Chunxian Guo

Carbon-Based Dots Co-doped with Nitrogen and Sulfur for High Quantum Yield and Excitation-Independent Emission†

Helpful elements: A facile bottom-up method using citric acid and L-cysteine as a precursor has been developed to prepare graphene quantum dots (GQDs) co-doped with nitrogen and sulfur. A new type and high density of surface state of GQDs arises, leading to high yields (more than 70u2009%) and excitation-independent emission. FLQY = fluorescence quantum yield.

Direct electrochemistry of hemoglobin on carbonized titania nanotubes and its application in a sensitive reagentless hydrogen peroxide biosensor.

Carbonized TiO(2) nanotubes (TNT/C) prepared by carbonization with organic polymers possess advantages combined from high conductivity of carbon and nanostructure of TiO(2) nanotubes. The material was used as a supporting matrix to immobilize a redox protein, hemoglobin (Hb), to explore its direct electron transfer ability. The apparent heterogeneous electron transfer rate constant (k(ET)) of Hb on TNT/C is 108s(-1), which is much higher than that in the reported works, demonstrating excellent direct electrochemistry behavior. The TNT/C-Hb modified glassy carbon electrode (GCE) demonstrates significant electrocatalytic activity for reduction of hydrogen peroxide with a small apparent Michaelis-Menten constant (87.5 microM). The TNT/C-Hb based H(2)O(2) sensor has a low detection limit (0.92 microM), fast response time (3s) and high dynamic response range (10(-6) to 10(-4)M), a much better performance than the reported works. These results demonstrate that a direct electrochemistry behavior can be significantly enhanced through simple carbon coating on a nanostructured material for higher reaction surface area and better conductivity. This work suggests that Hb-immobilized TNT/C has potential applications in a sensitive H(2)O(2) sensor.

Nanostructure control of graphene-composited TiO2 by a one-step solvothermal approach for high performance dye-sensitized solar cells

We present a one-step solvothermal approach to prepare uniform graphene-TiO(2) nanocomposites with delicately controlled TiO(2) nanostructures, including ultra-small 2 nm nanoparticles, 12 nm nanoparticles and nanorods. Using three composites as photoanode materials, the effect of nanostructure of graphene-composited TiO(2) on the performance of dye-sensitized solar cells was investigated, and results showed that the ultra-small 2 nm TiO(2)-graphene composite based photoanode exhibited the highest power conversion efficiency of 7.25%.

Nanochain-structured mesoporous tungsten carbide and its superior electrocatalysis

A unique nanochain-structured mesoporous tungsten carbide (m-NCTC) was synthesized through a simple combined hydrothermal reaction–post heat-treatment approach. When loaded with Pt, the nanostructure (Pt/m-NCTC), as a catalyst, demonstrates high unit mass electroactivity (323 A (g Pt)−1) and high resistance to CO poisoning for methanol oxidation, and is much superior to Pt/C, one of the known excellent electrocatalysts. Its high reaction activity and strong poison-resistivity is very likely due to the unique mesoporous nanochain structure and high specific surface area (113 m2 g−1). This work provides a universal and economic method to synthesize novel mesoporous structured materials and provides scientific insight of mesoporous structured electrocatalysis, thus leading to various important applications as a catalyst in fuel cells, solar cells, sensors and in organic synthesis reactions.

Reduction of Charge Recombination by an Amorphous Titanium Oxide Interlayer in Layered Graphene/Quantum Dots Photochemical Cells

The effect of an amorphous TiO(x) interlayer on layered graphene/quantum dots photochemical cells has been investigated. The addition of the TiO(x) interlayer eliminates the decay of photocurrent in the initial seconds after light illumination and significantly increases the slope of the steady-state photocurrent versus the light intensity. The open-circuit voltage decay measurements further illustrate a longer electron lifetime when an amorphous TiO(x) interlayer is applied. Consequently, the photocurrent and photovoltage of the photovoltaic cell with a TiO(x) interlayer are greatly increased. This work demonstrates that the graphene/amorphous TiO(x) composite structure effectively inhibits charge recombination while enhancing charge transfer, providing a promising scaffold for quantum dots and dye-sensitized photovoltaic cells.

Modification of a thin layer of α-Fe2O3 onto a largely voided TiO2 nanorod array as a photoanode to significantly improve the photoelectrochemical performance toward water oxidation

A largely voided TiO2 nanorod array was synthesized and further modified with a thin layer of α-Fe2O3 (Fe2O3@TiO2), by the pyrolysis of an FeCl3 ethanol solution, as a photoanode toward water oxidation, showing significantly improved photoelectrochemical performance over a TiO2 nanorod array. Among all of the Fe2O3 decorated TiO2-based photoanodes, the optimal voided Fe2O3@TiO2 nanorod array photoanode delivered the largest photocurrent density of 3.39 mA cm−2 at 1.23 V (vs. RHE) and the highest applied bias photon-to-current efficiency (ABPE) (1.153%) under 100 mW cm−2 UV-vis light illumination. In particular, the ABPE for the as-prepared photoanode was ∼3.3 times higher than that of the plain TiO2 nanorod array (0.35%), ∼11.3 times higher than that of the Fe2O3-modified randomly arranged TiO2 nanorods and ∼6.2 times higher than that of a Fe2O3-modified densely arranged TiO2 nanotube array. The significant enhancement mainly originates from the large voids in the nanorod array allowing a thin layer of Fe2O3 to fully modify the TiO2 nanorods, which improves the absorption of UV light, boosts the charge interface transfer rate, reduces the charge diffusion length and suppresses the charge recombination process. This work demonstrates a feasible route to improving the photoelectrochemical catalytic performance of TiO2 semiconductors toward water splitting.

Ga doping to significantly improve the performance of all-electrochemically fabricated Cu2O-ZnO nanowire solar cells.

Cu2O-ZnO nanowire solar cells have the advantages of light weight and high stability while possessing a large active material interface for potentially high power conversion efficiencies. In particular, electrochemically fabricated devices have attracted increasing attention due to their low-cost and simple fabrication process. However, most of them are partially electrochemically fabricated by vacuum deposition onto a preexisting ZnO layer. There are a few examples made via all-electrochemical deposition, but the power conversion efficiency (PCE) is too low (0.13%) for practical applications. Herein we use an all-electrochemical approach to directly deposit ZnO NWs onto FTO followed by electrochemical doping with Ga to produce a heterojunction solar cell. The Ga doping greatly improves light utilization while significantly suppressing charge recombination. A 2.5% molar ratio of Ga to ZnO delivers the best performance with a short circuit current density (Jsc) of 3.24 mA cm(-2) and a PCE of 0.25%, which is significantly higher than in the absence of Ga doping. Moreover, the use of electrochemically deposited ZnO powder-buffered Cu2O from a mixed Cu(2+)-ZnO powder solution and oxygen plasma treatment could reduce the density of defect sites in the heterojunction interface to further increase Jsc and PCE to 4.86 mA cm(-2) and 0.34%, respectively, resulting in the highest power conversion efficiency among all-electrochemically fabricated Cu2O-ZnO NW solar cells. This approach offers great potential for a low-cost solution-based process to mass-manufacture high-performance Cu2O-ZnO NW solar cells.

TiO2 nanowire FET device: encapsulation of biomolecules by electro polymerized pyrrole propylic acid.

Silane-based methods have become the standards for the conjugation of biomolecules, especially for the preparation of one-dimensional nanomaterial biosensors. However, the specific binding of those target molecules might raise problems with regard to the sensing and non-sensing regions, which may contaminate the sensing devices and decrease their sensitivity. This paper attempts to explore the encapsulation of biomolecules on a one-dimensional nanomaterial field effect transistor (FET) biosensor using polypyrrole propylic acid (PPa). Specifically, the encapsulation of biomolecules via the electropolymerization of pyrrole propylic acid (Pa), a self-made low-conductivity polymer, on TiO(2)-nanowire (NW)-based FETs is presented. The energy dispersive spectrum (EDS) was obtained and electrical analysis was conducted to investigate PPa entrapping anti-rabbit IgG (PPa/1°Ab) on a composite film. The specificity, selectivity and sensitivity of the sensor were analyzed in order to determine the immunoreaction of PPa/1°Ab immobilized NW biosensors. Our results show that PPa/1°Ab achieved high specificity immobilization on NWs under the EDS analysis. Furthermore, the TiO(2)-NW FET immunosensor developed in this work successfully achieved specificity, selectivity and sensitivity detection for the target protein rabbit IgG at the nano-gram level. The combination of PPa material and the electropolymerization method may provide an alternative method to immobilize biomolecules on a specific surface, such as NWs.

Pyro-synthesis of a nanostructured NaTi2(PO4)3/C with a novel lower voltage plateau for rechargeable sodium-ion batteries

A pair of novel reversible oxidation/reduction peaks at around 0.44V is discovered during the deep sodiation of NaTi2(PO4)3/C obtained by the pyro-synthetic approach. This novel low-voltage plateau doubles the charge/discharge capacity of NaTi2(PO4)3, thus turning it into a more promising anode for Na-ion batteries.

Soft- to network hard-material for constructing both ion- and electron-conductive hierarchical porous structure to significantly boost energy density of a supercapacitor.

Soft-material PEDOT is used to network hard Co3O4 nanowires for constructing both ion- and electron-conductive hierarchical porous structure Co3O4/PEDOT to greatly boost the capacitor energy density than sum of that of plain Co3O4 nanowires and PEDOT film. Specifically, the networked hierarchical porous structure of Co3O4/PEDOT is synthesized and tailored through hydrothermal method and post-electrochemical polymerization method for the PEDOT coating onto Co3O4 nanowires. Typically, Co3O4/PEDOT supercapacitor gets a highest areal capacitance of 160mFcm-2 at a current density of 0.2mAcm-2, which is about 2.2 times larger than the sum of that of plain Co3O4 NWs (0.92mFcm-2) and PEDOT film (69.88mFcm-2). Besides, if only PEDOT as active mass is counted, Co3O4/PEDOT cell can achieve a highest capacitance of 567.21Fg-1, this is the highest capacitance value obtained by PEDOT-based supercapacitors. Furthermore, this soft-hard network porous structure also achieves a high cycling stability of 93% capacitance retention after the 20,000th cycle. This work demonstrates a new approach to constructing both ion and electron conductive hierarchical porous structure to significantly boost energy density of a supercapacitor.