Structural,Optical and Electrical Conductivity Studies in Polycarbazole and its Metal Oxide Nano Composites

Polycarbazole (PCz) has been synthesized by chemical oxidation method using APS as an oxidizing agent and PCz/CuO and PCz/Fe₂O₃ nanocomposites by in situ polymerization method for different wt% of CuO and Fe₂O₃ at room temperature. XRD patterns confirmed crystalline nature of samples. FTIR indicated strong interaction between PCz and nano fillers. The morphological and optical absorption studies were carried out using SEM and UV–Vis respectively. Addition of CuO or Fe₂O₃ to PCz decreased its direct and indirect band gaps. However, band gap showed a small change with dopant contents up to 30%. Urbach energy decreased with the addition of dopants. But Urbach energy of the composites increased with increasing dopants content from 10 to 30%. DC conductivity of PCz and its nanocomposites has been measured by following two probe technique in the temperature range 300–423 K. The conductivity of both the nanocomposites is found to be less than the pure PCz and it is found to increase with wt% of CuO or Fe₂O₃ as the case may be. The activation energy has been determined by fitting Arrhenius expression to the dc conductivity data at high temperature. The activation energy of polycarbazole is determined to be less than that of the composites. In both the composites, activation energy decreased and conductivity increased with the increase of dopant content.

     

Hybridizing MWCNT with nano metal oxides and TiO2 in epoxy composites: Influence on mechanical and thermal performances

In this study, the effects of multi‐walled carbon nanotubes (MWCNT), and its hybrids with iron oxide (Fe₂O₃) and copper oxide (CuO) nanoparticles on mechanical characteristics and thermal properties of epoxy binder was evaluated. Furthermore, simultaneous effects of using MWCNT with TiO₂ as pigment and CaCO₃ as filler for epoxy composites were determined. To investigate effects of nano‐ and micro‐particles on epoxy matrix, the samples were evaluated by TGA and DTA. It was found that the hybrid of MWCNT with nano metal oxides caused considerable increment in the tensile and flexural properties of epoxy samples in comparison to the single MWCNT containing samples at the same filler contents. Significant improvement in the thermal conductivity of epoxy samples was obtained by using TiO₂ pigment along with MWCNT. The TiO₂ pigment also caused considerable improvement in mechanical properties of the epoxy matrix and the MWCNT containing nanocomposite. The best mechanical and thermal properties of epoxy nanocomposites were obtained at 1.5 wt % of MWCNT and 7 wt % of TiO₂ that it should be attributed to particle network forming of the particles which cause better nano/micro dispersion and properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43834.     

Dielectric,thermal and mechanical properties of hybrid PMMA/RGO/Fe2O3 nanocomposites fabricated by in-situ polymerization

Currently, the organic-inorganic hybrid materials have gained tremendous importance due to their unique applications in different technological fields. In this connection, the chemical synthesis of poly(methyl methacrylate) (PMMA) and its binary and ternary nanocomposites by in-situ bulk polymerization with various percentages of reduced graphene oxide (RGO) and hematite nanoparticles (Fe₂O₃ NPs) is presented. Dielectric properties of binary and ternary nanocomposites are investigated in the frequency range of 25 Hz-1 MHz for each composition. Ternary nanocomposite of PMMA with RGO:Fe₂O₃ NPs (2:2 wt%) exhibits a substantial enhancement of the dielectric constant up to ≈308 and suppressed dielectric loss of 0.12 at 25 Hz. Appearance of three types of interfaces in ternary PMMA nanocomposites accounts for the superior dielectric properties due to the accumulation of greater number of charges at the interfaces as compared to the binary nanocomposites with only one interface. The same optimized ternary PMMA nanocomposite shows a remarkable improvement in the thermal conductivity (2.04 W/mK), which is attributed to the formation of efficient thermal conducting pathways contributed by the synergic reduction in thermal resistance of both RGO and Fe₂O₃ NPs (2:2 wt%) relative to the binary nanocomposites PMMA/2 wt% RGO (1.04 W/mK) and PMMA/2 wt% Fe₂O₃ (0.98 W/mK). Thus, ternary nanocomposites prove to be the excellent candidates for thermal management applications. Furthermore, a comparison of the mechanical strength and thermal stability for all the binary and ternary nanocomposites is presented. In the last section, respective precursors and optimized binary and ternary nanocomposites are characterized by XRD, FTIR and SEM which reveal the strong interaction of respective nanofillers into PMMA matrix.     

A comparative study of thermal conductivity and thermal emissivity of high temperature solar absorber of ZrO2 /Fe2O3 and Al2O3/CuO ceramics

Oxide ceramics are considered as promising high temperature solar absorber materials. The major aim of this work is the development of a new solar absorber material with promising characteristics, high efficiency and low-cost processing. Hence, this work provides a comparative and inclusive study of densification behavior, microstructure features, thermal emissivity and thermal conductivity values of the two new high temperature solar absorbers of ZrO₂/Fe₂O₃ and Al₂O₃/CuO ceramics. Ceramic composites of ZrO₂/(10–30 wt%) Fe₂O₃ and Al₂O₃/(10–30 wt%) CuO were prepared by pressureless sintering method at a temperature of 1700 °C/2hrs. Identification of the solar to thermal efficiency of the composites was evaluated in terms of their measured thermal emissivity. Thermal efficiency and heat transfer homogeneity were investigated in terms of thermal conductivity and diffusivity measurement. The results showed that both composites exhibited comparable densification behavior, homogenous and harmonious microstructure. However, Al₂O₃/10 wt% CuO composite showed higher thermal and solar to thermal efficiencies than ZrO₂/Fe₂O₃ composites. It gave the lowest and the best thermal emissivity of 0.561 and the highest thermal conductivity of 15.4 W/m. K. These values proved to be the best amongst all those of the most known solar absorber materials made from the expensive SiC and AlN ceramics. Thus, Al₂O₃/CuO composites have succeeded in obtaining outstanding properties at a much lower price than its other competitive materials. These results may strongly identify Al₂O₃/CuO composites as promising high-temperature solar absorber materials instead of ZrO₂ and the other carbide and nitride ceramics.     

Synthesis and characterization of (Fe3O4/MWCNTs)/ epoxy nanocomposites

A sonochemical technique is used for in situ coating of iron oxide (Fe₃O₄) nanoparticles on outer surface of MWCNTs. These Fe₃O₄/MWCNTs were characterized using a high‐resolution transmission electron microscope (HRTEM), X‐ray diffraction, and thermogravimetric analysis. The as‐prepared Fe₃O₄/MWCNTs composite nanoparticles were further used as reinforcing fillers in epoxy‐based resin (Epon‐828). The nanocomposites of epoxy were prepared by infusion of (0.5 and 1.0 wt %) pristine MWCNTs and Fe₃O₄/MWCNTs composite nanoparticles. For comparison purposes, the neat epoxy resin was also prepared in the same procedure as the nanocomposites, only without nanoparticles. The thermal, mechanical, and morphological tests were carried out for neat and nanocomposites. The compression test results show that the highest improvements in compressive modulus (38%) and strength (8%) were observed for 0.5 wt % loading of Fe₃O₄/MWCNTs. HRTEM results show the uniform dispersion of Fe₃O₄/MWCNTs nanoparticles in epoxy when compared with the dispersion of MWCNTs. These Fe₃O₄/MWCNTs nanoparticles‐infused epoxy nanocomposite shows an increase in glass transition (T_g) temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Nanocomposites based on transition metal oxides in polyvinyl alcohol for EMI shielding application

In the present work, the nanocomposites based on different transition metal oxides like iron oxide (Fe₂O₃), zinc oxide (ZnO), silicon dioxide (SiO₂), zirconium dioxide (ZrO₂), and titanium dioxide (TiO₂) in PVA matrix have been studied for their suitability as electromagnetic interference (EMI) shielding materials in the frequency range of 4–8 GHz (C-band) and 8–12 GHz (X-band). The nanocomposites containing 0.1, 0.5, 1.0, 5.0, and 10.0 wt% of oxides in the matrix were synthesised by solvent casting method. The EMI attenuation studies in 4–12 GHz frequency range were carried out using the Vector Network Analyzer R & S: ZVA40 method by measuring the loss due to reflection. The minimum reflectivity values for the composites containing Fe₂O₃, ZnO, SiO_2, ZrO₂, and TiO₂ in PVA matrix at 10 wt% concentration level in the matrix were found to be ?38.85 dB (10.4 GHz), ?33.65 dB (10.4 GHz), ?41.90 dB (10.4 GHz), ?24.90 dB (11.0 GHz), and ?32.90 dB (9.76 GHz), respectively. Based on these results, the SiO₂- and Fe₂O₃-based composites, which also exhibit high thermal stability and mechanical strength, are found to be low-cost and efficient EMI shielding materials.     

Microwave absorption property of polyaniline nanocomposites containing TiO2 and Fe3O4 nanoparticles after FeCl36H2O treatment

It is important to manipulate the synthesis parameters or additives used in order to produce conducting polymer such as polyaniline (PAni) with moderate conductivity, magnetic and dielectric properties that could enhance its microwave absorbing and shielding properties. In this communication, novel PAni/HA/TiO₂/Fe₃O₄ nanomaterials with different Fe₃O₄ contents were prepared by template‐free method by using TiO₂ and Fe₃O₄ nanoparticles as dielectric filler and magnetic filler, respectively. Before addition of ammonium peroxydisulfate (APS) for polymerization, Fe₃O₄ aqueous solution was treated with FeCl₃6H₂O in order to disperse well the Fe₃O₄ in the mixture. The result shows that better dispersion of Fe₃O₄ in the mixture by FeCl₃6H₂O treatment could significantly improve the conductivity of the nanocomposites and also activate the formation of nanorods/tubes. Moreover, PAni/HA/TiO₂/Fe₃O₄ nanocomposites treated with FeCl₃6H₂O show better microwave absorption (99.950–99.999% absorption) compared with PAni/HA/TiO₂/Fe₃O₄ micro/nanocomposites (67.0− 99.4% absorption) without treatment in frequency range of 10–13 GHz. Among the prepared PAni/HA/TiO₂/Fe₃O₄ micro/nanocomposites and nanocomposites, PAni/HA/TiO₂/Fe₃O₄ nanocomposite (treated with FeCl₃6H₂O) with 40% Fe₃O₄ exhibit the best microwave absorption (99.999% absorption at 10 GHz) because of its high conductivity, high heterogeneity and moderate magnetization. POLYM. COMPOS., 2010. © 2010 Society of Plastics Engineers     

Uniform dispersion of CuO nanoparticles on mesoporous TiO2 networks promotes visible light photocatalysis

Here, we focus our efforts on synthesizing a uniform dispersion of CuO nanoparticles on mesoporous TiO₂ networks for the first time. H₂PtCl₆ was added through a photocatalytic reaction to produce 0.5% Pt/CuO–TiO₂ nanocomposites. XRD patterns confirmed that the prepared TiO₂ formed the anatase phase. TEM images showed close contacts between CuO and TiO₂ with 5–10 nm particle sizes. One of the advantages of the synthesized mesoporous CuO–TiO₂ nanocomposites was the high pore volume (0.540 cm³ g⁻¹) and large surface area (300 m² g⁻¹). The H₂ evolution over the mesoporous 3 wt% CuO–TiO₂ nanocomposites using a glucose hole scavenger [10 vol%] was determined to be ~13000 μmol/g, a value that was 1300 times greater than that of mesoporous TiO₂. The H₂ evolution rate was increased by up to 1300 and 20 times for 3 wt% CuO–TiO₂ and 0.1 wt% CuO–TiO₂ nanocomposites, respectively, compared with that of mesoporous TiO₂. The increase in H₂ evolution over mesoporous CuO–TiO₂ nanocomposites was explained by the increased light harvesting capacity, high glucose molecule diffusion and efficient charge carrier separation. Moreover, the construction of a heterostructure with a p–n CuO–TiO₂ heterojunction expedited the separation of charge carriers and promoted the evolution of H₂. In addition, H₂ evolution was substantially increased by the synergistic effects of Pt and CuO on the mesoporous TiO₂ networks. Photoelectrochemical and photoluminescence measurements were employed to prove the H₂ evolution mechanism over the CuO nanoparticles deposited on the mesoporous TiO₂ networks.     

Effect of metallic oxides on thermal stability of ethylene–propylene terpolymer

Thermal stability of ethylene–propylene terpolymer (EPDM) loaded with various metallic oxides (PbO, CuO, NiO, Fe₂O₃, Cr₂O₃, TiO₂, ZrO₂) was assessed by the oxygen uptake method. The effects of 5 phr oxide of thermal aging of elastomer were investigated under isothermal (180°C) and isobaric (air at normal pressure) conditions. The influence of this was pointed out. Some mechanistic considerations on the oxidative degradation of EPDM are presented. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2155–2158, 2001     

Preparation and thermal shock resistance of solar thermal absorbing corundum ceramics for concentrated solar power

The absorptivity of solar thermal absorber materials affects the heliothermal conversion efficiency of concentrated solar power systems. The solar absorbing ceramics were prepared by the fixed mixture of bauxit, Fe₂O₃, and TiO₂ with adding CuO in different percentages. The absorptivity and thermal shock resistance with the effect of adding CuO in different percentages were studied. Fe₂O₃ and TiO₂ have excellent optical properties, and CuO decreases the material's band gap to boost the electronic transition and increase the material absorptivity. The results showed that the material is sintered at 1380°C with an excellent absorptivity of 94.00% in the spectrum range of 0.3–2.5 μm, and the bending strength is 132.94 MPa. The bending strength was increased by 21.07% after 30 thermal shock cycles (1000°C-room temperature, air cooling). The liquid phase facilitates the synthesis of hercynite with excellent high temperature properties. The hercynite improves the thermal shock resistance of the material.     

Styrene epoxidation over gold supported on different transition metal oxides prepared by homogeneous deposition–precipitation

Epoxidation of styrene by anhydrous tert-butyl hydroperoxide over a number of transition metal oxide (viz. TiO₂, Cr₂O₃, MnO₂, Fe₂O₃, Co₃O₄, NiO, CuO, ZnO, Y₂O₃, ZrO₂, La₂O₃ and U₃O₈) supported nano-size gold catalysts, prepared by the homogeneous deposition–precipitation method, has been investigated. The supported gold catalysts (except Au/MnO₂ and Au/U₃O₈) showed good styrene conversion activity and selectivity for styrene oxide in the epoxidation. The Au loading, Au particle size and performance in the epoxidation of the supported gold catalysts are found to be strongly influenced by the transition metal oxide support used in the catalyst. The Au/TiO₂ and Au/CuO are promising catalysts for the selective epoxidation.     

Development of iron oxide sorbents for Hg removal from coal derived fuel gas: Sulfidation characteristics of iron oxide sorbents and activity for COS formation during Hg removal

The aim of this study is to develop a process for the removal of Hg⁰ using H₂S over iron oxides sorbents, which will be located just before the wet desulfurization unit and catalytic COS converter of a coal gasification system. It is necessary to understand the reactions between the iron oxide sorbent and other components of the fuel gas such as H₂S, CO, H₂, H₂O, etc. In this study, the sulfidation behavior and activity for COS formation during Hg⁰ removal from coal derived fuel gas over iron oxides prepared by precipitation and supported iron oxide (1 wt% Fe₂O₃/TiO₂) prepared by conventional impregnation were investigated. The iron oxide samples were dried at 110 °C (designated as Fe₂O₃-110) and calcined at 300 and 550 °C (Fe₂O₃-300 and Fe₂O₃-550). The sulfidation behavior of iron oxide sorbents in coal derived fuel gas was investigated by thermo-gravimetric analysis (TGA). COS formation during Hg⁰ removal over iron oxide sorbents was also investigated using a laboratory-scale fixed-bed reactor. It was seen that the Hg⁰ removal activity of the sorbents increased with the decrease of calcinations temperature of iron oxide and extent of sulfidation of the sorbents also increased with the decrease of calcination temperature. The presence of CO suppressed the weight gain of iron oxide due to sulfidation. COS was formed during the Hg⁰ removal experiments over Fe₂O₃-110. However, in the cases of calcined iron oxides (Fe₂O₃-300, Fe₂O₃-550) and 1 wt% Fe₂O₃/TiO₂, formation of COS was not observed but the Hg⁰ removal activity of 1 wt% Fe₂O₃/TiO₂ was high. Both FeS and FeS₂ were active for Hg⁰ removal in coal derived fuel gas without forming any COS.     

Radiation resistant metal decorated MWCNTs/PMMA nanocomposite films with enhanced thermomechanical properties

UV/O₃ radiation and chemical resistant nanocomposite films of functionalized/metal decorated multiwall carbon nanotubes (MWCNTs) with polymethylmethacrylate (PMMA) are synthesized. Silver nanoparticles are decorated on the surface of UV/O₃ functionalized MWCNTs by both reduction and in situ growth from AgNO₃ aqueous solution. Microscopic studies reflect the better dispersion of UV/O₃ functionalized/silver decorated MWCNTs in polymer matrix contributing in enhancement of thermal stability, thermomechanical strength, glass transition temperatures, and thermal conductivity of nanocomposites even at 0.25 wt% MWCNTs additions. The thermal stability of nanocomposite film (0.25 wt% loading), prepared by using a surfactant (Sodium dodecyl sulfate) is increased to about 27°C while the thermomechanical properties are raised up to 76% at 100°C. Thermal and thermomechanical behavior of pre‐ and post‐UV/O₃ irradiated nanocomposite films are compared with neat polymer. The results reveal that UV/O₃ functionalized MWCNTs can effectively disperse the radiation and have a dramatic reinforcement effect on the nature of the degradation of PMMA matrix. POLYM. COMPOS., 36:969–978, 2014. © 2014 Society of Plastics Engineers     

Promoting role of transition metal oxide on ZnTiO3–TiO2 nanocomposites for the photocatalytic activity under solar light irradiation

Transition metal oxide (Fe₂O₃, Co₃O₄ and CuO) loaded ZnTiO₃–TiO₂ nanocomposites were successfully prepared by solid state dispersion method. The structural, morphological and optical properties of samples were characterized by TGA/DTA, XRD, BET, FT-IR, DRS, PL, XPS and SEM techniques. The photocatalytic activity of samples was investigated by degradation of 4-chlorophenol in water under sunlight. The Fe₂O₃ loaded sample was found to exhibit much higher photocatalytic activity than the other composite powders. 7Fe₂O₃/ZnTi sample has the highest percentage of 4-chlorophenol degradation (100%) and highest reaction rate (1.27 mg L⁻¹ min⁻¹) was obtained in 45 min. The enhancement of photocatalytic activity for ZnTiO₃–TiO₂ sample with Fe₂O₃ addition may be attributed to its small particle size, the presence of more surface OH groups, lower band gap energy than other samples in this paper and the presence of more hexagonal ZnTiO₃ phase in the morphology.     

Dynamic cure kinetics of epoxy/TiO2/MWCNT hybrid nanocomposites

The effect of multi-walled carbon nanotubes (MWCNTs) on cure kinetic parameters of the epoxy/amine/TiO₂ (1 wt%) resin system was studied dynamically at four heating rates using DTA. The presence of MWCNT in various amounts (0.1, 0.2, 0.4 and 0.6 wt%) neither retarded nor accelerated the cure reaction of the epoxy/amine/TiO₂ system in a considerable extent. Addition of MWCNTs increased the extent of cure of the corresponding nanocomposites, especially at higher contents up to 0.4 wt% MWCNT filled composite. However, increasing the MWCNT content to 0.6 wt% adversely affected the extent of cure due to nanoparticle agglomeration. The fracture surface morphology of the nanocomposites revealed that the cracks deviated on reaching the MWCNTs, while propagating in the polymer matrix. Fractional extent of conversion (α) was calculated using genetic algorithm. Flynn–Wall–Ozawa and Kissinger methods were used to analyze the kinetic parameters. The presence of MWCNTs did not affect the autocatalytic cure mechanism of epoxy/amine/TiO₂ resin system and also did not cause any considerable barrier effect on the curing process. Activation energy data fitted well in the cubic polynomial regression equations and the changes of E _a with respect to α proved the autocatalytic cure mechanism, being followed by all the MWCNT-containing epoxy-based hybrid nanocomposites.     

Synthesis and characterization of alkali‐soluble photosensitive polysiloxane urethane acrylate

A new negative temperature coefficient of resistor (NTCR) thermistors based on nitrile butadiene rubber/magnetite (NBR/Fe₃O₄) nanocomposites were successfully fabricated by conventional roll milling technique. X‐ray diffraction and transmission (TEM) analysis showed that the product is mainly magnetite nanoparticles with diameter of 10‐13 nm. The microstructure of (NBR/Fe₃O₄) nanocomposites were examined by scanning electron microscopy (SEM) and FTIR spectroscopy. The dispersion of magnetite nanoparticles in the NBR rubber matrix and interfacial bonding between them were rather good. The thermal stability of nanocomposites was also obviously improved with the inclusion of the magnetite nanoparticles. The thermal conductivity, thermal diffusivity and specific heat of nanocomposites were investigated. The electrical conductivity of the NBR/Fe₃O₄ increases with the rise in temperature exhibiting a typical negative temperature coefficient of resistance (NTCR) behavior like a semiconductor. The nature of the temperature variation of electrical conductivity and values of activation and hopping energy, suggest that the transport conduction process is controlled by hopping mechanism. Values of characteristics parameters of the thermistors like thermistor constant, thermistor sensitivity and thermistor stability is quite good for practical application as NTCR devices at high temperature. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Improvement of microwave absorption for PAni/HA/TiO2/Fe3O4 nanocomposite after chemical treatment

In order to obtain efficient microwave absorbers that possess high conductivity, dielectric and magnetic properties, hexanoic acid doped polyaniline (PAni) nanocomposites which contain different ratios of ferum (II) oxide (Fe₃O₄) and titanium dioxide (TiO₂) nanoparticles were successfully prepared by in situ chemical polymerization through template free method. Chemical structure, conductivity, morphology, thermal stability, magnetic properties, and amorphous/crystalline behavior of PAni nanocomposites were characterized by Fourier transform infrared spectrometer (FTIR), four point probe, field emission scanning electron microscope (FESEM), thermal gravimetric analysis (TGA), vibrating samples magnetometer (VSM), and X‐ray diffractometer (XRD), respectively. From this study, conductivity was significantly improved from 8.48 × 10⁻⁴−1.23 × 10⁻² S/cm for PAni nanocomposites without any chemical treatment (during addition of Fe₃O₄) to 3.58 × 10⁻²−4.77 × 10⁻² S/cm for those with chemical treatment. PAni nanocomposites with chemical treatment show a narrow sharp reflection loss (RL) peak with high absorption (−48.9 dB) at lower frequency due to the limited individual Fe₃O₄ nanoparticles outside the nanorods/nanotubes as proved by the new proposed mechanism (Fig. 5 ), while it shows a broad RL peak with poor absorption (−13 dB) at higher frequency for those without chemical treatment. The novelty of this research has been focused on PAni with chemical treatment which yield better microwave absorption property (99.999% absorption), combination of high conductivity (3.58 × 10⁻²−4.77 × 10⁻² S/cm), high heterogeneity and moderate magnetization (Ms = 8.87–28.49 emu/g) compare to the PAni without chemical treatment. POLYM. COMPOS., 34:1186–1194, 2013. © 2013 Society of Plastics Engineers     

Preparation and characterization of corundum ceramics doped with Fe2O3 and TiO2 for high temperature thermal storage

High-temperature thermal storage materials have received urgent attention for efficient thermal transfer in solar thermal power generation. Corundum ceramics doped with Fe₂O₃ and TiO₂ were prepared via a pressureless sintering. A Fe₂O₃–TiO₂ system with different Fe₂O₃/TiO₂ ratios was applied to corundum ceramics. Phase composition, microstructural evolution, sintering properties, high temperature resistance and thermophysical properties were evaluated. The results indicated that Fe₂O₃ and TiO₂ rendered the grains highly active and enhanced the bonding between grains due to existing stably in the lattice of corundum. In addition, decrease in the Fe₂O₃/TiO₂ ratio led to a new phase of FeAlTiO₅, which refined the grains. These effects gave the samples good sintering properties and thermal shock resistance, but the thermal expansion coefficient mismatch between FeAlTiO₅ and corundum deteriorated the high-temperature (1300 °C) stability. Formula C1 (Fe₂O₃/TiO₂ ratio of 9:1) sintered at 1600 °C had the optimum comprehensive properties, possessing a bending strength loss rate of 1.54% after 30 cycles of thermal shock (1100 °C-room temperature, air cooling) and a constant strength retention rate of approximately 71.34% after 90 h high-temperature cycle. The corresponding thermal conductivity and specific heat capacity were 18.81 W/(m·K) and 1.02 J/(g·K) at 25 °C, which was suitable as a high-temperature thermal storage material.     

Nanocrystalline transition metal oxides and their composites with reduced graphene oxide and carbon nanotubes for photocatalytic applications

Transition metal oxide nanoparticles (CuO, ZnO & Fe₂O₃) and mixed metal oxides CuO. ZnO.Fe₂O₃ were fabricated by facile co-precipitation approach for photocatalytic treatment of organic dyes. The structural features, phase purity, crystallite size and morphology of individual and mixed metal oxides were analysed by X-rays diffraction patterns (XRD) and scanning electron microscopic (SEM) analysis. Electrical behaviour of CuO, ZnO, Fe₂O₃ and mixed metal oxides CuO. ZnO.Fe₂O₃ was explored by current-voltage (I-V) measurements. Functional groups present in the synthesized metal oxides were investigated by Fourier transform infrared spectroscopy (FTIR) which ensures the existence of M-O functional groups in the samples. The optical bandgap analysis was carried out by UV–visible spectroscopic technique which revealed that the blend of three different transition metal oxides reduced the bandgap energy of mixed metal oxides. The reason behind this reduced bandgap energy is formation of new electronic state which arises due to the metal-oxygen interactions. Moreover, the nanocomposites of CuO.ZnO.Fe₂O₃ with reduced graphene oxide (rGO) and carbon nanotubes (CNTs) were prepared to study the effect of the carbonaceous materials on the rate of photodegradation. These carbonaceous nanomaterials have plethora properties which can bring advancement in sector of photocatalytic treatment of wastewater. The photocatalytic experiments were performed using methylene blue (MB) as standard dye for comparative study of metal oxides and their composites with rGO and CNTs. The percentage degradation of methylene blue (MB) by nanocomposite CuO.ZnO.Fe₂O₃/rGO is 87% which is prominent among all samples. This result ascribed the photocatalytic aspects of reduced graphene oxide along with mixed metal oxides.     

Facile synthesis of Co0.5Zn0.5Fe2O4 nanoparticles decorated reduced graphene oxide hybrid nanocomposites with enhanced electromagnetic wave absorption properties

Herein, reduced graphene oxide/cobalt-zinc ferrite (RGO/Co_0.5Zn_0.5Fe₂O₄) hybrid nanocomposites were fabricated by a facile hydrothermal strategy. Results revealed that the contents of RGO could affect the micromorphology, electromagnetic parameters and electromagnetic wave absorption properties. As the contents of RGO increased in the as-synthesized hybrid nanocomposites, the dispersibility of the particles was improved. Meanwhile, numerously ferromagnetic Co_0.5Zn_0.5Fe₂O₄ particles were evenly anchored on the wrinkled surfaces of flaky RGO. Besides, the obtained hybrid nanocomposites exhibited superior electromagnetic absorption in both X and Ku bands, which was achieved by adjusting the RGO contents and matching thicknesses. Significantly, when the content of RGO was 7.4 wt%, the binary nanocomposites showed the optimal reflection loss of -73.9 dB at a thickness of 2.2 mm and broadest effective absorption bandwidth of 6.0 GHz (12.0–18.0 GHz) at a thin thickness of merely 2.0 mm. The enhanced electromagnetic absorption performance was primarily attributed to the multiple polarization effects, improved conduction loss caused by electron migration, and magnetic loss derived from ferromagnetic Co_0.5Zn_0.5Fe₂O₄ nanoparticles. Our results could provide inspiration for manufacturing graphene-based hybrid nanocomposites as high-efficient electromagnetic wave absorbers.