Qiaohui Guo

Supercapacitors based on hybrid carbon nanofibers containing multiwalled carbon nanotubes

Hybrid carbon nanofibers containing multiwalled carbon nanotubes (CNTs) were produced by electrospinning CNTs suspended in a solution of polyacrylonitrile in N,N-dimethylformamide, followed by carbonization and activation using a hydroperoxide–water steam mixture at 650 °C. Transmission electron microscopy and scanning electron microscopy were used to observe the morphology of the CNT-embedded carbon nanofibers. The specific surface area of the nanofibers was measured using the Brunauer–Emmett–Teller method. The electrochemical properties of the nanofibers were characterized by cyclic voltammetry and galvanotactic charge/discharge in 1 M H2SO4 electrolyte. The specific capacitance of electric double-layer capacitors containing CNT-embedded carbon nanofibers as electrodes reached 310 F g−1, which is almost double that obtained for capacitors containing virgin carbon nanofibers as electrodes. The CNTs embedded in the carbonized electrospun nanofibers provide improved conductive pathways for charge transfer in the electrodes and therefore lead to a significantly enhanced specific capacitance.

Nitrogen-Doped Carbon Nanotubes Supported by Macroporous Carbon as an Efficient Enzymatic Biosensing Platform for Glucose

Effective immobilization of enzymes/proteins on an electrode surface is very essential for biosensor development, but it still remains challenging because enzymes/proteins tend to form close-packed structures on the electrode surface. In this work, nitrogen-doped carbon nanotubes (NCNTs) supported by three-dimensional Kenaf Stem-derived porous carbon (3D-KSC) (denoted as 3D-KSC/NCNTs) nanocomposites were constructed as the supporting matrix to load glucose oxidase (GOD) for preparing integrated glucose biosensors. These NCNTs are vertically arrayed on the channel walls of the 3D-KSC via the chemical vapor deposition method, which could noticeably increase the effective surface area, mechanical stability, and active sites (originating from the doped nitrogen) of the nanocomposites. The integrated glucose biosensor exhibits some advantages over the traditional GOD electrodes in terms of the capability to promote the direct electron transfer of GOD, enhance the mechanical stability of the biosensor attributed to the strong interaction between NCNTs and GOD, and enlarge the specific surface area to efficiently load a large number of GODs. The as-prepared biosensor shows a good performance toward both oxygen reduction and glucose biosensing. This study essentially offers a novel approach for the development of biosensors with excellent analytical properties.

Hierarchically mesostructured porous TiO2 hollow nanofibers for high performance glucose biosensing

Effective immobilization of enzymes on an electrode surface is of great importance for biosensor development, but it still remains challenging because enzymes tend to denaturation and/or form close-packed structures. In this work, a free-standing TiO2 hollow nanofibers (HNF-TiO2) was successfully prepared by a simple and scalable electrospun nanofiber film template-assisted sol-gel method, and was further explored for glucose oxidase (GOD) immobilization and biosensing. This porous and nanotubular HNF-TiO2 provides a well-defined hierarchical nanostructure for GOD loading, and the fine TiO2 nanocrystals facilitate direct electron transfer from GOD to the electrode, also the strong interaction between GOD and HNF-TiO2 greatly enhances the stability of the biosensor. The as-prepared glucose biosensors show good sensing performances both in O2-free and O2-containing conditions with good sensitivity, satisfactory selectivity, long-term stability and sound reliability. The novel textile formation, porous and hierarchically mesostructured nature of HNF-TiO2 with excellent analytical performances make it a superior platform for the construction of high-performance glucose biosensors.

A glucose biosensor based on the polymerization of aniline induced by a bio-interphase of glucose oxidase and horseradish peroxidase

A novel glucose biosensor was developed based on a 4-amino thiophenol/Au nanoparticle/glucose oxidase (GOD)–horseradish peroxidase (HRP)/6-mercapto-1-hexanol-11-mercaptoundecanoic acid/Au electrode. The modified electrode could be used to detect glucose based on the polymerization of aniline induced by HRP and H2O2 which was produced by the reduction of O2 accompanied by the oxidation of glucose into gluconic acid via GOD. With the increase of glucose, more H2O2 molecules were produced and then a growing number of polyaniline (PANI) molecules were formed on the modified electrode surface, which resulted in the decrease of peak current of Fe(CN)63−/4− because the formed PANI hindered the electron transfer of Fe(CN)63−/4− toward the electrode surface. Based on the decrease of peak current of Fe(CN)63−/4−, the glucose concentration could be determined accurately and selectively. The resulted biosensor exhibited a wide linear range from 16.5 μM to 10.0 mM, a high sensitivity of 41.78 μA mM−1 cm−2 and good selectivity. The glucose biosensor exhibits some advantages over the traditional GOD electrodes in terms of a close to zero applied potential. Moreover, the used electrode might be used as a H2O2 sensor due to its good electrocatalytic response for H2O2.

Preparation of Ni(OH)2 nanoplatelet/electrospun carbon nanofiber hybrids for highly sensitive nonenzymatic glucose sensors

Ni(OH)2 nanoplatelet/electrospun carbon nanofiber (ECF) hybrids have been simply prepared for the construction of nonenzymatic glucose biosensors. The resulting Ni(OH)2/ECF hybrids were carefully examined using SEM, TEM, HRTEM, XRD, and XPS. For all hybrids, two-dimensional Ni(OH)2 nanoplatelets were uniformly anchored on the one-dimensional ECFs, forming a hierarchical nanostructure, and the thickness of Ni(OH)2 nanoplatelets could be readily tailored by controlling the content of Ni(OH)2 precursor. Cyclic voltammetric studies showed enhanced redox properties for Ni(OH)2/ECF-based electrodes relative to pure Ni(OH)2 nanoplatelet electrode and significantly improved the electrocatalytic activity for glucose oxidation. The application of Ni(OH)2/ECF-based electrodes to glucose detection was explored. A low limit of detection (0.1 μM), wide detection linear range (0.005–13.05 mM), and excellent signal stability and reproducibility were demonstrated by this novel Ni(OH)2/ECF-0.06 hybrid. The sensor was also applied in real serum samples, giving satisfactory results. The simple preparation, low cost, and enhanced electrocatalytic performance of these hybrids could pave the way for highly sensitive glucose sensors.

A novel CuO/TiO2 hollow nanofiber film for non-enzymatic glucose sensing

A novel CuO nanoparticle-loaded TiO2 hollow nanofiber film (CuO/TiO2) was prepared by a simple and scalable electrospun nanofiber film template-assisted sol–gel method. In this facile method, the synthesis of TiO2 hollow nanofiber film and the loading of CuO nanoparticle were integrated into a single step. This porous and nanotubular CuO/TiO2 with well-dispersed CuO nanoparticles provides a well-defined hierarchical nanostructure for glucose oxidation. In application to glucose detection, CuO/TiO2 showed high electrocatalytic activity towards the oxidation of glucose in alkaline media, and a nonenzymatic glucose sensor was constructed. Under optimal experimental conditions, the designed sensor exhibited a wide linear range (0.02 to 19.26 mM, R = 0.996), which was wider than the precious CuO-based glucose biosensors. Additionally, the sensor showed high sensitivity, acceptable reproducibility and excellent selectivity. The novel textile formation, porous and hierarchically mesostructured nature of CuO/TiO2 with excellent analytical performances make it a superior platform for the construction of high-performance glucose biosensors.

Facile synthesis of Ni(OH)2 nanoplates on nitrogen-doped carbon foam for nonenzymatic glucose sensors

In this work, ultrathin Ni(OH)2 nanoplates uniformly anchored on nitrogen-doped carbon foam (NCF) were facilely prepared for the construction of nonenzymatic glucose biosensors. The Ni(OH)2/NCF hybrid was prepared by the pyrolysis of melamine foam (utilizing it as a template) followed by the growth of Ni(OH)2 nanoplates via a microwave process. The Ni(OH)2/NCF with three-dimensional macroporous and hierarchical architectures can provide continuous channels for the rapid diffusion of an electrolyte to access the electrochemically active sites of Ni(OH)2 nanoplates. Moreover, the NCF with abundant active sites can effectively prevent the agglomeration of Ni(OH)2, and also could be a conductive core providing efficient electron transport for the fast redox reactions of Ni(OH)2. Being employed as a nonenzymatic glucose detection electrochemical electrode, it exhibits a wide linear response ranging from 5 µM to 9.15 mM, and a low detection limit (0.8 µM) with excellent selectivity. Meanwhile, the sensor was also applied to the detection of glucose content in real serum samples with satisfactory results. The simple preparation procedure, low cost, and enhanced electrocatalytic performance potentially pave a new, effective and promising way for highly sensitive glucose sensors.

Flexible and conductive titanium carbide–carbon nanofibers for the simultaneous determination of ascorbic acid, dopamine and uric acid

The development of novel materials for facile, cost-effective and quick practical application is a demanding research interest in electroanalytical chemistry. Titanium carbide (TiC), as one of the most important transition metal carbides, exhibits good chemical stability and electrical conductivity, and its electrocatalytic activity resembles that of metals, but is much cheaper. In this work, TiC nanoparticle (NP) loaded carbon nanofiber (CNF) films (TCNFs) are synthesized using an electrospinning and carbothermal technique, which facilely maintains their structural integrity with robust adhesion. Uniform TiC NPs are firmly embedded in the surface of CNFs, which integrates the large surface area and unique 3D, porous network structure of CNFs with the good conductivity and excellent electrocatalytic activity of TiC NPs. Simultaneous electrochemical sensing of ascorbic acid (AA), dopamine (DA) and uric acid (UA) at TCNFs displays excellent peak current signals with well-defined peak potentials. The linear ranges are 0.001-1.5 mM, 0.05-160 μM and 0.001-0.875 mM for AA, DA and UA, and the corresponding detection limits are 0.3 μM, 20 nM and 0.3 μM, respectively. In addition, TCNFs show long-term sensing stability and potential applications in real samples, and behave as good anti-interference agents towards KNO3, ZnSO4, glucose, etc. Most importantly, unlike some common carbon-based electrochemical sensor systems, an adsorption-less response is observed for the test analytes at the TCNF electrode. TCNFs show interesting potential as candidates for the construction of electrochemical sensors.

Flexible polypyrrolone-based microporous carbon nanofibers for high-performance supercapacitors

Flexible materials have drawn considerable attention due to the demand for wearable and flexible electronic products. Seeking new kinds of precursors for preparing carbon nanofibers with good flexibility for high-performance supercapacitors is a hot issue. In this work, a flexible polypyrrolone (BBB)/polyimide (PI) composite-based carbon nanofiber membrane (PBPICF) is prepared by a facile electrospinning and carbonization process. The PBPICF membranes exhibit a three-dimensional (3D) porous, fluffy and self-standing structure with good mechanical performance and flexibility, and can be arbitrarily bent and folded. PBPICF-65-35 (consisting of BBB (65 wt%) and PI (35 wt%)) exhibits a high specific capacitance of 172.44 F g−1 in 6 M KOH aqueous solution, which is two-fold more than that of commercial polyacrylonitrile-based carbon nanofibers. In addition, PBPICF-65-35 also displays good power density (90 W kg−1) and energy density (19.4 W h kg−1), and the capacitance remains at 96% even after 10 000 cycles at 1.0 A g−1. Therefore, the simple preparation and good capacitance performance of PBPICFs make them a promising binder-free electrode for wearable supercapacitors.

Three-dimensional N-doped carbon nanotube@carbon foam hybrid: an effective carrier of enzymes for glucose biosensors

Development of efficient, reliable, and cost-effective biosensors for accurate and convenient detection of glucose is highly desirable in the food industry, biotechnology, and clinical diagnosis. Carbon nanotube (CNT)-based enzyme biosensors have received considerable attention due to their excellent performance. However, the performance of these sensors is limited by the drawbacks of CNTs such as low electron transfer rate and catalytic area, and poor conductivity. Herein, three-dimensional (3D) nitrogen-doped CNTs (N-CNTs) supported by a carbon foam (N-CNT@CF) hybrid is fabricated as the carrier matrix to load glucose oxidase (GOD) for constructing high-performance glucose biosensors. A one-step chemical vapor deposition method is employed for the preparation of a N-CNT@CF hybrid, where N-CNTs are densely grown on the skeleton of carbon foam using iron as a catalyst. FT-IR spectroscopy shows that the N-CNT@CF is an effective carrier of GOD without enzyme denaturation. Combined with the extraordinary properties of 3D N-CNT@CF including large active surface area, high conductivity and fast mass transport dynamics, the GOD/N-CNT@CF biosensor achieves a large linear range (0.05–15.55 mM, R = 0.996) and a low detection limit (5.0 μM, S/N = 3) for the detection of glucose. Furthermore, the glucose biosensor exhibited high selectivity, good repeatability and stability.