Facile synthesis of graphene oxide-wrapped CNFs as high-performance microwave absorber

Graphene oxide/carbon nanofibers hierarchical structures have been successfully synthesized through a modified Hummers method. Owing to the harsh chemical exfoliation and oxidation, graphene oxide (GO) appears on the outer walls of carbon nanofibers (CNFs) with the preservation of the 3D fibrous network. By adjusting the oxidation time, the obtained sample exhibited excellent electromagnetic (EM) attenuation performance with a maximum reflection loss of −49.82 dB at a thickness of 1.5 mm. Meanwhile, an effective bandwidth of 2.48 GHz was also investigated. The superior EM absorbing performance of GO/CNFs is ascribed to the hierarchical structure. While the inner carbon skeleton endows the material with desirable conductive network, GO exhibits a larger surface area with abundant functional groups and defects that give rise to multiple polarizations and relaxation processes. Moreover, the resistance-capacitance coupled circuits formed in the GO/CNFs network are beneficial for dissipating the incident waves. Prospectively, the synthetic strategy applied in this research can be extended to assemble GO on carbonaceous materials to fabricate novel microwave absorbers.     

Improved output performance of hybrid composite films with nitrogen-doped reduced graphene oxide

In this research, graphene-based ceramic/polymer hybrid composite films for energy harvesting devices were prepared and analyzed. Nitrogen-doped reduced graphene oxide (N-rGO) conductive elements were embedded in a ceramic/polymer matrix as floating electrodes to form a micro-capacitor composite structure. The effects of nitrogen atom substitution on the rGO materials were investigated and their conducting properties improved. The employment of rGO- and N-rGO-based floating electrodes resulted in the formation of micro-capacitors and an increase in the potential energy of the composite films. The increase in the potential energy consequently increased the output energy of the energy harvesters. The highest voltage and energy density of the composite films were 8.5 V and 1.46 mJ/cm³, respectively, for the N-rGO based ceramic/polymer composite film.     

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.     

Tailoring the properties of cerium doped zinc oxide/reduced graphene oxide composite: Characterization,photoluminescence study,antibacterial activity

Ce doped ZnO/rGO composite materials were prepared by a one-pot hydrothermal process without any surfactant. The size, crystallography and morphology of the composite were investigated in detail by X- ray diffraction (XRD) studies, Raman spectroscopy, scanning electron microscopic (SEM), transmission electron microscopic (TEM) studies, UV–Vis spectroscopic analysis and X-ray photoelectron spectroscopic (XPS) analysis. The XRD pattern substantiates the formation of Ce doped ZnO/rGO composite revealing the wurtzite structure of ZnO. The SEM micrograph illustrates flower-like morphology for ZnO/rGO composite which coalesced further after cerium incorporation. Additionally, TEM image illustrated that ZnO hexagons were disoriented from its flower structure in Ce/ZnO/rGO composite. The XPS spectra further reaffirm the formation of cerium doped ZnO/rGO composite. The photoluminescence (PL) spectra confirms that emission occurs in the UV and visible region and several active sub-levels were observed in visible region on deconvolution, due to the incorporation of cerium. Antibacterial activity towards B. subtills and V. harveyi affirmed that the incorporation of Ce in ZnO/rGO composite leads to an improved antibacterial activity.     

Targeted design of polyaniline-graphene oxide,barium-strontium titanate,hard-soft ferrite,and polyester multi-phase nanocomposite for highly efficient microwave absorption

The current paper focuses on synthesizing a high-efficiency microwave absorber via incorporating the nanofillers of graphene oxide-polyaniline (GO-PANI), barium-strontium titanate (BST), and soft-hard ferrite within the polyester matrix. The nanocomposite magnets of (Ba_0.5Sr_0.5Fe₁₂O₁₉)_1-x hard/(CoFe₂O₄)_x soft (x = 0.2, 0.5, and 0.8) were prepared using sol-gel auto-combustion method. The GO-PANI and BST were successfully synthesized by in situ polymerization and improved polymerization, respectively. The phase structure, chemical structure, morphology, and microwave absorption properties of the synthesized nanocomposites were characterized by X-ray diffractometer (XRD), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM), vector network analyzer (VNA) techniques, respectively. The results showed that the synergistic effects of the combination of dielectric (BST), conductive (GO-PANI), and magnetic materials (hard-soft ferrites) provided the reflection loss values of less than ?20 dB (>99% absorption) in the X-band region. The minimum reflection loss of ?35 dB (>99.99% absorption) was obtained by the optimal formulation including (Ba_0.5Sr_0.5Fe₁₂O₁₉)_0.2 (CoFe₂O₄)_0.8, and the weight ratio of 1: 2 for both BST/soft-hard ferrite and hard-soft ferrite + BST/GO-PANI with the thickness of 1 mm. According to the results, the thickness factor plays a key role in improving the impedance matching. Consequently, the proposed nanocomposite can be employed as a novel kind of microwave absorbers with good impendence matching and high absorption.     

Microwave-assisted green synthesis of Ag/reduced graphene oxide nanocomposite as a surface-enhanced Raman scattering substrate with high uniformity

A nanocomposite of silver nanoparticles/reduced graphene oxide (Ag/rGO) has been fabricated as a surface-enhanced Raman scattering (SERS) substrate owing to the large surface area and two-dimensional nanosheet structure of rGO. A facile and rapid microwave-assisted green route has been used for the formation of Ag nanoparticles and the reduction of graphene oxide simultaneously with L-arginine as the reducing agent. By increasing the cycle number of microwave irradiation from 1 and 4 to 8, the mean diameters of Ag nanoparticles deposited on the surface of rGO increased from 10.3 ± 4.6 and 21.4 ± 10.5 to 41.1 ± 12.6 nm. The SERS performance of Ag/rGO nanocomposite was examined using the common Raman reporter molecule 4-aminothiophenol (4-ATP). It was found that the Raman intensity of 4-ATP could be significantly enhanced by increasing the size and content of silver nanoparticles deposited on rGO. Although the Raman intensities of D-band and G-band of rGO were also enhanced simultaneously by the deposited Ag nanoparticles which limited the further improvement of SERS detection sensitivity, the detectable concentration of 4-ATP with Ag/rGO nanocomposite as the SERS substrate still could be lowered to be 10⁻¹⁰ M and the enhancement factor could be increased to 1.27 × 10¹⁰. Furthermore, it was also achievable to lower the relative standard deviation (RSD) values of the Raman intensities to below 5%. This revealed that the Ag/rGO nanocomposite obtained in this work could be used as a SERS substrate with high sensitivity and homogeneity.     

One-pot synthesis of CdS sensitized TiO2 decorated reduced graphene oxide nanosheets for the hydrolysis of ammonia-borane and the effective removal of organic pollutant from water

A hybrid material of reduced graphene oxide (RGO) sheets decorated with CdS-TiO₂ NPs was prepared through a facile one-pot hydrothermal method. The assembly of CdS-TiO₂ nanoparticles (NPs) on RGO sheets was in-situ produced. As-synthesized nanocomposites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy disperse X-ray spectrum (EDS), fourier transform infrared spectroscopy (FTIR), and photoluminescence spectroscopy (PL). The obtained nanocomposites exhibited a good photocatalytic activity for the visible-light-induced decomposition of methylene blue (MB) dye and hydrolysis of ammonia borane. The results showed that by incorporation of CdS and TiO₂ NPs on graphene oxide sheets the photocatalytic efficiency was enhanced. The significant enhancement in the photocatalytic activity of CdS-TiO₂/RGO nanocomposites under visible light irradiation can be ascribed to the effect of CdS by acting as electron traps in TiO₂ band gap. Reduced graphene oxide worked as the adsorbent, electron acceptor and a photo-sensitizer to efficiently enhance the dye photo decomposition. Such nanocomposite photocatalyst might find potential application in a wide range of fields, including hydrogen energy generation, air purification, and wastewater treatment.     

Surfactant-free synthesis of homogeneous nano-grade cadmium sulfide grafted reduced graphene oxide composite as a high-activity photocatalyst in visible light

Zero-dimensional cadmium sulfide (CdS) nanoparticles with small size (∼50 nm) were grafted on the two-dimensional reduced graphene oxide (RGO) nanosheet via a facile hydrothermal method without any surfactant to synthesize CdS@RGO nanocomposites in this paper. The structural analysis confirms the strong attachment and interaction between CdS and RGO in CdS@RGO photocatalyst, which leads to a higher photocatalytic efficiency (95.3%) with superior anti-corrosion stability (almost no change of efficiency over three repeated experiments) to that of pure CdS in visible light. The unique hybrid nanostructure of CdS@RGO can effectively prevent the self-corrosion of CdS and facilitate the separation of electron-hole pairs. Consequently, these outstanding photocatalytic performances of CdS@RGO endow it with a promising prospect for the degradation of organic pollutants and this work can be extended to other graphene-based inorganic semiconductor composites.     

Plant-based synthesis of cerium oxide nanoparticles as a drug delivery system in improving the anticancer effects of free temozolomide in glioblastoma (U87) cells

Nowadays, nanocarriers were proven to contain the potential of improving cancer treatments and are utilized to carry anticancer medications to tumors. In this study, cerium oxide nanoparticles (CeO₂-NPs) were synthesized by using Caccinia macranthera leaf extract as the stabilizer and reducer agent, as well as cerium nitrate salt as the supplier source of cerium. The synthesized CeO₂-NPs were analyzed through different procedures such as UV–Vis, FTIR, FESEM/EDX/PSA, XRD, XPS, and TGA/DTA. The outcomes of XRD and FTIR analyses con?rmed the synthesis of pure and crystalline structures of CeO₂-NPs. The average size and zeta potential of our nanoparticles were about 30 nm and ?18.5 mV, respectively. According to the results of XPS analysis, the percentage of Ce⁴⁺ was more than that of the Ce³⁺ oxidation state in synthesized NPs. The CeO₂-NPs were loaded with Temozolomide (TMZ) as an anti-cancer drug through electrostatic interaction and the produced nano-drug (CeO₂-TMZ) was delivered to glioblastoma multiforme (GBM) tumor cells. In conformity to the observations, the drug loading content (DLC) and drug loading efficiency (DLE) of CeO₂-TMZ were about 89.10 and 20.29, respectively. In comparison to the TMZ drug, the in vitro assay exhibited the exertion of higher antiproliferative activities, cell cycle arrest, apoptosis, and expression of p53 by CeO₂-TMZ, which proves the promising capability of this drug as a remedial factor for cancer treatment.     

One-step hydrothermal synthesis and enhanced microwave absorption properties of Ni0.5Co0.5Fe2O4/graphene composites in low frequency band

Ni_0.5Co_0.5Fe₂O₄/graphene composites were synthesized successfully via one-step hydrothermal method. The crystal structure, morphology and corresponding elemental distribution, electromagnetic parameters and microwave absorption performances of the as-prepared composites were measured by XRD, SEM, TEM and VNA, respectively. The results indicated that the microwave absorbing performance can be obviously enhanced through the addition of graphene in a suitable range, the magnetic loss plays a dominant contribution for the microwave absorption of composites. The maximum reflection loss of ?30.92?dB at 0.84?GHz with a ?10?dB bandwidth over the frequency range of 0.58–1.19?GHz is obtained when the composite contains 12?wt% graphene and the thickness of sample is 4?mm. This investigation presents a simple method to prepare Ni_0.5Co_0.5Fe₂O₄/graphene composites with excellent microwave absorption performance in the low frequency band of 0.1–3?GHz.     

Fabrication of Ni/ZnO/C hollow microspheres decorated graphene composites towards high-efficiency electromagnetic wave absorption in the Ku-band

Developing light-weight, thin thickness and high-efficiency electromagnetic wave (EMW) absorbers is an effective strategy for dealing with the increasingly serious problem of electromagnetic radiation pollution. Herein, nickel/zinc oxide/carbon (Ni/ZnO/C) hollow microspheres decorated graphene composites were facilely prepared through the high-temperature pyrolysis of bimetallic NiZn metal-organic frameworks (MOFs) precursors. Morphological characterization results manifested that the Ni/ZnO/C microspheres with unique hollow structure were almost evenly anchored on the wrinkled surfaces of flake-like graphene. Moreover, the influences of additive amounts of graphene oxide (GO) in the MOFs precursors on the crystal structure, graphitization degree, micromorphology, magnetic properties, electromagnetic parameters and EMW absorption performance were investigated in detail. It was found that the superior EMW absorption performance could be achieved through facilely adjusting the additive amounts of GO in the precursors. As the additive amount of GO was equal to 60 mg, the obtained composite showed the comprehensive excellent EMW absorption performance. Notably, the optimal minimum reflection loss reached ?57.5 dB at 16.5 GHz in the Ku-band under an ultrathin matching thickness of merely 1.34 mm, and the broadest effective absorption bandwidth achieved 5.6 GHz (from 12.4 to 18 GHz) when the thickness was 1.5 mm. Furthermore, the underlying EMW absorption mechanisms of as-prepared composites were revealed. It was believed that our results could be valuable for the structural design and EMW absorption performance modulation for MOFs derived magnetic carbon composites.     

P(VDF-TrFE)-based polymer nanocomposites comprising of reduced graphene oxide decorated with CoFe2O4@MCM 41 for efficient microwave absorption in X-band

Lightweight polymer nanocomposites (PNCs) dispersed with nanofiller RGO/CoFe₂O₄@MCM41, namely RCM (using hydrothermal process), have been prepared and characterized. Using the solution cast technique, PNCs {(P(VDF-TrFE)/LiTFSI/EMIMTFSI) + x wt% RCM, where x = 5, 7.5, and 10 in wt%} have been successfully synthesized. The synthesized PNCs possess good structural, thermal, mechanical, and magnetic properties because of the dispersed nanofiller within the polymeric matrix, which forms a 3-dimensional interconnected conducting network. The optimized PFE15Li50IL7.5RCM polymer nanocomposite also exhibits total shielding effectiveness (SE_T) of ~19.88 dB at 9.2 GHz for a thickness of 1.18 mm corresponding to 89.07% effective absorption (A_eff) in the X-band (8.2–12.4 GHz).     

Facile preparation of silver/reduced graphene oxide/chitosan colloid and application of the nanocomposite in antibacterial and catalytic activity

Reduced graphene oxide (RGO) decorated with silver nanoparticles (AgNPs) was synthesized by a facile solution‐based approach in chitosan (CS) solution. The morphology and elemental composition of as‐prepared Ag/RGO/CS colloid were characterized by SEM and energy dispersive X‐ray spectroscopy, respectively. TEM images show that most of the AgNPs are uniformly dispersed in the CS matrix while the other nanoparticles are decorated on the RGO nanosheets. XRD indicates that the interlayer distance of RGO is between 0.34 and 1.87 nm while the diameter of face‐centered cubic AgNPs is no more than 30 nm. Fourier transform infrared spectroscopy of the Ag/RGO/CS colloid confirms the formation of AgNPs and RGO. X‐ray photoelectron spectroscopy proves that both the Ag ? O bond and the C ? N bond exist in the nanocomposite. Antimicrobial assays were performed using the most common species of Gram bacteria. The inhibitory effect indicates that the incorporation of AgNPs and RGO significantly improves the antimicrobial activity of CS colloid. In addition, the nanocomposite colloid exhibits significant catalytic activity toward the reduction of 4‐nitrophenol by NaBH₄. © 2018 Society of Chemical Industry     

Synthesis and characterization of hybrid materials based on graphene oxide and silica nanoparticles and their effect on the corrosion protection properties of epoxy resin coatings

This study focuses on the use of tetraethyl orthosilicate (TEOS) as a silica source to decorate the surface of graphene oxide (GO) nanosheets and the use of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (Z-6020) as a coupling agent through a one-step in-situ sol-gel process. The results of the Fourier transform infrared spectroscopy (FT-IR), UV-visible, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) revealed that fine SiO₂ nanoparticles have successfully been synthesized on the basal plane of GO by covalent bonding. The dispersion of GO sheets and GO–SiO₂ nanohybrids within the epoxy matrix was studied using XRD and SEM techniques. Then, the effect of incorporating 0.1?wt% GO sheets and GO–SiO₂ nanohybrids on the corrosion protection and barrier performance of the epoxy coating was also investigated. The results showed that the incorporation of GO–SiO₂ into the epoxy matrix improved its thermal stability. The electrochemical impedance spectroscopy (EIS) test, potentiodynamic polarization and cathodic disbonding test showed that the corrosion protection performance was significantly enhanced by the incorporation of GO–SiO₂ hybrids into the epoxy resin compared to epoxy/GO and neat epoxy resin, respectively. The water contact angle (CA) results confirmed the reduction of the hydrophobic nature of the surface after the incorporation of GO–SiO₂ hybrids.