Likun Pan

Electrosorption behavior of graphene in NaCl solutions

Graphene has been synthesized by the modified Hummers method and used as electrosorptive electrodes for capacitive deionization. Batch-mode experiments in NaCl solutions at low voltage (≤2 V) are conducted in a continuously recycling system to investigate the electrosorption performance of graphene. The results show that the graphene exhibits a high electrosorption capacity of 1.85 mg/g. The ion sorption follows a Freundlich isotherm, indicating monolayer adsorption. And the electrosorption of NaCl onto graphene electrodes is driven by a physisorption process by taking into account the thermodynamic parameters.

Electrosorptive desalination by carbon nanotubes and nanofibres electrodes and ion-exchange membranes.

A novel membrane capacitive deionization (MCDI) device, integrating both the advantages of carbon nanotubes and carbon nanofibers (CNTs-CNFs) composite film and ion-exchange membrane, was proposed with high removal efficiency, low energy consumption and low cost. The CNTs-CNFs film was synthesized by low pressure and low temperature thermal chemical vapor deposition. Several experiments were conducted to compare desalination performance of MCDI with capacitive deionization (CDI), showing that salt removal of the MCDI system was 49.2% higher than that of the CDI system. The electrosorption isotherms of MCDI and CDI show both of them follow Langmuir adsorption, indicating no change in adsorption behavior when ion-exchange membranes are introduced into CDI system. The better desalination performance of MCDI than that of CDI is due to the minimized ion desorption during electrosorption.

Electrospun carbon nanofibers as anode materials for sodium ion batteries with excellent cycle performance

A simple and scalable electrospinning process followed by thermal treatment was used to fabricate carbon nanofibers (CFs). The as-prepared CFs were investigated as anode materials for sodium ion batteries (SIBs). Remarkably, due to their weakly ordered turbostratic structure and a large interlayer spacing between graphene sheets, the CFs exhibit a dominant adsorption/insertion sodium storage mechanism that shows high reversibility. As a result, the CFs show excellent electrochemical performance, especially cycle stability (97.7% capacity retention ratio over 200 cycles). Reversible capacities of 233 and 82 mA h g−1 are obtained for the CFs at a current density of 0.05 A g−1 and even a high current density of 2 A g−1, respectively. The excellent cycle performance, high capacity and good rate capability make the CFs promising candidates for practical SIBs.

Microwave-assisted synthesis of ZnO–graphene composite for photocatalytic reduction of Cr(VI)

ZnO–graphene composites are successfully synthesized via microwave-assisted reaction of zinc sulfate in aqueous solution with a graphite oxide dispersion using a microwave synthesis system. Their morphology, structure and photocatalytic performance in reduction of Cr(VI) are characterized by scanning electron microscopy, X-ray diffraction spectroscopy and UV-vis absorption spectrophotometer, respectively. The results show that in the composite the graphene nanosheets are decorated densely by ZnO nanosheets, which display a good combination between graphene and ZnO nanosheets. The ZnO–graphene composite exhibits an enhanced photocatalytic performance in the reduction of Cr(VI) with a removal rate of 98% under UV light irradiation as compared with pure ZnO (58%) due to the increased light absorption intensity and range, as well as the reduction of electron–hole pair recombination with the introduction of graphene.

Mesoporous nanostructured Co3O4 derived from MOF template: a high-performance anode material for lithium-ion batteries

Mesoporous nanostructured Co3O4 was prepared by the direct pyrolysis of a Co-based metal organic framework (MOF) template at a relatively low temperature rather than a high temperature. When tested as an anode material for lithium-ion batteries (LIBs), this porous Co3O4 exhibited a greatly enhanced performance of lithium storage. The capacity of the porous Co3O4 retained 913 mA h g−1 after 60 cycles at a current rate of 200 mA g−1. Excellent rate capability was also achieved. We also found out that the Co3O4 prepared from the MOF template at a relatively low temperature has better electrochemical performance than that prepared at high temperature.

Reduced graphene oxide and activated carbon composites for capacitive deionization

In this paper, reduced graphene oxide (RGO) and activated carbon (AC) composites (GAC) have been synthesized by a facile chemical method for the capacitive removal of salt ions from brackish water. The as-prepared composites have been characterized by scanning electron microscopy, N2 adsorption–desorption and cyclic voltammetry. The GAC composite with 20 wt% graphene (GAC-20) exhibits the best electrochemical performance among all the samples, with a specific capacitance of 181 F g−1. The electrosorption capacity of the GAC-20 electrode is found to be much higher than that of the AC electrode, indicating that RGO can serve as a flexible bridge to form a “plane-to-point” (RGO-to-AC) conducting network, which is beneficial for decreasing the aggregation of AC particles, and improves the electron transfer within the composite electrode. GAC composite should be a promising candidate as an electrode material for capacitive deionization (CDI) applications.

Microwave-assisted synthesis of TiO2-reduced graphene oxide composites for the photocatalytic reduction of Cr(VI)

TiO2-reduced graphene oxide (RGO) composites are successfully synthesized via the microwave-assisted reduction of graphite oxide in a TiO2 suspension using a microwave synthesis system. Their morphology, structure and photocatalytic performance in the reduction of Cr(VI) are characterized by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction spectroscopy and UV-vis absorption spectrophotometer. The results show that in the composite the RGO nanosheets are densely decorated by TiO2 nanoparticles, which displays a good combination between RGO and TiO2. TiO2–RGO composites exhibit enhanced photocatalytic performance for the reduction of Cr(VI) with a maximum removal rate of 91% under UV light irradiation as compared with pure TiO2 (83%) and commercial TiO2 P25 (70%) due to the increased light absorption intensity and range as well as the reduction of electron-hole pair recombination in TiO2 with the introduction of RGO.

Electrophoretic deposition of reduced graphene-carbon nanotubes composite films as counter electrodes of dye-sensitized solar cells

Reduced graphene (RG)-carbon nanotubes (CNTs) composite films are successfully fabricated by electrophoretic deposition and used as counter electrodes of dye-sensitized solar cells. RG is obtained by microwave-assisted reduction of graphite oxide dispersion in aqueous solution using a microwave synthesis system. By the optimization of CNTs content, photovoltaic conversion efficiency of the cell with RG-CNTs counter electrode reaches a maximum of 6.17% at one sun (AM 1.5 G, 100 mW cm−2) which is comparable to the cell with conventional Pt counter electrode. The results suggest that the RG-CNTs composite films provide a potential feasibility for replacing conventional Pt counter electrodes for DSSCs.

CdS/CdSe-Cosensitized TiO2 Photoanode for Quantum-Dot-Sensitized Solar Cells by a Microwave-Assisted Chemical Bath Deposition Method

A CdS/CdSe quantum-dot (QD)-cosensitized TiO(2) film has been fabricated using a microwave-assisted chemical bath deposition technique and used as a photoanode for QD-sensitized solar cells. The technique allows a direct and rapid deposition of QDs and forms a good contact between QDs and TiO(2) films. The photovoltaic performance of the as-prepared cell is investigated. The results show that the performance of the CdS/CdSe-cosensitized cell achieves a short-circuit current density of 16.1 mA cm(-2) and a power conversion efficiency of 3.06% at one sun (AM 1.5 G, 100 mW cm(-2)), which is comparable to the one fabricated using conventional successive ionic layer adsorption and reaction technique.

Review on carbon-based composite materials for capacitive deionization

The last five decades have witnessed the rapid development of capacitive deionization (CDI) as a novel, low-cost and environment-friendly desalination technology. During the CDI process, salt ions are sequestered by the porous electrodes once exposed to an electric field. These electrodes, acting as an ion storage container, play a vital role during desalination. In this review, various carbon-based composite electrode materials, including carbon–carbon composites, carbon–metal oxide composites, carbon–polymer composites and carbon–polymer–metal oxide composites, are systematically presented. Applications of these carbon-based composite materials for the removal of the salt ions from solution are demonstrated and they exhibit improved CDI performances compared with pristine carbon electrodes.