Xun Feng

Discrimination and simultaneous determination of hydroquinone and catechol by tunable polymerization of imidazolium-based ionic liquid on multi-walled carbon nanotube surfaces

Tunable polymerization of ionic liquid on the surfaces of multi-walled carbon nanotubes (MWCNTs) was achieved by a mild thermal-initiation-free radical reaction of 3-ethy-1-vinylimidazolium tetrafluoroborate in the presence of MWCNTs. Successful modification of polymeric ionic liquid (PIL) on MWCNTs surfaces (PIL-MWCNTs) was demonstrated by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy. The resulting PIL-MWCNTs possessed unique features of high dispersity in aqueous solution and tunable thickness of PIL layer, due to positive imidazole groups along PIL chains and controllable ionic liquid polymerization by tuning the ratio of precursor. Based on cation-π interaction between the positive imidazole groups on PIL-MWCNTs surface and hydroquinone (HQ) or catechol (CC), excellent discrimination ability toward HQ and CC and improved simultaneous detection performance were achieved. The linear range for HQ and CC were 1.0×10(-6) to 5.0×10(-4) M and 1.0×10(-6) to 4.0×10(-4) M, respectively. The detection limit for HQ was 4.0×10(-7) M and for CC 1.7×10(-7) M (S/N=3), correspondingly.

Confining MoS2 nanodots in 3D porous nitrogen-doped graphene with amendable ORR performance

MoS2 nanodots (NDs) were successfully embedded in the three-dimensional (3D) porous frameworks of N-doped graphene (NGr) via in situ pyrolysis of glucose, a layered C3N4 sacrificial template and monolayered MoS2 NDs. The monolayered MoS2 NDs were hydrothermally pre-synthesized and acted as size-controlled precursors. By varying the content of the MoS2 NDs, a series of MoS2 NDs/NGr was obtained, which displayed amendable activity towards oxygen reduction reaction (ORR) in basic solution, due to the balance between the exposed edge sites of the MoS2 NDs and the internal conductive channels of the 3D porous NGr. The optimal composition generated an efficient Pt-free ORR catalyst with good four-electron selectivity, and was shown to have a more positive shift in both the onset and peak potentials than its counterparts. The novel catalyst also demonstrated superior tolerance against methanol and better durability than commercial Pt/C.

Incorporated oxygen in MoS2 ultrathin nanosheets for efficient ORR catalysis

Controllable engineering of high-electronegativity oxygen (O)-heteroatoms into MoS2 ultrathin nanosheets is realized via a facile post-modification process. The incorporated oxygen atoms impart a dramatically enhanced ORR activity to the pristine nanosheets, with a 7.8-fold current increase as well as 180 mV and 160 mV positive shifts in both onset and half-wave potentials that are almost comparable with the commercial Pt/C catalyst. Furthermore, oxygen incorporation also triggers a transformation of the process from two-electron to a four-electron process. The improved topical conductivity, as well as the preferential adsorption of oxygen molecules originating from the heteroatoms engineering is supposed to be responsible for the efficient ORR. The prospect of controllably engineering heteroatoms into MoS2 ultrathin nanosheets with versatile applications is also highlighted in this work.

One-Step Pyrolytic Synthesis of Nitrogen and Sulfur Dual-Doped Porous Carbon with High Catalytic Activity and Good Accessibility to Small Biomolecules

As one of promising catalysts that contain high density of active sites, N doped carbons have been extensively researched, while the reports for N, S dual-doped carbon materials are far less exhaustive. Herein, devoid of activation process and template, N, S dual-doped porous carbon (N-S-PC) was prepared for the first time via one-step pyrolysis of sodium citrate and cysteine. Possessing unique porous structure and large pore volume as well as good accessibility, N-S-PC demonstrates significantly improved electrocatalytic activity toward oxidation of ascorbic acid (AA), dopamine (DA), and uric acid (UA). In the coexisting system, the peak potential separation between AA and DA is up to 251 mV, which is much larger than for most of the other carbons. On the basis of large potential separation and high current response, selective and sensitive simultaneous determination of AA, DA, and UA was successfully accomplished by differential pulse voltammetry, displaying a linear response from 50 to 2000 μM, from 0.1 to 50 μM, and from 0.1 to 50 μM with a detection limit (S/N = 3) of 0.78, 0.02, and 0.06 μM. This work highlights the importance of N, S dual doping and hierarchical porous carbons for efficient catalysis.

Sodium dodecyl benzene sulfonate functionalized graphene for confined electrochemical growth of metal/oxide nanocomposites for sensing application

The electrochemical fructose sensor attracts considerable attention in the food industry and for clinical applications. Here, a novel fructose biosensor was developed based on immobilization of highly dispersed CuO-Cu nanocomposites on Graphene that was non-covalently functionalized by sodium dodecyl benzene sulfonate (SDBS) (denoted briefly as SDBS/GR/CuO-Cu). The structure and morphology of SDBS/GR/CuO-Cu were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemistry and electrocatalysis were evaluated by cyclic voltammetry (CV). The fructose sensing performances were evaluated by chronoamperometry (i-t). Those properties were also compared with that of CuO-Cu. Results revealed the distinctly enhanced sensing properties of SDBS/GR/CuOue5f8Cu towards fructose, showing significantly lowered overpotential of +0.40V, ultrafast (<1s) and ultra-sensitive current response (932 μAm M(-1)cm(-2)) in a wide linear range of 3-1000 μM, with satisfactory reproducibility and stability. Those could be ascribed to the good electrical conductivity, large specific surface area, high dispersing ability and chemical stability of GR upon being functionalized non-covalently by SDBS, as well as the outstanding cation anchoring ability of SDBS on GR to resist aggregation among Cu-based nanoparticles during electro-reduction. More importantly, an improved selectivity in fructose detection was achieved. SDBS/GR/CuO-Cu is one of the promising electrode materials for electrochemical detection of fructose.

One-step pyrolytic synthesis of small iron carbide nanoparticles/3D porous nitrogen-rich graphene for efficient electrocatalysis

Uniform iron carbide nanoparticles (Fe3C, ∼10 nm), size evolved from nano-scaled Fe-MIL-88b, were one-pot pyrolytically embedded in 3D porous N-rich graphene. Extra ORR catalytic activity with four-electron selectivity was achieved in an alkaline electrolyte. The onset and peak potential were 10 mV and 40 mV more positive, respectively, than commercial Pt/C.

Design of templated nanoporous carbon electrode materials with substantial high specific surface area for simultaneous determination ofbiomolecules

Nanoporous carbon materials have attracted significant interests in the design of electrodes for electrocatalysis and biosensors. Here, three templated nanoporous carbons (TNCs) materials with substantial different specific surface area were designed and synthesized by a nanocasting method, in which mesoporous silicates and acid were used as template and catalyst, respectively. The TNCs were then used as electrode materials for simultaneous detection of dopamine (DA), ascorbic acid (AA) and uric acid (UA) at physiological pH. The correlations between specific surface area, edge-plane defect sites in TNCs and their distinguishing ability towards AA, DA, and UA were investigated. For TNCs with substantial larger specific surface area and more defect sites, the oxidation peaks of AA, DA and UA were separated well and their oxidation currents increased remarkably. A highly sensitive electrochemical sensor for simultaneous detection of those biomolecules was achieved by designing TNCs1 with the largest specific surface area and the most defect sites as the electrode material. The sensitivity of AA, DA and UA at the sensor is 0.012, 4.031, 0.605 μA/μM respectively. Results suggest that TNCs1 is promising in biomolecules simultaneous detection. This work may also be valuable for scientists who search for excellent carbon materials for biosensing and electrocatalysis.

Sensing epinephrine with an ITO electrode modified with an imprinted chitosan film containing multi-walled carbon nanotubes and a polymerized ionic liquid

AbstractWe report on a sensor for epinephrine (EP) that is based on an ITO electrode modified with multi-walled carbon nanotubes pre-coated with a polymerized ionic liquid (PIL-MWNTs). A chitosan film was then electrodeposited on the ITO electrode in the presence of EP (the template) and the PIL-MWNTs. This film acts as an excellent recognition matrix due to its excellent film-forming ability and the many functional groups that favor hydrogen bond formation with the target (EP). The PIL-MWNTs, in turn, can improve the sensing performance due to their good electrical conductivity, high dispersity, and large surface area. The imprinted films were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform IR spectroscopy, and thermogravimetric analysis. The electrochemistry of the imprinted electrode was investigated by cyclic voltammetry, electrochemical impedance spectroscopy, differential pulse voltammetry and chronoamperometry. The response to EP is linear in the 0.2xa0μM to 0.67xa0mM concentration range, and the detection limit is as low as 60xa0nM (at an S/N of 3). The electrode is reusable and offers good reproducibility and stability.n FigureAn epinephrine imprinted electrode was facile achieved by electrodepositing chitosan on ITO surface in the presence of epinephrine and polymerized ionic liquid-functionalized carbon nanotubes, followed by removal of the epinephrine template molecule. Specific recognition of EP molecule and its determination were realized at this imprinted sensor.

Highly accessible Pt nanodots homogeneously decorated on Au nanorods surface for sensing.

Some nanostructures are reported to possess enzyme-mimetic activities similar to those of natural enzymes. Herein, highly-dispersed Pt nanodots on Au nanorods (HD-PtNDs@AuNRs) with mimetic peroxidase activity were designed as an active electrode modifier for fabrication of a hydrogen peroxide (H2O2) electrochemical sensor. The HD-PtNDs@AuNRs were synthesized by a seed-mediated growth approach and confirmed by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and UV-vis spectroscopy. The electrochemical and catalytical performances of HD-PtNDs@AuNRs towards H2O2 reduction were investigated in detail by cyclic voltammetry and amperometry. The HD-PtNDs@AuNRs modified electrode displayed a high catalytic activity to H2O2 at -0.10 V (versus SCE), a rapid response within 5 s, a wide linear range of 2.0-3800.0 μM, a detection limit of 1.2 μM (S/N=3), and a high sensitivity of 181 μA mM(-1) cm(-2). These results suggested a promising potential of fabricating H2O2 electrochemical sensor using HD-PtNDs@AuNRs.

Nitrogen-rich graphene from small molecules as high performance anode material

Nitrogen-rich graphene sheets were successfully achieved via facile thermal condensation of glucose and dicyandiamide at different temperatures during which dicyandiamide acts both as nitrogen source and sacrifice template. Devoid of surfactants or poisonous organic solvents, this small-molecule synthetic approach is a simple and cost-effective way to obtain nitrogen-rich graphene sheets (NRGS) with high specific surface area and large pore volume. Shown to be a promising anode material, the NRGS displayed high reversible capacity, excellent rate capability, and superior cycle performance. The superior lithium-storage performance is ascribed to the unique features of NRGS, including a large quantity of defects due to the high nitrogen doping level, favorable lithium ion transportation channels by virtue of the large surface area, and ultrahigh pore volume, as well as the crumpled two-dimensional structure.