Yuewu Zhao

Three-Dimensional Macroporous Polypyrrole-Derived Graphene Electrode Prepared by the Hydrogen Bubble Dynamic Template for Supercapacitors and Metal-Free Catalysts

We report a general method for the fabrication of three-dimensional (3D) macroporous graphene/conducting polymer modified electrode and nitrogen-doped graphene modified electrode. This method involves three consecutive steps. First, the 3D macroporous graphene (3D MG) electrode was fabricated electrochemically by reducing graphene oxide dispersion on different conducting substrates and used hydrogen bubbles as the dynamic template. The morphology and pore size of 3D MG could be governed by the use of surfactants and the dynamics of bubble generation and departure. Second, 3D macroporous graphene/polypyrrole (MGPPy) composites were constructed via directly electropolymerizing pyrrole monomer onto the networks of 3D MG. Due to the benefit of the good conductivity of 3D MG and pseudocapacitance of PPy, the composites manifest outstanding area specific capacitance of 196 mF cm(-2) at a current density of 1 mA cm(-2). The symmetric supercapacitor device assembled by the composite materials had a good capacity property. Finally, the nitrogen-doped MGPPy (N-MGPPy or MGPPy-X) with 3D macroporous nanostructure and well-regulated nitrogen doping was prepared via thermal treatment of the composites. The resultant N-MGPPy electrode was explored as a good electrocatalyst for the oxygen reduction reaction (ORR) with the current density value of 5.56 mA cm(-2) (-0.132 V vs Ag/AgCl). Moreover, the fuel tolerance and durability under the electrochemical environment of the N-MGPPy catalyst were found to be superior to the Pt/C catalyst.

Construction of Three-Dimensional Hemin-Functionalized Graphene Hydrogel with High Mechanical Stability and Adsorption Capacity for Enhancing Photodegradation of Methylene Blue

A three-dimensional hemin-functionalized graphene hydrogel (Hem/GH) was prepared by a facile self-assembly approach. The as-prepared Hem/GH showed good mechanical strength with a storage modulus of 609-642 kPa and a high adsorption capacity to organic dye contaminants (341 mg g-1 for rhodamine B). Moreover, Hem/GH could be used as a photosensitizer for the photocatalytic degradation of organic dyes and displayed superior photodegradation activity of methylene blue (MB). This result was better than that of counterparts such as graphene hydrogel (GH) and commercial catalyst P25. The excellent cycling performance of the Hem/GH was well maintained even after multiple cycles on adsorption process and photocatalytic reaction. Interestingly, after the photodegradation of MB, a light-induced pH change of the solution from alkaline pH 8.99 to acidic pH 3.82 was observed, and 10 wt % total organic carbon remained. The liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS) analysis confirmed the generation of acidic degradation products. The photocatalytic mechanism was further investigated by trapping experiments, which revealed that the MB degradation was driven mainly by the participation of O2•- radicals in the photocatalytic reaction. As an extended application, visually intuitive observation showed the as-prepared Hem/GH also had strong antibacterial properties. These results suggest that Hem/GH could be potentially used for practical application due to its high adsorption ability, excellent photocatalytic activity, and strong antibacterial properties.

Nanostructured 2D Diporphyrin Honeycomb Film: Photoelectrochemistry, Photodegradation, and Antibacterial Activity

Surface patterns of well-defined nanostructures play important roles in fabrication of optoelectronic devices and applications in catalysis and biology. In this paper, the diporphyrin honeycomb film, composed of titanium dioxide, protoporphyrin IX, and hemin (TiO2/PPIX/Hem), was synthesized using a dewetting technique with the well-defined polystyrene (PS) monolayer as a template. The TiO2/PPIX/Hem honeycomb film exhibited a higher photoelectrochemical response than that of TiO2 or TiO2/PPIX, which implied a high photoelectric conversion efficiency and a synergistic effect between the two kinds of porphyrins. The TiO2/PPIX/Hem honeycomb film was also a good photosensitizer due to its ability to generate singlet oxygen ((1)O2) under irradiation by visible light. This led to the use of diporphyrin TiO2/PPIX/Hem honeycomb film for the photocatalytic inactivation of bacteria. In addition, the photocatalytic activities of other metal-diporphyrin-based honeycomb films, such as TiO2/MnPPIX/Hem, TiO2/CoPPIX/Hem, TiO2/NiPPIX/Hem, TiO2/CuPPIX/Hem, and TiO2/ZnPPIX/Hem, were investigated. The result demonstrated that the photoelectric properties of diporphyrin-based film could be effectively enhanced by further coupling of porphyrin with metal ions. Such enhanced performance of diporphyrin compounds opened a new way for potential applications in various photoelectrochemical devices and medical fields.

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.

Synthesis of porphyrin-based two-dimensional metal–organic framework nanodisk with small size and few layers

A novel porphyrin-based two-dimensional metal–organic framework (MOF) nanodisk with small size and few layers was prepared by coordination chelation between meso-tetra(4-carboxyphenyl)porphine ligand and Zn(II) paddlewheel metal nodes. With 4,4′-biphenyldicarboxylic acid (BPDC) as nucleation modulator, the anisotropic growth of MOF was impeded by the increased steric hindrance, yielding small Zn–TCPP(BP) MOF crystals. The as-prepared MOF nanodisk exhibited good electrocatalytic activity and selectivity towards nitrite due to the independent distribution of the porphyrin molecules in the framework and the sandwich structure of the prepared Zn–TCPP(BP) nanodisk, which increased the accessible active sites.

Construction of iron-polymer-graphene nanocomposites with low nonspecific adsorption and strong quenching ability for competitive immunofluorescent detection of biomarkers in GM crops

We developed a new immunofluorescent biosensor by utilizing a novel nanobody (Nb) and iron-polymer-graphene nanocomposites for sensitive detection of 5-enolpyruvylshikimate-3-phosphate synthase from Agrobacdterium tumefaciens strain CP4 (CP4-EPSPS), which considered as biomarkers of genetically modified (GM) crops. Specifically, we prepared iron doped polyacrylic hydrazide modified reduced graphene nanocomposites (Fe@RGO/PAH) by in-situ polymerization approach and subsequent a one-pot reaction with hydrazine. The resulting Fe@RGO/PAH nanocomposites displayed low nonspecific adsorption to analytes (11% quenching caused by nonspecific adsorption) due to electrostatic, energetic and steric effect of the nanocomposites. After Nb immobilizing, the as-prepared Fe@RGO/PAH/Nbs showed good selectivity and high quenching ability (92% quenching) in the presence of antigen (Ag) and polyethylene glycol (PEG) modified CdTe QDs (Ag/QDs@PEG), which is a nearly 4 fold than that of the unmodified GO in same condition. The high quenching ability of Fe@RGO/PAH/Nbs can be used for detection of CP4-EPSPS based on competitive immunoassay with a linearly proportional concentration range of 5-100ng/mL and a detection limit of 0.34ng/mL. The good stability, reproducibility and specificity of the resulting immunofluorescent biosensor are demonstrated and might open a new window for investigation of fluorescent sensing with numerous multifunctional graphene based materials.