[en] Undoped and Cu-doped nanocrystals of TiO_2 having the size range of 8–11 nm were synthesized by peroxide gel method. XRD analysis using Rietveld refinement confirmed anatase phase with a small percentage of rutile content for undoped TiO_2 nanocrystals while a pure anatase phase with preferential growth along [004] direction was observed for nanocrystals of Cu-doped TiO_2. Variation in the intensity ratios of the XRD peaks of the doped samples compared to that of the undoped sample offered an evidence for the substitutional incorporation of Cu ions in the TiO_2 lattice. The preferential growth of the nanocrystals along the [004] direction was verified using HRTEM analysis. Cu doping extended the optical absorption edge of TiO_2 nanocrystals to the visible spectral region and caused a blue shift and broadening of the E_g (1) Raman active mode of anatase TiO_2. Undoped TiO_2 sample showed a weak ferromagnetism superimposed on a diamagnetic background while Cu-doped TiO_2 samples exhibited a weak ferromagnetism in the low-field region with a paramagnetic component in the high-field region. The magnetic moment exhibited by the doped samples is interpreted as the resultant of a weak ferromagnetic moment in the low-field region arising from the presence of defects near the surface of TiO_2 nanoparticles or from the interaction of the substituted Cu ions with the oxygen vacancies, and the paramagnetic contribution from the increased Cu dopant concentration near the surface of the particles arising from self-purification mechanism.

[en] Preparation of carbon nanotube (CNT) based conducting polypyrrole (PPy) composite and its posterior use for antimicrobial activity is attempted through this work. The chemically synthesized PPy and PPy-nanocomposite were characterized using FTIR and Raman Spectroscopy. Antimicrobial activity of the synthesized materials has been investigated with some bacterial species. The result depict that the nanocomposite has improved antibacterial activity when compared with bare polypyrrole. (author)

[en] The light soaking phenomenon, in chlorine-based mixed halide perovskite solar cells (PSC) with p-i-n configuration, is studied. Due to light soaking, the solar cells have shown improved open circuit voltage, fill factor (FF), and power conversion efficiency without much change in short circuit current. The devices have returned to their original state upon extended exposure to dark conditions. Capacitance spectroscopy is used to understand the effect of light soaking on various photovoltaic parameters. The observed increase of capacitance value with light soaking in the low frequency region of the capacitance-frequency (C–F) plot is elucidated, as the coupled effect of electronic and ionic processes involving defects. The decrement in the mid-frequency capacitance is attributed to an increase in the width of the depletion region which eventually facilitated the improvement in open circuit voltage and FF. Defect densities, and its distribution in the energy space, are deduced before and after light soaking. The defects density of states of PSC studied are found to reduce from 10¹⁶ to 10¹⁵ eV⁻¹ cm⁻³, with a Gaussian distribution, and having a peak energy shift from 0.27 to 0.26 eV. (paper)

[en] Doping in nanocrystals is a challenging process because of the self- purification mechanism which tends to segregate out the dopants resulting in a greater dopant concentration near the surface than at the interior of nanocrystals. In the present work nanocrystals of TiO_2 doped with different atom % of Co were synthesized by peroxide gel method. XRD analysis confirmed the tetragonal anatase structure and HRTEM images showed the rod-like morphology of the samples. Raman modes of anatase phase of TiO_2 along with weak intensity peaks of Co_3O_4 for higher Co dopant concentrations were observed for the samples. EPR measurements revealed the presence of cobalt in +2 oxidation state in the TiO_2 matrix. SQUID measurements indicated paramagnetic behavior of the Co doped TiO_2 nanocrystals. The paramagnetic behavior is attributed to an increased concentration of Co"2"+ ions and an increased presence of Co_3O_4 phase near the surface of the TiO_2 nanocrystals due to self-purification mechanism. - Graphical abstract: Variation of the intensity ratios of XRD peaks as a function of atomic ratio of Co. Inset: variation of structure factor for (101) reflection as a function of atomic ratio of Co. Display Omitted - Highlights: • Co doped TiO_2 nanocrystals were synthesized by peroxide gel method. • HRTEM images showed Co doped TiO_2 nanocrystals to be rod-like. • EPR spectra showed +2 oxidation states for Co in the samples. • Co doped TiO_2 nanocrystals showed paramagnetic behavior.

[en] Visible light active fluorine modified TiO₂ thin films were deposited through simple and low-cost nebulizer spray technique. The structural and morphological studies of the prepared films were investigated by X-ray diffraction and scanning electron microscopy. The chemical state of the elements over the film surface was analyzed by X- ray photoelectron spectroscopy. The optical absorption studies revealed a noticeable reduction in the band gap due to the inclusion of F atom into TiO₂ lattice. Photoluminescence spectra exhibited the enhancement of fluorine-induced oxygen vacancies and effective charge separation due to the formation of Ti³⁺ ions in F-TiO₂ thin films. Doping of fluorine on TiO₂ lattice showed an effective increase in photocatalytic degradation performance with good stability and repeatability under visible light.

[en] Cerium oxide (${\text{CeO}}_{2-<!--\; ???\; -->x}$) nanoparticles or nanoceria were synthesized by the chemical co-precipitation method using cerium nitrate hexahydrate and ammonium carbonate as starting materials and deoxyribonucleic acid (DNA) as a capping agent. The structural and optical characterization of the prepared nanoparticles was studied in depth by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy, Raman spectroscopy, UV–visible absorption and diffuse reflectance spectroscopy. The average crystallite size and lattice parameters of the cerium oxide nanoparticles at different calcination temperatures were studied using XRD analysis. The average crystallite size was found to be 6 nm and the size increases with calcination temperature. The polycrystalline nature and the size of the particles obtained are in close agreement with HRTEM and Raman analysis. The optical band gaps of all samples were measured by Tauc plot which showed a blue shift with a decrease in size due to the quantum confinement effect. The optical absorption spectrum of the synthesized nanoparticles showed the absorption of UVA, UVB and UVC light, and the variation in structural and optical properties with size makes them suitable for the optoelectronic application. To the best of our knowledge, this is the first report on using DNA in the synthesis of nanostructured ceria.

[en] Highlights: • Cost effective nebulizer spray route was adopted to prepare sulfur doped TiO₂ films. • Successful incorporation of sulfur in TiO₂ matrix confirmed from XPS analysis. • Enhanced photocurrent observed for sulfur doped films compared to pristine TiO₂. • Addition of sulfur improves the photocatalytic activity of TiO₂ under visible light. Pristine TiO₂ and sulfur doped TiO₂ (S-TiO₂) thin films were coated over the glass substrates by varying the concentration of sulfur source (thiourea – 2, 4, 6, 8 and 10 at%) using a cost-effective Jet nebulizer spray technique. The deposited thin films were in anatase phase with the tetragonal structure analyzed from the XRD pattern. The chemical state of the elements was determined from XPS analysis. Pristine TiO₂ and S-TiO₂ thin films depict the presence of spherical particles embedded over 3-D interconnected wire-like structure from SEM analysis. Optical studies revealed reduction in band gap of S-TiO₂ films on increasing the sulfur concentration (3.2–2.8 eV). The sulfur incorporation in TiO₂ lattice confirmed by the fall in intensity of near band edge emission as observed from room temperature PL spectra. The charge carrier dynamics of the prepared thin films were studied by means of steady state and transient photoconduction measurements. The photocatalytic performance of pristine TiO₂ and S-TiO₂ thin films for the degradation of malachite green dye was investigated under visible light.