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Due to its huge surface-to-volume ratio, graphene has become one of the most popular materials for sensors. However, H2O molecules in atmospheric environments can cause the instability of graphene devices, which greatly limits the practical applications of graphene devices. The charge transfer between graphene and adsorbed H2O molecules has been proved previously by first-principle studies, but experimental demonstrations are still lacking. Here, gate-polarity-dependent doping behaviors of adsorbed H2O molecules on a graphene/SiO2 field-effect transistor (GFET) are experimentally investigated. The results indicate that the orientation of the adsorbed H2O can be affected by the gate-voltage polarity due to the dipolar interaction, which leads to the amphoteric doping behavior of adsorbed H2O molecules. With reducing the graphene layer number, the amphoteric doping behavior is more sensitive to the gate voltage polarity. Our results are helpful for constructing high performance graphene-based sensors and enhancing the stability of GFETs. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries (SIBs) have aroused increasing interest as one of the most promising replacements for lithium-ion batteries (LIBs). Here, a novel organic–inorganic 3D Na4C6O6–graphene architecture was successfully fabricated from commercial Na2C6O6 and for the first time applied for sodium storage. Hence, the 3D Na4C6O6–graphene architecture exhibits a high reversible capacity, good cyclic performance and high-rate capability for sodium storage. [ABSTRACT FROM AUTHOR]

In this paper, linking with the butoxycarbonyl (BOC) protection of proline, a new tailed metalloporphyrin with many useful active functions, nickel (II) 5-[4-N-(tert-Butoxycarbonyl)- l -prolinecoxylpropyloxy]phenyl-10,15,20-triphenylporphyrin (NiTBLPyP), was designed and synthesized. And the NiTBLPyP polymer (poly(NiTBLPyP)) was successfully obtained via a low-cost electrochemical method and exploited as an efficient mimic enzyme. Subsequently, a noncovalent nanohybrid of poly(NiTBLPyP) with graphene (rGO) sheet (rGO-poly(NiTBLPyP)) was prepared through π–π stacking interaction for the ultrasensitive and selective detection of DA. The nanohybrid was characterized by UV–vis spectroscopy, Fourier transform infrared spectra, Raman spectroscopy, scanning electron microscopy and electrochemical impedance spectroscopy. Due to the excellent electrocatalytic ability of poly(NiTBLPyP) film and aromatic π–π stacking interaction between poly(NiTBLPyP and rGO sheet, the obtained rGO-poly(NiTBLPyP) film exhibited a great synergistic amplification effect toward dopamine oxidation. Under optimum experimental conditions, the logarithm of catalytic currents showed a good linear relationship with that of the dopamine concentration in the range of 0.01–200 μM with a low detection limit of 1.40 nM. With good sensitivity and selectivity, the present method was applied to the determination of DA in real sample and the results was satisfactory. Thus, the rGO-poly(NiTBLPyP) film is one of the promising mimetic enzyme for electrocatalysis and relevant fields. [ABSTRACT FROM AUTHOR]

Poly(diallydimethylammonium chloride) functionalized graphene/double-walled carbon nanotube composite (PDDA-GN/DWCNT) was synthesized by a facile microwave-assisted reduction reaction. PDDA-GN/DWCNT exhibits enhanced electrocatalytic activity towards nitrite oxidation. The direct electrooxidation behaviors of nitrite on PDDA-GN/DWCNT were investigated by cyclic voltammetry, amperometric i-t curve, and rotating disk electrode experiments. Under the optimum conditions, PDDA-GN/DWCNT was applied to the quantitative analysis of nitrite with a wide linear range covering 0.07-3000 µM and a low detection limit of 0.03 µM (S/N=3). Moreover, PDDA-GN/DWCNT exhibits satisfied results in the determination of nitrite that released from breast cancer cells. [ABSTRACT FROM AUTHOR]

β-Cyclodextrin functionalized graphene/Ag nanocomposite (β-CD/GN/Ag) was prepared via a one-step microwave treatment of a mixture of graphene oxide and AgNO3. β-CD/GN/Ag was employed as an enhanced element for the sensitive determination of 4-nitrophenol. A wide linear response to 4-nitrophenol in the concentration ranges of 1.0×10−8-1.0×10−7 mol/L, and 1.0×10−7-1.5×10−3 mol/L was achieved, with a low detection limit of 8.9×10−10 mol/L ( S/N=3). The mechanism and the heterogeneous electron transfer kinetics of the 4-nitrophenol reduction were discussed according to the rotating disk electrode experiments. Furthermore, the sensing platform has been applied to the determination of 4-nitrophenol in real samples. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H 2 O 2 ) is becoming significant due to its extensive applications, so determination of H 2 O 2 is very important topic in analytical chemistry. Metal-free “graphene alloy” – nitrogen (N) and sulfur (S) heteroatoms co-doped reduced graphene oxide (NS-rGO) was produced via a simple one-step thermal annealing procedure using a mixture of 5-amino-2-mercapto-1,3,4-thiadiazole (AMT) and graphene oxide (GO). The obtained metal-free NS-rGO composite showed better electrocatalytic activity toward the reduction of H 2 O 2 compared with the reduced graphene oxide (rGO). The enhanced performance was caused by the synergistic effect of N and S co-doping. Under optimum conditions, the constructed sensor demonstrated a linear response to H 2 O 2 in the range of 7–18000 μM, with a lower detection limit of 0.45 μM (S/N=3), even better than some reported sensors based on noble metal nanoparticles. Moreover, the proposed sensor exhibited excellent analytical performance in terms of acceptable selectivity, excellent reproducibility and long-time stability. These results indicated that the NS-rGO composite was a promising metal-free electrocatalytic material for constructing H 2 O 2 sensors. Additionally, NS-rGO composite was expected to be applied as catalysts for fuel cell applications, even for applications beyond fuel cells. [ABSTRACT FROM AUTHOR]

Flexible conductive materials have excellent stretchability and sensitivity, so they have great development potential in motion detection, artificial electronic skin and other fields. Three-dimensional (3D) carbon nanomaterials are important materials for preparing flexible conductive polymers with good electrical conductivity. But its cost is too high to be widely promoted. In this paper, the modified graphene (FGO) and carbon nanotubes (FMCNTs) were prepared to three-dimensional structures to provide excellent electrical conductivity for the polymer. The reversible bond was introduced into the waterborne polyurethane by using Diels-Alder (DA) chemical crosslinking. Then the conductive and self-healing flexible electronic materials FGO/FMCNTs/WPU were prepared by penetration. The results showed that the composites had excellent thermal and mechanical properties. When the content of nanomaterial was 6 mg/ml, the stress was 9.58 MPa, the strain was 207, and the electrical conductivity was 0.0283 S/m. Nanomaterials also showed good self-healing ability because they had three-dimensional structures. The application test of the composite material showed that it could accurately monitor the human body motion. This indicated that the composite material can be used to manufacture flexible electronic devices. Preparation of FGMWPU composite materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Heavy metal contamination has been demonstrated to possess the severe threats toward the whole ecosystems and public security even at trace levels. Therefore, it is essential to exploit an ultrasensitive technique to determine the levels of heavy metal ions. In this work, hierarchical MgFe-layered double hydroxide (MgFe-LDH) microspheres have been successfully immobilized on the graphene nanosheets surface via a facile one-step hydrothermal route. Benefiting from the synergistic effects associated with high specific surface area, strong affinity of hierarchical MgFe-LDH architecture toward heavy metal ions, good electrical conductivity and effective electron transfer efficiency of graphene, the resulting composite (denoted as MgFe-LDH/graphene) is explored as an electrochemical sensor for simultaneous detection of Pb(II) and Cd(II) in aqueous medium. As a consequence, MgFe-LDH/graphene modified electrode exhibits low detection limit of 5.9 nM for Cd(II) and 2.7 nM for Pb(II), which are dramatically lower than the respective values of 3 ppb (27 nM) and 10 ppb (48 nM) in domestic water permitted by the World Health Organization (WHO). Meaningfully, the proposed electrochemical sensor shows specific recognition capability to Pb(II) and Cd(II), excellent reproducibility in repetitive measurements as well as feasibility in real water analysis. [ABSTRACT FROM AUTHOR]

• MXene can effectively improve the dispersion stability of GR nanofluids. • The nanofluid with 2 wt% GR obtains maximum thermal conductivity enhancement of 65.34%. • The viscosity significantly decreases with an increase in MXene content. • The temperature at monitoring point decreases by 9.19 ℃ with 2.0 wt% GR relative to water. • The heat transfer efficiency of GR/MXene and GR nanofluids is almost the same. New nanofluids based on graphene (GR) and GR/MXene were prepared to enhance the thermal conductivity. The thermal conductivity and viscosity of nanofluids at various temperatures in the 5–60 °C range were tested, and their stability was investigated by zeta potential and visual observation. The thermal performance of the nanofluids was evaluated through numerical simulation analysis. The results demonstrate that MXene can effectively improve the dispersion stability of GR nanofluids. The nanofluid with 2.0 wt% GR at 60 °C exhibited the maximum thermal conductivity enhancement (65.34%) but also the maximum viscosity increment (70.69%). With the addition of MXene, the high thermal conductivity of nanofluids was maintained while the viscosity significantly decreased. GR can greatly improve the heat transfer efficiency of nanofluids, and the temperature at the monitoring point resulted from 2.0 wt% GR decreased by 9.19 ℃ compared to water. The heat transfer efficiency of GR/MXene nanofluids was almost identical to that of GR nanofluids. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mass ratio of CA-SA to MMT is 35:65 which can prevent the leakage of PCM. • CA-SA/MMT/GR has suitable phase change temperature and high latent heat. • CA-SA/MMT/GR can keep the thermal property after 300 thermal cycles. • The thermal conductivity of CA-SA/MMT/2 wt%GR increases by 156.4%. • CA-SA/MMT/GR significantly enhances the heat storage capacity of mortar. A novel composite phase change material (PCM) of capric-stearic acid/montmorillonite (CA-SA/MMT) with thermal conductivity enhanced by graphene (GR) was prepared. It was characterized by FT-IR, XRD, SEM, DSC and thermal conductivity tests. The temperature response of CA-SA/MMT/GR was evaluated by heating and freezing the composite PCMs in tinfoil cups. The phase change mortar containing CA-SA/MMT/2 wt%GR was also prepared, and its mechanical strength and thermal behavior were tested. The adsorption rate experiment results show that the mass ratio of CA-SA to MMT is 35:65, which can effectively prevent the leakage of PCM. The FT-IR, XRD and SEM results demonstrate that the prepared CA-SA/MMT/GR has good chemical compatibility and stability. The DSC results reveal that the CA-SA/MMT/GR has suitable phase change temperature and high latent heat, and it can retain the phase change behavior after 300 thermal cycles. The thermal conductivity of CA-SA/MMT/2 wt%GR increases by 156.4% compared with CA-SA/MMT. The heat transfer efficiency of CA-SA/MMT gradually increases with the increase of GR. The mechanical strength and thermal behavior results of phase change mortar demonstrate that the flexural strength and compressive strength decrease and the heat storage capacity increases with increasing the percentage of CA-SA/MMT/2 wt%GR. [ABSTRACT FROM AUTHOR]

The composite phase change materials (PCMs) of lauric-stearic acid/treated diatomite/graphene (LA-SA/Dt/GR) for heat storage in building envelope were prepared. It was characterized by Fourier transform infrared spectrum (FT-IR), X-ray diffraction (XRD), scanning electronic microscope (SEM), thermogravimetric analysis (TG), differential scanning calorimeter (DSC) and thermal conductivity tests. The thermal performance was tested by heating and cooling the composite PCMs in tinfoil cups. The FT-IR, XRD and SEM results show that there is no chemical reaction among LA-SA, Dt and GR, and the prepared LA-SA/Dt/GR can keep its chemical stability after 1000 thermal cycles. The TG results demonstrate that the prepared LA-SA/Dt/GR has good thermal stability. The DSC results manifest that the prepared LA-SA/Dt/GR has proper temperature and high latent heat, and can keep its thermal properties after 1000 thermal cycles. The thermal conductivity results demonstrate that GR can significantly enhance the thermal conductivity of LA-SA/Dt and the thermal conductivity of LA-SA/Dt/2wt%GR has increased by 274% compared with that of LA-SA/Dt. The thermal performance results reveal that the heat transfer efficiency of LA-SA/Dt/GR increases gradually with the increasing percentage of GR. Furthermore, the phase change mortar was prepared, and the mechanical strength and thermal performance were tested. The results testify that the mechanical strength decreases with the increasing percentage of LA-SA/Dt/GR, and GR can significantly enhance the heat storage efficiency of phase change mortar. [ABSTRACT FROM AUTHOR]