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•A polyvinyl alcohol/chitosan/graphene composite modified electrode was introduced for trace Pb(II) detection.•Highly sensitive and selective detection of Pb(II) can be obtained via ...the electrode.•Cost-effective, easy-to-use, and environmentally friendly detection without using complicated apparatus.•The electrode was successfully applied for Pb(II) detection in real water samples.
A novel polyvinyl alcohol/chitosan-thermally reduced graphene modified glassy carbon electrode (PVA/chitosan-TRG/GCE) has been studied for determination of lead (Pb) in aqueous samples by square wave anodic stripping voltammetry (SWASV). The graphene was obtained from thermal exfoliation-reduction of graphite oxide in the nitrogen atmosphere with an eco-friendly procedure. Chitosan was blended with polyvinyl alcohol to obtain advances in electrochemical and mechanical properties. The surface of the PVA/chitosan-TRG composite exhibited a homogeneous and well-dispersed status, as observed from FESEM images. The electrochemical characteristics of the electrode before and after the modification were characterized via electrochemical impedance spectroscopy (EIS) and SWASV. The effects of experimental conditions such as buffer pH, pre-concentration time, pre-concentration potential, ratio of graphene to PVA/chitosan were systematically investigated. The modified electrode displayed a significant enhancement in sensitivity and selectivity for the detection of Pb. Under optimized conditions, the modified electrode revealed a detection range from 1 ppb to 50 ppb for Pb with a correlation coefficient of 0.996. The limit of detection (LOD) at the modified electrode, based on the signal-to-noise ratio (S/N = 3), gave a value of 0.05 ppb with a preconcentration time of 5 min. The selectivity study revealed that most common foreign ions did not bring significant interference for Pb detection. Besides, the electrode has been successfully applied for Pb detection in real water samples. The proposed method offers scope for on-site detection of Pb at trace level in aqueous samples with a cost-effective, easy-to-use, and environmentally friendly procedure without using complicated apparatus.
•Corona plasma was used to treat silicon substrate surfaces•Reduced graphene oxide (rGO) was formed by short time annealing of spun GO layers•Large area and uniform rGO films were obtained•rGO films ...had sheet resistance of the order of 5-35 ohm/sq
Graphene is a material with excellent properties. However, the manufacture of a single-layer graphene film with a large area is challenging. It requires modern and expensive equipment. In this study, we suggested another approach to improve these problems. The raw material graphite was used to prepare graphene oxide solutions. The resulting graphene oxide solutions were then dispersed onto silicon substrates first treated with corona plasma, which increases the adhesion between materials and substrates. In the next step, these covered substrates were deoxygenated by heating at very high temperatures for a short time to form reduced graphene oxide, which has graphene-like properties. The reduced graphene oxide films formed had a uniform structure over a large area of 2 × 2 cm2 with an oxygen content of about 4%, a film roughness of less than 5 nm, and a sheet resistance of 4-5 ohm/square.
A sputtered platinum thin film was fabricated by using photolithography, sputtering, and a lift-off method. The sputtered Pt grains were uniformly dispersed in the film as observed from FE-SEM images ...to form a compact film with fairly homogeneous size. Square wave voltammetry was used to directly detect Fe(III) with this electrode, typically at a working potential of 0.63 V (vs. Ag/AgCl). The method had a 90 ppb detection limit and worked in the 0.3–5 ppm concentration range. This value meets the requirements set by the World Health Organization. In addition, the stability and reproducibility of the electrode were superior (with RSDs of 3.363% for 5 repetitive measurements). For real tap and well water samples, the electrode gave the well-defined peak for Fe(III) without showing any enrichment in Fe(III). The results from real water analyses were in agreement with those obtained by the UV–Vis method.
Abstract
Copper nanoparticles, due to their interesting properties, low cost preparation and many potential applications in catalysis, cooling fluid or conductive inks, have attracted a lot of ...interest in recent years. In this study, copper nanoparticles were synthesized through the chemical reduction of copper sulfate with sodium borohydride in water without inert gas protection. In our synthesis route, ascorbic acid (natural vitamin C) was employed as a protective agent to prevent the nascent Cu nanoparticles from oxidation during the synthesis process and in storage. Polyethylene glycol (PEG) was added and worked both as a size controller and as a capping agent. Cu nanoparticles were characterized by Fourier transform infrared (FT-IR) spectroscopy to investigate the coordination between Cu nanoparticles and PEG. Transmission electron microscopy (TEM) and UV–vis spectrometry contributed to the analysis of size and optical properties of the nanoparticles, respectively. The average crystal sizes of the particles at room temperature were less than 10 nm. It was observed that the surface plasmon resonance phenomenon can be controlled during synthesis by varying the reaction time, pH, and relative ratio of copper sulfate to the surfactant. The surface plasmon resonance peak shifts from 561 to 572 nm, while the apparent color changes from red to black, which is partly related to the change in particle size. Upon oxidation, the color of the solution changes from red to violet and ultimately a blue solution appears.
In this paper, ceria flowers containing nano-sized catalyst Ni particles were prepared on alumina-silica fiber network for production of hydrogen from biogas. The CeO2 flowers were prepared using ...hydrothermal method and then NiO was loaded on the CeO2 flowers by impregnation method. The Paper-structured catalysts (PSCs) were prepared from alumina-silica fibers and the CeO2–NiO flowers using conventional paper making method. The loaded NiO particles were uniformly dispersed on the CeO2 flowers with the use of polyvinylpyrrolidone as a dispersion enhancer, which was observed by FE-SEM and EDX analysis. The NiO particles were then reduced into Ni by using H2. The PSCs containing CeO2–Ni flowers with various Ni contents (2.1, 3.4, and 4.6%) were used for dry reforming of CH4. It was found that 3.4% amount of Ni on the PSC was suitable for reforming reaction, and the higher amount of Ni (4.6%) did not increase the CH4 conversion. The PSC with the CeO2 flowers had porous structure and large surface area leading to the better dispersion of the Ni particles with smaller size. This helped increase in catalytic performance, prevention of agglomerated particle catalysts at high temperature and coke forming after a long time operation. The CH4 conversion of the PSCs containing CeO2–NiO flowers in the dry reforming of CH4 was much higher (nearly 90%) with a smaller Ni content in comparison with the PSC without the CeO2 flowers (with higher Ni content of 8.6%). Moreover, the PSCs with the flowers exhibited an excellent catalytic stability with the degradation of CH4 conversion of only 3.1% after 50 h of reforming. In addition, the high oxygen storage capacity and oxygen mobility of CeO2 resulted in a partial removal of coke forming on the catalyst particles during reforming. This indicated that the catalytic activity of the Ni particles dispersed on the CeO2 flowers for dry reforming of CH4 was superior to that of various Ni-based catalyst systems which had much higher Ni contents. Therefore, it is possible to use the PSCs containing CeO2–Ni flowers to generate hydrogen for use as fuels from dry reforming of CH4.
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•5 μm spherical CeO2 flowers had open porous structure and high surface area.•NiO particle catalysts were uniformly dispersed on the CeO2 flowers.•Paper-structured catalysts (PSC) with the dispersed flowers had a great porosity.•PSCs with small Ni content exhibited excellent catalytic activity in CH4 reforming.•PSCs exhibited degradation of CH4 conversion of only 3.1% after 50 h of reforming.
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•Thermally reduced graphene/nafion modified platinum disk electrode for Fe sensitive detection.•Graphene was synthesized by thermal exfoliation of graphite oxide in nitrogen ...atmosphere.•Electrochemical characterization was conducted by CV and EIS.•A limit of detection was 0.08 ppb for Fe, with 180 s of pre-concentration.•Successful determination of iron in real samples of well water and river water.
This paper presents a thermally reduced graphene/nafion modified platinum disk electrode (TRG/NF/PDE) for sensitive detection of iron (Fe) using square wave voltammetry (SWV). The graphene was synthesized by thermal exfoliation of graphite oxide in nitrogen atmosphere with an eco-friendly procedure. The morphologies of thermally reduced graphene and thermally reduced graphene/nafion were characterized by field emission scanning electron microscopy (FESEM). Electrochemical behaviors of the electrode before and after modification were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under optimized conditions, the TRG/ND/PDE exhibited excellent electrocatalysis toward Fe. A linear calibration curve was established in the range from 1 to 200 ppb for Fe. With a pre-concentration time of 180 s, a limit of detection based on three times of the background noise was calculated to be 0.08 ppb for Fe. The method was successfully employed for the detection of Fe in real water samples.
A Nafion modified platinum electrode-on-chip for the electrochemical detection of iron in 0.1 M HCl has been demonstrated. The platinum electrode was patterned on a silicon substrate by a combination ...of microfabrication processes followed by spin coating deposition of a Nafion layer. The quality of the thin-film chip structure and the low surface roughness of the Nafion coated platinum nano-grains were observed by FE-SEM and AFM techniques. These features contributed to a significant improvement in the electrode performance in terms of sensitivity as it can offer: (i) a low and stable baseline current, (ii) a high faradic current with respect to the reduction of Fe3+. Under optimum conditions, the electrode operates in the range of 1 ppb to 250 ppb with a detection limit of 0.31 ppb. It also exhibits an excellent reproducibility with a relative standard deviation (RSD) of 6.11% for 20 repeated measurements. The electrode has been successfully applicable for detecting iron concentrations in natural water samples.
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•A modified chip-type electrode whose surface is a combination of Nafion and Pt nanostructure.•Low surface roughness of the Nafion coated platinum nano-grains was observed.•Excellent sensitivity with the working range of 1 ppb to 250 ppb and a detection limit of 0.31 ppb iron.•The reproducibility of platinum/nafion electrode was 6.11% for 20 repeated measurements•A reliable electrode for the detection of iron at low concentrations.
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•Effective transducer for all-solid-state ion-selective electrodes based on gold nanoparticle-reduced graphene oxide.•AuNP-rGO composite was synthesized via a simple, eco-friendly, ...and one-pot method.•AuNP-rGO layer possesses a large surface area, high capacitance, and good hydrophobicity.•The electrode exhibited a rapid potential response to NH4+ ions without water layer formation.•The electrode offered good reproducibility, long operating life, and insensitivity to interferences.
An effective transducer for all-solid-state ion-selective electrodes (SC-ISEs) was developed based on gold nanoparticle-reduced graphene oxide (AuNP-rGO) hybrid material. The AuNP-rGO composite was synthesized via a simple, eco-friendly, and one-pot method with sodium citrate as the reducing agent and the stabilizer. The nanocomposite was deposited on the GC substrate via the drop-casting method and then covered with an ammonium ion-selective membrane (NH4+-ISM) to form the potentiometric electrode. The AuNP-rGO layer possessed a large surface area, high capacitance, and good hydrophobicity; thereby effectively enhancing the potential stability of the electrode without the formation of an aqueous layer. The electrode also exhibited a rapid potential response (<10 s) to NH4+ ions, an excellent Nernstian response with a slope of 56.94 (±1.57) mV/decade, a detection range of 10-5 − 10-2 M, and a detection limit of 3.80 × 10-6 M. The proposed electrode also exhibited outstanding properties including insensitivity to interferences (light, oxygen, carbon dioxide, and redox species), good reproducibility, and long operating life. The electrode has been successfully applied for NH4+ detection in real water samples, which makes it a promising alternative for developing effective and robust SC-ISEs.
In this paper we present silver nanoparticles ink synthesis targeting conductive patterns for micro fabricated devices by inkjet printing technology. The well dispersed nanoparticles ink was composed ...of silver colloid with an average particle diameter less than 10 nm. These nanoparticles were protected by a capping layer of poly(N-vinylpyrrolidone) (PVP) even at silver concentration of 20 wt%. Stable aqueous inks were formulated by using a combination of solvent and co-solvents and under vigorous stirring. Various factors affecting the adhesion between the ink and the substrate were investigated, such as solvent and co-solvent content. The ink containing 20 wt% silver has a viscosity of about 9.5 cP and a surface tension of 32 to 36 mN m super(-1) at room temperature, meeting inkjet printer requirements. The ink stored under ambient conditions was stable against aggregation for more than one month. Silver nanoparticles patterns have been successfully printed on various substrates.
Biological symmetry breaking is a mechanism in biosystems that is necessary for human survival, and depends on chemical physics concepts at both microscopic and macroscopic scales. In this work, we ...present a few mechanisms of the signaling phenomenon that have been studied in various tissues of human origin. We exhibit that anatomical asymmetry in the structure of a membrane can produce a flow of extracellular fluid. Furthermore, we exhibit that membrane asymmetry is a misbalance in the composition of the aqueous phases and interaction forces with the protein trans-membrane. Various biological membranes such as DPPC, DMPC, DLPC, and so on, have considerable electrostatic voltages that extend across the phosphor lipids bilayer. For studying these phenomena, we modeled DPPC, DMPC, and DLPC lipid bilayers with a net charge misbalance across the phospholipids. Because asymmetric membranes create the shifted voltages among the various aqueous tissues, this effect makes the charge misbalances cause a voltage of 1.3 V across the DPPC bilayer and 0.8 V across the DMPC bilayer. This subject exhibits the importance of membrane structures on electrostatic potential gradients. Finally, we exhibited that a quantum effect was created in small parts of the cell’s thickness due to the symmetry breaking of asymmetrical phospholipid bilayers.
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