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A facile and effective strategy has been successfully developed to synthesize reduced graphene oxide-multiwalled carbon nanotubes-tin oxide nanoparticles (rGO-CNT-SnO 2 ) hybrids by hydrothermal method. The combined characterizations of X-ray diffraction, Raman spectrum and Transmission electron microscopy were used to characterize the samples thus obtained, indicating the successful preparation of rGO-CNT-SnO 2 hybrids. A room temperature NO 2 sensor was fabricated by dropping the dispersion of rGO-CNT-SnO 2 hybrids on the surface of ceramic substrate previously printed Au electrodes. Most importantly, the sensor based on rGO-CNT-SnO 2 hybrids shows high response, fast response and recovery rate, high selectivity and good stability, which are much better than NO 2 sensors based on pure rGO and rGO-SnO 2 hybrids. [ABSTRACT FROM AUTHOR]

Developing efficient approachs to synthesize nitrogen-doped graphene materials is significantly important. Herein, it is reported that nitrogen-doped reduced graphene oxide (N-rGO) had been successfully prepared by pyrolysis of poly(p -phenylenediamine)-rGO (P p PD-rGO) hybrids. The combined characterizations of Infrared (IR) spectra, Raman spectra, scanning electron microscopy (SEM) were used to characterize the structure of N-rGO. Most importantly, such N-rGO shows good sensing performances for simultaneous detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The linear ranges of the sensors for AA, DA, and UA are 0.1 mM–4 mM, 1 μM–60 μM and 1 μM–30 μM. The detection limit for detection of AA, DA and UA are 9.6 μM, 0.1 μM and 0.2 μM, respectively. This work provides a highly effective approach for preparation of graphene-based materials for electrochemical sensing applications. • Nitrogen-doped reduced graphene oxide (N-rGO) had been prepared by pyrolysis of poly(p -phenylenediamine)-rGO (P p PD-rGO) hybrids. • The N-rGO shows good sensing performances for simultaneous detection of ascorbic acid, dopamine and uric acid. • This work provides a highly effective approach for preparation of graphene-based materials for electrochemical sensing applications. [ABSTRACT FROM AUTHOR]

Herein, a two-step electrodepostion method was carried out for in situ growth of Ag metal-reduced graphene oxide-carbon nanotube on indium tin oxide (Ag-rGO-CNT/ITO). Firstly, rGO-CNT hybrids have been synthesized on ITO electrode by electrodeposition of GO-CNT dispersion, and then, Ag metal has been deposited on the surface of rGO-CNT/ITO by the electrodeposition method. Combining unique properties of rGO-CNT hybrids and excellent catalytic activity of Ag metal, Ag-rGO-CNT/ITO exhibits good catalytic activity for electrocatalytic reduction of hydrogen peroxide (H 2 O 2 ). The non-enzymatic H 2 O 2 sensor based on Ag-rGO-CNT/ITO electrode shows the linear detection range about 0.05–1.40 mM (R = 0.999), and the detection limit is estimated to be 1.32 μM at a signal-to-noise ratio of 3. Furthermore, the Ag-rGO-CNT/ITO electrode exhibits good anti-interference capability, compared to other interferences such as ascorbic acid, dopamine, uric acid, NaNO 3 , NaNO 2 and glucose. [ABSTRACT FROM AUTHOR]

A novel NO 2 gas sensor has been constructed using Ag nanoparticles-SnO 2 nanoparticles-reduced graphene oxide (AgNPs-SnO 2 -rGO) hybrids as sensing materials. AgNPs-SnO 2 -rGO hybrids were prepared by a two-step wet-chemical method. Firstly, SnO 2 -rGO hybrids were synthesized by hydrothermal treatment of aqueous dispersion of GO in the presence of SnCl 4 . Then, AgNPs-SnO 2 -rGO hybrids were obtained by in situ reduction of AgNO 3 on the surface of SnO 2 -rGO hybrids. The combined characterizations of UV–vis spectroscopy, X-ray diffraction (XRD), energy-dispersive X-ray spectrometer (EDX), elemental mapping, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and Raman spectra were used to investigate the structure of AgNPs-SnO 2 -rGO hybrids. Most importantly, the sensor based on AgNPs-SnO 2 -rGO hybrids exhibits good sensing performance for NO 2 sensing operating at room temperature. For example, the response time and recovery time of the sensor based on AgNPs-SnO 2 -rGO hybrids for 5 ppm NO 2 are 49 s and 339 s, which are much shorter than that of SnO 2 -rGO hybrids (415 s and 740 s), indicating that the sensing performances for NO 2 sensing at room temperature have been tremendously enhanced by introduction of AgNPs into SnO 2 -rGO hybrids. [ABSTRACT FROM AUTHOR]

Three-dimensional reduced graphene oxide (3D-rGO) materials have been successfully prepared by a template-assisted self-assembly method using polystyrene spheres (PSs) as sacrificial templates. PSs-rGO hybrids were prepared by self-assembly of PSs and GO through the π–π interaction, followed by reduction of such hybrids using hydrazine as reducing agent. 3D-rGO materials were obtained after removal of PSs in PSs-rGO hybrids by toluene. The combined characterizations of field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) indicate the successful preparation of 3D-rGO materials. More importantly, 3D-rGO materials thus obtained exhibit good sensing performances for electrochemical detection of dopamine (DA), leading to a high-performance DA sensor. The DA sensor based on 3D-rGO materials has been evidenced to exhibit a better sensing performances than that of rGO and poly-(vinylpyrrolidone) (PVP)-stabilizing rGO. Furthermore, differential pulse voltammetry (DPV) indicates that the 3D-rGO-based DA sensor could be effectively used for DA sensing in the presence of ascorbic acid (AA) and uric acid (UA), indicating high selectivity of the DA sensor based on 3D-rGO materials. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • In this work, the obtained Zn 2 SnO 4 -RGO hybrids exhibited outstanding sensing performance for detecting oxidizing gases (NO 2 and O 3) with very low cross sensitivities to reducing gases, such as C 2 H 5 OH, CH 3 COCH 3 and CO. • The Zn 2 SnO 4 -RGO based sensors exhibited high response values of up to 3.50 for 500 ppb NO 2 , which is higher than that for detection of 500 ppb O 3 (1.78) at 30 °C under 50% relative humidity (RH). • The surface reaction between Zn 2 SnO 4 -RGO hybrids and NO 2 can be concluded from Operando diffuse reflectance infrared Fourier transformed spectroscopy (Operando DRIFT). Abstract Highly selective oxidizing gas sensors are of great importance for environmental pollution monitoring. In this work, a hybrid material containing Zn 2 SnO 4 nanoparticles (NPs) and immobilized reduced graphene oxide (Zn 2 SnO 4 -RGO) was developed as a high performance gas sensing material for the detection of ppb-levels of oxidizing gases (NO 2 and O 3). The structural, morphological and compositional properties of the Zn 2 SnO 4 -RGO hybrids were systematically characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), which demonstrated the successful anchoring of Zn 2 SnO 4 NPs on RGO nanosheets. The obtained Zn 2 SnO 4 -RGO hybrids exhibited outstanding sensing performance for detecting oxidizing gases (NO 2 and O 3) with very low cross sensitivities to reducing gases, such as C 2 H 5 OH, CH 3 COCH 3 and CO. The Zn 2 SnO 4 -RGO based sensors exhibited high response values of up to 3.50 for 500 ppb NO 2 , which is higher than that for detection of 500 ppb O 3 (1.78) at 30 °C under 50% relative humidity (RH). Moreover, the NO 2 sensing performances of Zn 2 SnO 4 -RGO-based sensors were investigated under various RH. In all cases, the sensors based on RGO and Zn 2 SnO 4 -RGO hybrids presented p-type behavior. The sensors based on Zn 2 SnO 4 -RGO hybrids also exhibited high response values of up to 3.62 for 1 ppm NO 2 at 50 °C in 80% RH, which is much higher than that of pure RGO (1.31). The excellent sensing performances are mainly ascribed to the synergetic effect of Zn 2 SnO 4 NPs and RGO. Furthermore, the surface reaction between Zn 2 SnO 4 -RGO hybrids and NO 2 can be concluded from Operando diffuse reflectance infrared Fourier transformed spectroscopy (Operando DRIFT). [ABSTRACT FROM AUTHOR]

Development of room-temperature gas sensors with excellent sensing performances for detection of dimethyl methylphosphonate (DMMP, a simulant of organophosphate) has aroused considerable attention. However, the weak adsorption ability of sensing materials toward DMMP molecules causes poor sensing performances. In this work, a multisite strategy for enhancing sensitivity was proposed by introduction of both N-doped carbon nanoparticles (N-CNPs) and copper ions onto the surface of rGO (designated as GNC). Impressively, optimal GNC-3 exhibits the response value of 10.2% toward 100 ppm DMMP, which is 5.3 times higher than that of pristine rGO. This mechanism for multisite-assisted enhanced DMMP sensing performances was investigated by combined characterizations of Fourier-transform infrared spectra, UV-Vis spectra, photoluminescence spectra and Mott-Schottky curves. Besides the construction of multisite, improvement of hydrogen bonding interactions between DMMP molecules and N-CNPs in hybrids assisted by copper ions, and decrease of conduction band potential by formation of ternary hybrids also contribute to enhance the sensitivity of DMMP sensors. These findings not only provided new insights into designing high-performance room-temperature gas sensors, but also promoted the fundamental research on sensing mechanism for room-temperature gas sensors. • A multisite strategy for enhancing sensitivity was proposed by constructing three kinds of DMMP adsorption active sites. • GNC hybrids demonstrate 5.3-fold improvement in response to 100 ppm DMMP compared to pristine rGO hybrids. • This mechanism for multisite-assisted enhanced DMMP sensing performances was confirmed by the spectroscopy. [ABSTRACT FROM AUTHOR]

In this paper, SnO 2 nanoparticles (NPs) decorated reduced graphene oxide hybrids with abundant vacancies (designated as SnO 2 -RGO-OVs) have been successfully prepared by a combined hydrothermal synthesis and chemical solution deposition method. It is found that high density SnO 2 NPs with the size of 3–5 nm are uniformly distributed on the surface of RGO nanosheets. Most importantly, SnO 2 -RGO-OVs hybrids exhibit excellent room-temperature NO 2 sensing properties with the low detection limit of 50 ppb. When SnO 2 -RGO-OVs-based sensor was exposed to 1 ppm NO 2 , the response is 3.80 and response time and recovery time are 14 s and 190 s, respectively. These sensing performances are superior to those of most reported room-temperature NO 2 sensors based on RGO-based materials and other materials. The excellent sensing performances of SnO 2 -RGO-OVs hybrids can be attributed to their specific structure, e.g., RGO that could facilitate transferring carriers during sensing progress, and abundant OVs that could facilitate adsorption of more NO 2 molecules onto SnO 2 NPs in SnO 2 -RGO-OVs hybrids. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Pd-SR-V O is fabricated by Pd nanoparticles and oxygen vacancy to modulate SnO 2 modified RGO. • Impressively, the response value of Pd-SR-V O for 1 ppm NO 2 at room temperature reaches to 9.8. • Notably, the response even could reach to 3.0 in 100 ppb NO 2 at room temperature. • The improvement of sensitivity is attributed to the synergy of Pd NPs and oxygen vacancies. Reduced graphene oxides (RGO)-based materials exhibit high carrier mobility and selective recognition ability to NO 2 , making them constitute promising platform for room-temperature NO 2 detection. However, the low sensitivity becomes the main bottleneck for their further development. Here, we demonstrate that synergy of Pd nanoparticles (NPs) and oxygen vacancies can modulate the surface active sites over SnO 2 NPs modified RGO hybrids (labeled as SR), leading to improving the sensitivity of room-temperature NO 2 sensors. Experimentally, a wet-chemical method was used to introduce oxygen vacancies onto SR, leading to forming SR with rich oxygen vacancies (labeled as SR-Vo), which were subsequently deposited with Pd NPs, resulting in preparing Pd NPs loaded SR-Vo hybrids (labeled as Pd-SR-Vo). Impressively, the response value to 1 ppm NO 2 of Pd-SR-Vo hybrids reaches to 9.8, which is much higher than that of R-Vo hybrids (5.6) and SR hybrids (3.3). The improvement of sensitivity toward NO 2 for Pd-SR-Vo hybrids is attributed to the synergy effect of Pd NPs and oxygen vacancies, including shortening the band gap of Pd-SR-Vo hybrids with raising conduction band level, widening the width of electron depletion layer between SnO 2 -Vo and RGO, introducing Schottky contact between Pd and SnO 2 -Vo, improving efficiency for gas sensing reaction. This work not only provides an efficient approach to fabricate high-performance NO 2 sensors, but also opens a new avenue for sensing materials design and modification. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (RGO)-based NO 2 sensors have attracted considerable attention due to their excellent advantages of low power consumption and manufacturability to facilitate massive deployment. However, it is still a great challenge to fabricate RGO-based room-temperatureNO 2 sensors with excellent sensing performances. Herein, we have demonstrated a combined surface modification and heteroatom doping approach to enhance the sensing performances of RGO-based room-temperature NO 2 sensors, where SnO 2 nanoparticles modified nitrogen-doped RGO (SnO 2 /N-RGO) hybrids had been used as sensing materials. The SnO 2 /N-RGO hybrids were prepared by hydrothermal synthesis method using SnCl 4 , GO and urea as precursors. The combined characterizations of X-ray diffraction (XRD), energy-dispersive X-ray spectrometer (EDS), elemental mapping, X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), Raman spectra as well as N 2 sorption isotherm were used to characterize the materials thus obtained, indicating the successful preparation of SnO 2 /N-RGO hybrids. During the hydrothermal progress, SnCl 4 conversed into SnO 2 nanoparticles (NPs), and GO was reduced into RGO, while urea was decomposed into nitrogen-containing molecule and doped into RGO. It is found that SnO 2 NPs with the size of 3–5 nm are uniformly dispersed on N-RGO nanosheets. Most importantly, SnO 2 /N-RGO hybrids-based sensor exhibits superior sensing performances toward NO 2 operated at room temperature, which are better than those of pure RGO and SnO 2 /RGO hybrids. For example, SnO 2 /N-RGO hybrids show response of 1.38 to 5 ppm NO 2 with the response time and recovery time of 45 s and 168 s. The excellent sensing performances are attributed to incorporation of N atoms into RGO and the modification of RGO with SnO 2 NPs. This novel sensor based on SnO 2 /N-RGO hybrids promises to provide an essential sensing platform for the detection of NO 2 with excellent sensing performances at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: SnO2 nanoparticles-reduced graphene oxide (SnO2-rGO) nanocomposites have been successfully prepared by a facile method via hydrothermal treatment of aqueous dispersion of GO in the presence of Sn salts. The combined characterizations including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) indicate the successful formation of SnO2-rGO nanocomposites. To demonstrate the product on sensing application, gas sensors are fabricated using SnO2-rGO nanocomposites as sensing materials and investigated for detection of NO2 at low operating temperature (50°C). It is found that SnO2-rGO nanocomposites exhibit high response of 3.31 at 5ppm NO2, which is much higher than that of rGO (1.13), and rapid response, good selectivity and reproducibility. Furthermore, the reason for enhancing sensing performance by addition of SnO2 nanoparticles has also been discussed. [Copyright &y& Elsevier]

Abstract: In this paper, we develop a cost-effective and simple route for the synthesis of Au nanoparticles (AuNPs) decorated graphene oxide (GO) nanosheets using polyoxyethylene sorbitol anhydride monolaurate (TWEEN 20) as a stabilizing agent for GO as well as a reducing and immobilizing agent for AuNPs. The AuNPs assemble on the surface of TWEEN-functionalized GO by the in situ reduction of HAuCl4 aqueous solution. The morphologies of these composites were characterized by atomic force microscopy (AFM) and transmission electron microscopy (TEM). It is found that the resultant AuNPs decorated GO nanosheets (AuNPs/TWEEN/GO) exhibit remarkable catalytic performance for hydrazine oxidation. This hydrazine sensor has a fast amperometric response time of less than 3s. The linear range is estimated to be from 5μM to 3mM (r =0.999), and the detection limit is estimated to be 78nM at a signal-to-noise ratio of 3. The AuNPs/TWEEN/GO composites also exhibit good catalytic activity toward 4-nitrophenol (4-NP) reduction and the GO supports also enhance the catalytic activity via a synergistic effect. [Copyright &y& Elsevier]

• Polypyrrole decorated-reduced graphene oxide (PPy-rGO) hybrids were successfully synthesized by a self-redox strategy. • The PPy-rGO-3-based sensor exhibits a higher response and fast response and recovery behavior to DMMP than pristine rGO. • The enhanced DMMP sensing properties were attributed to formation of hydrogen bonds between DMMP and PPy. The development of fast-response, high sensitivity and selectivity gas sensors for monitoring of organophosphorus is essential, where two dimensional graphene-based materials possessing exceptionsal carrier mobility are considered as promising candidates for room-temperature organophosphorus detection. However, it is challenging to fabrication of graphene-based gas sensors for detection of organophosphorus with excellent sensing performances. Herein, we develope a self-redox strategy to synthesize polypyrrole decorated-reduced graphene oxide hybrids (PPy-rGO) by redox reactions between pyrrole and GO during hydrothermal treatment process. This self-redox strategy results in the formation of perfact interfical strucutre between PPy and rGO through the π-π interactions without the impurity from the conventional oxidation/reducing agents. Most importantly, such PPy-rGO hybrids can be used as novel sensing materials for detection of dimethyl methylphosphonate (DMMP) at room temperature. Specially, the response of PPy-rGO-based sensor towards 100 ppm DMMP can reach 12.9 %, which is 3-fold higher than that pristine rGO-based sensor. Meanwhile, PPy-rGO-based sensor exhibits short response time/recovery time (43 s/75 s), low detection limit (5 ppm), excellent repeatability, and high selectivity. By combination of FT-IR and N 2 sorption isotherms, the enhanced DMMP sensing performances of PPy-rGO hybrids are concluded as following two aspects. Firstly, the formation of hydrogen bonds between PPy-rGO hybrids and DMMP molecules regulates the adsorption/desorption of DMMP. Secondly, increasing BET surface area by introduction of PPy into rGO matrix is beneficial to DMMP diffusion among the sensing materials. Our work would offer a new strategy for rational development of graphene-based materials for detection of organophosphorus at room temperature. [ABSTRACT FROM AUTHOR]

Due to its good biodegradability and mechanical properties, magnesium alloys are considered as the ideal candidate for the cardiovascular stents. However, the rapid degradation in human physiological environment and the poor biocompatibility seriously limit its application for biomaterials. In the present study, a chitosan/heparinized graphene oxide (Chi/HGO) multilayer coating was constructed on the AZ31B magnesium alloy surface using layer-by-layer (LBL) method to improve the corrosion resistance and biocompatibility. The results of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectrum (RAMAN), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) showed that a dense and compact Chi/HGO multilayer coating was fabricated on the magnesium alloy surface. The results of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), pH value changes and magnesium ion release suggested that the multilayer coating can significantly enhance the corrosion resistance of the magnesium alloy. Moreover, the Chi/HGO multilayer coating could not only significantly reduce the hemolysis rate and platelet adhesion, but also promote the adhesion and proliferation of endothelial cells. Therefore, the Chi/HGO multilayer coating can simultaneously improve the corrosion resistance and biocompatibility of the magnesium alloys. • A chitosan/heparinized graphene oxide multilayer coating is obtained by LBL. • The corrosion resistance of AZ31B is obviously improved by the coating. • The coating enhances the biocompatibility of the material surface. • This method can be used in the application of magnesium alloy in vascular stents. [ABSTRACT FROM AUTHOR]