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.     

One-pot synthesis of antimony oxide and bismuth oxide nanocomposites for the selective electrochemical determination of the anticancer drug methotrexate in biomedical samples

Methotrexate (MTRX) is an anticancer drug that is also used for several chronic illnesses; however, a high dosage of MTRX can cause adverse effects, so it is necessary to monitor the MTRX level in blood and urine samples. This work reports the electrochemical determination of MTRX based on Sb₂O₃ and Bi₂O₃ composite material (Sb₂O₃@Bi₂O₃)modified electrodes. The one-pot sonohydrolysis synthesis method is employed for the preparation of the Sb₂O₃@Bi₂O₃ composite, which reveals high crystallinity with mixed phases of monoclinic Bi₂O₃ and cubic Sb₂O₃. Furthermore, the phases are identified by XRD, Raman spectroscopy, XPS, and HRTEM analysis. This composite reveals nanoneedle and nanocube morphologies. The Sb₂O₃@Bi₂O₃modified GCE shows excellent electrochemical activity for the detection of the anticancer drug methotrexate (MTRX). The activity is compared with the individual Sb₂O₃ and Bi₂O₃ compounds. Sb₂O₃@Bi₂O₃/GCE shows good electroanalytical characteristics in chronoamperometric analysis. Sb₂O₃@Bi₂O₃/GCE exhibits a linear range of approximately 0.01 μM to 174.6 μM, a sensitivity of 1.46 μA cm^-2μM^-1, and an LOD of 2.9 nM. Moreover, Sb₂O₃@Bi₂O₃/GCE delivered high selectivity among highly interfering compounds in blood and urine samples.     

RGO/KMn8O16 composite as supercapacitor electrode with high specific capacitance

Reduced graphene oxide/cryptomelane (RGO/KMn₈O₁₆) composites are successfully synthesized from α-MnO₂ nanorods and GO using a water-bathing precipitation method. The unique structure of KMn₈O₁₆ nanorods, with a length of 2–4 μm, dispersed on the surface of RGO leads to a much enhanced electrical conductivity and ionic transport, finally achieving composites with an improved electrochemical performance. Electrochemical measurement results show a specific capacitance of 222.3 F/g at a current density of 0.2 A/g, much higher than that of the original α-MnO₂. After 500 cycles at 2.0 A/g, the RGO/KMn₈O₁₆ composite electrode still retains 92.6% of its initial specific capacitance. The excellent electrochemical performance and durability observed for this composite electrode suggest its potential application for electrochemical capacitors.     

Designing effective and stable S-scheme RGO/AgVO3/AgBr hybrid with enhanced photocatalytic performance

The low separation of photogenerated electron-hole pairs and cycle stability has been the main bottleneck which restricts the development of photocatalytic technology for water purification. Here, RGO/AgVO₃ composites were fabricated by photo-ultrasonic assisted reduction method, and AgBr nanoparticles were assembled on the surface of RGO/AgVO₃ via an in situ ion exchange method. A series of characterization and experimental results indicated that the introduction of RGO influenced the growth of crystal phase for AgVO₃ nanorods, resulting that AgVO₃ nanorods became thicker and shorter with the increase in RGO content. Moreover, RGO could also work as a bridge to promote the migration of electrons, leading different improvement for photocatalytic activity. Furthermore, in situ growth of AgBr on the surface of AgVO₃ nanorods could prevent its agglomeration and exfoliation, thus improving the photocatalytic activity and cycle stability of composites. RGO_1%/AgVO₃/AgBr_30% exhibited excellent photocatalytic activity and stability for methylene blue (MB) degradation due to its unique structure, and its removal ratio reached at 96.2% within 50 min. Meanwhile, the separation of photogenerated electron-hole pairs of AgVO₃ was markedly improved due to the introduction of RGO and AgBr. Based on the trapping experiments and theoretical calculation of band gap, a possible S-scheme photocatalytic mechanism for improved photocatalytic activity was proposed.     

Optical properties of Yb-doped ZnO/MgO nanocomposites

Yb³⁺ doped ZnO/MgO nanocomposite were prepared by combustion synthesis method. The samples were further heated to 1000 °C to improve their crystallinity and photoluminescent efficiency. The concentrations of Yb³⁺ and Mg²⁺ were varied between 1–2% and 5–70% respectively in prepared samples. The nano-powders were characterized by Scanning Electron Microscopy and X-ray Diffraction for morphology and structural determination. XRD studies have revealed the wurtzite structure for Mg_xZn_1−xO for Mg concentrations below 30%. Higher concentrations of Mg results in Yb³⁺ doped ZnO/MgO nanocomposite containing three phases; the wurzite hexagonal phase typical of ZnO, the cubic phase of MgO and a small amount of cubic Yb₂O₃ phase. As expected, the amount of cubic phase in nano-powders increased with the increase of Mg concentration in ZnO. The crystallite size of ZnO/MgO composites decreased from 55 nm to 30 nm with increase of Mg content. SEM images of Yb³⁺ doped ZnO/MgO nanocomposite with higher Mg content (>50%) showed clearly distinct hexagonal and cubical shaped nano-particles. Photoluminescent emission showed a broad band in the range (435 nm to 700 nm). Pure ZnO nano-phosphor showed an emission peak around 545 nm, which is blue shifted with Mg content. The photoluminescence intensity increased with increase of Mg content in ZnO and it became maximum with 30% Mg concentration. Time resolved decay curves of photoluminescence indicated decay time in microsecond time scale.     

Synthesis of butterfly-like BiVO4/RGO nanocomposites and their photocatalytic activities

A simple and high efficient method was proposed for the synthesis of uniform three dimensional(3D) BiVO_4/reduced graphene oxide(RGO) nanocomposite photocatalyst by adopting the microwave assistant and using Bi(NO_3)_3·5H_2O, graphene oxide(GO) and NH_4VO_3 as precursor. The as-obtained composites were well characterized with the aid of various techniques to study the morphology, structure, composition, optimal and electrical property. In the as-obtained composites, the GO sheets were fully reduced into RGO, and monoclinic structure BiVO_4 crystallized completely into butterfly-like BiVO_4 lamellas and well bonded with the RGO lamellas. The length and the width of the butterfly-like BiVO_4 particle were about 1.5 μm, and the thickness of the flake was about 20 nm. Photocatalytic performances of BiVO_4/RGO composite and pure BiVO_4 particle have been evaluated by investigating the reduction of Cr(Ⅵ) ion-contained wastewater under simulated solar light irradiation, where the BiVO_4/RGO composite displayed enhanced photocatalytic activity. It is found that the pseudo-first-order rate constants(k) for the photocatalytic reduction of Cr(VI) by BiVO_4/RGO composite was about 4 times as high as that of the pure BiVO_4. The present work suggested that the combination of BiVO_4 and RGO displayed a remarkable synergistic effect, which led to enhanced photo-catalytic activity on Cr(Ⅵ) reduction.     

Amorphous carbon nanofibres inducing high specific capacitance of deposited hydrous ruthenium oxide

Composites consisting of ruthenium oxide particles deposited on amorphous carbon nanofibres are prepared by a repetitive impregnation procedure. The choice of amorphous carbon nanofibres as support of amorphous ruthenium oxide leads to composites in which the deposited oxide consists of aggregates of extremely small primary particles (1–1.5 nm-size) and showing high porosity (specific surface area of 450 m² g⁻¹). This special deposition of the oxide seems to favour: (i) high oxide capacitance (1000 Fg⁻¹) at high oxide loadings (up to 20 wt%) and (ii) high capacitance retention (ca. 80% from the initial oxide capacitance) at high current densities (200 mA cm⁻²). Amorphous carbon nanofibres are suitable supports for amorphous ruthenium oxide and perhaps for other amorphous oxides acting as active electrode materials.     

Fabrication of NiO-ZnO/RGO composite as an anode material for lithium-ion batteries

NiO-ZnO/RGO composite was obtained by the annealing of an Ni (OH)₂-Zn (OH)₂/RGO precursor, which has been fabricated by in situ ultrasonic agitation. Moreover, the NiO-ZnO nanoflakes are evenly distributed on the RGO sheets based on the scanning electron microscope (SEM) and transmission electron microscope (TEM) characterization results. When the NiO-ZnO/RGO composite was used as an anode material in lithium-ion batteries (LIBs), the electrodes exhibited a high reversible capacity of 1017 mA h/g at a current density of 100 mA/g after 200 cycles and a specific capacity of 458 mA h/g at 500 mA/g even after 400 cycles. The electrode even reached a capacity of 185 mA h/g at a current density of 2000 mA/g. The excellent electrochemical properties of the NiO-ZnO/RGO composite might be attributable to the NiO-ZnO nanoflakes offering rich electrochemical reaction sites and shortening the diffusion length for lithium ion (Li⁺), as well as the RGO sheets improving the transfer rates of Li⁺ and electron during the charge-discharge process.     

MgO/C负载磺化酞菁钴催化剂制备条件对其硫醇氧化性能的影响

采用浸渍法制备了系列MgO/C负载磺化酞菁钴（CoPcS）脱硫醇催化剂,讨论了Mg与C物质的量比、干燥温度和浸渍溶剂等对催化剂活性的影响。采用XRD、BET、DTA-TG和FTIR等表征方法对催化剂的物性结构进行了研究。结果表明，在反应初始阶段，催化剂活性由催化剂碱量和比表面积共同决定。随着反应的进行，催化剂活性主要由催化剂碱量决定。当Mg与C物质的量比为0.2、干燥温度200 ℃和采用甲醇（非水溶剂）浸渍时，催化剂稳定性提高，具有最佳物性结构，催化剂活性最好。     

Catalytic ozonation of humic acids with Fe/MgO

Humic acids were degraded by ozone at room temperature in a stirred tank reactor and a fixed bed reactor with Fe/MgO catalysts. Experimental results show that the ozonation with Fe/MgO induced a significant reduction in UV absorbance of humic acids as compared to ozone alone. Fe/MgO was the most efficient catalyst to degrade humic acids in the presence of ozone. GPC (gel permeation chromatography) showed that the humic acids with high molecular weight could be severely decomposed into organic compounds with low molecular weight on the Fe/MgO catalyst, indicating that humic acids could be catalytically decomposed. The continuous reaction experiments with the palletized catalysts supported that humic acids can be removed by catalysis as well as adsorption.     

The effect of Nb2O5 and ZrO2 additions on the behaviour of Li/MgO and Li/Na/MgO catalysts for the oxidative coupling of methane

Incorporation of Nb₂O₅ or ZrO₂ into both Li/MgO and Li/Na/MgO systems produced ternary and quaternary catalysts, respectively, capable of attaining optimal C₂ yields and selectivities at lower temperatures relative to the unpromoted materials. The degree of enhancement effected by these metal oxide additives was compared to that produced by Li/MgO and Li/Na/MgO catalysts promoted with SnO₂ or Co₃O₄. At reaction temperatures < 700°C, the Li/Co/MgO ternary system showed marked differences in behaviour compared to the other ternary catalysts tested. This was particularly evident in the variation in C₂ selectivity with time on stream during ageing studies of (i) untreated materials, (ii) materials pretreated in CO₂, and (iii) materials dosed periodically with CHCI₃.     

SiO2/还原氧化石墨烯复合材料的简易制备及对罗丹明B的吸附

以正硅酸乙酯（TEOS）为硅源,氧化石墨烯（GO）为载体,在不添加任何还原剂的情况下,通过水热法简易制备SiO₂/还原氧化石墨烯（SiO₂/RGO）复合材料。采用TEM、FTIR、XRD、TG-DSC、N₂-吸附对复合材料的微观结构进行表征,分析表明：负载量为76.60%（质量分数）的SiO₂纳米颗粒均匀分散在RGO表面上,且部分以Si-O-C键进行配位;具有多级孔结构的SiO₂/RGO复合材料孔径主要分布在1~7nm,比表面积高达676m²/g。以罗丹明B为目标污染物,考察了pH、投入量、温度和接触时间等因素对复合材料吸附性能的影响,结果表明：在pH为2、35℃时,复合材料具有最佳的吸附效果,吸附量为127.8mg/g。动力学分析表明吸附过程符合准二级动力学模型,热力学参数揭示吸附过程为自发吸热过程。     

Pretreatment effects on the active site for methane activation in the oxidative coupling of methane over MgO and Li/MgO

The effects of high temperature pretreatments on the activity of MgO and Li/MgO catalysts for the oxidative coupling of methane have been studied. The MgO powder catalyst exhibited a turnover frequency of 3.0×10^–3 molecules/sites, at 990K, whereas the Li/MgO catalyst showed a turnover frequency of 7.0×10^–2 molecules/sites, under the same reaction conditions. The initial C₂ formation rate was observed to increase with pretreatment temperature over the MgO catalyst, supporting our previous proposal that F-type defects are responsible for methane activation.     

新型三元复合可见光催化剂Au/Bi_2WO_6/RGO的制备及其性能

采用溶剂热法制备钨酸铋/石墨烯(Bi_2WO_6/RGO)光催化剂,然后利用光还原法将Au纳米颗粒沉积于该二元光催化剂表面,制备出Au/Bi_2WO_6/RGO三元复合可见光催化剂。运用X射线衍射(XRD)、紫外可见漫反射吸收光谱(UV-Vis DRS)和透射电镜(TEM)对催化剂的晶体结构、光吸收性能、形貌性能进行了分析表征。以罗丹明B (Rh B)为模拟污染物,评价了该催化剂的可见光催化性能。结果表明,RGO和Au纳米颗粒的引入,增强了Bi_2WO_6可见光吸收,同时抑制了光生载流子的复合,从而提高Bi_2WO_6可见光催化降解RhB的性能。     

Nitrile butadiene rubber/hindered phenol nanocomposites with improved strength and high damping performance

A hindered phenol (AO-80) was studied to prepare rubber nanocomposites with nitrile butadiene rubber (NBR). The NBR/AO-80 rubber nanocomposites were successfully developed by applying the adopted preparation procedure/conditions, especially by introducing mechanical kneading of the NBR/AO-80 composites at a temperature higher than the melting point of AO-80, followed by the crosslinking of NBR molecules during the subsequent hot-pressing/vulcanization process. The nanocomposites consisted of two phases: (1) the AO-80 enriched phase (nanoparticles with the average size of approximately 20 nm) and (2) the NBR enriched phase (matrix). The generation and uniform distribution of the nanoparticles were attributed to the high temperature mechanical kneading process, the strong intermolecular interactions between AO-80 and NBR molecules, and the formation of a three-dimensional NBR network. The morphological, structural and mechanical properties of the composites were systematically investigated in each preparation step using SEM, TEM, DSC, XRD, FT-IR, DMTA and a tensile tester. The results indicated that the prepared NBR/AO-80 rubber nanocomposites had single relaxation transitions, improved tensile strengths, high dynamic mechanical loss values, and reasonably good stabilities. The NBR/AO-80 rubber nanocomposites are expected to have important applications as a high performance damping material.     

Low-temperature exfoliated graphene oxide incorporated with different types of natural rubber latex: Electrical and morphological properties and its capacitance performance

A simple with cost-effective method in the production and fabrication of graphene-based rubber nanocomposites as electrode materials is still remain a global challenge. In this work, we proposed one- and two-step approaches to fabricate an exfoliated graphene oxide (GO) as nanofiller in three different types of rubber latex polymer, namely, low ammonia natural rubber latex (NRL), radiation vulcanized NRL (RVNRL), and epoxy NRL 25 (ENRL 25). The electrical conductivity and capacitive behavior of nanocomposite samples were investigated under a four-point probe and cyclic voltammetry measurements, respectively. Meanwhile, the morphological properties were observed using field emission scanning electron microscopy, energy dispersive X-ray, optical polarization microscope, high-resolution transmission electron microscopy, Fourier-transform infrared spectroscopy, micro-Raman spectroscopy, and X-ray diffraction. The thermal stabilities of the nanocomposites were also investigated by thermogravimetric analysis. Among all, the GO/RVNRL polymer nanocomposite samples performed a better homogeneity with an improved electrical conductivity (~8.6 × 10⁻⁴ Scm⁻¹) as compared with the GO/ENRL 25 (~3.1 × 10⁻⁴ Scm⁻¹) and GO/NRL (~2.6 × 10⁻⁴ Scm⁻¹) polymer nanocomposite samples. In addition, the GO/RVNRL polymer nanocomposite electrodes showed acceptable specific capacitance (5 Fg^-1). The successfully fabricated conductive GO-based rubber nanocomposites are suitable for new supercapacitor electrodes.     

Nitrogen-doped-CNTs/Si3N4 nanocomposites with high electrical conductivity

Novel highly electrically conducting nanocomposites consisting of a silicon nitride (Si₃N₄) ceramic matrix containing up to 13.6 vol.% of nitrogen-doped multi-walled carbon nanotubes (CNx) were fabricated. As-synthesized CNx were treated with hydrogen peroxide in order to efficiently detach/isolate the nanotubes from bundles, then they were mixed with the ceramic powders and fully densified using the spark plasma sintering (SPS) technique. Composites containing 13.6 vol.% CNx reached an electrical conductivity of 2174 S m⁻¹ that is the highest value reported hitherto for carbon nanotubes/Si₃N₄ nanocomposites. The nitrogen doping also favored a strong mechanical interlocking between the nanotubes and the Si₃N₄ matrix; when compared to the undoped carbon nanotubes. These novel nanocomposites could be used in devices associated to power generation or telecommunications.     

有机／无机纳米复合材料的制备方法

综述了近年来国内外有机/无机纳米复合材料的制备方法及其最新进展情况。     

Dual-functional hybrid ZnSnO/Graphene nanocomposites with applications in high-performance UV photodetectors and ozone gas sensors

Dual-functional metal oxide semiconductors that can detect the values of two different physical quantities, such as light intensity and gas concentration, have been the subject of many studies because they are used in the Internet of Things (IoT). However, the opposite sensing mechanisms for photons and gas molecules pose challenges for material design. In this study, we developed a dual-functional sensor that uses hybrid amorphous ZnSnO (a-ZTO)/graphene nanosheet (GNS) composite films. GNSs were incorporated into a-ZTO films so that the recombination process for photo-generated electron/hole pairs was suppressed owing to the favorable band alignment at the ZTO/GNS interface. The a-ZTO/GNS dual-functional sensor had a responsivity of 26.39 A/W at 350 nm and exhibited a fast response speed, with a rise time of 0.71 s and a decay time of 0.95 s. ZTO/GNS nanocomposite film also featured a smaller cluster size so that more electrons were produced for the chemical reaction of gas. Under UV illumination of 10 mW/cm², the dual-functional sensor exhibited a gas response of 12.8, against a 5-ppm concentration of ozone gas. These results demonstrate that this dual-functional device can serve as not only a high-performance UV photodetector but also a highly sensitive gas sensor.     

Gas transport properties of MgO filled poly(1-trimethylsilyl-1-propyne) nanocomposites

Magnesium oxide (MgO) nanoparticles were dispersed via solution processing in poly(1-trimethylsilyl-1-propyne) (PTMSP) to form polymer nanocomposites. Transmission electron microscopy was used to determine the extent of particle aggregation in the composites. Both nanocomposite density and CO₂, CH₄, N₂, and H₂ permeability were influenced by nanoparticle loading. Nanocomposite densities were markedly lower than predicted by a two phase additive model. For example, in films containing 75 nominal volume percent MgO, the polymer-particle composite density was 68 percent lower than expected based on an additive model. At this loading, gas permeability coefficients were, depending on the gas, 17-50 times higher than in unfilled PTMSP at similar conditions. The changes in permeability with particle content were interpreted in terms of measured changes in gas solubility with particle content and diffusion coefficients calculated from the permeability and solubility data.