Priyesh V. More

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.

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.

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.

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.

In situ SeO2 promoted synthesis of CdSe/PPy and Se/PPy nanocomposites and their utility in optical sensing for detection of Hg2+ ions

Avoiding the use of any external oxidising agent or initiator for the polymerisation process, pyrrole was successfully polymerised to polypyrrole (PPy) using SeO2 as an internal oxidant which leads to the in situ synthesis of selenium and cadmium selenide polypyrrole (Se/PPy and CdSe/PPy) nanocomposites by chemical and microwave methods. PPy formation during the reaction was monitored by UV-Visible absorption spectroscopy. XRD measurements indicated the formation of the confirmed CdSe/PPy and Se/PPy nanocomposites. SEM images show the aggregation of small particles in the form of large globules with smooth surfaces. HRTEM images reveal the presence of spherical CdSe and Se nanoparticles homogeneously embedded in the polypyrrole matrix with interplanar distances of 0.35 nm and 0.4 nm for the (111) and (100) atomic planes, respectively. The as-synthesized CdSe/PPy and Se/PPy nanocomposites were tested for the detection of heavy metal ions. CdSe/PPy and Se/PPy successfully detected mercury ions at 25, 50 and 100 ppm. This article also describes the use of pre-synthesized Se/PPy nanocomposites as precursors for the synthesis of CdSe/PPy nanocomposites.

Synthesis of shape and size controlled copper indium diselenide (CuInSe2) via extrusion of selenium from 1,2,3-selenadiazole

Extrusion of selenium from cyclohexeno-1,2,3-selenadiazole (SDZ) was successfully utilized for the synthesis of CuInSe2 nanoparticles. Changes in various reaction parameters such as reaction temperature, concentration of oleic acid (OLA) and various other capping agents showed changes in the physical characteristics of the CISe nanoparticles. The reactions performed at various temperatures resulted in alteration in physical appearance, shape and size of the CISe nanoparticles which was confirmed by XRD, Williamson Hall analysis, particle size analyzer, SEM and TEM analysis. The variation in the amount of OLA only affected the particle size. Optical studies of as-synthesized CISe NPs revealed band gap ranging between 1.1–1.7 eV. HRTEM analysis confirmed the presence of CISe with a variety of shapes and lattice spacings of 0.33 nm corresponding to the (112) crystal plane.

Band engineered p-type RGO–CdS–PANI ternary nanocomposites for thermoelectric applications

A ternary hybrid nanocomposite of RGO–CdS–polyaniline (PANI) is prepared by a simple two stage in situ method for its thermoelectric studies. For this purpose, CdS quantum dots were first prepared with varying concentrations in the presence of reduced graphene oxide to form RGO–CdS nanocomposites using 3-mercaptopropionic acid as a linker. Polyaniline was then prepared in situ in the presence of RGO–CdS nanocomposites to eventually obtain RGO–CdS–PANI nanocomposites. The electrical conductivity, Seebeck coefficient and power factor of the RGO–CdS–PANI nanocomposites were calculated with various loadings of RGO–CdS nanocomposites in PANI. The final RGO–CdS–PANI nanocomposites delivered a high electric conductivity in the order of 105 S m−1 and showed strong re-dispersion in DMF and ethanol. The effective band alignment and decreased thermal conductivity in RGO–CdS–PANI nanocomposites resulted in p-type behaviour and a high power factor value.

Selective Synthesis of α or β-HgS Nanocrystals via Core/Shell Formation Using Surface Modified CdS Quantum Dots

Chalogenides (CdS, CdSe, ZnSe etc.) are well known to undergo cation exchange reactions with other cations, including metals. The cation exchange methods are highly efficient in obtaining core/shell as well as alloy type of nanostructures. Such synthesis approach is particularly useful for producing CdHgX (X = S, Se) alloys, CdX/HgX core/shell and HgX nanostructures as organometallic mercury precursors are very inconvenient to handle. In this work, we have first synthesized hydrophilic CdS quantum dots using various capping agents and studied its cation exchange reaction with Hg2+ ions. The CdS QDs readily reacts with Hg2+ ions at ambient conditions and neutral pH to form either HgS or CdS/HgS core/shell nanostructures. Interestingly, we have observed that capping agent of CdS QDs plays an crucial role in formation of specific form of HgS (α and β). The growth of HgS shell on CdS core with systematic increase in Hg ion concentration is also explored.

Microwave synthesis of bis(cycloalkeno)-1,4-diselenins: a novel source of Se for CdSe QDs

This paper describes the formation of a series of bis(cycloalkeno)-1,4-diselenins from the corresponding cycloalkeno-1,2,3-selenadiazoles by a microwave irradiation (MW) method. The bi-radical dimerization reaction of 1,2,3-selenadiazoles was performed by a new synthetic strategy under solvent-free conditions using 100 Watt microwave irradiation for about 20 minutes. The current synthesis afforded a feasible approach for the preparation of various 1,4-diselenins. The so-prepared alkyl selenides were characterized by various spectroscopic tools, viz. UV-visible, FTIR, 1H, 13C, DEPT and 77Se NMR spectroscopy, ESI-MS and TGA analysis. Additionally, bis(cyclohepteno)-1,4-diselenin has been effectively utilised as a novel selenium precursor for the synthesis of CdSe quantum dots (QDs). This Se-rich precursor can likely be used for the preparation of other metal selenides also.

Polymer based graphene/zinc oxide nano crystal (GZnNC): an outstanding thermoelectrical energy conversion material

This work presents the synthesis of a new material, graphene/zinc oxide nano composite (GZnNC) by employing ultrasonication techniques where nano-ZnO and graphene nano-sheet have been dispersed in ethanol followed by microwave irradiation. The GZnNC was well characterized by XRD, HRTEM, FTIR, and Raman spectroscopy. Also, polymer based GZnNC has been subjected to the measurement of energy harvesting/thermoelectric properties. Present study includes PVAc, PVAc/PEDOT: PSS, and PEDOT: PSS based compositions with concentration variation of GZnNC/graphene and measurement of thermoelectric properties like electrical conductivity, Seebeck coefficient, power factor (PF), thermal conductivity and figure of merit(ZT). PEDOT: PSS/GZnNC composite showed the twelvefold increase in electrical conductivity and two times increase in Seebeck coefficient as compared to the PVAc-graphene composite. Interestingly, the calculated power factor for PEDOT: PSS/GZnNC composite increases up to 50 times as compared to PVAc/graphene composite. Thermal conductivity gets reduced to 3.01 W/mK Hence, figure of merit is reached up to 0.0051. This value is comparatively very high compare to the existing nanocomposites. Correspondence to: Arun K. Sikder, EMR Division, High Energy Material Research Lab, Sutarwadi, Pune-411021, India, E-mail: ak_sikder@rediffmail.com