A temperature-responsive biosensing film consisting of the temperature-responsive block co-polymer poly (N-isopropylacrylamide)-b-poly(2-acrylamidoethyl benzoate) (referred to as PNIPAM-b-PAAE), graphene oxide (GO), and hemoglobin (Hb) was fabricated and used to modify a glassy carbon electrode (GCE). The film provides a favorable micro-environment for Hb to facilitate the electron transfer to the GCE. Hb at PNIPAM-b-PAAE/GO/Hb (PGH) film exhibits a couple of well-defined redox peaks with a formal potential of ?0.371 V (vs. SCE) and displays intrinsic electro-catalytic activity toward H2O2. The sensing film also shows temperature-tunable catalytic activity toward H2O2 that can be stimulated by temperature. Large peak currents can be seen in amperometry at 0.4 V (vs. SCE) in pH 7.0 phosphate buffer only if the temperature is above the lower critical solution temperature (LCST) of 32 °C. The response of the modified GCE is linear in the 0.1 to 3.7 μmol L?1 concentration range if operated at above 32 °C, but in the 0.2 to 3.7 μmol L?1 concentration range at below 30 °C. This behavior is attributed to the temperature-dependent phase transition of PNIPAM-b-PAAE and cooperative effect of GO. The strategy presented here in our perception meets the requirements of switchable sensors for use in bioscience and biotechnology.
Graphical abstract A temperature-responsive biosensing film consisting of temperature-responsive polymer, graphene oxide and hemoglobin has been fabricated. This film displays favorable electrochemical property and good electro-catalytic activity toward H2O2. It also exhibits catalytic activity change upon temperature stimuli.
We describe a chemical exfoliation method for the preparation of MoS2 nanosheets. The nanosheets were incorporated into poly(3,4-ethylenedioxythiophene) (PEDOT) by electrodeposition on a glassy carbon electrode (GCE) to form a nanocomposite. The modified GCE is shown to enable simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). Due to the synergistic effect of MoS2 and PEDOT, this electrode displays better properties in terms of electrocatalytic oxidation of AA, DA and UA than pure PEDOT, which is illustrated by cyclic voltammetry and differential pulse voltammetry (DPV). Under optimum conditions and at pH 7.4, the respective sensitivities and best working potentials are as follows: AA: 1.20 A?mM?1?m?2, 30 mV; DA: 36.40 A?mM?1?m?2, 210 mV; UA: 105.17 A?mM?1?m?2, 350 mV. The calculated detection limits for AA, DA and UA are 5.83 μM, 0.52 μM and 0.95 μM, respectively. The modified electrode was applied to the detection of the three species in human urine samples and gave satisfactory results.
Graphical abstract MoS2 nanosheets were prepared by a facile chemical exfoliation method. MoS2 and poly(3,4-ethylenedioxythiophene) nanocomposite modified glassy carbon electrodes were fabricated, which are shown to enable simultaneous determination of ascorbic acid, dopamine and uric acid with high sensitivity and selectivity.
The authors describe a cataluminescence (CTL) based sensing method via signals generated at the surface of In3LaTi2O10 nanoparticles for simultaneous determination of trimethylamine, formaldehyde and benzene in air. The analytical wavelengths are 340 nm, 440 nm and 600 nm, and the best surface temperature of the catalytic material is 275 °C. The limits of detection of this method are 0.3 mg?m?3 for trimethylamine, 0.07 mg?m?3 for formaldehyde, and 0.2 mg?m?3 for benzene. The linear ranges of CTL intensity versus gas/vapor concentration are from 1.0 to 65.1 mg?m?3 for trimethylamine, from 0.2 to 72.5 mg?m?3 for formaldehyde, and from 0.5 to 77.5 mg?m?3 for benzene. The recoveries after testing 10 standard samples ranged from 98.1% to 102.6% for trimethylamine, from 98.1% to 102.6% for formaldehyde, and from 97.7% to 103.8% for benzene. Gaseous ammonia, acetaldehyde, toluene, ethylbenzene, ethanol, sulfur dioxide and carbon dioxide do not interfere. The relative deviation of the CTL signals after 200 h of continuous detection of trimethylamine, formaldehyde and benzene is <3%.
Graphical abstract Schematic of a cataluminescence (CTL) based method for simultaneous determination of trimethylamine (TMA), formaldehyde (HCHO) and benzene (C6H6) in air. The linear ranges of CTL intensity versus gas/vapor concentration are from 1.0 to 65.1 mg?m?3 for TMA, from 0.2 to 72.5 mg?m?3 for HCHO, and from 0.5 to 77.5 mg?m?3 for C6H6.
The authors describe an electrochemical sensor for hydrogen peroxide (H2O2). It was constructed by consecutive, selective modification of a glassy carbon electrode (GCE) with Prussian Blue (PB), layered molybdenum disulfide (MoS2), and reduced graphene oxide (rGO). The properties of the modified GCE were characterized via high-resolution transmission electron microscopy, UV-vis spectroscopy and X-ray diffraction. The electrochemical properties of the electrode were studied using cyclic voltammetry and electrochemical impedance spectroscopy. The sensor exhibits excellent electrocatalytic activity for the reduction of hydrogen peroxide in comparison to GCEs modified with MoS2-rGO or PB only. Response is linear in the 0.3 μM to 1.15 mM H2O2 concentration range at a working analytical voltage of 0.1 V, with a 0.14 μM detection limit. The electrochemical sensitivity is 2883.5 μA·μM?1·cm?2, and response is fast (<10 s). The sensor is selective, stable and reproducible. This is attributed to the efficient electron transport properties of the MoS2-rGO composite and the high loading with PB.
Graphic abstract Prussian Blue nanoparticles were deposited on MoS2-rGO modified glassy carbon electrode by electrochemical method. This sensor was used for the detection of H2O2 in tap water and river water.
Li[Ni1/3Co1/3Mn1/3]O2 (NCM 111) is a promising alternative to LiCoO2, as it is less expensive, more structurally stable, and has better safety characteristics. However, its capacity of 155 mAh g?1 is quite low, and cycling at potentials above 4.5 V leads to rapid capacity deterioration. Here, we report a successful synthesis of lithium-rich layered oxides (LLOs) with a core of LiMO2 (R-3m, M?=?Ni, Co) and a shell of Li2MnO3 (C2/m) (the molar ratio of Ni, Co to Mn is the same as that in NCM 111). The core–shell structure of these LLOs was confirmed by XRD, TEM, and XPS. The Rietveld refinement data showed that these LLOs possess less Li+/Ni2+ cation disorder and stronger M*–O (M*?=?Mn, Co, Ni) bonds than NCM 111. The core–shell material Li1.15Na0.5(Ni1/3Co1/3)core(Mn1/3)shellO2 can be cycled to a high upper cutoff potential of 4.7 V, delivers a high discharge capacity of 218 mAh g?1 at 20 mA g?1, and retains 90 % of its discharge capacity at 100 mA g?1 after 90 cycles; thus, the use of this material in lithium ion batteries could substantially increase their energy density.
Graphical Abstract Average voltage vs. number of cycles for the core–shell and pristine materials at 20 mA g?1 for 10 cycles followed by 90 cycles at 100 mA g?1
A dual-responsive sandwich-type immunosensor is described for the detection of interleukin 6 (IL-6) by combining electrochemiluminescent (ECL) and electrochemical (EC) detection based on the use of two kinds of TiO2 mesocrystal nanoarchitectures. A composite was prepared from TiO2 (anatase) mesocages (AMCs) and a carboxy-terminated ionic liquid (CTIL) and then placed on a glassy carbon electrode (GCE). In the next step, the ECL probe Ru(bpy)3(II) and antibody against IL-6 (Ab1) were immobilized on the GCE. Octahedral anatase TiO2 mesocrystals (OAMs) served as the matrix for immobilizing acid phosphatase (ACP) and secondary antibody (Ab2) labeled with horseradish peroxidase (HRP) to form a bioconjugate of type Ab2-HRP/ACP/OAMs. It was self-assembled on the GCE by immunobinding. 1-Naphthol, which is produced in-situ on the surface of the GCE due to the hydrolysis of added 1-naphthyl phosphate by ACP, is oxidized by HRP in the presence of added H2O2. This results in an electrochemical signal (typically measured at 0.4 V vs. Ag/AgCl) that increases linearly in the 10 fg·mL?1 to 90 ng·mL?1 IL-6 concentration range with a detection limit of 0.32 fg·mL?1. Secondly, the oxidation product of 1-naphthol quenches the ECL emission of Ru(bpy)32+. This leads to a decrease in ECL intensity which is linear in the 10 ag·mL?1 to 90 ng·mL?1 concentration range, with a detection limit of 3.5 ag·mL?1. The method exhibits satisfying selectivity and good reproducibility which demonstrates its potential in clinical testing and diagnosis.
Graphical abstract A dual-responsive sandwich-type immunosensor was fabricated for the detection of interleukin 6 by combining electrochemiluminescence and electrochemical detection based on the use of two kinds of TiO2 mesocrystal nanoarchitectures.
Hydrothermally synthesized Co3O4 microspheres were anchored to graphite oxide (GO) and thermally reduced graphene oxide (rGO) composites at different cobalt weight percentages (1, 10, and 100 wt%). The composite materials served as the active materials in bulk electrodes for two-electrode cell electrochemical capacitors (ECCs). GO/Co3O4–1 exhibited a high energy density of 35 W kg?1 with a specific capacitance (Csp) of 196 F g?1 at a maximum charge density of 1 A g?1. rGO/Co3O4-100 presented high specific power output values of up to 23.41 kW h kg?1 with linear energy density behavior for the charge densities applied between 0.03 and 1 A g?1. The composite materials showed Coulombic efficiencies of 96 and 93 % for GO/Co3O4–1 and rGO/Co3O4–100 respectively. The enhancement of capacitive performance is attributed to the oxygenated groups in the GO ECC and the specific area in the rGO ECC. These results offer an interesting insight into the type of carbonaceous support used for graphene derivative electrode materials in ECCs together with Co3O4 loading to improve capacitance performance in terms of specific energy density and specific power.
The authors have prepared organized assemblies of a hemoglobin-chitosan(CS)@Fe3O4 composite on glassy carbon electrodes (GCEs) via three strategies with the aim of preparing tunable Hb-coated GCEs with good stability and long-term oxygen storage capability. The formation and morphology of the Hb-CS@Fe3O4 composite was characterized by scanning electrochemical microscopy, XRD and UV–vis spectroscopy. It is shown that Hb is fully integrated into the CS@Fe3O4 and can be manipulated by a magnetic field whilst maintaining its biological activity. In the absence of oxygen, a surface-controlled electrode process occurs with an interfacial electron transfer rate (ks) of 2.14 s?1. The modified GCE also has a favorable oxygen storage lifetime (almost 6 h). One Hb-CS@Fe3O4 film on the electrode displays particularly good electrocatalytic reduction activity towards oxygen. The linear range for detection of O2 is 1.2?×?10?7?~?2.0?×?10?4 mol L?1 with a detection limit of 4.0?×?10?8 mol L?1. In our opinion, this method has great potential in terms of enhanced oxygen storage capability of Hb, which can be applied in special situations such as space operations, down hole mining, mountaineering and diving.
Graphical Abstract Hb-CS@Fe3O4 composites were prepared by three strategies, and oxygen carrying capability was studied. The corresponding modified electrode constructed on the basis of the magnetic field environment was superior in terms of stability, sensitivity and O2 storage time, showing wider linear range and lower detection limit.
A porous, hollow, microspherical composite of Li2MnO3 and LiMn1/3Co1/3Ni1/3O2 (composition: Li1.2Mn0.53Ni0.13Co0.13O2) was prepared using hollow MnO2 as the sacrificial template. The resulting composite was found to be mesoporous; its pores were about 20 nm in diameter. It also delivered a reversible discharge capacity value of 220 mAh g?1 at a specific current of 25 mA g?1 with excellent cycling stability and a high rate capability. A discharge capacity of 100 mAh g?1 was obtained for this composite at a specific current of 1000 mA g?1. The high rate capability of this hollow microspherical composite can be attributed to its porous nature.
The authors report on the preparation of a hollow-structured cobalt ferrite (CoFe2O4) nanocomposite for use in a non-enzymatic sensor for hydrogen peroxide (H2O2). Silica (SiO2) nanoparticles were exploited as template for the deposition of Fe3O4/CoFe2O4 nanosheets, which was followed by the removal of SiO2 template under mild conditions. This leads to the formation of hollow-structured Fe3O4/CoFe2O4 interconnected nanosheets with cubic spinel structure of high crystallinity. The material was placed on a glassy carbon electrode where it acts as a viable sensor for non-enzymatic determination of H2O2. Operated at a potential of ?0.45 V vs. Ag/AgCl in 0.1 M NaOH solution, the modified GCE has a sensitivity of 17 nA μM?1 cm?2, a linear response in the range of 10 to 1200 μM H2O2 concentration range, and a 2.5 μM detection limit. The sensor is reproducible and stable and was applied to the analysis of spiked urine samples, where it provided excellent recoveries.
Graphical abstract Schematic of a cobalt ferrite (CoFe2O4) hollow structure for use in electrochemical determination of H2O2. The sensor shows a low detection limit, a wide linear range, and excellent selectivity for H2O2.
A series of Ni0.37Co0.63S2-reduced graphene oxide nanocomposites with different graphene contents (NCS@rGO-x) has been successfully prepared via a facile one-step hydrothermal method and applied as the catalysts for the oxygen evolution reaction (OER) and degradation of organic pollutants. The XRD and FESEM analyses revealed that the phase structure and morphology of NCS nanoparticles were substantially influenced by the graphene contents. The phase structure of NCS nanoparticles gradually transformed from primary NiCo2S4 to Ni0.37Co0.63S2 and the morphology and size of NCS nanoparticles were found to become more regular and homogeneous with the increase of graphene concentration. On the NCS@rGO-x nanocomposites, the NCS@rGO-2 sample demonstrated the best catalytic activity toward the OER, which delivers a stable current density of 10 mA cm?2 at a small overpotential of ～276 mV (vs. RHE) with a Tafel slope as low as 48 mV dec?1. Furthermore, the NCS@rGO-2 sample showed the remarkable photocatalytic activity for degradation of methylene blue (MB), which may be attributed to the increased reaction sites and high separation efficiency of photogenerated charge carries due to the electronic interaction between NCS nanoparticles and rGO. All these impressive performances indicate that the NCS@rGO-2 nanocomposite is a promising catalyst in energy and environmental fields.
Graphical abstract A series of Ni0.37Co0.63S2-reduced graphene oxide nanocomposites with different graphene contents has been successfully prepared and applied as the catalysts for the oxygen evolution reaction (OER) and degradation of organic pollutants. The NCS@rGO-2 catalyst-modified stainless steel wire mesh (SSWM) electrode delivers a stable current density of 10 mA cm?2 at a small overpotential of ～276 mV (vs. RHE) with a Tafel slope as low as 48 mV dec?1. At the same time, the NCS@rGO-2 catalyst is also first investigated as an efficient photocatalyst for degradation of MB.
There is a growing need for the electrode with high mass loading of active materials, where both high energy and high power densities are required, in current and near-future applications of supercapacitor. Here, an ultrathin Co3S4 nanosheet decorated electrode (denoted as Co3S4/NF) with mass loading of 6 mg cm?2 is successfully fabricated by using highly dispersive Co3O4 nanowires on Ni foam (NF) as template. The nanosheets contained lots of about 3～5 nm micropores benefiting for the electrochemical reaction and assembled into a three-dimensional, honeycomb-like network with 0.5～1 μm mesopore structure for promoting specific surface area of electrode. The improved electrochemical performance was achieved, including an excellent cycliability of 10,000 cycles at 10 A g?1 and large specific capacitances of 2415 and 1152 F g?1 at 1 and 20 A g?1, respectively. Impressively, the asymmetric supercapacitor assembled with the activated carbon (AC) and Co3S4/NF electrode exhibits a high energy density of 79 Wh kg?1 at a power density of 151 W kg?1, a high power density of 3000 W kg?1 at energy density of 30 Wh kg?1 and 73 % retention of the initial capacitance after 10,000 charge-discharge cycles at 2 A g?1. More importantly, the formation process of the ultrathin Co3S4 nanosheets upon reaction time is investigated, which is benefited from the gradual infiltration of sulfide ions and the template function of ultrafine Co3O4 nanowires in the anion-exchange reaction.
Graphical abstract The ultrathin 2D Co3S4 nanosheets fabricated on 3D Ni foam and the formation process of the ultrathin Co3S4 nanosheets upon reaction times has been investigated. At the same time, the Co3S4/NF electrode displays an outstanding specific capacitance of 2420 F g?1 at 1 A g?1 with high mass loading of 6 mg cm?2.
The three-dimensional porous Li3V2(PO4)3/nitrogen-doped reduced graphene oxide (LVP/N-RGO) composite was prepared by a facile one-pot hydrothermal method and evaluated as cathode material for lithium-ion batteries. It is clearly seen that the novel porous structure of the as-prepared LVP/N-RGO significantly facilitates electron transfer and lithium-ion diffusion, as well as markedly restrains the agglomeration of Li3V2(PO4)3 (LVP) nanoparticles. The introduction of N atom also has positive influence on the conductivity of RGO, which improves the kinetics of electrochemical reaction during the charge and discharge cycles. It can be found that the resultant LVP/N-RGO composite exhibits superior rate properties (92 mA h g?1 at 30 C) and outstanding cycle performance (122 mA h g?1 after 300 cycles at 5 C), indicating that nitrogen-doped RGO could be used to improve the electrochemical properties of LVP cathodes for high-power lithium-ion battery application.
Graphical abstract The three-dimensional porous Li3V2(PO4)3/nitrogen-doped reduced graphene oxide composite with significantly accelerating electron transfer and lithium-ion diffusion exhibits superior rate property and outstanding cycle performance.
A composite material obtained by ultrasonication of graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) was loaded with manganese dioxide (MnO2), poly(diallyldimethylammonium chloride) and gold nanoparticles (AuNPs), and the resulting multilayer hybrid films were deposited on a glassy carbon electrode (GCE). The microstructure, composition and electrochemical behavior of the composite and the modified GCE were characterized by transmission electron microscopy, Raman spectra, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The electrode induces efficient electrocatalytic oxidation of dopamine at a rather low working voltage of 0.22 V (vs. SCE) at neutral pH values. The response is linear in the 0.5 μM to 2.5 mM concentration range, the sensitivity is 233.4 μA·mM￣1·cm￣2, and the detection limit is 0.17 μM at an SNR of 3. The sensor is well reproducible and stable. It displays high selectivity over ascorbic acid, uric acid and glucose even if these are present in comparable concentrations.
Graphical abstract Gold nanoparticles were self-assembled onto the surface of the MnO2 decorated graphene oxide-carbon nanotubes composites with poly(diallyldimethylammonium chloride) (PDDA) as a coupling agent. Further, a sensitive electrochemical sensor of dopamine was developed via immobilizing this nanocomposite on a glassy carbon electrode (GCE).
In this work, Bi3.64Mo0.36O6.55 nanoparticles (NPs) were successfully prepared by a facile hydrothermal method and utilized in pseudocapacitor for the first time. Within a redox potential range from ?1.0 to 0 V vs. Hg/HgO in a 1 M aqueous KOH solution by cyclic voltammetry (CV), chronopotentiometry (CP) and AC impendence, the specific capacitance could reach 998 F g?1 at 1 A g?1, which is possibly ascribed to the higher Bi content of Bi3.64Mo0.36O6.55 NPs. Furthermore, the Bi3.64Mo0.36O6.55 NP electrode exhibited good cycle stability maintaining over 85 % after 5000 cycles. These results demonstrated Bi3.64Mo0.36O6.55 NPs might be a promising electrode material for pseudocapacitor.
Graphical abstract The fabrication of uniform Bi3.64Mo0.36O6.55 nanoparticles with a diameter of 100 nm were succefully reported by a facial hydrothermal method, which exhibits a extraordinary electronic performance with 998 F g-1 at 1 A g-1 and cycling stability
In this paper, the LiNi0.5Mn1.5O4 cathode materials of lithium-ion batteries are synthesized by a co-precipitation spray-drying and calcining process. The use of a spray-drying process to form particles, followed by a calcination treatment at the optimized temperature of 750 °C to produce spherical LiNi0.5Mn1.5O4 particles with a cubic crystal structure, a specific surface area of 60.1 m2 g?1, a tap density of 1.15 g mL?1, and a specific capacity of 132.9 mAh g?1 at 0.1 C. The carbon nanofragment (CNF) additives, introduced into the spheres during the co-precipitation spray-drying period, greatly enhance the rate performance and cycling stability of LiNi0.5Mn1.5O4. The sample with 1.0 wt.% CNF calcined at 750 °C exhibits a maximum capacity of 131.7 mAh g?1 at 0.5 C and a capacity retention of 98.9% after 100 cycles. In addition, compared to the LiNi0.5Mn1.5O4 material without CNF, the LiNi0.5Mn1.5O4 with CNF demonstrates a high-rate capacity retention that increases from 69.1% to 95.2% after 100 cycles at 10 C, indicating an excellent rate capability. The usage of CNF and the synthetic method provide a promising choice for the synthesis of a stabilized LiNi0.5Mn1.5O4 cathode material.
Graphical Abstract Micro/nanostructured LiNi0.5Mn0.5O4 cathode materials with enhanced electrochemical performances for high voltage lithium-ion batteries are synthesized by a co-precipitation spray-drying and calcining routine and using carbon nanofragments (CNFs) as additive.
The authors describe an electrochemical approach for the preparation of a glassy carbon electrode (GCE) modified with graphene oxide and silver nanodentrites (AgNDs). The coating was obtained by using an aqueous solution containing silver nitrate, phosphate and ammonia. The phosphate anions act as a scaffold for the improved deposition of AgNDs. The effects of deposition potential and time and concentration of electrolyte on the formation of the AgNDs were optimized. The modified GCE displays good electrocatalytic activity towards the oxidation of dissolved hydrazine. The electron transfer coefficient and diffusion coefficient are 0.60 and 4.64 × 10?5 cm2 s?1 respectively. The electrode exhibits a linear response over the 100 nM to 670 μM hydrazine concentration range and a detection limit (LOD) of 33 nM. The sensitivity of the modified electrode is 2077 μA mM?1 cm?2 at a typical working voltage of 0.1 V (vs Ag/AgCl). This LOD is much lower than that of the allowable concentration of hydrazine in drinking water as defined by the US EPA and the WHO.
Graphical abstract Schematic of the 2-step fabrication of a glassy carbon electrode (GCE) modified with graphene oxide (GO) and silver nanodendrites (AgND) for use in a hydrazine sensor. First, Ag3PO4 is formed by adding AgNO3 and phosphate. Secondly, the formed Ag3PO4 is converted to a colorless complex by adding ammonia and by electrolytic growth of AgND on the GO/GCE.
Tungsten disulfide (WS2) nanosheets were obtained by exfoliating WS2 bulk crystals in N-methylpyrrolidone by ultrasonication. Gold nanoparticles (GNPs) were synthesized by in-situ ultrasonication of sodium citrate and HAuCl4 while fabricating the WS2 nanosheets. In this way, the GNPs were self-assembled on WS2 nanosheets to form a GNPs/WS2 nanocomposite through interaction between sulfur and gold atoms. The photoelectrochemical response of WS2 nanosheets is significantly enhanced after integration of the GNPs. The GNPs/WS2 nanocomposite was coated onto a glassy carbon electrode (GCE) to construct a sensing interface which then was modified with an antibody against the carcinoembryonic antigen (CEA) to obtain a photoelectrochemical immunosensor for CEA. Under optimized conditions, the decline in relative photocurrent is linearly related to the logarithm of the CEA concentration in the range from 0.001 to 40 ng mL?1. The detection limit is 0.5 pg mL?1 (at S/N =?3). The assay is sensitive, selective, stable and reproducible. It was applied to the determination of CEA in clinical serum samples.
Graphical abstract Schematic presentation of the fabrication of Au/WS2 nanocomposites by in-situ ultrasonication and the procedure for the CEA photoelectrochemical immunosensor preparation, and the photocurrent response towards the carcinoembryonic antigen.
We describe an amperometric sensor for nitrite that is based on a glassy carbon electrode modified with a 3-dimensional network consisting of Ni7S6 and multi-walled carbon nanotubes. The nickel sulfide was prepared by a hydrothermal method starting from nickel chloride and thiourea. The morphology and catalytic properties of the sensor material were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, cyclic and linear sweep voltammetry, electrochemical impedance spectroscopy, and chronoamperometry. The results showed the Ni7S6/MWCNTs to possess improved catalytic activity towards the oxidation of nitrite when compared to plain Ni7S6. The sensor is best operated at 0.425 V (vs. Ag/AgCl) in 0.1 M NaOH solution where it shows a linear response in the 1.0 μM to 4.2 mM nitrite concentration range, with a sensitivity as high as 185.0 μA·mM?1·cm?2 and a 0.3 μM detection limit (at a signal-to-noise ratio of 3). These features are mainly attributed to the large specific surface area of Ni7S6, the good electrical conductivity of the MWCNTs, and the synergy between Ni7S6 and the MWCNTs. The method was applied to the determination of nitrite in (spiked) water samples where it gave recoveries that ranged between 98.6 and 100.1 %.
Graphical abstract Ni7S6 was synthesized by a hydrothermal method. The sensor based on Ni7S6/MWCNTs is best operated at 0.425 V (vs. Ag/AgCl), where it shows a linear response in the 1.0 μM - 4.2 mM nitrite concentration range, with a sensitivity as high as 185.0 μA·mM￣1·cm￣2 and a 0.3 μM detection limit. SC(NH2)2: thiourea; EA: ethanolamine; MWCNTs: multi-walled carbon nanotubes
A nanocomposite consisting of cetyltrimethylammonium bromide (CTAB), Fe3O4 nanoparticles and reduced graphene oxide (CTAB-Fe3O4-rGO) was prepared, characterized, and used to modify the surface of a glassy carbon electrode (GCE). The voltammetric response of the modified GCE to 4-nonylphenol (NPh) was investigated by cyclic voltammetry and revealed a strong peak at around 0.57 V (vs. SCE). Under optimum conditions, the calibration plot is linear in the ranges from 0.03 to 7.0 μM and from 7.0 to 15.0 μM, with a 8 nM detection limit which is lower that that of many other methods. The modified electrode has excellent fabrication reproducibility and was applied to the determination of NPh in spiked real water samples to give recoveries (at a spiking level of 1 μM) between 102.1 and 99.1%.
Graphical abstract A nanocomposite consisting of cetyltrimethylammonium bromide (CTAB), Fe3O4 nanoparticles and reduced graphene oxide (CTAB-Fe3O4-rGO) was prepared and used to modify the surface of a glassy carbon electrode (GCE) for the differential pulse voltammetric (DPV) determination of 4-nonylphenol (NPh).
