of acetonitrile on gold nanorods by non-resonant Raman measurements and density functional theory calculations

Adsorption of acetonitrile (Ac) molecules on gold (Au) nanorods has been investigated by Raman spectroscopic measurements and density functional theory (DFT) calculations. DFT calculations provide a valuable insight into the underlying structure of the metal-molecule complex. From the best agreement between the observed and the calculated Raman frequencies and also from other spectroscopic observations, we propose that Ac molecules interact with Au nanorods and form an [Ac+2Au](0)-like complex on the surface of nanostructures. The environmental effect has also been taken into consideration to explain the Raman activity of the complex.