Linqun Zhang

Chemically Modulated Carbon Nitride Nanosheets for Highly Selective Electrochemiluminescent Detection of Multiple Metal-ions

Chemical structures of two-dimensional (2D) nanosheet can effectively control the properties thus guiding their applications. Herein, we demonstrate that carbon nitride nanosheets (CNNS) with tunable chemical structures can be obtained by exfoliating facile accessible bulk carbon nitride (CN) of different polymerization degree. Interestingly, the electrochemiluminescence (ECL) properties of as-prepared CNNS were significantly modulated. As a result, unusual changes for different CNNS in quenching of ECL because of inner filter effect/electron transfer and enhancement of ECL owing to catalytic effect were observed by adding different metal ions. On the basis of this, by using various CNNS, highly selective ECL sensors for rapid detecting multiple metal-ions such as Cu(2+), Ni(2+), and Cd(2+) were successfully developed without any labeling and masking reagents. Multiple competitive mechanisms were further revealed to account for such enhanced selectivity in the proposed ECL sensors. The strategy of preparing CNNS with tunable chemical structures that facilely modulated the optical properties would open a vista to explore 2D carbon-rich materials for developing a wide range of applications such as sensors with enhanced performances.

Label-free electrochemical detection of methyltransferase activity and inhibitor screening based on endonuclease HpaII and the deposition of polyaniline.

Detection of DNA methylation and methyltransferase (MTase) activity are important in determining human cancer because aberrant methylation was linked to cancer initiation and progression. In this work, we proposed an electrochemical method for sensitive detection of DNA methylation and MTase activity based on methylation sensitive restriction endonuclease HpaII and the deposition of polyaniline (PANI) catalyzed by HRP-mimicking DNAzyme. In the presence of methylated DNA, HRP-mimicking DNAzyme catalyzed the polymerization of aniline on the dsDNA template, producing huge DPV current. In the presence of non-methylated DNA, dsDNA are cleaved and digested by HpaII and exonuclease III, as a result, no PANI are deposited. This method can be used to determine DNA methylation at the site of CpG. It exhibits a wide linear response toward M.SssI MTase activity in the range of 0.5-0.6 U mL(-1) with the detection limit of 0.12 U mL(-1). G-rich DNA forms HRP mimicking DNAzyme, which avoids complex labeling procedures and is robust. The method is simple, reliable, sensitive and specific, which has been successfully applied in human serum samples and been used to screen the inhibitors. Thus, the proposed method may be a potential and powerful tool for clinical diagnosis and drug development in the future.

Synthesis of B-doped hollow carbon spheres as efficient non-metal catalyst for oxygen reduction reaction

The oxygen reduction reaction (ORR) is one of the crucial reactions in fuel cells and metal–air batteries. Heteroatom doped carbon spheres can serve as alternative low-cost non-metal electrocatalysts for ORR. Herein, we developed an effective route to the synthesis of uniform and electrochemically active B-doped hollow carbon nanospheres (BHCSs). BHCSs were synthesized via the carbonization of a boric phenolic resin supported by SiO2, followed by etching the SiO2 template. The content of B, B dopant species and specific surface area were adjusted by changing the content of the B precursor and the calcination temperature. Moreover, their influence on the performance of electrocatalytic activity was explored. It was found that, among these B-doping type materials (BC2O, BCO2, B4C and BC3), B–C bonds (B4C and BC3) played a crucial role on improving the electrocatalytic activity. Compared with the hollow carbon nanospheres (HCSs), a 70 mV positive shift of the onset potential and 1.7 times kinetic current density could be clearly observed with BHCSs. In addition, the BHCSs revealed better stability and methanol tolerance than commercial Pt/C (HiSPEC™ 3000, 20%). Thus, the as-prepared BHCSs, as inexpensive and efficient non-metal ORR catalysts, may have a promising application in direct methanol fuel cells.

Manganese oxide nanowires wrapped with nitrogen doped carbon layers for high performance supercapacitors.

In this study, manganese oxide nanowires wrapped by nitrogen-doped carbon layers (MnO(x)@NCs) were prepared by carbonization of poly(o-phenylenediamine) layer coated onto MnO2 nanowires for high performance supercapacitors. The component and structure of the MnO(x)@NCs were controlled through carbonization procedure under different temperatures. Results demonstrated that this composite combined the high conductivity and high specific surface area of nitrogen-doped carbon layers with the high pseudo-capacitance of manganese oxide nanowires. The as-prepared MnO(x)@NCs exhibited superior capacitive properties in 1 M Na2SO4 aqueous solution, such as high conductivity (4.167×10(-3) S cm(-1)), high specific capacitance (269 F g(-1) at 10 mV s(-1)) and long cycle life (134 F g(-1) after 1200 cycles at a scan rate of 50 mV s(-1)). It is reckoned that the present novel hybrid nanowires can serve as a promising electrode material for supercapacitors and other electrochemical devices.

Effect of annealing temperature and element composition of titanium dioxide/graphene/hemin catalysts for oxygen reduction reaction

The oxygen reduction reaction (ORR) plays an important role at the cathode of fuel cells in practical applications. Herein, a titanium dioxide/graphene supported hemin (TiO2/Gr/Hem) composite material with a flower-like superstructure was successfully prepared through a two-step solvothermal reaction. By a further heat-treatment at 300–900 °C, the electrocatalytic activity of the as-obtained catalysts was examined, and it was found that the pyrolysis at 700 °C gave rise to the best catalytic activity for the ORR in alkaline media. This heat-treatment temperature was found to be crucial in determining the activity and stability of catalysts, due to the enhanced structural defects, active sites, geometrical complexity, and larger fraction of the pyridinic nitrogen and pyrrolic nitrogen groups. The titanium dioxide/graphene (TiO2/Gr) and graphene/hemin (Gr/Hem) were also studied and compared, and it was revealed that the catalytic activity of TiO2/Gr/Hem catalysts for ORR can be further enhanced. In addition, the chemically bonded element iron in the heat-treated TiO2/Gr/Hem catalysts showed an inhibition effect for ORR and Ti–C–N materials garnered high catalytic activity compared with Ti–C–N–Fe materials in alkaline media. The higher methanol tolerance and durability of the TiO2/Gr/Hem composite materials during ORR were also confirmed. These results reflected the critical influences of the pyrolysis temperature and the chemically bonded element dopants to be the key factor for ORR.

Label-free DNA detection based on oligonucleotide-stabilized silver nanoclusters and exonuclease III-catalyzed target recycling amplification

As an emerging class of metal nanoclusters, oligonucleotide-stabilized silver nanoclusters (DNA–Ag NCs) show a number of applications in biosensing and bionanotechnology. Herein, we develop a label-free DNA sensor based on DNA–Ag NCs and exonuclease III (Exo III)-catalyzed target recycling amplification. The fluorescence of single-strand DNA-stabilized Ag NCs can be enhanced through hybridization with the guanine-rich DNA. With the addition of target DNA, the fluorescence intensity decreases comparable with that of DNA duplex-stabilized Ag NCs, which is attributed to the competitive hybridization reaction. With the addition of Exo III, the fluorescence intensity decreases more obviously. The calibration range for target DNA is 0.3 to 30 nM, and the detection limit is 0.2 nM. The sensor offers 100-fold improvement in detection sensitivity compared with that obtained without Exo III. The proposed strategy also shows excellent selectivity, which can differentiate between perfectly matched and mismatched target DNA. Therefore, the strategy presents a promising platform for DNA detection with high sensitivity and selectivity.

Nitrogen-doped porous carbon with a hierarchical structure prepared for a high performance symmetric supercapacitor

Here, we present a facile approach to synthesizing nitrogen-doped porous carbon materials (NPCs) through carbonization of poly(o-phenylenediamine) (PoPD) by using molten-salt as a template. The as-prepared NPCs exhibit hierarchically micro-nanometric porous structure and unprecedented nitrogen content (14.86 wt%). The micrometric pores are interconnected which form from the micrometric salt droplets during carbonization, while the nanopores are generated by the exclusion of small molecular gases. This unique structure and high nitrogen content endows the NPCs with excellent specific capacitance (364.93 F g−1 at 2 mV s−1) and good cycling stability (92.3% capacitance retention at 10 A g−1 after 5000 cycles) in 6 M KOH electrolyte. Moreover, the symmetric supercapacitor array fabricated with the NPCs can easily power a light-emitting diode (LED), demonstrating the practical application of the NPCs in energy storage.