Jin Qu

Direct Reduction of Graphene Oxide by Ni Foam as a High-Capacitance Supercapacitor Electrode

Three dimensional reduced graphene oxide (RGO)/Ni foam composites are prepared by a facile approach without using harmful reducing agents. Graphene oxide is reduced by Ni foam directly in its aqueous suspension at pH 2 at room temperature, and the resultant RGO sheets simultaneously assemble around the pillars of the Ni foam. The RGO/Ni foam composite is used as a binder-free supercapacitor electrode and exhibits high electrochemical properties. Its areal capacitance is easily tuned by varying the reduction time for different RGO loadings. When the reduction time increases from 3 to 15 days, the areal capacitance of the composite increases from 26.0 to 136.8 mF cm(-2) at 0.5 mA cm(-2). Temperature is proven to be a key factor in influencing the reduction efficiency. The composite prepared by 5 h reduction at 70 °C exhibits even better electrochemical properties than its counterpart prepared by 15 day reduction at ambient temperature. The 5 h RGO/Ni foam composite shows an areal capacitance of 206.7 mF cm(-2) at 0.5 mA cm(-2) and good rate performance and cycling stability with areal capacitance retention of 97.4% after 10000 cycles at 3 mA cm(-2). Further extending the reduction time to 9 h at 70 °C, the composite shows a high areal capacitance of 323 mF cm(-2) at 0.5 mA cm(-2). Moreover, the good rate performance and cycling stability are still maintained.

Graphene Oxide/Chitosan Aerogel Microspheres with Honeycomb-Cobweb and Radially Oriented Microchannel Structures for Broad-Spectrum and Rapid Adsorption of Water Contaminants

Multifunctional graphene oxide (GO)/chitosan (CS) aerogel microspheres (GCAMs) with honeycomb-cobweb and radially oriented microchannel structures are prepared by combining electrospraying with freeze-casting to optimize adsorption performances of heavy metal ions and soluble organic pollutants. The GCAMs exhibit superior adsorption capacities of heavy metal ions of Pb(II), Cu(II), and Cr(VI), cationic dyes of methylene blue (MB) and Rhodamine B, anionic dyes of methyl orange and Eosin Y, and phenol. It takes only 5 min to reach 82 and 89% of equilibrium adsorption capacities for Cr(VI) (292.8 mg g-1) and MB (584.6 mg g-1), respectively, much shorter than the adsorption equilibrium time (75 h) of a GO/CS monolith. More importantly, the GCAMs maintain excellent adsorption capacity for six cycles of adsorption-desorption. The broad-spectrum, rapid, and reusable adsorption performance makes the GCAMs promising for highly efficient water treatments.

Highly Efficient High-Pressure Homogenization Approach for Scalable Production of High-Quality Graphene Sheets and Sandwich-Structured α-Fe2O3/Graphene Hybrids for High-Performance Lithium-Ion Batteries

A highly efficient and continuous high-pressure homogenization (HPH) approach is developed for scalable production of graphene sheets and sandwich-structured α-Fe2O3/graphene hybrids by liquid-phase exfoliation of stage-1 FeCl3-based graphite intercalation compounds (GICs). The enlarged interlayer spacing of FeCl3-GICs facilitates their efficient exfoliation to produce high-quality graphene sheets. Moreover, sandwich-structured α-Fe2O3/few-layer graphene (FLG) hybrids are readily fabricated by thermally annealing the FeCl3 intercalated FLG sheets. As an anode material of Li-ion battery, α-Fe2O3/FLG hybrid shows a satisfactory long-term cycling performance with an excellent specific capacity of 1100.5 mA h g-1 after 350 cycles at 200 mA g-1. A high reversible capacity of 658.5 mA h g-1 is achieved after 200 cycles at 1 A g-1 and maintained without notable decay. The satisfactory cycling stability and the outstanding capability of α-Fe2O3/FLG hybrid are attributed to its unique sandwiched structure consisting of highly conducting FLG sheets and covalently anchored α-Fe2O3 particles. Therefore, the highly efficient and scalable preparation of high-quality graphene sheets along with the excellent electrochemical properties of α-Fe2O3/FLG hybrids makes the HPH approach promising for producing high-performance graphene-based energy storage materials.

Preparation of α-Fe2O3/polyacrylonitrile nanofiber mat as an effective lead adsorbent

α-Fe2O3 nanoparticles have been widely used in water purification because of their effective adsorption performance. However, aggregation and difficulty in separation limit their practical application. Herein, we presented a polyacrylonitrile (PAN) nanofiber mat decorated with α-Fe2O3 as an adsorbent for effective removal of Pb2+ from contaminated water, which can solve the above problems easily. The α-Fe2O3/PAN nanofiber mats were prepared via electrospinning followed by a facile hydrothermal method and characterized by SEM, HRTEM, FTIR and XRD. We demonstrated that the formation mechanism of α-Fe2O3 anchored on the PAN nanofiber surface consists of the adsorption of iron ions on the surface of PAN, and then the nucleation and growth of α-Fe2O3. The pH value of FeCl3 solution has a great impact on the formation process of the α-Fe2O3/PAN nanofiber mat, which leads to the variation of morphology and quantity of the coating coverage. When the pH value was 2.4, polyhedral particles were coated on PAN nanofibers uniformly and the optimized α-Fe2O3/PAN nanofiber mat was obtained. Control experiments were carried out to quantify the adsorption capacities of different samples and adsorption kinetics. The isotherm data from our experiments fitted well to the Langmuir model and the adsorption process can be described using the pseudo-second-order model. Finally, the adsorption mechanism for Pb2+ was investigated and the results revealed that ion exchange between the proton of surface hydroxyl groups and Pb2+ accounted for the adsorption.

Fabrication of a compressible PU@RGO@MnO2 hybrid sponge for efficient removal of methylene blue with an excellent recyclability

To enhance the recyclability while maintaining the high efficiency for the removal of organic dyes, monolithic polyurethane@reduced graphene oxide@manganese dioxide (PU@RGO@MnO2) hybrid sponge with a hierarchical structure and satisfactory flexibility is fabricated by self-assembly of RGO on a PU sponge followed by uniform coating of MnO2 nanoparticles onto RGO by means of an in situ redox reaction between RGO and KMnO4. RGO acts as an ideal substrate to accommodate MnO2 nanoparticles and prevents their aggregation, whereas the numerous hydrophilic MnO2 nanoparticles play dual roles of adsorption and catalytic degradation of methylene blue (MB) dye. The resultant hybrid sponge shows a hierarchical porous structure that provides fast transport channels and abundant active sites, benefiting the diffusion and removal of MB. By enhancing the mass transfer with the help of a micro-pump, the monolithic hybrid sponge acts as a filter for dye removal. Under the dynamic mode, the adsorption efficiency of the PU@RGO@MnO2 hybrid sponge for MB (50 ppm, 30 mL) reaches 94% after 20 min, whereas it is as low as 5% under the static mode. With the assistance of H2O2, the removal efficiency of the hybrid sponge is 96% at first time under the dynamic mode, whereas it is only 14% in the static mode. The monolithic hybrid sponge is highly efficient in adsorption and catalytic degradation of MB based on an adsorption–oxidation–desorption process. Even after being used 4 times, it still maintains excellent removal efficiency and recyclability.

K2Mn4O8/Reduced Graphene Oxide Nanocomposites for Excellent Lithium Storage and Adsorption of Lead Ions

Ion diffusion efficiency at the solid-liquid interface is an important factor for energy storage and adsorption from aqueous solution. Although K2 Mn4 O8 (KMO) exhibits efficient ion diffusion and ion-exchange capacities, due to its high interlayer space of 0.70u2005nm, how to enhance its mass transfer performance is still an issue. Herein, novel layered KMO/reduced graphene oxide (RGO) nanocomposites are fabricated through the anchoring of KMO nanoplates on RGO with a mild solution process. The face-to-face structure facilitates fast transfer of lithium and lead ions; thus leading to excellent lithium storage and lead ion adsorption. The anchoring of KMO on RGO not only increases electrical conductivity of the layered nanocomposites, but also effectively prevents aggregation of KMO nanoplates. The KMO/RGO nanocomposite with an optimal RGO content exhibits a first cycle charge capacity of 739u2005mAu2009hu2009g-1 , which is much higher than that of KMO (326u2005mAu2009hu2009g-1 ). After 100 charge-discharge cycles, it still retains a charge capacity of 664u2005mAu2009hu2009g-1 . For the adsorption of lead ions, the KMO/RGO nanocomposite exhibits a capacity of 341u2005mgu2009g-1 , which is higher than those of KMO (305u2005mgu2009g-1 ) and RGO (63u2005mgu2009g-1 ) alone.

Dual-Carbon Confined Fe7S8 Anodes with Enhanced Electrochemical Catalytic Conversion Process for Ultralong Lithium Storage

Although the electrochemical catalytic conversion process is effective in increasing the reversible capacity of lithium-ion batteries, the low contact efficiency between metal catalyst and substrate and pulverization of the solid electrolyte interface (SEI) film without protection are not beneficial for the electrochemical reactions. Herein, Fe7 S8 nanoparticles are confined by both reduced graphene oxide (RGO) and in-situ-formed amorphous carbon (C) to form dual-carbon-confined Fe7 S8 as a lithium-ion anode. The dual-carbon-confined structure provides a confined space to prevent pulverization of the SEI film and increases the local concentration of intermediate phases, which could be electrocatalytically decomposed by Fe nanoparticles formed in situ to increase the reversibility of the electrochemical reactions and gain high reversible capacity. In addition, the dual-carbon-confined structure ensures fast transfer of electrons and boosts transport of lithium ions due to the highly conductive dual-carbon shell. Thus, the Fe7 S8 /C/RGO anode delivers an excellent rate performance and long cycling stability. At current densities of 2000 and 5000u2005mAu2009g-1 , the reversible capacities are 520u2005mAu2009hu2009g-1 over 1500u2005cycles and 294u2005mAu2009hu2009g-1 over 2000u2005cycles, respectively.

One-pot synthesis of bismuth silicate heterostructures with tunable morphology and excellent visible light photodegradation performances

Construction of a heterostructure to prolong the life of electron-hole pairs is a very important approach to endow it with excellent photodegradation performances. Particularly, one-pot synthesis of heterostructures with the same component but different crystal structures to form a proper band gap is still challenging. Herein, bismuth silicate (BSO) heterostructures are synthesized using a one-pot hydrothermal approach without adding any other inorganic components. The crystal phase, morphology, surface state, and photochemical properties of the BSO materials are precisely tuned to fabricate two kinds of bismuth silicate heterostructures: rod-like Bi2SiO5/Bi12SiO20 and flower-like Bi2SiO5/Bi4Si3O12 heterostructures. Thanks to the two heterostructures and clean surface, the optimized BSO material exhibits a highly active photocatalytic performance with a remarkable cycling stability. It photodegrades Rhodamine B under visible light irradiation as fast as 15min with the reaction rate constants k and ks to be 0.399min-1 and 0.698min-1Lm-2, respectively, which is up to 189 times faster than reported.