Solution-processed Au@rGO/GaN nanorods hybrid-structure for self-powered UV,visible photodetector and CO gas sensors

Although metal nanoparticles (NPs) have been widely reported, Au NPs functionalized reduced graphene oxide (rGO)/GaN nanorods (NRs) for multi-functional applications are rarely discussed. The rGO is a well known transparent electrode and has been considering an alternative electrode to ITO in the current optoelectronic community. In this work, Au NPs functionalized rGO (Au@rGO)/GaN NRs hybrid structure probed for photodetector and CO gas sensing applications. The hybrid structure was characterized by scanning electron microscopy, transmission electron microscope, current-voltage characteristics, photo conductivity, and gas sensor measurements. The Au@rGO/GaN NRs showed higher photoresponsivity (λ = 382 nm, 516 nm) compared to rGO/GaN NRs at room temperature. The rising and falling times of Au@rGO/GaN NRs are faster than that of rGO/GaN NRs. The hybrid structure Au@rGO/GaN NRs exhibited high CO gas response compared to rGO/GaN NRs at room temperature (∼38% to the 20 ppm). Au NPs played an important role in terms of electronic and chemical changes in the hybrid structure for improving both photodetectors the CO gas response. Such a multi-functional hybrid device is an interest of various room temperature applications.     

Fabrication of nanoporous AuPt nanoparticles modified indium tin oxide electrode and their electrocatalytic effect

This paper describes the synthesis of nanoporous AuPt nanoparticles (np-AuPt NPs) by galvanic replacement reactions that involve large-sized silver nanoparticles (Ag NPs) electrodeposited upon an indium tin oxide (ITO) film glass as a sacrificial template. Compared to a previous synthetic route based on the formation and dealloying of Ag/Au alloy nanoparticles, this method can easily fabricate nanoporous Au nanoparticles (np-Au NPs), as well as nanoporous AuPt nanoparticles. Structural characterization indicated that the products had a particle size of ～170 nm with a ligament size of tens of nanometers. The fabricated np-Au NPs/ITO and np-AuPt NPs/ITO electrode were also tested and compared for the oxidation of hydrogen peroxide in a phosphate buffer solution (pH 7.0). The np-AuPt NPs/ITO electrode showed a much higher electrocatalytic efficiency and detection sensitivity to hydrogen peroxide than the np-Au NPs/ITO electrode.     

A novel graphene-chitosan-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite modified sensor for sensitive and selective electrochemical determination of a monoamine neurotransmitter epinephrine

A novel sensitive electrochemical sensor has been developed by modification of glassy carbon electrode (GCE) with graphene (GRP), chitosan (CHIT), and bismuth oxide (Bi₂O₃) nanoparticles. The morphological characteristics of nanocomposite (GRP-CHIT-Bi₂O₃ or GCB) were studied by scanning electron microscope and atomic force microscopy. The electrochemical behavior of epinephrine at nanocomposite modified GCE (GCB/GCE) was investigated in pH 7.4 phosphate buffer solution using cyclic voltammetry and square wave voltammetry. GCB/GCE showed an enhancement in the current response as compared to bare GCE. Electrochemical impedance spectra showed a reduction of charge transfer resistance and higher electrocatalytic behavior of the sensor. The electrooxidation process of epinephrine at the modified sensor was found to be diffusion controlled. GCB/GCE showed a linear response to epinephrine in the range 100 to 500 nM. The limit of detection and limit of quantification were found to be 3.56 and 11.85 nM, respectively, which is lower than many other sensors reported for epinephrine in literature. The modified sensor showed high sensitivity (1.3 nA/nM) and selectivity for epinephrine. The method was employed for quantification of epinephrine in pharmaceutical formulation and human blood serum samples.     

Ultrasonic preparation and nanosheets supported binary metal oxide nanocomposite for the effective application towards the electrochemical sensor

Binary metal oxides (La₂O₃@SnO₂) decorated reduced graphene oxide nanocomposite was synthesized by ultrasound process in an environmentally benign solvent with a working frequency of 25 and 40 kHz (6.5 l200 H, Dakshin, India and maximum input power 210 W). Further, to enhance the electrocatalytic activity, the reduced graphene oxide (rGO) was prepared from graphene oxide by ultrasonication method. As prepared La₂O₃@SnO₂/rGO was scrutinized using XRD, TEM, EDX and quantitative test for the structural and morphology properties. As modified La₂O₃@SnO₂/rGO nanocomposite exhibits better electrochemical activity towards the oxidation of methyl nicotinate with higher anodic current compared to other modified and unmodified electrode for the detection of methyl nicotinate with larger linear range (0.035–522.9 µM) and lower limit of detection (0.0197 µM). In addition, the practical feasibility of the sensor was inspected with biological samples, reveals the acceptable recovery of the sensor in real samples.     

A new analytical device incorporating a nitrogen doped lanthanum metal oxide with reduced graphene oxide sheets for paracetamol sensing

The novel N-CeO₂ nanoparticles decorated on reduced graphene oxide (N-CeO₂@rGO) composite has been synthesized by sonochemical method. The characterization of as prepared nanocomposite was intensely performed by UV–Vis, FT-IR, EDX, FE-SEM, HR-TEM, XRD, and TGA analysis. The synthesized nanomaterial was further investigated for its selective and sensitive sensing of paracetamol (PM) based on a N-CeO₂@rGO modified glassy carbon electrode. A distinct and improved reversible redox peak of PM is obtained at N-CeO₂@rGO nanocomposite compared to the electrodes modified with N-CeO₂ and rGO. It displays a very good performance with a wide linear range of 0.05–0.600 μM, a very low detection limit of 0.0098 μM (S/N = 3), a high sensitivity of 268 μA µM⁻¹ cm⁻² and short response time (<3 s). Also, the fabricated sensor shows a good sensibleness for the detection of PM in various tablet samples.     

One-pot sonochemical synthesis of CuS nanoplates decorated partially reduced graphene oxide for biosensing of dopamine neurotransmitter

The sonochemical methods have been used as a straight forward method for the synthesis of various composite materials, including the transition metal dichalcogenide composites. In the present work, we report a simple sonochemical synthesis of CuS nanoplates decorated partially reduced graphene oxide (PrGO) nanocomposite for the first time. The PrGO-CuS nanocomposite was synthesized using bath-sonication (frequency: 37 kHz; power: 150 W) of graphene oxide (GO), and CuS precursors at 80 °C for 60 min. The physicochemical characterization (FESEM, XRD, FTIR, and Raman spectroscopy) results confirmed the successful formation of CuS nanoplates on PrGO nanosheets. The as-synthesized PrGO-CuS nanocomposite was further utilized for electroanalysis of dopamine neurotransmitter. The obtained electroanalytical results revealed that PrGO-CuS nanocomposite has superior electrochemical activity towards dopamine than those obtained for GO, CuS, and GO-CuS composite. The fabricated biosensor shows a lower limit of detection (0.022 µM) with a more comprehensive linear response range (0.1–155.1 µM) for the detection of dopamine. Moreover, the PrGO-CuS nanocomposite electrode was successfully used for the detection of dopamine in bovine serum albumin.     

Ultrasound-assisted synthesis of 3D flower-like zinc oxide decorated fMWCNTs for sensitive detection of toxic environmental pollutant 4-nitrophenol

Sonochemical synthesis of functionalized multi-walled carbon nanotubes (fMWCNTs) embellished 3D flower-like zinc oxide (ZnO) nanocomposite based novel electrochemical sensor for the detection of toxic environmental pollutant 4-nitrophenol (4-NP) is detailed in this paper. We have used laser-assisted synthesis technique in the development of 3D flower-like ZnO nanoparticles (NPs) and ultrasonication method was employed in preparation of ZnO NPs@fMWCNTs nanocomposite using a high-intensity ultrasonic bath DC200H with power of 200 W/cm² and 40 KHz frequency. The nanocomposite was meticulously fabricated on screen printed carbon electrode (SPCE) to carry out various electrochemical analysis. Different characterizations such as Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, UV visible spectroscopy (UV–Vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) of the materials used in this work were taken. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques are used in electrochemical investigations. We have observed well-defined oxidation and reduction peak currents representing electrochemical mechanism of 4-NP at very low potentials for ZnO NPs@fMWCNTs/SPCE. Furthermore, we were able to achieve efficient electrochemical determination of 4-NP using the developed sensor with a high sensitivity of 11.44 μA μM⁻¹ cm⁻² and very low detection limit (LOD) of 0.013 μM in a broad linear range of 0.06–100 μM. All the significant features of a good sensor including anti-interference, good stability, excellent repeatability, and reproducibility were exhibited by the sensor. Moreover, we have tested practical feasibility of sensor by carrying out real sample analysis on different water samples.     

Reduced graphene oxide field-effect transistor with indium tin oxide extended gate for proton sensing

In this study, the reduced graphene oxide field-effect transistor (rGO FET) with indium tin oxide (ITO) extended gate electrode was demonstrated as a transducer for proton sensing application. In this structure, the proton sensing area of the ITO extended gate electrode is isolated from the active area of the rGO FET. The proton sensing properties based on the rGO FET transducer were analyzed. The rGO FET device with encapsulation by a tetratetracontane (TTC) layer showed good stability in electrolytic solutions. The device showed an ambipolar behavior with shifts in Dirac point as the pH of the electrolyte is varied. The pH sensitivity based on the Dirac point shift as a sensing parameter was about 43–50 mV/pH for a wide range of pH values from 2 to 12. The ITO extended gate rGO FET may be considered a potential transducer for sensing of H⁺ in electrolytes. Its sensing area can be modified further for various ions sensing applications.     

ZnO nanoparticle-modified ionic liquid-carbon paste electrodefor voltammetric determination of folic acid in food and pharmaceutical samples

In this work, a ZnO/nanoparticles (NPs) modified carbon ionic liquid paste electrode (ZnO/NP/CILPE) was fabricated and used to investigate the electrochemical behavior of folic acid. ZnO/NP/CILPE was prepared by mixing hydrophilic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim]-[PF₆])), ZnO/NPs, graphite powder, and liquid paraffin together. The fabricated ZnO/NP/CILPE showed great electrocatalytic ability to the oxidation of folic acid, and an irreversible oxidation peak appeared at 0.75 V (vs. Ag/AgCl) with improved peak current. Under the optimized conditions of pH 9.0, the plot of peak current vs. folic acid concentration consisted of two linear segments with slopes of 1.776and 0.033 μA/μM in the concentration ranges of 0.05–1.5 μM and 1.5–550.0 μM, respectively. The detection limit was 0.01 μM (3σ). The proposed sensor was successfully applied for the determination of folic acid in fortified food and pharmaceutical samples.     

Enhanced catalytic hydrogenation activity of Ni/reduced graphene oxide nanocomposite prepared by a solid-state method

A simple solid-state method has been applied to synthesize Ni/reduced graphene oxide (Ni/rGO) nanocomposite under ambient condition. Ni nanoparticles with size of 10–30 nm supported on reduced graphene oxide (rGO) nanosheets are obtained through one-pot solid-state co-reduction among nickel chloride, graphene oxide, and sodium borohydride. The Ni/rGO nanohybrid shows enhanced catalytic activity toward the reduction of p-nitrophenol (PNP) into p-aminophenol compared with Ni nanoparticles. The results of kinetic research display that the pseudo-first-order rate constant for hydrogenation reaction of PNP with Ni/rGO nanocomposite is 7.66 × 10^?3 s^?1, which is higher than that of Ni nanoparticles (4.48 × 10^?3 s^?1). It also presents superior turnover frequency (TOF, 5.36 h^?1) and lower activation energy (E_a, 29.65 kJ mol^?1) in the hydrogenation of PNP with Ni/rGO nanocomposite. Furthermore, composite catalyst can be magnetically separated and reused for five cycles. The large surface area and high electron transfer property of rGO support are beneficial for good catalytic performance of Ni/rGO nanocomposite. Our study demonstrates a simple approach to fabricate metal-rGO heterogeneous nanostructures with advanced functions.

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Synthesis of Li3V2(PO4)3/reduced graphene oxide cathode material with high-rate capability

The Li₃V₂(PO₄)₃/reduced graphene oxide (LVP/rGO) composite is successfully synthesized by a conventional solid-state reaction with a high yield of 10 g, which is suitable for large-scale production. Its structure and physicochemical properties are investigated using X-ray diffraction, Raman spectra, field-emission scanning electron microscopy, transmission electron microscopy, and electrochemical methods. The rGO content is as low as ~3 wt%, and LVP particles are strongly adhered to the surface of the rGO layer and/or enwrapped into the rGO sheets, which can facilitate the fast charge transfer within the whole electrode and to the current collector. The galvanostatic charge–discharge tests show that the LVP/rGO electrode delivers an initial discharge capacity of 177 mAh g^?1 at 0.5 C with capacity retention of 88 % during the 50th cycle in a wide voltage range of 3.0–4.8 V. A superior rate capability is also achieved, e.g., exhibiting discharge capacities of 137 and 117 mAh g^?1 during the 50th cycle at high C rates of 2 and 5 C, respectively.     

Layered nanocomposite of zinc sulfide covered reduced graphene oxide and their implications for electrocatalytic applications

Herein, we have synthesized zinc sulfide nanospheres (ZnS NPs) encapsulated on reduced graphene oxide (RGO) hybrid by an ultrasonic bath (50 kHz/60 W). The physical and structural properties of ZnS NPs@RGO hybrid were analyzed by TEM, XRD, EIS and EDS. As-prepared ZnS NPs@RGO hybrid was applied towards the electrochemical determination of caffeic acid (CA) in various food samples. The ZnS NPs@RGO hybrid modified electrode (GCE) exhibited an excellent electrocatalytic performance towards caffeic acid detection and determination, when compared to other modified electrodes. Therefore, the electrochemical sensing performance of the fabricated and nanocomposite modified electrode was significantly improved owing to the synergistic effect of ZnS NPs and RGO catalyst. Furthermore, the hybrid materials provide highly active electro-sites as well as rapid electron transport pathways. The proposed electrochemical caffeic acid sensor produces a wide linear range of 0.015–671.7 µM with a nanomolar level detection limit (3.29 nM). In addition, the real sample analysis of the proposed sensor has applied to the determination of caffeic acid in various food samples.     

Modification and photovoltaic properties of reduced graphene oxide/acetylene black composite electrode

A simple and high efficient reduced graphene oxide/acetylene black (rGO/ACET) nano-composite electrode was prepared as the substitute of high-cost Pt counter electrode in dye-sensitized solar cells (DSSCs). Surface-modified method called solvent-substituting (SS) was firstly used to avoid agglomeration of rGO sheets. The Brunner-Emmet-Teller (BET)-specific surface area of rGO was increased from 195.823 to 355.210 m²/g after modifying with ethanol. Then ACET particles were introduced between rGO layers to improve the electronic transportation properties. The chemical compositions, microstructures, and pore size distributions of rGO/ACET composites were investigated. Electrochemical impedance spectroscopy (EIS) indicated that rGO/ACET counter electrode had a lower charge transfer resistance (R_ct) and its S-shaped current–voltage curves disappeared obviously. The highest power conversion efficiency up to 6.62% was achieved for the DSSCs with rGO/ACET nano-composite counter electrode.     

A feasible sonochemical approach to synthesize CuO@CeO2 nanomaterial and their enhanced non-enzymatic sensor performance towards neurotransmitter

A nanostructured and high conductive cupric oxide (CuO NPs) with hierarchical CeO₂ sheets-like structure was synthesized by a facile sonochemical approach. Furthermore, CuO/CeO₂ nanostructure is synthesized by high-intensity ultrasonic probe (Ti-horn, 50 kHz and 100 W) at ambient air. Moreover, the synthesized CuO/CeO₂ material was characterized by various analytical techniques including FESEM, EDX, XRD and electrochemical methods. Then, the synthesized CuO/CeO₂ composite was applied for the electrocatalytic detection of dopamine using CV and DPV techniques. In addition, the CuO/CeO₂ modified electrode has good electrocatalytic performance with high linear range from 0.025 to 98.5 µM towards the determination of dopamine drug and high sensitivity of the CuO/CeO₂ modified drug sensor was calculated as 16.34 nM and 4.823 μA·µM⁻¹·cm⁻², respectively. Moreover, a repeatability, reproducibility and stability of the CuO@CeO₂ mixture modified electrode were analyzed towards the determination of dopamine biomolecule. Interestingly, the real time application of CuO@CeO₂ modified electrode was established in different serum and drug samples.     

Nanomolar detection limit for determination of norepinephrine in the presence of acetaminophen and tryptophan using carbon nanotube-based electrochemical sensor

A carbon paste electrode modified by carbon nanotubes and a synthesized hydroquinone derivative (abbreviated as DHB) was fabricated. It was used as an electrochemical sensor for simultaneous determination of norepinephrine (NE), acetaminophen (AC), and tryptophan (Trp). Oxidation potential of NE decreased about 220 mV at the modified electrode in comparison with unmodified electrode because of electrocatalysis of oxidation of NE via E? mechanism at the modified electrode. Differential pulse voltammetry was used for obtaining the calibration plot of NE and two linear range of 0.2–20.0 μM and 20.0–1,500.0 μM and an interesting detection limit (3σ) of 40.0 nM were obtained for NE. Also, simultaneous determination of NE, AC, and Trp was described by the proposed sensor and linear range of 20.0–800.0 μM was found for AC and Trp. Finally, the electrochemical sensor was used for the determination of NE, AC, and Trp in mixture.     

Nitrobenzene electrochemical sensor based on silver nanoparticle supported on poly-melamine functional multi-walled carbon nanotube

A novel and convenient electrochemical sensor, based on multi-walled carbon nanotube (MWCNT)–poly-melamine(PMel)–silver nanoparticle (AgNP) composite-modified glassy carbon electrode (GCE), was fabricated for the determination of nitrobenzene (NB). The modified electrode not only played an efficient electrocatalytic role for the reduction of NB but also significantly reduced the overpotential of NB, and the peak current increased greatly compared with bare GCE or other modified electrodes. The excellent performance of NB sensor can be ascribed to the synergistic effect between MWCNT and AgNP. The synergistic effect promoted the electron transfer between MWCNT and AgNP significantly and enhanced the electrochemical reduction ability of NB remarkably. Besides, PMel has huge nitrogen and amine groups, which contributes to the dispersion of silver nanoparticles and also improves the electrocatalytic activity and sensitivity of the sensor. The integration of PMel/MWCNT with AgNP provided a high-performance platform for the NB determination. Under the optimized experimental conditions, the developed sensor showed a wide linear calibration ranges from 20 to 1000 μM and from 1000 to 6000 μM, with a low detection limit (0.55 μM) for the detection of NB. At the same time, the modified electrode exhibited good stability and reproducibility and acceptable selectivity. Moreover, the proposed sensors were successfully employed to determine NB in real samples, and the recoveries were between 97.2 and 104.6 %.     

Porous WO<Subscript>3</Subscript>/reduced graphene oxide composite film with enhanced electrochromic properties

The porous WO₃/reduced graphene oxide (rGO) composite films are prepared on indium–tin oxide (ITO) glass by sol-gel method. The mixture sol combines peroxotungstic acid solution with rGO dispersion reduced by ethylene glycol (EG). The excessive EG and other organic additives are subsequently removed by annealing, which leads to the formation of porous structure. Compared with pure WO₃ film, WO₃/rGO composite film shows improved electrochromic performance because of enhanced double insertion/extraction of ions and electrons. It realizes a large optical modulation (64.2 % at 633 nm), fast switching speed (9.5 s for coloration and 4.5 s for bleaching), good cycling stability as well as reversibility.     

Fabrication of g-C3N4/NiO heterostructured nanocomposite modified glassy carbon electrode for quercetin biosensor

Herein, we report a one-pot synthesis of structurally uniform and electrochemically active graphitic carbon nitride/nickel oxide (g-C₃N₄/NiO) nanocomposite and an investigation on the electrocatalytic oxidation of quercetin (QR). The synthesized g-C₃N₄/NiO nanocomposite has uniform surface distribution, which was characterized with scanning electron microscopy (SEM). Moreover, the composition of synthesized g-C₃N₄/NiO nanocomposite was characterized by UV–vis-spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR spectra), BET, SEM and HRTEM. The g-C₃N₄/NiO was electrochemically treated in 0.1 MPBS solution through cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The peak current response increases linearly with QR concentration from 0.010 μM to 250 µM with a fast response time of less than 2 s and a detection limit of 0.002 μM. To further evaluate the feasibility of using this sensor for real sample analysis, QR content in various real samples including green tea, green apple, honey suckle were determined and satisfactory results were achieved.     

Polypyrrole–NiO hybrid nanocomposite films: highly selective,sensitive, and reproducible NO2 sensors

Polypyrrole–nickel oxide (PPy–NiO) hybrid nanocomposite thin-film sensor was prepared by spin-coating method on glass substrate. The PPy–NiO hybrid nanocomposite thin film sensors were used to study room temperature gas-sensing properties for oxidizing (NO₂, Cl₂) as well as reducing (NO₂, H₂S, C₂H₅OH, NH₃, and Cl₂) gases. It was revealed that PPy–NiO (50 %) hybrid nanocomposite thin-film sensor could detect NO₂ at low concentration (100 ppm) with very high selectivity (47 % compared with Cl₂) and high sensitivity (47 %), with better stability (90 %) and reproducibility. The response and recovery times were changed significantly with NO₂ concentration.     

Sonochemical synthesis of nickel-manganous oxide nanocrumbs decorated partially reduced graphene oxide for efficient electrochemical reduction of metronidazole

In the present work, we report on the synthesis of crump-like nickel manganous oxide nanoparticles decorated partially reduced graphene oxide (NiMnO@pr-GO) nanocomposite through high-intensity ultrasonic bath sonication (ultrasonic frequency = 37 kHz and power = 150 W). The NiMnO@pr-GO nanocomposite modified glassy carbon electrode (GCE) was then employed for the electrochemical reduction of detrimental metronidazole (MNZ). The crystalline phase and formation of the NiMnO@pr-GO nanocomposites were confirmed by X-ray diffraction and other spectroscopic techniques. The cyclic voltammetry results demonstrate that this NiMnO@pr-GO nanocomposite modified GCE has a lower reduction potential and higher catalytic activity towards MNZ than do NiMnO and GO modified GCEs. Under optimized conditions, the fabricated NiMnO@pr-GO electrode can detect metronidazole over a wide linear range with a lower limit of detection of 90 nM. The sensitivity of the sensor was 1.22 µA µM^-1cm⁻² and was found to have excellent selectivity and durability for the detection of MNZ.