Synthesis and characterization of ordered mesoporous carbon as electrocatalyst for simultaneous determination of epinephrine and acetaminophen

In this research, we report an easy method for synthesis of ordered mesoporous carbon (OMC) with hexagonal arrays of tubes (CMK-5). The synthesized OMC was characterized using X-ray diffraction (XRD), scanning electronic microscopy (SEM) and nitrogen sorption isotherms techniques. Due to the large surface area and high conductivity of OMC, OMC-modified glassy carbon (OMCs/GC) electrode was prepared. The unique electrochemical activity of OMCs/GC electrode was illustrated using cyclic voltammetry (CV) and electron impedance spectroscopy (EIS) in which OMC showed a faster electron transfer rate, as compared with glassy carbon electrode. The electrochemical behavior of epinephrine (EN) and acetaminophen (AP) at OMC/GC electrode was also investigated using cyclic voltammetry. The OMC/GC electrode exhibited high electrocatalytic activities toward oxidation of EN and AP and displayed good voltammetric peak separation between them. In differential pulse voltammetry technique, both EN and AP give sensitive oxidation peaks at 120?mV and 320?mV, respectively. Therefore, investigated method was applied for simultaneous determination of EN and AP. AP and EN give linear response over the range of 0.2–15?μM and 4–100?μM, respectively. The lower detection limits were found to be 0.07?μM for AP and 0.94?μM for EN.     

Voltammetric detection of riboflavin based on ordered mesoporous carbon modified electrode

The potential application of ordered mesoporous carbon (OMC)-modified glassy carbon electrode (OMC/GCE) in electrochemistry as a novel electrode material was investigated. X-ray diffraction, transmission electron micrographs, and cyclic voltammetry were used to characterize the structure and electrochemical behaviors of this material. Compared to GC electrode, the peak currents of potassium ferricyanide (K₃[Fe(CN)₆]) increase and the peak potential separation (ΔE _p) decreases at the OMC/GC electrode. These phenomena suggest that OMC-modified GC electrode possesses larger electrode area and faster electron transfer rate, as compared with bare GC electrode. Furthermore, riboflavin was detected using OMC/GC electrode in aqueous solutions. The results showed that, under an optimum condition (pH 7.0), the OMC/GC electrode exhibited excellent response performance to riboflavin in the concentration range of 4.0 × 10⁻⁷ to 1.0 × 10⁻⁶ M with a high sensitivity of 769 μA mM⁻¹. The detection limit was down to around 2 × 10⁻⁸ M. With good stability and reproducibility, the present OMC/GC electrode was applied in the determination of vitamin B₂ content in vitamin tablets, and satisfactory results were obtained.     

Electrochemical properties of ordered mesoporous carbon and its electroanalytical application for selective determination of dopamine

The electrochemical properties of one novel carbon material, ordered mesoporous carbons (OMC), synthesized by templating SBA-15 mesoporous silica materials and the electrocatalytic behaviors of OMC modified electrode towards the oxidation of dopamine (DA) and ascorbic acid (AA) were studied. Cyclic voltammetry was used to evaluate the electrochemical behaviors of OMC in 5 mM K₃Fe(CN)₆/0.1 M KCl solution. OMC showed a faster electron transfer rate, as compared with glass carbon (GC) electrode. The higher electron transfer kinetics can be attributed to the existence of a large amount of edge plane defect sites in the OMC materials, which was verified by Raman spectroscopy. The cyclic voltammetric studies also showed the presence of oxygen-containing functional groups on the surface of OMC. Furthermore, the OMC modified electrode showed high electrocatalytic activities toward the oxidation of DA and AA, and resolved their voltammetric responses into two well-defined peaks with peak separation of ca. 0.210 V. The OMC modified electrode could be effectively used for the selective electrochemical determination of DA in the presence of AA.     

Bio-electrocatalysis of NADH and ethanol based on graphene sheets modified electrodes

Characterization and application of graphene sheets modified glassy carbon electrodes (graphene/GC) have been presented for the electrochemical bio-sensing. A probe molecule, potassium ferricyanide is employed to study the electrochemical response at the graphene/GC electrode, which shows better electron transfer than graphite modified (graphite/GC) and bare glassy carbon (GC) electrodes. Based on the highly enhanced electrochemical activity of NADH, alcohol dehydrogenase (ADH) is immobilized on the graphene modified electrode and displays a more desirable analytical performance in the detection of ethanol, compared with graphite/GC or GC based bio-electrodes. It also exhibits good performance of ethanol detection in the real samples. From the results of electrochemical investigation, graphene sheets with a favorable electrochemical activity could be an advanced carbon electrode materials for the design of electrochemical sensors and biosensors.     

Electrochemistry and electrocatalysis of polyoxometalate-ordered mesoporous carbon modified electrode

In this work, we have developed a convenient and efficient method for the functionalization of ordered mesoporous carbon (OMC) using polyoxometalate H₆P₂Mo₁₈O₆₂·xH₂O (P₂Mo₁₈). By the method, glassy carbon (GC) electrode modified with P₂Mo₁₈ which was immobilized on the channel surface of OMC was prepared and characterized for the first time. The large specific surface area and porous structure of the modified OMC particles result in high heteropolyacid loading, and the P₂Mo₁₈ entrapped in this order matrix is stable. Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption-desorption isotherm and X-ray diffraction (XRD) were employed to give insight into the intermolecular interaction between OMC and P₂Mo₁₈. The electrochemical behavior of the modified electrode was studied in detail, including pH-dependence, stability and so on. The cyclic voltammetry (CV) and amperometry studies demonstrated that P₂Mo₁₈/OMC/GC electrode has high stability, fast response and good electrocatalytic activity for the reduction of nitrite, bromate, idonate, and hydrogen peroxide. The mechanism of catalysis on P₂Mo₁₈/OMC/GC electrode was discussed. Moreover, the development of our approach for OMC functionalization suggests the potential applications in catalysis, molecular electronics and sensors.     

Ordered Mesoporous Carbon Functionalized with Polythionine for Electrocatalytic Application

A polythionine (PTH) functionalized ordered mesoporous carbon (OMC) material (PTH/OMC) was presented. The electrochemistry kinetic characteristics of this material are investigated and compared with pure OMC. The results showed that compared with OMC, PTH/OMC possesses a much higher electron transfer rate. For the application of this material, an electrocatalytic based NADH biosensor was constructed on glassy carbon electrode (GCE). Instead of 0.592 V on bare GCE and 0.206 V on OMC/GCE, the amperometric detection of NADH could be effectively performed on the present biosensor with operation potential be set at 0.0 V. In addition, the sensor showed good reproducibility and stability.     

Electrochemical Properties of Ordered Mesoporous Carbon Film Adsorbed onto a Self‐Assembled Alkanethiol Monolayer on Gold Electrode

A stable ordered mesoporous carbon (OMC) film electrode was successfully constructed by adsorbing OMC onto a self‐assembled monolayer (SAM) of C₁₈H₃₇SH chemisorbed on the Au electrode. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and electrochemical methods were used to characterize the properties of the OMC film electrode. The adsorbed OMC can restore the heterogeneous electron transfer almost totally blocked by the alkanethiol monolayer. Nyquist plots show a sharply decrease of the charge transfer resistance (R_ct) of the Fe(CN) couple at the OMC film electrode. Furthermore, the OMC film electrode is found to possess a significantly reduced interfacial capacitance and largely enhanced current response of hydrogen peroxide. This novel approach to the fabrication of stable OMC film electrode with excellent electrochemical properties is believed to be very attractive for electrochemical studies and electroanalytical applications.     

Electrochemical behavior of methyl parathion and its sensitive determination at a glassy carbon electrode modified with ordered mesoporous carbon

Ordered mesoporous carbon (OMC) was synthesized and used to modify the surface of a glassy carbon (GC) electrode. Due to the unique properties of OMC, a decrease in the overvoltage of the reduction potential of methyl parathion (MP) (to ca. 219 mV) and a 76-fold increase in the peak current are observed (compared with a bare GC electrode). The absorption capacity of the surface of the electrode for MP was determined by chronocoulometry. The results show that the Г value of the modified electrode (2.34?×?10^–9 mol cm^–2) is 9.5 times as large as that of the GC electrode (2.47?×?10^–10 mol cm^–2). The new electrode exhibits synergistic electrocatalytic and accumulative effects on MP. MP can be determined by linear sweep voltammetry (LSV) which displays a linear relationship between peak current and MP concentration in the range from 0.09 to 61 μM, with a detection limit as low as 7.6 nM (at an S/N of 3) and after an accumulation at 0 V for 5 min. The electrode was successfully applied to the determination of MP in spiked lake water samples.

Simultaneous and Sensitive Detection of Cd(II) and Pb(II) Using a Novel Bismuth Film/Ordered Mesoporous Carbon‐molecular Wire Modified Graphite Carbon Paste Electrode

An electrochemical sensor for the simultaneous and sensitive detection of Cd(II) and Pb(II) is proposed on the basis of square‐wave anodic stripping voltammetry (SWASV) experiments using a novel bismuth film/ordered mesoporous carbon‐molecular wire modified graphite carbon paste electrode (Bi/OMC‐MW/GCPE). Ordered mesoporous carbon (OMC) and molecular wire (MW) (diphenylacetylene) were used as the modifier and binder, respectively. The Bi/OMC‐MW/GCPE was prepared with the addition of graphite powder, OMC and DPA at the ratio of 2 : 1 : 1. The electrochemical properties and morphology of the electrode were characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), SWASV and scanning electron microscopy (SEM). The parameters affecting the stripping current response were investigated and optimized. The experimental results show that the prepared electrode exhibited excellent electrochemical performance, good electrical conductivity and a high stripping voltammetric response. Under optimized conditions, a linear range was achieved over a concentration range from 1.0 to 70.0 μg/L for both Cd(II) and Pb(II) metal ions, with detection limits of 0.07 μg/L for Cd(II) and 0.08 μg/L for Pb(II) (S/N=3) with the deposition time 150 s. Moreover, the sensor exhibited improved sensitivity and reproducibility compared to traditional CPEs. The fabricated electrode was then successfully used to satisfactorily detect Cd(II) and Pb(II) in real soil samples.     

碳纳米管的快速功能化及电催化

将耐尔兰(Nile Blue, NB)分子修饰到碳纳米管(CNT)表面形成NB-CNT纳米复合体, 谱学结果表明, NB不仅能快速、高效地修饰到CNT表面, 而且还能有效地改善CNT在水溶液中的分散性能. 将NB-CNT修饰到玻碳(GC)电极表面制备了NB-CNT/GC电极, 循环伏安结果显示, 其伏安曲线上不仅表现出一对良好的、几乎对称的NB单体的氧化还原峰, 式量电位E⁰'几乎不随扫速而变化[其平均值为(－0.422±0.002) V (vs. SCE, 0.1 mol/L PBS, pH 7.0)]; 而且还显示出NB聚合体分子的氧化还原峰, E⁰'为－0.191 V (100 mV/s时). 进一步的实验结果表明, NB和CNT对NADH(即还原型β-烟酰胺腺嘌呤二核苷酸, 又称还原型辅酶I)的电化学氧化具有协同催化作用, 能使其氧化过电位降低多于560 mV; NB-CNT/GC电极还能较好地响应脱氢酶催化底物氧化过程中体系内NADH浓度的变化. 本文对碳纳米管功能化方法具有简单快速、电极制作容易以及催化效率高等优点, NB-CNT/GC电极有望在制作脱氢酶传感器方面得到应用.     

有序介孔碳/石墨烯/镍泡沫的制备及其对多巴胺的高灵敏度和高选择性检测

柔性生物传感器在可穿戴电子设备中有着广泛的应用前景. 为了获得柔性电化学多巴胺传感器,作者在本工作中首先在镍泡沫表面通过化学气相沉积生长石墨烯,随后通过高温碳化嵌段共聚物与酚醛树脂在石墨烯表面共组装形成的薄膜制备了有序介孔碳/石墨烯/镍泡沫（OMC/G/Ni）复合材料. 其中,镍泡沫可以为复合材料提供具有高导电性和良好柔韧性的金属骨架,而具有垂直排列介孔阵列的有序介孔碳层为复合材料提供了高的电活性表面积,且有利于活性位点的暴露. 值得注意的是,夹在有序介孔碳层和镍泡沫之间的石墨烯极大地增强了各组分之间的相容性,有利于进一步提升复合材料的电化学性能. 作为电化学传感器中的工作电极,OMC/G/Ni体现出优异的多巴胺检测能力. 不但具有宽的线性检测范围（0.05 ~ 58.75 μmol·L^-1）和低检测限（0.019 μmol·L^-1）,还具有良好的选择性、重现性和稳定性. 此外,OMC/G/Ni在弯曲状态下依旧能够保持对多巴胺的高检测能力,证明了其在柔性生物传感器中的应用潜力.     

Selective Voltammetric Determination of Uric Acid in the Presence of Ascorbic Acid at Ordered Mesoporous Carbon Modified Electrodes

A novel chemically modified electrode was fabricated by immobilizing ordered mesoporous carbon (OMC) onto a glassy carbon (GC) electrode. The electrocatalytic behavior of the OMC modified electrode towards the oxidation of uric acid (UA) and ascorbic acid (AA) was studied. Compared to a glassy carbon electrode, the OMC modified electrode showed a faster electron transfer rate and reduced the overpotentials greatly. Furthermore, the OMC modified electrode resolved the overlapping voltammetric responses of UA and AA into two well‐defined voltammetric peaks with peak separation of ca. 0.38 V. All results show that the OMC modified electrode has a good electrocatalytic ability to UA and AA, and has an excellent response towards UA even in the presence of high concentration AA.     

Poly(4-amino-1-1'-azobenzene-3, 4'-disulfonic acid) coated electrode for selective detection of dopamine from its interferences

Here, we described a new method for electrochemically selective detection of dopamine (DA). In this report, for the first time, electrochemical polymerization of 4-amino-1-1'-azobenzene-3,4'-disulfonic acid (acid yellow 9 dye (AY)) was carried out onto the surface of glassy carbon (GC) electrode and indium tin oxide coated electrode (ITO) from acidic solution containing AY monomers. A polymerized film of acid yellow on the surface of a glassy carbon electrode was characterized by cyclic voltammetry (CV). The redox response of the poly(AY) film on the GC electrode showed a couple of redox peak in 0.1M sulfuric acid solution and the pH dependent peak potential was -58mV/pH which was close to the Nernst behavior. The poly(AY) film-coated GC electrode (GC/PAY) exhibited excellent electrocatalytic activity towards the oxidations of dopamine (DA) in 0.1M phosphate buffer solution (PBS, pH 7.0) and increased the anodic peak current three time higher than bare GC electrode. GC/PAY did not reduce the considerable overpotential for oxidation of DA when compare to bare GC electrode. However, in contrast to other polymer modified electrode, due to the strong negatively charged back bone of poly(AY) highly repelled the important interference of DA, such as ascorbic acid (AA), uric acid (UA) and reduced form of nicotinamide adenine dinucleotide (NADH) in 0.1M PBS (pH 7.0) and did not showed any response for oxidation of these interferences. This behavior makes the GC/PAY for selective detection of DA in the presence of higher concentrations AA, UA and NADH. Using differential pulse voltammetry the calibration curves for DA were obtained over the range of 1-100muM with good selectivity and sensitivity. The proposed method provides a simple method for selective detection of DA from its interferences.     

Amperometric Ethanol Biosensor Based on Integration of Alcohol Dehydrogenase with Meldola's Blue/Ordered Mesoporous Carbon Electrode

An amperometric ethanol biosensor was fabricated by integration of alcohol dehydrogenase (ADH) with meldola's blue (MB)/ordered mesoporous carbon (OMC) composite modified glassy carbon electrode (MB/OMC/GCE). The MB/OMC/GCE was highly sensitive for nicotinamide adenine dinucleotide (NADH) measurement (9.1±0.25 μA/mM) and gave a low detection limit of 0.21±0.02 μM. The ethanol biosensor exhibited a wide linear range up to 6 mM with a lower detection limit of 19.1±0.58 μM as well as a high sensitivity of 34.58±2.43 nA/mM without suffering any interference from some common electroactive compounds.     

NAD+ hydrogenation on Au electrode deposited on modified glassy carbon

Gold nanoparticles(AuNP) were electrodeposited on a glassy carbon(GC) which was electrochemically modified by potentiodynamic cyclic polarization in acidic medium. The AuNP deposits were characterized by scanning electron microscopy, cyclic voltammetry, chronoamperometry and linear sweep voltammetry. Results of these studies showed that very small sized AuNP are deposited with significantly high particle density which is attributed to the surface modification of GC. The resulted AuNP/GC electrode showed high catalytic activity for electrochemical reduction of NAD⁺ to NADH, indicating its potential for electrocatalytic applications.     

Boron-doped carbon nanotubes modified electrode for electroanalysis of NADH

Boron-doped carbon nanotubes (BCNTs) as a novel carbon nanomaterial have higher catalytic activity. Electroanalysis of dihydronicotinamide adenine dinucleotide (NADH) based on the BCNTs modified electrode has been investigated. Comparing with the bare glassy carbon (GC) and carbon nanotubes (CNTs)/GC electrodes, the BCNTs/GC electrode allowed highly sensitive amperometric detection of NADH at the lower applied potential, and minimization of surface contamination. Therefore, BCNTs are useful and promising material for the detection of NADH and are attractive for dehydrogenase-based amperometric biosensor or other analytical applications.     

Temperature-Responsive Electrocatalysis Based on Poly(N-Isopropylacrylamide)-Modified Graphene Oxide (PNIPAm-GO)

Poly(N-isopropylacrylamide)-modified graphene oxide (PNIPAm-GO), which is a type of thermally responsive GO, was designed and synthesized through a covalent “grafting-from” strategy. The as-prepared modified nanosheets integrated the individual advantages of two components, such as the thermal sensitivity of the PNIPAm terminal as well as the conductivity and the open 2D structure of the GO substrate. PNIPAm-GO was able to perform the reversible regulation of hydrophilicity/hydrophobicity in aqueous solution upon variations in the temperature. Such a unique property might also lead to the utilization of PNIPAm-GO as an intelligent electrode material to achieve a switchable electrochemical response toward a [Fe(CN)₆]^3−/4− probe. The PNIPAm-GO modified glassy carbon electrode (PNIPAm-GO/GC electrode) was able to exhibit better electrochemical performance in an ON/OFF switching effect than the PNIPAm-modified glassy carbon electrode (PNIPAm/GC electrode) without GO owing to the intrinsic properties and large surface area of the introduced GO. Moreover, it was found that the PNIPAm-GO/GC electrode also displayed excellent thermally responsive electrocatalysis toward the detection of 1,4-dihydro-β-nicotinamide adenine dinucleotide (NADH) and dopamine (DA), which resulted in two different catalytic statuses on the same electrode. This kind of switchable catalytic performance of the PNIPAm-GO/GC electrode might greatly enhance the flexibility of its application, and thus it is expected to have wide potential for applications in the fields of biosensors and biocatalysis.     

Electrochemical and Photoelectrochemical Sensing of NADH and Ethanol Based on Immobilization of Electrogenerated Chlorpromazine Sulfoxide onto Graphene‐CdS Quantum Dot/Ionic Liquid Nanocomposite

Here, a simple one‐step solvothermal procedure was employed to synthesize a nanocomposite containing graphene‐nanosheets and CdS quantum dots (GNs‐CdS QDs). The electrochemical oxidation of chlorpromazine (CPZ) to chlorpromazine‐sulfoxide (CPZ‐SO) onto a GNs‐CdS QDs/ionic liquid (IL) nanocomposite modified glassy carbon (GC) electrode give rise to redox‐active products which showed excellent electrocatalytic and photoelectrocatalytic activity toward NADH oxidation at reduced overpotential. A linear response up to 200 µM was obtained for photoamperometric determination of NADH with detection limit 1 µM. Immobilizing alcohol dehydrogenase(ADH) onto the modified electrode via a simple cross linking procedure, the photoelectrochemical capability of the proposed system toward ethanol biosensing was clearly shown.     

Electrocatalytic Activities of 1,2-Naphthoquinone Modified Carbon Nanotube to the Electrochemical Oxidation of β-Nicotinamide Adenine Dinucleotide

The carbon nanotube (CNT) was functionalized with the electroactive species of 1,2-naphthoquinone (Nq) by a method of adsorption to form Nq-CNT nanocomposite. The Nq-CNT was characterized by spectroscopic techniques, for example UV-Vis, FTIR, SEM, etc., and the results showed that Nq can rapidly and effectively be adsorbed on the surface of CNT with high stability. Moreover, it was shown that the dispersion ability of CNT in aqueous solution had a significant improvement after CNT functionalized with Nq. The Nq-CNT/GC electrode was fabricated by modifying Nq-CNT nanocomposite on the GC electrode surface and its electrochemical properties were investigated by voltammetry, which indicated that CNT could improve the electrochemical behavior of Nq and greatly enhance its redox peak currents. The Nq-CNT/GC electrode exhibited a pair of well-defined and nearly symmetrical redox peaks with the formal potential of –87.3 ± 4.5 mV (vs. SCE, 0.1 M PBS, pH 7.0), which was almost independent on the scan rates. The experimental results also demonstrated that Nq and CNT could synergistically catalyze the electrochemical oxidation of NADH, and Nq-CNT exhibited a high performance with lowering the overpotential by more than 510 mV. The presented method had some advantages, such as rapid and facile CNT functionalization, easy electrode fabrication, and high electrocatalytic activity, etc.     

Rapid functionalization of carbon nanotube and its electrocatalysis

It was reported that carbon nanotube (CNT) was functionalized with the electroactive Nile blue (NB), which is a phenoxazine dye, by a method of adsorption to form a NB-CNT nanocomposite. The NB-CNT nanocomposite was characterized by several spectroscopic techniques, for example, Ultraviolet-visible spectroscopy (UV-VIS), Fourier transform infrared (FTIR), Raman spectroscopy and scanning electron microscopy (SEM) etc., and the results showed that NB could rapidly and effectively be adsorbed on the surface of CNT with a high stability without changing the native structure of NB and the structure properties of CNT. Moreover, it was shown that the dispersion ability of CNT in aqueous solution had a significantly improvement after CNT functionalized with NB even at a level of high concentration, for example, 5 mg of NB-CNT per 1 mL of H₂O. The NB-CNT/ glasssy carbon (GC) electrode was fabricated by modifying NB-CNT nanocomposite on the GC electrode surface and its electrochemical properties were investigated by cyclic voltammetry. The cyclic voltammetric results indicate that CNT can improve the electrochemical behavior of NB and greatly enhance its redox peak currents. While the NB-CNT/GC electrode exhibited a pair of well-defined and nearly symmetrical redox peaks with the formal potential of (−0.422±0.002) V (versus SCE, 0.1 mol/L PBS, pH 7.0), which was almost independent on the scan rates, for electrochemical reaction of NB monomer; and the redox peak potential of NB polymer located at about −0.191 V. The experimental results also demonstrated that NB and CNT could synergistically catalyze the electrochemically oxidation of NADH (β-nicotinamide adenine dinucleotide, reduced form) and NB-CNT exhibited a high performance with lowing the overpotential of more than 560 mV. The NB-CNT/GC electrode could effectively sense the concentration of NADH, which was produced during the process of oxidation of substrate (e.g. ethanol) catalyzed by dehydrogenase (e.g. alcohol dehydrogenase). The presented method for functionalization of CNT had several advantages, such as rapid and facile CNT functionalization, easy electrode fabrication and high electrocatalytic activity, etc., and could be used for fabrication electrochemical biosensor on the basis of dehydrogenase. __________ Translated from Acta Chimica Sinica, 2007, 65(1): 1–9 [译自: 化学学报]