Pawan K. Khanna

Photodegradation of organic dyes based on anatase and rutile TiO2 nanoparticles

The present work highlights a simple nanochemistry based clean and efficient process for effective degradation of various organic dyes by use of anatase and rutile TiO2 nanoparticles. Based on photodegradation studies it was observed that at certain experimental parameters, rutile TiO2 was as effective as anatase for the degradation of indigo carmine (IC) dye in aq. solution. However, anatase TiO2 was found to be much more efficient against methylene blue (MB), methyl orange (MO), rhodamine B (RB) and eriochrome black T (EBT) under short UV irradiation. The photodegradation study of these organic dyes was also performed under long UV irradiation employing both anatase and rutile titania and the results showed similar trends. However, only EBT photodegradation indicated equal photocatalytic activity by both phases. The catalytic degradation of the organic dyes was studied by degradation kinetics. The maximum degradation efficiency using anatase and rutile titania photocatalysts was found to be 88% and 77% in the case of MB under short UV irradiation while about 65% was found in the case of EBT under long UV irradiation. The reuse of photocatalyst even after five cycles retained the degradation efficiency of 83% and 71% respectively for anatase and rutile when tested against MB.

A graphene titanium dioxide nanocomposite (GTNC): one pot green synthesis and its application in a solid rocket propellant

A green process was developed for a graphene–titanium dioxide nanocomposite (GTNC) synthesis by dispersing titanium dioxide (TiO2) nanoparticles and graphene nano-sheets (GNSs) in ethanol via ultrasonication followed by microwave irradiation. The synthesized GTNC was well characterized by various tools: viz. XRD, HRTEM, FTIR and Raman spectroscopy. Also, Simultaneous Thermal Analysis (STA) and Differential Scanning Calorimetry (DSC) techniques have been employed to study the enhancement of the catalytic activity of the GTNC for the decomposition of Ammonium perchlroate (AP). The GTNC with 5 wt% in AP was found to be a highly effective catalyst for the AP decomposition. The decomposition temperature decreases from 412.87 °C to 372.50 °C and ΔH increases from 2053 to 3903 J g−1. Furthermore, the GTNC was identified as an effective burn rate enhancer (i.e. combustion catalyst) for an AP based composite propellant for solid rocket propellants as confirmed by STA, DSC, activation energy calculations and burn rate measurements. The results show that the burn rate of the propellant increases by 24% for the TiO2 nanoparticle based composition compared to the base composition, whereas a significant increase of 50% is achieved in the presence of the GTNC. Hence, the performance is improved significantly for the solid rocket propellant.

Impact of microwave irradiation on cyclo-octeno-1,2,3-selenadiazole: formation of selenium nanoparticles and their polymorphs

In this work one-pot microwave assisted synthesis of selenium nanoparticles by decomposition of cyclo-octeno-1,2,3-selenadiazole in the presence of oleic acid and diphenyl ether is described. Three different forms of Se nanoparticles i.e. red, black amorphous and crystalline red were synthesized by varying the reaction time with microwave irradiation. The formation of Se nanoparticles from such a microwave reaction was monitored by UV-Visible spectroscopy at specific intervals. X-ray diffraction (XRD) measurement and Raman spectroscopy confirmed the trigonal crystal structure of the Se nanoparticles so-isolated. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the globular morphology of the red and black Se particles. The particle size distribution was found to be between 1–20 nm for red Se. Thermogravimetric analysis (TGA) revealed a decomposition range between 180–240 °C leading to the possibility of interconversion of the crystal structure. A %wt loss between 94-99% was observed for various forms of Se.

Transparent ZnO/polycarbonate nanocomposite for food packaging application

Abstract Zinc oxide (ZnO)–polycarbonate (PC) nanocomposite films were prepared by blade coating method by using pre-synthesized spherical ZnO nanoparticles of 15–20 nm size and pre-dissolved polycarbonate. The blend was homogenized by sonication and the films were dried in an oven at moderate temperature. Various films with different % loading of ZnO nanoparticles in PC were prepared and their effect on antibacterial properties was studied. It is observed that increasing wt-% loading of ZnO nanoparticles in PC leads to enhanced antibacterial properties against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The freshly prepared ZnO nanoparticles were thoroughly characterized by XRD, SEM, UV-visible and photoluminescence spectroscopy before their use in preparing nanocomposite films. Contact angle measurement of the films was studied to ascertain their hydrophobic behavior. Such nanocomposite films have potential in various packaging applications because of their effective antibacterial and UV-blocking properties and hydrophobic nature.

Synthesis, Characterization, and Studies of PVA/Co-Doped ZnO Nanocomposite Films

ABSTRACT Polymer nanocomposites are made up of two or more phases wherein the inorganic particles are dispersed in a polymer matrix. The present article deals with Co-doped ZnO embedded in a polyvinyl alcohol (PVA) matrix using a sol-gel method. The synthesized nanocomposites were structurally characterized using X-ray diffraction (XRD) and the optical properties were studied using photoluminescence and ultraviolet-visible (UV-Vis) spectroscopy. Thermal studies including thermogravimetric analysis (TGA) were conducted to the study stability of the nanocomposites.

Synthesis and Characterization of Conducting Polyaniline Doped with Polymeric Acids

Conducting polyaniline doped with polymeric acids was synthesized by a in situ chemical polymerization method. The synthesized polymers were characterized by using UV‐Visible, FT‐IR spectroscopy and SEM analysis. Thermal stability of these polymers was evaluated by using TGA/DSC analysis. Among the three polymeric acids used for doping purpose, poly(vinyl sulphonic acid) doped polyaniline is found to be more conducting than those doped with other acids. From the temperature dependent conductivity measurements, an increase in conductivity with increase in temperature was observed.

Core–shell ZnSe–CdSe quantum dots: a facile approach via decomposition of cyclohexeno-1,2,3-selenadiazole

For the first time ever cyclohexeno-1,2,3-selenadiazole (SDZ) has been employed for the synthesis of core–shell ZnSe–CdSe quantum dots thus promoting an eco-friendly and reasonably less toxic synthesis method for such quantum dot hetero-structures. The synthesized dark-red colored core–shell structures were characterized by UV-Visible and photoluminescence (PL) spectroscopy to examine their band-gap. The absorption and emission spectra also showed gradual red-shifts in wavelength with respect to zinc selenide (core). Also, the band-gap of such core–shell quantum dots can be tuned by varying the shell layer thickness and/or particle size. The findings from the XRD analysis, near-to-homogenous particle size distribution, formation of a decent nano-crystalline product and a good agreement with Vegards law, signify that the present synthesis approach could be highly effective for the precise tailoring of core–shell QDs.

Versatile SiO2 Nanoparticles@Polymer Composites with Pragmatic Properties

In the present work, we report the fabrication of silica nanoparticles embedded polymeric (SiO2 nanoparticles@polymer) composite films for numerous traits like texture, folding endurance, crystallinity, size, thermal behavior, spectral analysis, and bioactivity. Significant facets of bulky, inert, inorganic materials are known to burgeon out due to the high surface area of nanosized particles. Nature and proportion of silica nanoparticles as well as polymers exhibited remarkable impact on the fabrication and quality of casted films. Hydrophilic silica nanoparticulate-PVA films depicted better mechanical properties like thermal plus photo stability. Hydrophobic silica nanoparticulate-PMMA films showed qualities of a robust, active, thermostable, antimicrobial material that could resist extreme storage and processing conditions. Overall, these metal oxide nanoparticle-polymer composite films possess qualities reflecting their potential in food, pharmaceutical, and cosmetic industry.

Rapid microwave synthesis of white light emitting magic sized nano clusters of CdSe: role of oleic acid

A rapid, green and one-pot microwave synthesis of magic sized nano clusters (MSNCs) of CdSe is presented by use of various cycloalkeno-1,2,3-selenadiazoles as a selenium source. The effect of different parameters i.e. time, surfactant and solvent on the morphology and the cluster size have been investigated. Oleic acid (OLA) is preferred as the capping agent which promotes the growth of MSNCs due to a long carbon chain structure and also due to its non-interaction with the CdSe surface, chemically. The optical spectroscopy studies (UV-visible and PL) revealed the formation of various clusters of CdSe MSNCs families having band gap absorptions at 390 and 450 nm (CdSe13 to CdSe34). The combination of various clusters in the sample leads to white light emission when illuminated under a 365 nm UV light source. It is believed that, in the present studies the white light is generated by well known surface related defects due to large non-coordinating Se or Cd atoms on the surfaces. The samples were thoroughly characterized and stable white light emission was observed for more than 2 months.

An efficient solventless synthesis of cycloalkeno-1,2,3-selenadiazoles, their antimicrobial studies, and comparison with parent semicarbazones

A series of heterocyclic organoselenium compounds, cycloalkeno-1,2,3-selenadiazoles (cyclopenteno, cyclohexeno, cyclohepteno, and cycloocteno-1,2,3-selenadiazoles), was synthesized at room temperature in one step under solventless conditions from the corresponding semicarbazones. The synthesized 1,2,3-selenadiazoles and their parent semicarbazones were screened for their antimicrobial activity against various pathogenic bacteria using agar disc diffusion method. All compounds were found active against E. coli, S. aureus, S. typhi, and P. aeruginosa. Among all the tested selenadiazoles, cyclopenteno-1,2,3-selenadiazole showed excellent inhibition against highly resistant P. aeruginosa. It is observed that selenadiazoles showed higher activity compared with the respective semicarbazones.