Modified Electrode Material Research Articles

A simple electrochemical sensor based on rGO/MoS2/CS modified GCE for highly sensitive detection of Pb(ii) in tobacco leaves.

High-performance electrode modification materials play a crucial role in improving the sensitivity of sensor detection in electrochemical determination of heavy metals. In this study, a rGO/MoS2/CS nanocomposite modified glassy carbon electrode (GCE) was used to construct a sensitive sensor for detecting lead ions in tobacco leaves. The reduced graphene oxide (rGO) was used to increase the conductivity of the sensor, and the nano-flowered MoS2 could provide a large reaction specific surface area and a certain active site for heavy metal reaction. Chitosan (CS) was used to improve the enrichment ability of heavy metals and increase the electrocatalytic activity of electrode. Thus, an electrochemical sensor with excellent performance in reproducibility, stability and anti-interference ability was established. The stripping behavior of Pb(ii) and the application conditions of the sensor were studied by square wave anodic stripping voltammetry (SWASV). The investigation indicated that the sensor exhibited high detection sensitivity in the range of 0.005–0.05–2.0 μM, and the limit of detection (LOD) was 0.0016 μM. This work can provide a fast and effective method for determination of Pb(ii) in samples with low content, such as tobacco leaves.

Electrochemical sensor based on N-doped carbon dots decorated with manganese oxide nanospheres for simultaneous detection of p-aminophenol and paracetamol.

Nitrogen doped carbon dots were synthesized using the hydrothermal reaction of cellulose and urea, and then carbonized in a N2 atmosphere at a high temperature to prepare N-doped carbon dots decorated with manganese oxide nanospheres (N-CMOS) formed using cetyltrimethylammonium bromide (CTAB) and MnO. The introduction of N-CMOS resulted in a large specific surface area, abundant pores, favourable conductivity and an excellent electrocatalytic performance. A glassy carbon electrode modified with N-CMOS was used for the simultaneous identification of paracetamol (AP) and p-aminophenol (PAP) utilising differential pulse voltammetry. Under optimum conditions, the electrical sensor showed a wide linear range of 0.1-100 μM for PAP and 0.1-80 μM for AP, with detection limits of 0.0456 and 0.0303 μM (S/N = 3), respectively. The sensitivities for detecting PAP and AP were calculated as 1.615 and 1.971 μA μM-1 cm-2, respectively. The sensitivity and limit of detection (LOD) meet the requirements of detection of drug impurity limits in tablets. In addition, the sensor has been successfully applied to detect PAP and AP in paracetamol tablets. The constructed sensor not only possesses a superior repeatability, reproducibility and stability, but a relatively wide linear range, and a superior detection limit and sensitivity.

Energetic Alignment‐Related Effect on Carrier Extraction in Organic Photovoltaic Devices with Cathode Conducting Layer

The performance of organic photovoltaic (OPV) devices is strongly dependent on the electronic structure at the interface, including energetic offset induced by the electronic coupling of the materials and how the materials link to each other. Herein, the studies on modification of the interface of active layer and cathodes with insertion of carrier selective materials are reported. The thermalization of hot metal diffusion via X‐ray photoemission spectroscopy (XPS) as well as the energetic offset via ultraviolet photoemission spectroscopy (UPS) in situ is characterized. These investigations allow them to investigate the mechanisms at the interface and correlate these findings with the device performance, such as the correlation between interfacial energy band alignment and charge carrier transport, recombination, and extraction. Finally, the influence of cathode modification materials with various energetic offsets or transport behaviors on Voc and OPV performance parameters is investigated. With these studies, it is suggested that the incorporation of electrode modification materials with energetic favorable band alignment can achieve better photovoltaic performance.

Effects of sonochemical approach and induced contraction of core–shell bismuth sulfide/graphitic carbon nitride as an efficient electrode materials for electrocatalytic detection of antibiotic drug in foodstuffs

Ultrasonic-enhanced surface-active bismuth trisulfide based core–shell nanomaterials were developed and used as an efficient modified electrode material to construct a highly sensitive antibiotic sensor. The core–shell Bi2S3@GCN electrode material was directly synthesized by in-situ growth of GCN on Bi2S3 to form core–shell like nanostar (Ti-horn, 30 kHz, and 70 W/cm2). The electrocatalyst of Bi2S3@GCN nanocomposites was efficaciously broadened towards electrochemical applications. As synthesized Bi2S3@GCN promoted the catalytic ability and electrons of GCN to transfer to Bi2S3. The single-crystalline GCN layers were uniformly grown on the surface of the Bi2S3 nanostars. Under the optimal conditions of electrochemical analysis, the CPL sensor exhibited responses directly proportional to concentrations (toxic chemical) over a range of 0.02–374.4 μM, with a nanomolar detection limit of 1.2 nM (signal-to-noise ratio S/N = 3). In addition, the modified sensor has exhibited outstanding selectivity under high concentrations of interfering chemicals and biomolecules. The satisfactory CPL recoveries in milk product illustrated the credible real-time application of the proposed Bi2S3@GCN sensors for real samples, indicating promising potential in food safety department and control. Additionally, the proposed electrochemical antibiotic sensor exhibited outstanding performance of anti-interfering ability, high stability and reproducibility.

Investigation of template-assisted (MCM-41) mesoporous Co3O4 nanostructures and its superior supercapacitive retention

Abstract The supercapacitors are a static energy storage device that can stock and supply energy at an enhanced rate. They exhibit a high-power density coupled with long cycling life which are highly significant for the superior energy storage platforms. In such a way, we prepared cobalt oxide nanostructures using mesoporous silica (M41) as template and used as an electrochemical supercapacitor. The synthesized M41/m-Co3O4 nanobuds were thoroughly characterized for its crystallinity, morphology, composition and surface area. The M41/m-Co3O4 nanobuds were utilized as a modified electrode material in the electrochemical system and studied in 1 M KOH as an electrolyte solution for cyclic voltammetry (CV) and electro impedance spectroscopy studies (EIS). The EIS ensures the effortless charge transfer mechanism which facilitates rapid ion diffusion leading to the high accumulation of charges. Thus, an impressive specific capacitance of 228.87 F g−1 with excellent cycling stability of 87.5% over 1000 cycles was achieved through our investigation.

A polyethyleneimine reduced graphene oxide/gold nanocubes based electrochemical aptasensor for chloramphenicol detection using single-stranded DNA-binding protein

Developing a simple and reliable method for the detection of the highly concerning antibiotic, Chloramphenicol (CAP), is of great importance to food safety monitoring. In this study, the authors take the advantages of polyethyleneimine-functionalized reduced graphene oxide and gold nanocubs (PEI-rGO/AuNCs) composite as electrode modification material to develop an electrochemical aptasensor for the detection of CAP using single-stranded DNA-binding protein. PEI-rGO/AuNCs warrants good electrical conductivity and a high surface-to-volume ratio to achieve the purpose of signal amplification. The CAP-binding aptamers were immobilized on the PEI-rGO/AuNCs modified gold electrode via Au-S affinity. Based on the property that single-stranded DNA-binding protein (SSB) can bind to free single-stranded oligonucleotides without binding to folded oligonucleotides, in the presence of CAP, only a small number of SSB will be immobilized on the aptasensor surface results in a larger peak current, which is typically measured at 0.176 V (vs. Ag/AgCl). The assay has a linear response in the 5 pmol·L−1 to 1 μmol·L−1 concentration range, with a 2.08 pmol·L−1 detection limit. Moreover, the proposed method has been applied to detect CAP in spiked chicken samples with satisfactory results.

Research on electrocatalytic reduction of CO2 by microorganisms with a graphene modified carbon felt

At present, reduction of CO2 to organics with microbial electrosynthesis (MES) has been a popular research direction in environmental fields. One key factor that governs electron exchange is the electrode material. This study evaluated the effect of graphene as electrode modification materials on organics production from CO2 in microbial electrosynthesis with a mixed-culture biocathode. The Cathode potential was set to −0.8 V (vs Ag/AgCl), When the cathode material changed from a non-modified carbon felt electrode to the graphene modified carbon felt, the density of current of MES was increased from 1.4 ± 0.1 A·m−2 to 2.6 ± 0.1 A·m−2, the density of current has increased by 85.7%, and acetate accumulation increased from 142 mg/L to 262 mg/L, butyrate accumulation increased from 45.8 mg/L to 84.8 mg/L. The total electron recovery of MES more than 90%. The results of SEM analysis showed that compared with non-modified carbon felt, the amorphous shape of graphene makes graphene-modified carbon felt exhibit a three-dimensional structure, which gave the electrode surface a larger specific surface area and enrich more microorganisms and a large number of graphene/bacteria composites shaped on the graphene modified electrode surface, which indicated that the graphene had good biocompatibility. The results of the cyclic voltammetry curve show that the MES of the graphene modified electrode has better electrochemical performance.

Prussian blue-carboxylated MWCNTs/ZIF-67 composite: a new electrochemical sensing platform for paracetamol detection with high sensitivity

In this study, the composite of Prussian blue-carboxylated MWCNTs/ZIF-67 (PB-MWCNTs-COOH/ZIF-67) was synthesized and used as modified electrode material to fabricate an electrochemical sensor for the determination of paracetamol (PAR). In this sensor system, negatively charged MWCNTs-COOH as support for the immobilization of positively charged PB can effectively avoid the agglomeration of PB and enhance the stability, conductivity and catalytic activity of the composite. ZIF-67 particles coating outside PB-MWCNTs-COOH promotes the concentration of PAR. Benefiting from the synergistic effect, the PB-MWCNTs-COOH/ZIF-67 based sensor exhibits significantly improved electrochemical sensing behavior toward the oxidation of PAR. Under the optimum conditions, the PAR sensor presents wide linear ranges of 0.01–70 μM with a low limit of detection of 3.3 nM (S/N = 3). The method also possesses long-term stability, good reproducibility and selectivity, and was employed to the determination of PAR contents in PAR tablets sample.

Preparation of a Hollow Nanocomposite with Gold‐Embedded Zeolitic Imidazolate Framework‐67 for the Electrochemical Determination of Dopamine

AbstractThis work employed a polystyrene sphere as a template to synthesize a hollow nanocomposite with gold‐embedded zeolitic imidazolate framework‐67 (H‐Au@ZIF‐67). The morphological and structural characteristics of the prepared composite were investigated by using scanning electron microscopy, transmission electron microscopy, X‐ray diffraction and energy‐disperse spectroscopy, indicating that H‐Au@ZIF‐67 with a sunflower‐shaped cross section was successfully prepared. The synthesized H‐Au@ZIF‐67 was used to construct a dopamine electrochemical sensor, which showed good linearity scope of 0.25–438.75 μM with a high sensitivity of 332.1 μA mM−1 cm−2 and low detection limit of 0.04 μM. These results showed that the H‐Au@ZIF‐67 can be a good electrode modification material for dopamine sensing.

Sensitive and specific detection of ractopamine: An electrochemiluminescence immunosensing strategy fabricated by trimetallic Au@Pd@Pt nanoparticles and triangular gold nanosheets

A competitive electrochemiluminescence (ECL) immunosensor has been designed for the detection of ractopamine (RAC) in the system of peroxydisulfate/oxygen (S2O82−/O2). In order to augment the signal of ECL response, trimetallic Au@Pd@Pt core-shell nanoparticles (Au@Pd@Pt NPs) was applied as catalyst and a composite co-reactant, norfloxacin−L-cysteine (NC) was coated on the surface of Au@Pd@Pt NPs to increase the performance of signal amplification. Triangular gold nanosheets (Au TNSs) was selected as the platform material to connect the antigen of RAC since the ultra-thin two-dimensional structure could reduce the barrier effect of electrode modification materials on the process of electron transfer. Consequently, the proposed immunosensor performed ideal detection sensitivity (0.03 pg mL−1) for RAC with a wide linear range from 0.0001 to 1000 ng mL−1.

Novel flexible bifunctional amperometric biosensor based on laser engraved porous graphene array electrodes: Highly sensitive electrochemical determination of hydrogen peroxide and glucose

Polyimide-laser-engraved porous graphene (LEPG) are hopeful electrode modification materials for flexible electrochemical sensing based on its high-efficiency preparation and low cost. Herein, a flexible, multi-patterned, and miniaturized electrode was fabricated via a simple and novel direct laser engraving. 3D LEPG with porous network structure can selective decorated with Pt nanoparticles (Pt NPs) by in situ electrochemical depositions (Pt-LEPG) as sensitively H2O2 sensors with a wide range of linear (0.01–29 nM) and high sensitivity (575.75 μA mM−1 cm-2). Subsequently, a glucose biosensor was successfully constructed through immobilized glucose oxidases (GOD) onto Pt-LEPG electrode. New-designed GOD/Pt-LEPG glucose sensor exhibited a noteworthy lower limit of detection (0.3 μM, S/N = 3) and high sensitivity (241.82 μA mM-1 cm-2), as much a wide-range of linear (0.01–31.5 mM) at near-neutral pH conditions, enabling detect glucose in real human serum specimens with satisfactory results. Predictably, these outstanding performance sensors have great potential in terms of flexible and wearable electronics.

Nb.BbvCI powered DNA walking machine-based Zr-MOFs-labeled electrochemical aptasensor using Pt@AuNRs/Fe-MOFs/PEI-rGO as electrode modification material for patulin detection

A Nb.BbvCI powered DNA walking machine as signal enhancer, gold-platinum core-shell nanorods/iron-based metal-organic frameworks/polyethyleneimine-reduced graphene oxide composites (Pt@AuNRs/Fe-MOFs/PEI-rGO) as electrode modification material and Zr-based metal-organic frameworks-labeled oligonucleotides load with methylene blue (MB@Zr-MOFs-cDNA) as signal probes has been fabricated to obtain a sensitive electrochemical aptasensor for patulin (PAT) detection. In the DNA walking machine, PAT takes the aptamer away from the DNA walking chain (wDNA), and wDNA can repeatedly dissociate the MB@Zr-MOFs-cDNA under the Nb.BbvCI power to amplify the detection signal. In addition, Pt@AuNRs/Fe-MOFs/PEI-rGO modified gold electrode provides high stability (60 scans without significant change), catalytic performance (compared to bare gold electrode signal enhancement 250%), and high conductivity (calculated apparent electron transfer rate constant is 1.64 s−1). With such design, the as- prepared aptasensor exhibits good sensitivity from 5.0 × 10−5 ng·mL−1 to 5.0 × 10−1 ng·mL−1 with a detection limit of 4.14 × 10−5 ng·mL−1. This aptasensor construction mode can supply one efficient approach to improve signal amplification, which also open an avenue for sensitivity enhancement in detection of analytes.

Electrochemical method to remove nitrate in high-salt water

Nitrate removal is an important target for the treatment of high-salt water such as marine aquaculture tail water or reverse osmosis concentrated water. The purpose and requirements of high salt water to remove nitrate are different from groundwater or domestic sewage. The salinity of the marine aquaculture tail water is about 3.5%, and the carbon and nitrogen are relatively low (less than 10:1), marine aquaculture tail water needs to be recycled, so it is necessary to remove the nitrate while retaining the other salt ions. Reverse osmosis concentrated water generally achieves solid-liquid separation by evaporation. The separated salt residue includes sulfate, chloride and nitrate. If sulfate or chloride with higher purity can be separated, it can be used as a resource. At present, nanofiltration technology can be used to separate divalent salts from monovalent salts, but nitrate and chloride are both monovalent salts, and it is difficult to separate further. So these special requirements make the nitrate removal technology for groundwater or domestic sewage not suitable for high-salt water. Ion exchange, reverse osmosis and electrodialysis only separate nitrate from waste water but not removing it, meanwhile reverse osmosis and electrodialysis technology will remove nitrate and other ions (such as Cl−) from the water together. The biological denitrification process cannot adapt to the high salt environment. Electrochemical reduction denitrification can achieve the conversion of nitrate to nitrogen through electron transfer, and high salt environment can provide the higher conductivity required by this process. Electrochemical methods are expected to meet the special requirement of high-salt water removal for nitrate. Electrode material is the core of electrochemical reduction of nitrate which will directly affect the N2 selectivity, current efficiency and reaction kinetics of electrochemical reduction of nitrate. This review briefly introduces the cathode materials used in electrochemical reduction nitrate including metal materials, carbon materials, and modified electrode materials. The factors of pH and current density that affect the performance of cathode reduction of nitrate to produce nitrogen, the effects of pH on the rate of nitrate reduction vary with electrode materials, and acidic conditions are conducive to the adsorption of hydrogen on the electrode surface, so that the electrode surface is in a reduced state, which is conducive to the formation of N−H bonds and can promote the formation of NH4+, alkaline conditions are more conducive to the accumulation of NO2−. With the increase of current density, the removal rate and reduction rate of nitrate increase. But if the current density is too high, the energy consumption increases more, the side reaction of brine electrolysis increases, and the current efficiency decreases. Therefore, it is necessary to find a balance between reducing energy consumption and NO3− treatment requirements in order to obtain highly impressive treatment performance. This paper outlines the technical characteristics of total nitrogen removal with the coordination of cathode and anode. At present, most studies only use unipolar to remove nitrate, the products of electrocatalytic reduction of nitrate are mainly ammonia and nitrite, and the N2 selectivity is still low. In order to solve this problem, the researchers used the cathode and anode coordination method, by adding chloride ions in the electrolyte which generating HClO, Cl· and ClO· to oxidize NH4+ to N2, sodium chloride is generally selected as the added chloride salt. The review summarizes the research process of electrochemical removal of nitrate and gives suggestions for the application of electrochemical technology in high-salt water denitrification at last.

Chiral PDTDH-based electrode modification material for L/D-tartaric acid electrochemical sensing

In this work, a kind of chiral helical polymer PDTDH of 9,9-dipropynylfluorene skeleton structure were prepared. The structure and chiral properties of the obtained polymer were characterized by Nuclear Magnetic Resonance (NMR) and Circular Dichroism (CD) Spectroscopy. These chiral PDTDH polymers were used to fabricate chiral sensors and to investigate the enantioselective recognition of D−/L- tartaric acid enatiomer. The results indicated that the (S)-PDTDH/GCE sensor showed obvious response toward the tested tartaric acid enantiomer, which was confirmed by two parameters: Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) tests. These findings expand the scope for the application of chiral polymer as electrode modification material in the electrochemical chiral recognition field.

Sensitive and selective determination of paracetamol using a composite of carbon nanotubes and nanoparticles of samarium oxide and zirconium oxide

A glassy carbon electrode (GCE) was modified with a composite of carbon nanotubes, samarium oxide (Sm2O3) and zirconium oxide (ZrO2) nanoparticles. The electrode modifying material of (Sm2O3@ZrO2/CNT) was characterized by means of techniques of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction spectroscopy (XRD). The electrochemical platform was utilized for the determination of paracetamol in the presence of ascorbic acid and tramadol. The proposed platform exhibited well-defined redox couple and large enhancement in the magnitude of the current response for paracetamol in comparison with unmodified GCE and a GCE modified with CNTs. Interestingly, 10 mV, 9 mV, 7 mV and 4 mV were obtained for the potential separations (ΔEp) in the anodic and cathodic peaks for paracetamol at CNTs/GCE, Sm2O3/CNTs/GCE, ZrO2/CNTs/GCE and Sm2O3@ZrO2/CNTs/GCE, respectively. Such an observation of might be attributed to a great acceleration of electro-oxidation of paracetamol at the proposed electrochemical platform. In addition, no interference of ascorbic acid and tramadol were observed for the detection of paracetamol. The calibration of paracetamol was carried out in the presence of ascorbic acid and tramadol using square wave voltammetry (SWV). The proposed electrochemical platform enabled a linear plot over a concentration range of 3.7 × 10−9–2.2 × 10−6 M with a detection limit of 3.4 × 10−10 M. The novel platform was successfully applied to pharmaceutical preparation and blood sample for the determination of paracetamol. Such a sensitive determination method for paracetamol is of great interest for the public health.

Flexible Type Symmetric Supercapacitor Electrode Fabrication Using Phosphoric Acid-Activated Carbon Nanomaterials Derived from Cow Dung for Renewable Energy Applications.

Porous-activated carbon (PAC) materials have been playing a vital role in meeting the challenges of the ever-increasing demand for alternative clean and sustainable energy technologies. In the present scenario, a facile approach is suggested to produce hierarchical PAC at different activation temperatures in the range of 600 to 900 °C by using cow dung (CD) waste as a precursor, and H3PO4 is adopted as the nonconventional activating agent to obtain large surface area values. The as-prepared cow dung-based PAC (CDPAC) is graphitic in nature with mixed micro- and mesoporous textures. High-resolution scanning electron microscopy depicts the morphology of CDPAC as nanoporous structures with a uniform arrangement. High-resolution transmission electron microscopy reveals spherical carbon dense nanoparticles with dense tiny spherical carbon particles. N2 adsorption–desorption isotherms show a very high specific surface area of 2457 m2/g for the CDPAC 9 (CD 9) sample with a large pore volume of 1.965 cm3/g. Electrochemical measurements of the CD 9 sample show a good specific capacitance (Cs) of 347 F/g at a lower scan rate (5 mV/s) with improved cyclic stability, which is run up to 5000 cycles at a low current density (0.5 A/g). Hence, we choose an activated carbon prepared at 900 °C to fabricate the modified electrode material. In this regard, a flexible type symmetric supercapacitor device was fabricated, and the electrochemical test results show a supercapacitance value (Cs) of 208 F/g.

Clay/au nanoparticle composites as acetylcholinesterase carriers and modified-electrode materials: A comparative study

This work presents the first comparative study on syntheses, characterization, and applications of different clay/gold nanoparticle composites (clay/AuNPs) as acetylcholinesterase (AChE) carriers and modified-electrode materials to detect chlorpyrifos, an organophosphate pesticide. The selected based-clays were plate-like kaolinite (Kaol; 1:1 aluminum phyllosilicate), globular montmorillonite (Mt; 2:1 aluminum phyllosilicate), globular bentonite (Bent; 2:1 aluminum phyllosilicate), and fibrous sepiolite (Sep; 2:1 inverted ribbons of magnesium phyllosilicate). The clay/AuNPs were synthesized using in situ chemical reduction of the gold precursor with anchoring 3-aminopropyl triethoxysilane (APTES) on the clay surfaces. The studied materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen adsorption/desorption, Fourier transformed infrared (FTIR) spectroscopy, thermogravimetric analyzer (TGA), zeta-potential analysis, and electrochemical impedance spectroscopy (EIS). Surface area, surface charges, and hydrophilic/hydrophobic nature of based-clays and the clay/AuNPs played major roles on AChE loading, residual activity, and sensor storage stability. The Mt/AuNPs was determined, among the studied clays, as the best supports for AChE loading and residual activities due to its high specific surface area and weak electrostatic interaction with the immobilized enzyme. Since apparent catalytic efficiencies kcatapp/KMappof the immobilized AChE in the four clay/AuNPs were found statistically similar, Mt/AuNPs which contained the highest enzyme loading was the favorite modified-electrode material. For chlorpyrifos detection, Kaol/AuNPs-based sensors resulted in the lowest detection limit, presumably due to the strong hydrophobic surface that helps to concentrate the nonpolar pesticide to the vicinity of the immobilized enzyme. Unfortunately, the highest electrostatic repulsion between the Kaol/AuNPs and AChE, and the dehydrated Kaol surface resulted in the lowest storage stability of the AChE pesticide sensors. Overall, Mt/AuNPs showed the highest potential as the AChE carrier and the modified electrode material for chlorpyrifos determination.

A Novel Electrochemical Sensor Based on Carbon Dots-Nafion Composite Modified Bismuth Film Electrode for Simultaneous Determination of Cd2+ and Pb2+

Introduction Bismuth film electrodes (BiFEs) have become a hopeful alternative to mercury drop and film electrodes due to their non-toxicity and equal or even superior electrochemical performance towards heavy-metal-ion detection [1]. Meanwhile, various carbon nanomaterials (e.g., graphene oxide, carbon nanotubes, etc.) had been composited with bismuth for improving the sensitivity and reproducibility of BiFEs. However, one primary problem with the BiFEs is that the hydrophobicity of these carbon nanomaterials may have a negative impact on the performance of the electrodes in aqueous media.It has been reported that carbon dots (CDs), as a new hydrophilic carbon nanomaterial, may have similar properties to other carbon nanomaterials, thus CDs can be used as modified electrode materials to improve the performance of electrochemical sensors [2]. CDs have not been used for the enhancement of the electrochemical performance of bismuth-based electrodes. Due to the composited feasibility of CDs and bismuth, they have been successfully applied in photocatalysis[3] and energy storage[4]. Therefore, it would be of special potential to fabricate a novel bismuth-based electrode based on CDs for improving the electrode detection performance for heavy metals.The objective of this study is to develop inexpensive, highly selective, rapid and environmental friendly sensors for Cd2+ and Pb2+ detection. In this work, CDs, Nafion, and bismuth were deposited onto the glassy carbon electrodes (GCEs) sequentially to form a novel chemical sensor for Cd2+ and Pb2+ ions rapid detection. Methods CDs were prepared with a facile one-pot hydrothermal method using glucose as the carbon source[5]. To fabricate BiF/CDs/Nafion/GCE, the bare GCEs were polished well with a diamond suspension solution for the further modified. Then, the CDs were electrodeposited on the GCE using cyclic voltammetry in H2SO4 solution containing CDs. Finally, 5 μL of 1 wt.% Nafion film was used as an adhesive to stabilize the CDs and improve the reproducibility of the modified electrode. The obtained electrochemical sensor was abbreviated as CDs/Nafion/GCE. For comparison, Nafion/GCE was prepared using a similar method. Bismuth was in situ deposited onto the CDs/Nafion/GCE from non-deaerated HAc-NaAc (pH 4.5) buffer solution in the presence of 1000 μg L-1 Bi3+ with model target metals. A conventional three-electrode system was adopted to analyze Cd2+ and Pb2+ concentrations using an Autolab PGSTAT204 workstation (Metrohm). Conclusions Fig. 1 and Table 1 present the differential pulse voltammetry (DPV) electrochemical performance of bare GCE, Nafion/GCE, CDs/Nafion/GCE and BiF/Nafion/GCE in 0.1 M acetate buffer (pH 4.5) containing 0.25 μg mL-1 Cd2+ and Pb2+. The DPV curves of both bare GCE and Nafion/GCE display two weak stripping peaks for Cd2+ and Pb2+. After modification on the GCE surface with CDs-Nafion film, the stripping peak currents of Cd2+ and Pb2+ significantly increased, indicating that the CDs may have the ability to spur the electron transfer rate of the detection system [6]. More importantly, BiF/CDs/Nafion/GCE showed a higher sensitivity for simultaneous detection of Cd2+ and Pb2+ compared with bare GCE and CDs/Nafion/GCE. The Cd2+ current obtained with BiF/CDs/Nafion/GCE was 71.02 and 4.85 times higher than with bare GCE and CDs/Nafion/GCE, respectively. The Pb2+ current obtained with BiF/CDs/Nafion/GCE was 51.85 and 6.31 times higher than those with bare GCE and CDs/Nafion/GCE, respectively.Fig. 2 and Table 2 show the simultaneous stripping analysis of Cd2+ and Pb2+ using the BiF/CDs/Nafion/GCE. The DPV curves show individual peaks at approximate -0.75 V for Cd2+ and -0.55 V for Pb2+. The separation between two peaks was approximately 200 mV, a difference that is sufficient to detect Cd2+ and Pb2+ simultaneously and selectively. The inset in Fig. 2 presents the linear relationship between the peak currents and the concentrations of Cd2+ and Pb2+ (The linear equations: Ip=18.82C+3.49 (R2=0.994) for Cd2+ and Ip=25.12C+3.55 (R2=0.993) for Pb2+). The calculated detection limits (3δ method) for Cd2+ and Pb2+ are 0.003 and 0.002 mg L-1, respectively.The low detection limits suggest that the BiF/CDs/Nafion/GCE is a feasible sensor to simultaneously detect Cd2+ and Pb2+, which has great potential for application in the fields of environmental monitoring. Table 1. Electrochemical performances of the bare GCE, Nafion/GCE, CDs/Nafion/GCE and BiF/CDs/Nafion/GCE in simultaneous detection of Cd2+ and Pb2+. Bare GCE Nafion/GCE CDs/Nafion/GCE BiF/CDs/Nafion/GCE Cd2+ I/μA 0.116 0.045 1.697 8.239 E/V -0.782 -0777 -0.797 -0.772 Pb2+ I/μA 0.192 0.103 1.577 9.957 E/V -0.540 -0.525 -0.565 -0.520 Table 2. The analytical performance of BiF/CDs/Nafion/GCE in simultaneous detection of Cd2+ and Pb2+. Analytes Linear range (mg L-1) LOD (mg L-1) R2 Simultaneous analysis Cd2+ 0.05 - 0.50 0.003 0.994 Pb2+ 0.05 - 0.50 0.002 0.993 Keywords: Carbon points; Bismuth film; Cadmium; LeadFunding: This work was financially supported by the Major Science and Technology Program for Water Pollution Control and Treatment (Project no. 2018ZX07109003).

Smart functionalized thin gel layers for electrochemical sensors, biosensors and devices

Abstract Combining hydrogels sensitive to external stimuli with conducting surfaces opens new possibilities in electrochemistry. Thin hydrogel layers as unique electrode-modifying materials provide highly permeable matrix for easy diffusion of analytes. In addition, larger individuals, for example, nanoparticles and enzymes, can be straightforwardly immobilized in the polymeric networks at electrode surfaces. Such properties are strongly desired for construction of sensors and biosensors. In addition, sensitivity to external stimuli allows to significantly enhance or weaken the electroanalytical signal. Recently, a significant number of articles concerning switchable sensors/biosensors, switchable electrochemical systems and signal–responsive interfaces have been published. This report is also focused on the construction of various devices based on electrode surfaces modified with smart hydrogel layers, for example, logic gates and electroresponsive hydrogel layers as potentially advanced drug delivery systems, artificial muscles and electrochemical valves.

Application of Graphene-Based Nanocomposites in Electrochemical Detection of Heavy Metal Ions

The purpose of this study was to explore the application of graphene-based nanocomposites in electrochemical detection of heavy metal ions. In this study, Graphene oxide (GO) was synthesized with improved Hummers method, and flower-like MoS2/rGO nanocomposite was synthesized with hydrothermal method and used as electrode modification material. In addition, scanning electron microscopy (SEM) and X-ray images were used to observe the characterization of the prepared samples and to detect the sensitivity of four heavy metal ions under optimal experimental conditions. The results showed that the reduced graphene oxides were coated with a large number of flower-like MoS2 and laid on the reduced graphene oxides. And in electrochemical experiments, adsorption experiments and interference tests, MoS2/rGO nanocomposites showed satisfactory performance for Pb(II). Therefore, this study provided a new strategy for the development of new nanocomposites composites as electrochemical sensors to detect the heavy metal ions in the aquatic environment.