A novel,highly sensitive electrochemical 1,4-dioxane sensor based on reduced graphene oxide–curcumin nanocomposite

1,4-Dioxane is a carcinogenic, non-biodegradable, organic water pollutant which is used as a solvent in various industries. It is also formed as an undesired by-product in the cosmetic and pharmaceutical industry. Given its carcinogenicity and ability to pollute, it is desirable to develop a sensitive and selective sensor to detect it in drinking water and other water bodies. Current works on this sensor are very few and involve complex metal oxide composite systems. A sensitive electrochemical sensor for 1,4-dioxane was developed by modifying a glassy carbon electrode (GCE) with a reduced graphene oxide–curcumin (rGO–CM) nanocomposite synthesized by a simple solution approach. The prepared rGO–CM was characterized by X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) Spectroscopy, Raman spectroscopy, UV-Vis spectroscopy, and Scanning Electron Microscopy (SEM). The rGO–CM/GCE sensor was employed for the detection of 1,4-dioxane in the range of 0.1–100 μM. Although, the detection range is narrower compared to reported literature, the sensitivity obtained for the proposed sensor is far superior. Moreover, the limit of detection (0.13 μM) is lower than the dioxane detection target defined by the World Health Organization (0.56 μM). The proposed rGO–CM/GCE also showed excellent stability and good recovery values in real sample (tap water and drinking water) analysis.

Reduced graphene oxide–curcumin (rGO–CM) nanocomposite was prepared from graphite oxide using curcumin. The rGO–CM/GCE was used for highly sensitive 1,4-dioxane detection. The LOD obtained (0.13 μM) was lower than the WHO guideline value.     

Self-assembled layer-by-layer partially reduced graphene oxide–sulfur composites as lithium–sulfur battery cathodes

Constructing a reliable conductive carbon matrix is essential for the sulfur-containing cathode materials of lithium–sulfur batteries. A ready-made conductive matrix infiltrated with sulfur as the cathode is the usual solution. Here, a partially reduced graphene oxide–sulfur composite (prGO/S) with an ordered self-assembled layer-by-layer structure is introduced as a Li–S battery cathode. The prGO/S composites are synthesized through a facile one-step self-assembly liquid route. An appropriate amount of sulfur is in situ deposited on the surface of the prGO nanosheets by adjusting the reduction degree of the GO nanosheets. The combined effect of the electrostatic repulsions and surface energy makes the sulfur wrapped prGO nanosheets self-assemble to form an ordered layer-by-layer structure, which not only ensures the uniform distribution of sulfur but also accommodates the volume change of the sulfur species during cycling. Moreover, the conductivity of the prGO/S composites improves when the reduction time increases. XPS spectra confirm that sulfur is still chemically bonded to the prGO. After applying the prGO coating of the prGO/S composite particle and as an interlayer in a lithium–sulfur battery configuration, a high initial discharge capacity of 1275.8 mA h g⁻¹ is achieved and the discharge capacity of the 100th cycle is 1013.8 mA h g⁻¹ at 0.1C rate.

The general procedures for the synthesis of the self-assembled layer-by-layer prGO/S composites.     

Enhanced electron transfer mediated detection of hydrogen peroxide using a silver nanoparticle–reduced graphene oxide–polyaniline fabricated electrochemical sensor

The current study aims at the development of an electrochemical sensor based on a silver nanoparticle–reduced graphene oxide–polyaniline (AgNPs–rGO–PANI) nanocomposite for the sensitive and selective detection of hydrogen peroxide (H₂O₂). The nanocomposite was fabricated by simple in situ synthesis of PANI at the surface of rGO sheet which was followed by stirring with AEC biosynthesized AgNPs to form a nanocomposite. The AgNPs, GO, rGO, PANI, rGO–PANI, and AgNPs–rGO–PANI nanocomposite and their interaction were studied by UV-vis, FTIR, XRD, SEM, EDX and XPS analysis. AgNPs–rGO–PANI nanocomposite was loaded (0.5 mg cm⁻²) on a glassy carbon electrode (GCE) where the active surface area was maintained at 0.2 cm² for investigation of the electrochemical properties. It was found that AgNPs–rGO–PANI–GCE had high sensitivity towards the reduction of H₂O₂ than AgNPs–rGO which occurred at −0.4 V vs. SCE due to the presence of PANI (AgNPs have direct electronic interaction with N atom of the PANI backbone) which enhanced the rate of transfer of electron during the electrochemical reduction of H₂O₂. The calibration plots of H₂O₂ electrochemical detection was established in the range of 0.01 μM to 1000 μM (R² = 0.99) with a detection limit of 50 nM, the response time of about 5 s at a signal-to-noise ratio (S/N = 3). The sensitivity was calculated as 14.7 μA mM⁻¹ cm⁻² which indicated a significant potential as a non-enzymatic H₂O₂ sensor.

The current study aims at the development of an electrochemical sensor based on a silver nanoparticle–reduced graphene oxide–polyaniline (AgNPs–rGO–PANI) nanocomposite for the sensitive and selective detection of hydrogen peroxide (H₂O₂).     

Simultaneous electrochemical determination of levodopa and piroxicam using a glassy carbon electrode modified with a ZnO–Pd/CNT nanocomposite

A highly conductive electrochemical sensor was constructed for the simultaneous electrochemical determination of levodopa and piroxicam by modification of a glassy carbon electrode with a ZnO–Pd/CNT nanocomposite (GCE/ZnO–Pd/CNTs). The ZnO–Pd/CNT nanocomposite was synthesized by the sol–gel procedure and was characterized by EDAX, MAP and SEM. The sensor was shown to improve the oxidation signal of levodopa and piroxicam by ∼70.2-fold and ∼41.5-fold, respectively. This marks the first time that the electrochemical behavior of levodopa and piroxicam have been investigated at the surface of GCE/ZnO–Pd/CNTs. The voltammogram showed a quasi-reversible signal and an irreversible redox signal for electro-oxidation of levodopa and piroxicam, respectively. The GCE/ZnO–Pd/CNTs showed a linear dynamic range of 0.6 to 100.0 μM (at a potential of ∼180 mV) and 0.1 to 90 μM (at a potential of ∼480 mV) with detection limits of 0.08 and 0.04 μM for the determination of levodopa and piroxicam, respectively. GCE/ZnO–Pd/CNTs were then applied for the determination of levodopa and piroxicam in real samples.

A highly conductive electrochemical sensor was constructed for the simultaneous electrochemical determination of levodopa and piroxicam by modification of a glassy carbon electrode with a ZnO–Pd/CNT nanocomposite (GCE/ZnO–Pd/CNTs).     

Fabrication of an antimony doped tin oxide–graphene nanocomposite for highly effective capacitive deionization of saline water

In this study, antimony doped tin oxide loaded reduced graphene oxide (ATO–RGO) nanocomposites were synthesized via a facile hydrothermal approach. As a typical N-type semiconductor, the ATO in the composite can enhance the conductivity between graphene sheets, thus improving the specific capacitance and electrosorption performance. Under the optimal conditions, the largest surface area was 445.2 m² g⁻¹ when the mass content of ATO in the nanocomposite was 20 wt%. The synthesized optimal ATO–RGO electrode displayed excellent specific capacity (158.2 F g⁻¹) and outstanding electrosorptive capacity (8.63 mg g⁻¹) in sodium chloride solution, which were much higher than the corresponding results of pristine graphene (74.3 F g⁻¹ and 3.98 mg g⁻¹). At the same applied voltage, electrosorption capacity and charge efficiency of the ATO–RGO (20 wt%) material were better than those of reported carbon materials in recent years.

Antimony doped tin oxide–graphene nanocomposites synthesized via a facile hydrothermal approach displayed good specific capacity and electrosorptive capacity.     

Atmospheric-pressure-plasma-jet processed carbon nanotube (CNT)–reduced graphene oxide (rGO) nanocomposites for gel-electrolyte supercapacitors

This study evaluates DC-pulse nitrogen atmospheric-pressure-plasma-jet processed carbon nanotube (CNT)–reduced graphene oxide (rGO) nanocomposites for gel-electrolyte supercapacitor applications. X-ray photoelectron spectroscopy (XPS) indicates decreased oxygen content (mainly, C–O bonding content) after nitrogen APPJ processing owing to the oxidation and vaporization of ethyl cellulose. Nitrogen APPJ processing introduces nitrogen doping and improves the hydrophilicity of the CNT–rGO nanocomposites. Raman analysis indicates that nitrogen APPJ processing introduces defects and/or surface functional groups on the nanocomposites. The processed CNT–rGO nanocomposites on carbon cloth are applied to the electrodes of H₂SO₄–polyvinyl alcohol (PVA) gel-electrolyte supercapacitors. The best achieved specific (areal) capacitance is 93.1 F g⁻¹ (9.1 mF cm⁻²) with 15 s APPJ-processed CNT–rGO nanocomposite electrodes, as evaluated by cyclic voltammetry under a potential scan rate of 2 mV s⁻¹. The addition of rGOs in CNTs in the nanoporous electrodes improves the supercapacitor performance.

This study demonstrates ultrafast (15 s) atmospheric-pressure-plasma-jet (APPJ) processed CNT–rGO nanocomposite gel-electrolyte supercapacitors.     

A reduced graphene oxide–borate compound-loaded melamine sponge/silicone rubber composite with ultra-high dielectric constant

Herein, at first, graphene oxide (GO) was prepared by a modified Hummers'' method, compounded with borates and then loaded onto a melamine sponge (MS) skeleton by an impregnation–reduction method to obtain a reduced graphene oxide (rGO)–borate compound (rGB)-loaded MS. Then, MS/rGB/silicone rubber (SR) composites were prepared by a vacuum infusion process. Moreover, the microstructures, electrical conductivity, and dielectric properties of the composites were investigated. The results showed that rGO presented a sheet-like structure, compounding with borates produced during the reduction of GO by sodium borohydride. rGB was co-loaded onto the MS skeleton, and a three-dimensional percolation network was successfully constructed in the MS/rGB/SR composite. In addition, there was an efficient synergistic effect between rGO and borates, which significantly improved the dielectric constant of the composites. At the rGO volume fraction of 1.89 vol%, the composite had the volume resistivity of 6.57 × 10⁴ Ω cm, the ultra-high dielectric constant of 2.71 × 10⁴ with the dielectric loss of 1.36 at 1 kHz, and the relatively low percolation threshold of 0.815 vol%. Furthermore, the composite exhibited high compression sensitivity at low compressive strains.

A reduced graphene oxide–borate compound-loaded melamine sponge/silicone rubber composite with the ultra-high dielectric constant of 2.71 × 10⁴.     

Enhanced catalytic performance of reduced graphene oxide–TiO2 hybrids for efficient water treatment using microwave irradiation

Towards achieving efficient waste water treatment, the degradation of a common water pollutant, Orange G azo dye, was studied using a new hybrid catalyst and microwave irradiation. The fabrication of a hybrid catalyst based on reduced graphene oxide–titania (rGO–TiO₂), was first achieved in a single mode microwave cavity by reducing the precursor consisting of graphene oxide (GO) and titania. Catalytic performance was then assessed in both microwave assisted and conventional heat treatment conditions. The hybrid catalyst showed significant improvement under microwave irradiation, with more than 88% dye degradation after 20 minutes of treatment at 120 °C. The microwave effect was found to be more dominant in the early stages of the catalysis – the hybrid catalyst decomposed ∼65% of the dye in just 5 minutes of microwave treatment compared to only 18% degradation obtained during conventional heating. The improved performance with microwaves is mainly attributed to the formation of the hot spots at the surface of the hybrid catalyst which ultimately results in higher degradation rates. The morphological and catalytic properties of the hybrid catalyst are investigated using High Resolution Transmission Electron Microscopy (HRTEM) and UV-Vis Spectroscopy, respectively. Successful reduction of GO to rGO was confirmed using Raman spectroscopy and X-ray diffraction. The outstanding performance of microwave irradiated hybrids offers a viable low energy, low carbon footprint process with a new catalyst for wastewater treatment and for highly polluted wastewater conditions where photocatalysis is deemed not feasible.

Microwave irradiated graphene-based hybrid catalysts for short reaction time, low carbon footprint treatment processes for highly polluted wastewater.     

Simultaneous detection of acetaminophen,catechol and hydroquinone using a graphene-assisted electrochemical sensor

Simple, rapid and sensitive analysis of drug-derived pollutants is critically valuable for environmental monitoring. Here, taking acetaminophen, hydroquinone and catechol as a study example, a sensor based on an ITO/APTES/r-GO@Au electrode was developed for separate and simultaneous determination of phenolic pollutants. ITO electrodes that are modified with 3-aminopropyltriethoxysilane (APTES), graphene (GO) and Au nanoparticles (Au NPs) can significantly enhance the electronic transport of phenolic pollutants at the electrode surface. The redox mechanisms of phenolic pollutants include the electron transfer with the enhancement of r-GO@Au. The modified ITO electrode exhibits excellent electrical properties to phenolic pollutants and a good linear relationship between ECL intensity and the concentration of phenolic pollutants, with a limit of detection of 0.82, 1.41 and 1.95 μM, respectively. The separate and simultaneous determination of AP, CC and HQ is feasible with the ITO/APTES/r-GO@Au electrode. The sensor shows great promise as a low-lost, sensitive, and rapid method for simultaneous determination of drug-derived pollutants.

Simple, rapid and sensitive analysis of drug-derived pollutants is critically valuable for environmental monitoring.     

A probe-free electrochemical immunosensor for methyl jasmonate based on a Cu-MOF–carboxylated graphene oxide platform

Methyl jasmonate (MeJA) is an important phytohormone which can regulate plant growth and stress tolerance. It is very necessary to develop sensitive and accurate detection methods for MeJA. In this work, a probe-free electrochemical immunosensor for MeJA detection was developed based on a Cu-MOF–carboxylated graphene oxide (COOH-GO) platform. The Cu²⁺ in the Cu-MOFs was used to provide redox signals, which avoids the application of an external redox probe in the electrolyte solutions as conventional immunosensors. COOH-GO was used to improve the structural stability and provide more sites for binding MeJA antibodies. The linear range of the MeJA immunosensor is from 10 pM to 100 μM, which can cover the whole concentration range of MeJA in most plants. And its detection limit is very low (0.35 pM), and it can detect very low concentrations of MeJA. This immunosensor is simple, low cost, and does not need redox probe solutions for measurements. It shows remarkable potential for on-site application in precision agriculture.

A probe-free electrochemical immunosensor for methyl jasmonate has been developed based on a Cu-MOF-carboxylated graphene oxide platform.     

Ionic-liquid-assisted one-pot synthesis of Cu2O nanoparticles/multi-walled carbon nanotube nanocomposite for high-performance asymmetric supercapacitors

Finding earth-abundant and high-performance electrode materials for supercapacitors is a demanding challenge in the energy storage field. Cuprous oxide (Cu₂O) has attracted increasing attention due to its theoretically high specific capacitance, however, the development of Cu₂O-based electrodes with superior capacitive performance is still challenging. We herein report a simple and effective ionic-liquid-assisted sputtering approach to synthesizing the Cu₂O nanoparticles/multi-walled carbon nanotubes (Cu₂O/MWCNTs) nanocomposite for high-performance asymmetric supercapacitors. The Cu₂O/MWCNTs nanocomposite delivers a high specific capacitance of 357 F g⁻¹, good rate capability and excellent capacitance retention of about 89% after 20 000 cycles at a current density of 10 A g⁻¹. The high performance is attributed to the uniform dispersion of small-sized Cu₂O nanoparticles on conductive MWCNTs, which offers plenty of redox active sites and thus improve the electron transfer efficiency. Oxygen vacancies are further introduced into Cu₂O by the NaBH₄ treatment, providing the oxygen-deficient Cu₂O/MWCNTs (r-Cu₂O/MWCNTs) nanocomposite with significantly improved specific capacitance (790 F g⁻¹) and cycling stability (∼93% after 20 000 cycles). The assembled asymmetric supercapacitor based on the r-Cu₂O/MWCNTs//activated carbon (AC) structure achieves a high energy density of 64.2 W h kg⁻¹ at 825.3 W kg⁻¹, and long cycling life. This work may form a foundation for the development of both high capacity and high energy density supercapacitors by showcasing the great potential of earth-abundant Cu-based electrode materials.

A one-pot room-temperature-ionic-liquid-assisted sputtering approach is designed to synthesize Cu₂O/MWCNTs nanocomposite with high capacitance and long cycling life due to synergistic effects of oxygen-deficient Cu₂O and conductive MWCNTs.     

Recovery of lanthanum cations by functionalized magnetic multi-walled carbon nanotube bundles

Rare-earth elements (REE), including La, are critical raw materials in many technological advancements. Collection of physically adsorbed REEs on clay minerals can be realized first by ion-exchange leaching, followed by adsorption enrichment. Ever increasing demand and limited resources of REEs have fueled the development of nanostructured adsorbents. In this paper, multi-walled carbon nanotubes (MWCNTs) were purified using concentrated H₂SO₄ and HNO₃, then coupled with magnetic Fe₃O₄ nanoparticles to make low concentration La ion extraction from water possible. The MWCNT@Fe₃O₄ composites were further crosslinked with 0.1 wt% epichlorohydrin and functionalized with 0.5 wt% carbon disulfide to achieve a La³⁺ adsorption capacity of 23.23 mg g⁻¹. We fully probed the morphology, crystallinity, chemical composition, and magnetic properties of the as-prepared adsorbent by scanning/transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, vibrating-sample magnetometry, and thermal gravimetry. These results indicated that the MWCNT@Fe₃O₄ nanohybrid may be a promising candidate for recovering La ions from aqueous solutions.

Epichlorohydrin crosslinked magnetic multiwalled-carbon nanotubes were functionalized with CS₂ for efficient low concentration La³⁺ recovery.     

A dopamine electrochemical sensor based on a platinum–silver graphene nanocomposite modified electrode

A platinum–silver graphene (Pt–Ag/Gr) nanocomposite modified electrode was fabricated for the electrochemical detection of dopamine (DA). Electrochemical studies of the Pt–Ag/Gr nanocomposite towards DA detection were performed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The CV analysis showed that Pt–Ag/Gr/GCE had enhanced electrocatalytic activity towards DA oxidation due to the synergistic effects between the platinum–silver nanoparticles and graphene. The DPV results showed that the modified sensor demonstrated a linear concentration range between 0.1 and 60 μM with a limit of detection of 0.012 μM. The Pt–Ag/Gr/GCE presented satisfactory results for reproducibility, stability and selectivity. The prepared sensor also showed acceptable recoveries for a real sample study.

A platinum–silver graphene nanocomposite was synthesized and characterized. A nanocomposite modified electrode was fabricated in order to investigate the electrochemical detection of dopamine.     

Electrodeposited nickel–graphene nanocomposite coating: effect of graphene nanoplatelet size on its microstructure and hardness

In this study, the effect of graphene nanoplatelet (GNP) size on the microstructure and hardness of the electrodeposited nickel–graphene nanocomposite coatings were investigated. GNPs with different sizes were prepared by using a high energy ball milling technique. The experimental result revealed the high energy ball milling technique could reduce the size, increase the surface area, and improve the dispersion ability of GNPs. The microstructure, hardness, and components of the nanocomposite coatings were greatly affected by GNP sizes. The highest microhardness was measured to be 273 HV for the nanocomposite coatings containing 5 h-milled GNPs, which is increased up to ∼47% compared to pristine Ni coating. The enhancement in the hardness is attributed to the uniform dispersion of the small GNP sizes inside the Ni matrix and the Ni grain size reduction when using milled GNPs.

The effect of graphene nanoplatelet size on the microstructure and hardness of electrodeposited nickel–graphene nanocomposite coatings was investigated.     

Benzophenone assisted UV-activated synthesis of unique Pd-nanodendrite embedded reduced graphene oxide nanocomposite: a catalyst for C–C coupling reaction and fuel cell

In this work we report the use of benzophenone (BP) for the synthesis of a palladium (Pd) embedded on reduced graphene oxide (rGO) nanocomposite (Pd/rGO) using a simple aqueous solution and UV irradiation. The simple and facile evolution of thermodynamically unstable branched Pd(0) nanodendrites was achieved by BP photoactivation, circumventing the growth of more stable nanomorphologies. The synthesis of Pd(0)-embedded rGO nanosheets (PRGO-nd) was made possible by the simultaneous reduction of both the GO scaffold and PdCl₂ by introducing BP into the photoactivation reaction. The nanocomposites obtained in the absence of BP were common triangular and twinned Pd(0) structures which were also implanted on the rGO scaffold (PRGO-nt). The disparity in morphologies presumably occurs due to the difference in the kinetics of the reduction of Pd²⁺ to Pd⁰ in the presence and absence of the BP photoinitiator. It was observed that the PRGO-nd was composed of dense arrays of multiple Pd branches around nucleation site which exhibited (111) facet, whereas PRGO-nt showed a mixture of (100) and (111) facets. On comparing the catalytic efficiencies of the as-synthesized nanocatalysts, we observed a superiority in efficiency of the thermodynamically unstable PRGO-nd nanocomposite. This is due to the evolved active facets of the dendritic Pd(0) morphology with its higher surface area, as testified by Brunauer–Emmett–Teller (BET) analysis. Since both PRGO-nd and PRGO-nt contain particles of similar size, the dents and grooves in the structure are the cause of the increase in the effective surface area in the case of nanodendrites. The unique dendritic morphology of the PRGO-nd nanostructures makes them a promising material for superior catalysis, due to their high surface area, and the high density of surface atoms at their edges, corners, and stepped regions. We investigated the efficiency of the as-prepared PRGO-nd catalyst in the Suzuki–Miyaura coupling reaction and showed its proficiency in a 2 h reaction at 60 °C using 2 mol% catalyst containing 0.06 mol% active Pd. Moreover, the electrochemical efficiency for the catalytic hydrogen evolution reaction (HER) was demonstrated, in which PRGO-nd provided a decreased overpotential of 68 mV for a current density of 10 mA cm⁻², a small Tafel slope of 57 mV dec⁻¹ and commendable stability during chronoamperometric testing for 5 h.

Benzophenone photoinitiator aided synthesis of Pd-nanodendrite embedded rGO nanocatalyst possessing superior potential in C–C coupling reaction and fuel cell application.     

Highly sensitive sensing of hydroquinone and catechol based on β-cyclodextrin-modified carbon dots

In the proposed study, an efficient method for a carbon dot@β-cyclodextrin (C-dot@β-CD)-based fluorescent probe was developed for the analyses of catechol (CC) and hydroquinone (HQ) at trace levels in water samples. The properties of C-dot@β-CD nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The sensing behaviors of C-dot@β-CD toward CC and HQ were investigated by fluorescence spectroscopy. Based on the host–guest chemistry between C-dot@β-CD and phenolic compounds, which can quench C-dot@β-CD fluorescence, the prepared C-dot@β-CD nanocomposites could be used for the sensitive and selective detection of CC or HQ across a wide linear range (0.1 to 10 μM) with detection limits of 47.9 and 20.2 nM, respectively. These results showed that the synthesized C-dot@β-CD nanocomposite exhibited strong fluorescence and high degree of water solubility and thus, it is suitable for use as a nanoprobe for detecting CC or HQ in real water samples.

In the proposed study, an efficient method for a carbon dot@β-cyclodextrin (C-dot@β-CD)-based fluorescent probe was developed for the analyses of catechol (CC) and hydroquinone (HQ) at trace levels in water samples.     

An ultrasensitive fluorescent aptasensor for detection of cancer marker proteins based on graphene oxide–ssDNA

A novel biosensing platform was developed by integrating a new ssDNA aptamer and graphene oxide (GO) for highly sensitive and selective detection of liver cancer biomarkers (alpha-fetoprotein, AFP). The key concept of this biosensing platform is that the fluorescence of dye-modified ssDNA can be effectively quenched by GO after forming the hybrid structure of graphene oxide–ssDNA (GO–ssDNA). The AFP can selectively react with GO–ssDNA and lead to the decomposition of GO–ssDNA, which results in the recovery of fluorescence, and an increase in fluorescence intensity with the increasing concentration of AFP in the range of 0 to 300 pg mL⁻¹. The linear range was obtained from 1 to 150 pg mL⁻¹ and the detection limit was 0.909 pg mL⁻¹. Moreover, this biosensing platform can be applied to serum and cell imaging for the detection of AFP. The results show that the proposed biosensor has great potential application in AFP-related clinical diagnosis and research.

A novel biosensing platform was developed by integrating a new ssDNA aptamer and graphene oxide (GO) for highly sensitive and selective detection of liver cancer biomarkers (AFP).     

Functionalization of pristine graphene for the synthesis of covalent graphene–polyaniline nanocomposite

Polyaniline (PANI) is one of the most studied conducting polymers owing to its high electrical conductivity, straightforward synthesis and stability. Graphene-supported PANI nanocomposite materials combine the superior physical properties of graphene, synergistically enhancing the performance of PANI as well as giving rise to new properties. Covalent nanocomposites have shown to give higher stability and better performance than their non-covalent counterparts, however, the covalent graphene–PANI nanocomposite are primarily prepared from graphene oxide. We report a new method to synthesize covalent graphene–PANI nanocomposites from pristine graphene. Using few-layer graphene (FLG) flakes as the model system, we first conjugated aniline to FLG via a perfluorophenyl azide (PFPA)-mediated coupling chemistry. A subsequent in situ polymerization of aniline gave polyaniline covalently grafted on the FLG surface. Characterization by FTIR, TEM, SEM, XPS, XRD and electrochemistry confirmed the successful conjugation of PANI to FLG. The grafting density of PANI was estimated by thermal analysis to be ∼26%. As the PFPA-mediated coupling chemistry is applicable to other carbon materials including carbon nanotubes and fullerene, the method developed in this work can be readily adapted to grow PANI on these materials.

Polyaniline was covalently grafted on pristine few-layer graphene via a perfluorophenyl azide-mediated coupling chemistry.     

Synergistic effect of reduced graphene oxide/carbon nanotube hybrid papers on cross-plane thermal and mechanical properties

Graphene paper has attracted great attention as a heat dissipation material due to its excellent thermal conductivity and mechanical properties. However, the thermal conductivity of graphene paper in the normal direction is relatively poor. In this work, the cross-plane thermal conductivities (K_⊥) and mechanical properties of the reduced graphene oxide/carbon nanotube papers with different CNT loadings were studied systematically. It was found that the K_⊥ decreased from 0.0393 W m⁻¹ K⁻¹ for 0 wt% paper to 0.0250 W m⁻¹ K⁻¹ for 3 wt% paper, and then increased to 0.1199 W m⁻¹ K⁻¹ for 20 wt% paper. The papers demonstrated a maximum elastic modulus of 6.1 GPa with 10 wt% CNT loading. The CNTs acted as scaffolds to restrain the graphene sheets from corrugating and to reinforce the mechanical properties of the hybrid papers. The more CNTs that filled the gaps between graphene sheets, the greater the number of channels of the transmission of phonons and the looser the structure in the cross-plane direction. Further mechanism analysis revealed the synergistic effects of CNT loadings and graphene sheets on enhancing the thermal and mechanical performance of the papers.

The top-view SEM images for (a) rGO, (b) rGO/CNT-3%, (c) rGO/CNTs-20% and the corresponding schematic diagram of photon transmission with different spacer CNTs loadings (a-i, b-ii, c-iii).     

Simultaneous and selective electrochemical determination of hydroquinone,catechol and resorcinol at poly(1,5-diaminonaphthalene)/glassy carbon-modified electrode in different media

The electrochemical behavior of phenolic isomers hydroquinone (HQ), catechol (CC) and resorcinol (RC) was examined in poly(1,5-diaminonaphthalene)/glassy carbon-modified electrode (P1,5-DAN/GC M.E.) by cyclic voltammetry (CV), square wave voltammetry (SWV) and chronoamperometry (CA) techniques in perchloric acid (HClO₄) and phosphate buffer solution (PBS, pH 7.0). P1,5-DAN/GC M.E. was investigated for simultaneous determination of HQ, CC and RC in single, binary and ternary systems. Oxidation peak potentials were negatively shifted with increasing oxidation peak current for HQ, CC and RC at P1,5-DAN/GC M.E. compared with bare GC electrode. The obtained results illustrate that the former electrode exhibits better performance towards the three isomers in PBS rather than in HClO₄ solution. The catalytic currents for different concentrations of HQ, CC and RC showed good relationship in the range of 0.1–100 μM for all analytes and low detection limits (LOD) of 0.034, 0.059 and 0.14 μM for them, respectively, in a ternary system in PBS at pH 7.0. This method has been practically applied for the detection of these isomers in tap water with acceptable results.

Electrochemical behaviors of hydroquinone, catechol and resorcinol were examined at poly(1,5-diaminonaphthalene)/glassy carbon-modified electrode by cyclic voltammetry, square wave voltammetry and chronoamperometry techniques in different media.