Fabrication of Electrochemical Sensor Based on CeO2−SnO2 Nanocomposite Loaded on Pd Support for Determination of Nitrite at Trace Levels

Here, an electrochemical sensor based on CeO₂‐SnO₂/Pd was prepared and used for highly selective and sensitive determination of nitrite in some real samples. This nanocomposite was characterized by various methods like X‐ray photoelectron spectroscopy, X‐ray diffraction, energy dispersive spectroscopy, Fourier‐transform infrared spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The electrochemical behavior of the sensor was evaluated by cyclic voltammetry. The results showed excellent catalytic property of the nanocomposite as a an electrocatalyst for nitrite oxidation. In the following, the experimental parameters affecting the analytical signal for nitrite were optimized. Under the optimal conditions, the limit of detection and sensitivity of the sensor were calculated as 0.10 μM and 652.95 μA.mM^?1.cm^?2, respectively. Also, the response of the sensor was linear in the range of 0.36 to 2200 μM of nitrite. Finally, some of the inherent features of the sensor such as repeatability, reproducibility and stability were examined after evaluation of the sensor selectivity in the presence of several interfering species.     

Synthesis and Electronic/ionic Transport Properties of MoO2/rGO Anode for Lithium Ion Batteries

MoO₂/rGO (reduced graphite oxide) composites have been synthesized by hydrothermal method followed by anneal and characterized by X‐ray diffraction (XRD) and scanning electron microscope (SEM). Galvanostatic charge/discharge testing and electrochemical impedance spectroscopy (EIS) techniques are employed to evaluate the kinetic behaviors of the MoO₂/rGO during lithiation/delithiation. The obtained MoO₂‐based materials have monoclinic crystal structure, and worm like shape with average dimensions of 100‐200 nm width and 500 nm‐1 μm length. There are two steps of lithium ion intercalation/de‐intercalation for the MoO₂/rGO anode at the potential ranging from 1.0 to 3.5 V, locating at E_Li/Li⁺ = 1.60/1.75 V, 1.25/1.40 V, and the first discharge and charge capacities are, respectively, 221.0 and 185.4 mAh g^?1. The resistances of R_SEI and R_CT for the MoO₂/rGO anode are 2‐4 Ω and below 5 Ω. Moreover, the lithium diffusion coefficient calculated from the EIS measurement is about 3.6×10^?9 cm² s^?1.     

Dual‐Doped Molybdenum Trioxide Nanowires: A Bifunctional Anode for Fiber‐Shaped Asymmetric Supercapacitors and Microbial Fuel Cells

A novel in situ N and low‐valence‐state Mo dual doping strategy was employed to significantly improve the conductivity, active‐site accessibility, and electrochemical stability of MoO₃, drastically boosting its electrochemical properties. Consequently, our optimized N‐MoO_3?x nanowires exhibited exceptional performances as a bifunctional anode material for both fiber‐shaped asymmetric supercapacitors (ASCs) and microbial fuel cells (MFCs). The flexible fiber‐shaped ASC and MFC device based on the N‐MoO_3?x anode could deliver an unprecedentedly high energy density of 2.29 mWh cm^?3 and a remarkable power density of 0.76 μW cm^?1, respectively. Such a bifunctional fiber‐shaped N‐MoO_3?x electrode opens the way to integrate the electricity generation and storage for self‐powered sources.     

Electrochemical Probe of the Reduced Graphene Oxide Modified by Bare Gold Nanoparticles Functionalized Zr(IV)-based Metal-organic Framework for Detecting Nitrite

Widely presented nitrite in drinking water, food and even physiological system endangers human health. Here,bare gold nanoparticles functionalized Zr-based metal-organic framework modified reduced graphene oxide (GNPs/UiO-66-NH₂/rGO) nanocomposites were prepared by hydrothermal method. This experiment studies the morphology, composition, structure and electrochemical behavior of the sensor. The experimental results show that the sensor has a peak potential of 0.9 V, the concentration range of NO₂⁻ is 5.0 μM to 768 μM, the linear regression equation of the calibration curve is I_pa=0.3646+0.00642 C (R²=0.9998), and the LOD is as low as 3.7 μM (S/N=3). Therefore, an electrochemical sensor platform for trace detection of NO₂⁻ was successfully constructed.     

Detection of Dexamethasone Sodium Phosphate in Blood Plasma: Application of Hematite in Electrochemical Sensors

We studied sensor application of a graphene oxide and hematite (α‐Fe₂O₃/GO) composite electrode well‐characterized by the SEM and XRD. Through differential pulse voltammetry (DPV), oxidation of dexamethasone sodium phosphate (DSP) was studied at the surface of a glassy carbon electrode (GCE) modified with graphene oxide nanosheets (GO) and the α‐Fe₂O₃/GO composite. The values of the transfer coefficient (α) and the diffusion coefficient (D) of DSP were 0.5961 and 4.71×10^?5 cm² s^?1 respectively. In the linear range of 0.1–50 μM, the detection limit (DL) was 0.076 μM. In the second step, a GCE was modified with α‐Fe₂O₃/GO composite and the DSP measurement step was repeated to analyzed and compare the effects of hematite nanoparticles present on graphene oxide surfaces. According to the results, α and D were 0.52 and 2.406×10^?4 cm² s^?1 respectively and the DL was 0.046 μM in the linear range of 0.1–10.0 μM. The sensor is simple, inexpensive and uses blood serum.     

A Novel Cerium Tungstate Nanosheets Modified Electrode for the Effective Electrochemical Detection of Carcinogenic Nitrite Ions

In this present scenario, for the first time, we propose a facile and simple wet chemical approach for the fabrication of two‐dimensional (2D) cerium tungstate (CeW₂O₉;CeW) nanosheets and evaluated as an electrochemical sensor for the detection of nitrite ions. The successful formation of CeW₂O₉ nanosheets was confirmed by various physicochemical techniques such as X‐ray diffraction, Fourier transform infrared spectroscopy, Raman, Scanning electron microscope, Transmission electron microscope and Energy dispersive X‐ray studies. The electrochemical properties of the CeW nanosheets were studied by using cyclic voltammograms (CV) and chronoamperometric techniques. As an electrochemical sensor, the CeW nanosheets modified glassy carbon electrode (GCE) showed superior electrocatalytic activity in the oxidation of nitrite in terms of higher anodic peak current and lower oxidation potential when compared with unmodified GCE. CeW nanosheets based electrochemical sensor has been fabricated which detect nitrite in wide linear response range, good sensitivity and very low detection limit of 0.02–986 μM, 2.85 μA μM⁻¹ cm⁻² and 8 nM, respectively. Moreover, the CeW nanosheets modified GCE exhibited excellent selectivity even in the presence of common metal ions and biologically co‐interfering compounds. For the practical viability of the prepared amperometric sensor has been utilized in various water samples such as tap, lake and drinking water and the obtained recoveries are appreciable.     

Electrocatalytical Oxidation of Nitrite and Its Determination Based on Au@Fe3O4 Nanoparticles

A promising electrochemical nitrite sensor was fabricated by immobilizing Au@Fe₃O₄ nanoparticles on the surface of L ‐cysteine modified glassy carbon electrode, which was characterized by scanning electron microscopy, X‐ray photoelectron spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The proposed sensor exhibited excellent electrocatalytic activity toward nitrite oxidation. The kinetic parameters of the electrode reaction process were calculated, (1–α)n_α was 0.38 and the heterogeneous electron transfer coefficient (k) was 0.13 cm s^?1. The detection conditions such as supporting electrolyte and pH value were optimized. Under the optimized conditions, the linear range for the determination of nitrite was 3.6×10^?6 to 1.0×10^?2 M with a detection limit of 8.2×10^?7 M (S/N=3). Moreover, the as‐prepared electrode displayed good stability, repeatability and selectivity for promising practical applications.     

Synthesis of Tri‐functional Core‐shell CuO@carbon Quantum Dots@carbon Hollow Nanospheres Heterostructure for Non‐enzymatic H2O2 Sensing and Overall Water Splitting Applications

A core‐shell structure with CuO core and carbon quantum dots (CQDs) and carbon hollow nanospheres (CHNS) shell was prepared through facile in‐situ hydrothermal process. The composite was used for non‐enzymatic hydrogen peroxide sensing and electrochemical overall water splitting. The core‐shell structure was established from the transmission electron microscopy image analysis. Raman and UV‐Vis spectroscopy analysis confirmed the interaction between CuO and CQDs. The electrochemical studies showed the limit of detection and sensitivity of the prepared composite as 2.4 nM and 56.72 μA μM^?1 cm^?2, respectively. The core‐shell structure facilitated better charge transportation which in turn exhibited elevated electro‐catalysis towards hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and overall water splitting. The overpotential of 159 mV was required to achieve 10 mA cm^?2 current density for HER and an overpotential of 322 mV was required to achieve 10 mA cm^?2 current density for OER in 1.0 M KOH. A two‐electrode system was constructed for overall water splitting reaction, which showed 10 and 50 mA cm^?2 current density at 1.83 and 1.96 V, respectively. The prepared CuO@CQDs@CHNS catalyst demonstrated excellent robustness in HER and OER catalyzing condition along with overall water splitting reaction. Therefore, the CuO@CQDs@CHNS could be considered as promising electro‐catalyst for H₂O₂ sensing, HER, OER and overall water splitting.     

A MnOOH‐Polyaniline Nanocomposite Modified Gold Electrode for Electrochemical Sensing of Nitrite

A novel non‐enzymatic nitrite sensor was fabricated by immobilizing MnOOH‐PANI nanocomposites on a gold electrode (Au electrode). The morphology and composition of the nanocomposites were investigated by transmission electron microscopy (TEM ) and Fourier transform infrared spectrum (FTIR ). The electrochemical results showed that the sensor possessed excellent electrocatalytic ability for NO₂⁻ oxidation. The sensor displayed a linear range from 3.0 μmol•L⁻¹ to 76.0 mmol•L⁻¹ with a detection limit of 0.9 μmol•L⁻¹ (S/N = 3), a sensitivity of 132.2 μA •L•mol⁻¹•cm⁻² and a response time of 3 s. Furthermore, the sensor showed good reproducibility and long‐term stability. It is expected that the MnOOH‐PANI nanocomposites could be applied for more active sensors and used in practice for nitrite sensing.     

Synthesis of Ferrocene Based Naphthoquinones and its Application as Novel Non‐enzymatic Hydrogen Peroxide

At present, a highly sensitive hydrogen peroxide (H₂O₂) sensor is fabricated by ferrocene based naphthaquinone derivatives as 2,3‐Diferrocenyl‐1,4‐naphthoquinone and 2‐bromo‐3‐ferrocenyl‐1,4‐naphthoquinone. These ferrocene based naphthaquinone derivatives are characterized by H‐NMR and C‐NMR. The electrochemical properties of these ferrocene based naphthaquinone are investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) on modified glassy carbon electrode (GCE). The modified electrode with ferrocene based naphthaquinone derivatives exhibits an improved voltammetric response to the H₂O₂ redox reaction. 2‐bromo‐3‐ferrocenyl‐1,4‐naphthoquinone show excellent non‐enzymatic sensing ability towards H₂O₂ response with a detection limitation of 2.7 μmol/L a wide detection range from 10 μM to 400 μM in H₂O₂ detection. The sensor also exhibits short response time (1 s) and good sensitivity of 71.4 μA mM^?1 cm^?2 and stability. Furthermore, the DPV method exhibited very high sensitivity (18999 μA mM^?1 cm^?2) and low detection limit (0.66 μM) compared to the CA method. Ferrocene based naphthaquinone derivative based sensors have a lower cost and high stability. Thus, this novel non‐enzyme sensor has potential application in H₂O₂ detection.     

Micelle‐Directing Synthesis of Ag‐Doped WO3 and MoO3 Composites for Photocatalytic Water Oxidation and Organic‐Dye Adsorption

In this paper, an Ag‐doped WO₃ (and MoO₃) composite has been prepared by following a simple micelle‐directed method and high‐temperature sintering route. The as‐prepared samples were characterized by X‐ray diffraction, inductively coupled plasma, transmission electron microscopy, X‐ray photoelectron spectroscopy, UV/Vis diffuse reflectance spectroscopy, Brunauer–Emmett–Teller, photoluminescence spectroscopy, and electrochemical impedance spectroscopy techniques. The photocatalytic experiments reveal that their oxygen‐production rates are up to 95.43 μmol (75.45 μmol) for Ag‐doped WO₃ (MoO₃), which is 9.5 (7.3) times higher than that of pure WO₃: 9.012 μmol (MoO₃: 9.00 μmol) under visible‐light illumination (λ ≥420 nm), respectively. The improvement of their photocatalytic activity is attributed to the enhancement of their visible‐light absorption and the separation efficiency of photogenerated carriers by Ag doping. Moreover, Ag‐doped WO₃ (MoO₃) also shows excellent adsorption of rhodamine B (RhB) and methylene blue (MB) in aqueous solution, with maximum adsorption capacities towards RhB and MB of 822 and 820 mg g⁻¹ for Ag‐doped WO₃, and 642 and 805 mg g⁻¹ for Ag‐doped MoO₃, respectively.     

A Nitrite Biosensor Based on Coimmobilization of Nitrite Reductase and Viologen‐Modified Polysiloxane on Glassy Carbon Electrode

Copper containing nitrite reductase (Cu‐NiR) and viologen‐modified sulfonated polyaminopropylsiloxane (PAPS‐SO₃H‐V) were co‐immobilized on glassy carbon electrode (GCE) by hydrophilic polyurethane (HPU) drop‐coating, and the electrode was tested as a reagentless electrochemical biosensor for nitrite detection. The newly synthesized PAPS‐SO₃H‐V as an electron transfer (ET) mediator between electrode and NiR was effective, and could be effectively immobilized in HPU membrane. The NiR and PAPS‐SO₃H‐V co‐immobilized GCE used as a nitrite biosensor showed the following performance factors: sensitivity=12.0 nA μM^?1, limit of detection (LOD)=60 nM (S/N=3), linear response range=0–18 μM (r²=0.996) and response time (t_90%)=60 s, respectively. Lineweaver–Burk plot shows that apparent Michaelis–Menten constant (K is 101 μM. Storage stability of the sensor is 51 days (80% of initial activity) in condition of storing in ambient air at room temperature. The sensor showed a relative standard deviation (RSD) of 3.2% (n=5) even in condition of injection of 1 μM nitrite. Interference study showed that common anions in water sample such as chlorate, chloride, sulfate and sulfite do not interfere with the nitrite detection. However, nitrate interfered with a relative sensitivity of 80% due to inherent character of the enzyme used.     

Disposable Screen‐Printed Edge Band Ultramicroelectrodes for Use as Nitric Oxide Gas Sensor in Designing an Easily Applicable Method for Real Sample Analysis of Nitrite with Superior Selectivity and Sensitivity

We report here an easily applicable method for the quantification of nitrite (NO₂^?) in real samples. This approach simplified the two steps of sample preparation and detection into a 2‐in‐1 single step process. Samples were digested in sulfuric acid and the as‐generated nitric oxide (NO) was detected by an electrochemical sensor in the gas phase. It eliminated almost all of the interferents in the solution phase and hence resulted in a highly selective determination of nitrite suitable for food samples with complicated matrix. We successfully demonstrated the determination of nitrite in sausage and vegetables and further validated the results with an AOAC official reference method.     

Core–Shell α‐Fe2O3@α‐MoO3 Nanorods as Lithium‐Ion Battery Anodes with Extremely High Capacity and Cyclability

α‐Fe₂O₃ nanoparticles are uniformly coated on the surface of α‐MoO₃ nanorods through a two‐step hydrothermal synthesis method. As the anode of a lithium‐ion battery, α‐Fe₂O₃@α‐MoO₃ core–shell nanorods exhibit extremely high lithium‐storage performance. At a rate of 0.1 C (10 h per half cycle), the reversible capacity of α‐Fe₂O₃@α‐MoO₃ core–shell nanorods is 1481 mA h g^?1 and a value of 1281 mA h g^?1 is retained after 50 cycles, which is much higher than that retained by bare α‐MoO₃ and α‐Fe₂O₃ and higher than traditional theoretical results. Such a good performance can be attributed to the synergistic effect between α‐Fe₂O₃ and α‐MoO₃, the small size effect, one‐dimensional nanostructures, short paths for lithium diffusion, and interface spaces. Our results reveal that core–shell nanocomposites have potential applications as high‐performance lithium‐ion batteries.     

Electrochemical Detection of Nitrite in Meat and Water Samples Using a Mesoporous Carbon Ceramic SiO2/C Electrode Modified with In Situ Generated Manganese(II) Phthalocyanine

Mesoporous carbon ceramic SiO₂/50 wt % C (S_BET=170 m² g^?1), where C is graphite, were prepared by the sol‐gel method. The materials were characterized using N₂ sorption isotherms, scanning electron microscopy, and conductivity measurements. The matrix was used as support for the in situ immobilization of Mn(II) phthalocyanine (MnPc) on their surface. XPS was used to determine the Mn/Si atomic ratios of the MnPc‐modified materials. Pressed disk electrodes were prepared with the MnPc‐modified matrix, and tested as an electrochemical sensor for nitrite oxidation. The linear response range, sensitivity, detection limit and quantification limit were 0.79–15.74 µmol L^?1, 17.31 µA L µmol^?1, 0.02 µmol L^?1 and 0.79 µmol L^?1, respectively, obtained using cyclic voltammetry. The repeatability of the proposed sensor, evaluated in terms of relative standard deviation was 1.7 % for 10 measurements of a solution of 12.63 µmol L^?1 nitrite. The sensor employed to determine nitrite in sausage meat, river and lake water samples showed to be a promising tool for this purpose.     

Novel Nonenzymatic Hydrogen Peroxide Sensor Based on Ag/Cu2O Nanocomposites

The nanocomposites of Ag nanoparticles supported on Cu₂O were prepared and used for fabricating a novel nonenzymatic H₂O₂ sensor. The morphology and composition of the nanocomposites were characterized using the scanning electron microscope (SEM), transmission electron microscope (TEM), energy‐dispersive X‐ray spectrum (EDX) and X‐ray diffraction spectrum (XRD). The electrochemical investigations indicate that the sensor possesses an excellent performance toward H₂O₂. The linear range is estimated to be from 2.0 μM to 13.0 mM with a sensitivity of 88.9 μA mM^?1 cm^?2, a response time of 3 s and a low detection limit of 0.7 μM at a signal‐to‐noise ratio of 3. Additionally, the sensor exhibits good anti‐interference.     

Molybdenum‐tungsten Oxide Nanowires Rich in Oxygen Vacancies as An Advanced Electrocatalyst for Hydrogen Evolution

Electrolysis of water is a promising way to produce hydrogen fuel in large scale. The commercialization of this technology requires highly efficient non‐noble metal electrocatalysts to decease the energy input for the hydrogen evolution reaction (HER). In this work, a novel nanowire structured molybdenum‐tungsten bimetallic oxide (CTAB‐D‐W₄MoO₃) is synthesized by a simple hydrothermal method followed with post annealing treatment. The obtained metal oxides feature with enhanced conductivity, rich oxygen vacancies and customized electronic structure. As such, the composite electrocatalyst exhibits excellent electrocatalytic performance for HER in an acidic environment, achieving a large current density of 100 mA cm^?2 at overpotential of only 286 mV and a small Tafel slope of 71.2 mV dec^?1. The excellent electrocatalytic HER performance of CTAB‐D‐W₄MoO₃ is attributed to the unique nanowire structure, rich catalytic active sites and promoted electron transfer rate.     

Self‐Assembled Prussian Blue Nanoparticles Based Electrochemical Sensor for High Sensitive Determination of H2O2 in Acidic Media

In this paper, self‐assembled Prussian blue nanoparticles (PBNPs) on carbon ceramic electrode (CCE) were developed as a high sensitive hydrogen peroxide (H₂O₂) electrochemical sensor. The PBNPs film was prepared by a simple dipping method. The morphology of the PBNPs‐modified CCE was characterized by scanning electron microscopy (SEM). The self‐assembled PB film exhibited sufficient mechanical, electrochemical stability and high sensitivity in compare with other PB based H₂O₂ sensors. The sensor showed a good linear response for H₂O₂ over the concentration range 1 μM–0.26 mM with a detection limit of ca. 0.7 μM (S/N=3), and sensitivity of 754.6 mA M^?1 cm^?2. This work demonstrates the feasibility of self‐assembled PBNPs‐modified CCE for practical sensing applications.     

Poly(Taurine‐Glutathione)/Carbon Nanotube Modified Glassy Carbon Electrode as a New Levofloxacin Sensor

A new highly sensitive and selective electrochemical levofloxacin sensor based on co‐polymer‐carbon nanotube composite electrode was developed. Taurine and Glutathione were electrochemically co‐polymerized on multiwalled carbon nanotubes modified glassy carbon electrode (Poly(TAU‐GSH)/CNT/GCE) and used as a levofloxacin sensor in pH 6 phosphate buffer solution. The new composite electrode surfaces were characterized by scanning electron microscopy, atomic force microscopy and electrochemical impedance spectroscopy. Under the optimized conditions, two linear segments were obtained for increasing LEV concentrations between 20 nmol L^?1‐1 μmol L^?1 and 1.5 μmol L^?1‐55 μmol L^?1 LEV with a detection limit of 9 nmol L^?1 using amperometry. Poly(TAU‐GSH)/CNT/GCE exhibited high sensitivity, selectivity with good stability. The new sensor was employed for real samples of LEV tablets and urine. Promising results were obtained with good accuracy which were also in accordance with LC‐MS/MS analysis.