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Three-dimensional macroporous graphene-wrapped zero-valent copper nanoparticles (3D-GN@Cu0) were synthesized using a self-assembly process of liquid-phase reduction and characterized by field emission scanning electron microscopy, nitrogen adsorption/desorption isotherms, X-ray diffraction, Raman spectrum analysis, and X-ray photoelectron spectroscopy. The catalytic activity of 3D-GN@Cu0 was evaluated in view of the effects of various systems, the pH value, catalyst dosage, initial metronidazole concentration and temperature, and it showed a high efficiency for removing metronidazole with saturated dissolved oxygen (without adding extra H2O2) in a wide range of pH value from 3.2 to 9.8. Combined with the results of dissolved oxygen activation, determination of reactive oxidizing species, and X-ray photoelectron spectroscopy (XPS) analysis, the surface-bounded ·OHads formed by the reaction of the in situ generation H2O2 with 3D-GN@Cu0 was mainly responsible for the removal of metronidazole. The charge distribution and electrostatic potential (ESP) of 3D-GN@Cu0 further illustrated the distribution and transfer of electrons on the catalyst surface, which predicted a micro-electrolysis-promoted Fenton-like reaction mechanism.

Optimization of the synthesis process and promotion of the catalytic efficiency are crucial to develop low-cost and effective catalysts for the removal of antibiotics from wastewater. In our previous work, a kind of hybrid material of nanoscale copper particles anchored on three-dimensional macroporous graphene (3D-GN@Cu) has been proved to be a satisfying Fenton-like catalyst. Herein, the self-assembly methods of 3D-GN@Cu preparation by a facile liquid-phase reduction was further investigated with field emission scanning electron microscopy, nitrogen adsorption/desorption isotherms, Raman spectrum analysis, X-ray diffraction, X-ray photoelectron spectroscopy and cyclic voltammograms measurements. The effects of various reduction methods, reduction time and reducing agent dosage on the physicochemical properties and catalytic performances of 3D-GN@Cu were investigated, and the preparation process was optimized. It was found that 3D-GN@Cu prepared by method A with 1.0 M KBH4 for 24 h had the largest surface area, the more defects and the best catalytic properties for the removal of metronidazole. In the combination of experimental results and density functional theory (DFT) calculations, the assembly and optimization law for preparing 3D-GN@Cu and the corresponding mechanisms were illustrated. This provides the theoretical basis and new insights for the preparation of graphene-encapsulated nanometals and related composites, which have a promising application potential in the fields of catalysis, electronics, sensors, bioapplications and environmental pollution control.

This paper presents the way to harvest mechanical energy from asphalt pavement by piezoelectric generator. Results show that the potential energy in asphalt pavement can be up to 150 kW/h per lane per kilometre. Part of the mechanical energy can be harvested by piezoelectric transducers. The performance of seven typical transducers is examined through finite element analysis. Results show that PZT piles and multilayer, cymbal and bridge can work in asphalt pavement environment. PZT piles and multilayer have higher energy converting rate. However, the total harvested energy is small if these transducers are embedded directly in pavement. A prototype pavement generator is developed using PZT piles to increase the harvested energy. The generator can harvest more than 50 kW/h energy from the pavement under heavy traffic. 8–16 PZT piles are recommended for one generator. Round shape is suggested for the PZT piles to reduce the concentration of stress. And multilayer structure is recommended for PZT piles to decrease the electric potential of generator. The generator can be extended as sensor in the asphalt pavement, which can be used to monitor the traffic, pavement stress and temperature.