Jianbo Jiang

High-sensitivity paracetamol sensor based on Pd/graphene oxide nanocomposite as an enhanced electrochemical sensing platform

Well-dispersed Pd nanoparticles were facilely anchored on graphene oxide (Pd/GO) via a one-pot chemical reduction of the Pd(2+) precursor without any surfactants and templates. The morphology and composition of the Pd/GO nanocomposite were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and energy dispersive analysis of X-ray (EDX). The stepwise fabrication process of the Pd/GO modified electrode and its electrochemical sensing performance towards paracetamol was evaluated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The experimental results indicate that the as-synthesized Pd nanoparticles are relatively uniform in size (5-10 nm) without large aggregation and uniformly distributed in the carbon matrix with the overall Pd content of 28.77 wt% in Pd/GO. Compared with the GO modified electrode, the Pd/GO modified electrode shows a better electrocatalytic activity to the oxidation of paracetamol with lower oxidation potential and larger peak current, so the Pd/GO nanocomposite can be used as an enhanced sensing platform for the electrochemical determination of paracetamol. The kinetic parameters of the paracetamol electro-oxidation at Pd/GO electrode were studied in detail, and the determination conditions were optimized. Under the optimal conditions, the oxidation peak current is linear to the paracetamol concentration in the ranges of 0.005-0.5 μM and 0.5-80.0 μM with a detection limit of 2.2 nM. Based on the high sensitivity and good selectivity of the Pd/GO modified electrode, the proposed method was successfully applied to the determination of paracetamol in commercial tablets and human urines, and the satisfactory results confirm the applicability of this sensor in practical analysis.

Facile synthesis of α-MoO3 nanobelts and their pseudocapacitive behavior in an aqueous Li2SO4 solution

α-MoO3 nanobelts were successfully prepared by a facile hydrothermal method with sodium molybdate (Na2MoO4) as the Mo source and NaCl as the capping agent. The as-prepared products were characterized using Fourier transformation infrared spectrophotometry (FT-IR), X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selected area electronic diffraction (SAED) and their pseudocapacitive properties were investigated in a 0.5 M aqueous Li2SO4 solution by cyclic voltammetry (CV), chronopotentiometry (CP) and AC impendence. The results show that the dimensions of the as-prepared α-MoO3 nanobelts are 200–400 nm in width, ca. 60 nm in thickness and 3–8 µm in length. The redox potential for the α-MoO3 nanobelts is found in the range of −0.3 to −1.0 V vs. SCE, which indicates that the α-MoO3 nanobelts can be used as anode electrode materials for hybrid supercapacitors. The specific capacitances of the α-MoO3 nanobelts at 0.1, 0.25, 0.5 and 1 A g−1 are 369, 326, 256 and 207 F g−1, respectively. The maximum specific capacitance of the α-MoO3 nanobelts is much higher than those of MoO3 nanoplates with 280 F g−1, MoO3 nanowires with 110 F g−1 and MoO3 nanorods with 30 F g−1 recently reported in literature. Furthermore, the α-MoO3 nanobelt electrode exhibits a good cycle stability with more than 95% of the initial specific capacitance maintained after 500 cycles. Additionally, the present route to prepare nanostructured MoO3 is much less expensive than those with Mo powders as the Mo source. Overall, the obtained high performance α-MoO3 nanobelts could be a promising electrode material for supercapacitors.

Designed synthesis of a novel BiVO4–Cu2O–TiO2 as an efficient visible-light-responding photocatalyst

A novel visible-light-responding BiVO4-Cu2O-TiO2 ternary heterostructure composite was successfully fabricated via the preparation of BiVO4-TiO2 followed by coupling with Cu2O through facile wet chemistry methods based on the strategy of energy gap engineering. The as-fabricated composite was characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, UV-vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. Benefited from the rational design and construction, BiVO4-Cu2O-TiO2 exhibits a significantly enhanced photocatalytic activity for the degradation of rhodamine B (RhB) under the visible-light irradiation as compared with Cu2O and Cu2O-TiO2. Specifically, under the irradiation with an ordinary 9 W energy-saving fluorescent lamp for 8h, the photocatalytic degradation ratio of RhB for 5 wt%BiVO4-40 wt%Cu2O-TiO2 reaches 97.8%. The enhanced photocatalytic activity of BiVO4-Cu2O-TiO2 can be ascribed to the matched band edge positions of BiVO4, Cu2O and TiO2, the heterojunction formations among them as well as the lower charge transfer resistance, favoring the separation of the photo-generated electron-hole pairs. A possible mechanism of the visible-light photocatalytic degradation of RhB is also proposed.

Ag/N-doped reduced graphene oxide incorporated with molecularly imprinted polymer: An advanced electrochemical sensing platform for salbutamol determination

In this work, the metallic silver and non-metallic nitrogen co-doped reduced graphene oxide (Ag-N-RGO) was first synthesized by a simple and cost-effective strategy, and then a molecularly imprinted polymer (MIP) was formed in situ at the surface of the prepared composite via electropolymerization of o-phenylenediamine in the presence of salbutamol as the template molecule. The electrochemical characterizations demonstrate that the bifunctional graphene-based composite shows improved catalytic performance than that of pristine graphene doped with one-component or none. The MIP sensor based on Ag-N-RGO owns high porous surface structure, resulting in the increased current response and enhanced recognition capacity than that of non-imprinted sensor. The outstanding performance of the developed sensor derives from the combined advantages of Ag-N-RGO with effective catalytic property and MIP with excellent selectivity. Under the optimal conditions, the electrochemical response of the developed sensor is linearly proportional to the concentration of salbutamol in the range of 0.03-20.00µmolL-1 with a low detection limit of 7 nmol L-1. The designed sensor has exhibited the multiple advantages such as low cost, simple manufacture, convenient use, excellent selectivity and good reproducibility. Finally, the proposed method has been extended for the determinations of salbutamol in human urine and pork samples, and the satisfactory recoveries between 98.9-105.3% are achieved.

Facile assembly of a 3D rGO/MWCNTs/Fe2O3 ternary composite as the anode material for high-performance lithium ion batteries

A three-dimensional (3D) reduced graphene oxide (rGO)/multi-walled carbon nanotubes (MWCNTs)/Fe2O3 ternary composite was fabricated by a facile, green and economical one-step urea-assisted hydrothermal approach as a promising anode material for high-performance lithium ion batteries. Designing and tailoring the 3D porous hierarchical nanostructure of rGO/MWCNTs/Fe2O3 contributes to a robust hybrid material with overwhelmingly superior electrochemical performances compared with bare Fe2O3, MWCNTs/Fe2O3, rGO/Fe2O3 and a physical mixture of rGO/Fe2O3 and MWCNTs, due to the strong synergistic effects among the individual component. The 3D rGO/MWCNTs/Fe2O3 composite exhibits highly enhanced specific capacity, cycling performance and rate capability: initial discharge and charge capacities of 1692 and 1322 mAh g−1 at 100 mA g−1, respectively, 1118 mAh g−1 after 50 cycles at 100 mA g−1 and 785 mAh g−1 at 1000 mA g−1. The assembling mechanism well illustrates the simple strategy, and the comprehensive electrochemical investigations further demonstrate its supernormal effectiveness, which could be extended to various transition metal oxides for energy storage and conversion.

Facile synthesis of 3D porous nitrogen-doped graphene as an efficient electrocatalyst for adenine sensing

In this work, a simple, low-cost and eco-friendly strategy for fabricating the three-dimensional porous nitrogen-doped graphene (3D-N-GN) is demonstrated by combining the hydrothermal assembly and freeze-drying process without using any framework support. The desired features for 3D-N-GN, such as rich macroporosity, nitrogen-doping structure and high active surface area have been confirmed by scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical techniques, respectively. In comparison with two-dimensional graphene (2D-GN) and nitrogen-doped graphene (2D-N-GN), 3D-N-GN makes a more negative shift in the oxidation peak potential of adenine together with a remarkable increase in the oxidation peak current, highlighting the importance of the nitrogen-doping and 3D construction of the graphene-based support for improving the electrocatalytic performance. It also indicates that 3D-N-GN can be used as an efficient electrocatalyst for adenine sensing. Furthermore, the sensing conditions are optimized and the resulting sensor displays excellent analytical performance in the detection of adenine at low concentrations ranging from 0.02 to 1.20 μM, with a detection limit of 8 nM. Finally, this proposed method not only exhibits preferable reproducibility, stability and adequate sensitivity, but also demonstrates good efficiency in the detection of adenine in biological fluids.

One-step solution-phase synthesis of Co3O4/RGO/acetylene black as a high-performance catalyst for oxygen reduction reaction

On the way to become promising oxygen reduction reaction (ORR) catalysts, the hybrids composed of reduced graphene oxide (RGO) and transition metal oxides are suffering from stacking of RGO sheets. In this work, a Co3O4/RGO/acetylene black (AB) hybrid was successfully synthesized via a facile one-step solution-phase route with sandwiching of AB particles between the RGO sheets during the synthesis of Co3O4/RGO, which can effectively tackle the stacking of RGO sheets. Compared with Co3O4/RGO, Co3O4/RGO/AB-P (mixing AB with the pre-prepared Co3O4/RGO with stirring), Co3O4/RGO/AB-M (mixing AB with Co3O4/RGO during the fabrication of the Co3O4/RGO catalytic layer for ORR) and commercial 10 wt% Pt/C, the Co3O4/RGO/AB hybrid exhibits increases of 50.6%, 32.5%, 37.9% and 8.9% in the ORR current density, respectively. This indicates that the introduction strategy of AB to Co3O4/RGO plays a vital role in the enhancement of ORR catalytic activity. Moreover, the Co3O4/RGO/AB hybrid shows a subtle ascending trend in the ORR current density during continuous operation for 72 000 s, while Pt/C exhibits a 9.0% decrease. The exceptional ORR catalytic performance of Co3O4/RGO/AB can also be ascribed to the large specific surface area, well-anchored Co3O4 nanoparticles on the RGO sheets, and low ohmic and kinetic impedances for ORR. We hope this work will be conducive for the extensive commercial applications of fuel cells.

Facile fabrication of sandwich-structured Co3O4/N-rGO/AB hybrid with enhanced ORR electrocatalytic performances for metal-air batteries

Exploring alternative catalysts with low cost and high catalytic performance to the existing Pt and Pt-based catalysts used in oxygen reduction reactions (ORR) is crucial for the extensive commercial application of metal–air batteries and fuel cells. Herein, we have rationally designed and facilely synthesized a sandwich-structured Co3O4/N-reduced graphene oxide (rGO)/acetylene black (AB) hybrid as a novel ORR catalyst for these renewable energy conversion/storage devices. With N doped to rGO, the size of the Co3O4 nanoparticles decreases pronouncedly and the ORR activity enhances significantly when compared to Co3O4/rGO/AB and Co3O4/rGO. At the same time, rotating-disk electrode measurements reveal that the electrocatalytic reduction process using Co3O4/N-rGO/AB is a 4e transfer pathway, while Co3O4/rGO/AB and Co3O4/rGO hybrids possess a reduction process of dominant 4e with partial 2e. Remarkably, Co3O4/N-rGO/AB displays superior electrochemical performance including activity and durability in comparison with commercially available Pt/C, which is further confirmed by the full cell tests for aluminum–air batteries with them as the electrocatalysts, suggesting that Co3O4/N-rGO/AB is a promising candidate as an alternative to Pt and Pt-based catalysts.

One-pot in situ synthesis of a CoFe2O4 nanoparticle-reduced graphene oxide nanocomposite with high performance for levodopa sensing

In this work, a simple and facile protocol for the synthesis of a cobalt-ferrite magnetic nanoparticle-reduced graphene oxide nanocomposite (CoFe2O4/RGO) was achieved using an in situ chemical co-precipitation method. The characteristics of the synthesized nanocomposite were carefully investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy and electrochemical technologies, respectively. The results reveal that the abundant CoFe2O4 nanoparticles are successfully formed with particle sizes in the range of 460–510 nm and uniformly anchored on the RGO nanosheets. Due to the imbedding of CoFe2O4 nanoparticles, the nanocomposite exhibits a larger surface area and superior electrocatalytic activity towards the oxidation of levodopa, which could be used as an efficient electrocatalyst for levodopa sensing. The parameters that influence the sensing property were investigated in detailed. Under the optimum conditions, the oxidation peak currents obtained by differential pulse voltammetry and chronoamperometry show linear responses for levodopa concentrations in the ranges of 0.02–45 μM and 10–420 μM respectively, and a low detection limit of 12 nM is achieved. Compared with those of the existing analogues reported for levodopa detection, the CoFe2O4/RGO-based sensor demonstrates outstanding properties such as high sensitivity, low detection limit and wide linear dynamic range. Finally, the practical analytical application of the developed sensor was assessed by the determination of levodopa in commercially available tablets and urine samples, and satisfactory recoveries were obtained in the range of 97.8–103.2%.

N-doped carbon coated anatase TiO2 nanoparticles as superior Na-ion battery anodes

N-doped carbon coated TiO2 nanoparticles (TiO2@NC) were synthesized through a simple two-step route, in which dopamine was simultaneously utilized as both nitrogen and carbon sources. With TiO2@NC applied in the Na-ion battery (SIB) anodes, the continuous and uniform N-doped carbon layer can not only enhance the electrical conductivity of TiO2 and facilitate the surface pseudocapacitive process, but also serve as a buffer layer to accommodate the volume expansion during the sodiation-desodiation processes. The as-prepared TiO2@NC exhibits excellent electrochemical performance when utilized as the SIB anodes, which delivers a remarkably high reversible capacity of 250.2 mAh g-1 at a rate of 0.25C (84 mA g-1) after 200 cycles and still retains 122.1 mAh g-1 at 10C (3.35 A g-1) even after 3000 cycles accompanied with a 95.3% retention of the maximum capacity, outperforming most of the reported TiO2/C-based composites as SIB anodes. To our best knowledge, the preparation of TiO2@NC with dopamine as both nitrogen and carbon sources and its application in the SIB anodes are reported for the first time.