Enhanced Performance of a Microbial Fuel Cell with a Capacitive Bioanode and Removal of Cr (VI) Using the Intermittent Operation

This study investigated a system which simultaneously produced electricity and stored energy in the MFC integrated MnO₂-modified capacitive bioanode. Compared to the noncapacitive anode, the maximum power density of MFC with MnO₂-modified bioanode reached 16.47 W m^?3, which was 3.5 times higher than that of the bare anode (4.71 W m^?3). During the charging-discharging experiment, the MFC with a capacitance bioanode has a higher average peak current density of 5.06 mA cm^?2 and 36 times larger than that with the bare bioanode. With the capacitive electrode, it is possible to let the MFC at the same time for production and storage of renewable electricity. Then two different operations (intermittent operation and continuous operation) of the MFC with a capacitive bioanode were studied to degrade Cr (VI) in cathode chamber. Results showed that the Cr (VI) removal rates of intermittent operation are much higher than that of continuous operation under the same time in the closed circuit state. This is due to the good ability of storing and releasing electron of the biological capacitor with MnO₂ modified material. And this study showed that MFC with a capacitive bioanode is better adapted to treat heavy metal pollutants by intermittent mode.     

生物质羟基磷灰石作为模板制备三维石墨烯

As a new 2D material with excellent chemical stability, good electric conductivity, and high specific surface area, graphene has been widely used in energy storage and conversion devices. However, 2D graphene layers are easily stacked, which may significantly reduce the surface area and degrade the excellent electrical properties of graphene. To avoid this, one of the most effective methods is to construct 3D graphene (3DG) with specific porous microstructures. Chemical vapor deposition (CVD) is an important method for the synthesis of high-quality 3DG, where templates play a defining role in controlling the structure and cost of 3DG. Metallic materials with 3D microstructures, such as nickel foam, have proven to be useful as substrates for the growth of high-quality 3DG. However, metal substrates are usually expensive, and the pickling solution generated after etching may cause environmental problems. Therefore, non-metallic substrate materials with lower costs have been investigated for the preparation of 3DG. Herein, we developed a novel template material, mammal bone ashes, for the CVD preparation of 3DG. Mammal bone ash is an inexpensive and abundant biomass hydroxyapatite. During the high-temperature CVD reaction, the bone ash powders were slightly sintered to form a continuous porous structure with graphene coating. The morphology of 3DG is inherited from the microstructure of bone ash templates. After removing the bone ash template with hydrochloric acid, the template-grown 3DG was obtained with a unique bicontinuous structure, i.e. both the graphene framework and the void space were continuous. In addition, the pickling solution of the bone ash templates after etching was exactly the same as that for the raw materials for the production of phosphoric acid to achieve high atom utilization. We further optimized the graphitization degrees, layer number, and porous morphology of 3DGs. The microstructure evolution of 3DG is highly relevant to the layer thickness and uniformity of graphene layers. A short growth time would lead to a non-uniform and thin layer of graphene, which is not able to support a complex 3D porous structure. In contrast, a uniform graphene layer with proper thickness is capable of forming a robust 3D architecture. In addition, the facile CVD method can be extended to a series of metal phosphate templates, including tricalcium phosphate [Ca₃(PO₄)₂], trimagnesium phosphate [Mg₃(PO₄)₂], and aluminum phosphate [AlPO₄]. 3DG with bicontinuous morphology is promising as a conductive frame material in electrochemical energy storage devices. As an illustration, high-performance Li-S batteries were fabricated by the uniform composition of an S cathode on 3DG. In comparison with heavily stacked 2D graphene sheets in reduced graphene oxide / S composite, the non-flat structure of 3DGs remained unchanged even after the harsh melt-diffusion process of high-viscosity liquid sulfur. The resulting 3DG/S cathode delivered a high specific capacity of ~550 mAh∙g^-1 at a high current rate (2C). Our work opens an avenue to the low-cost and high-utility production of 3D graphene, which could be integrated with the well-developed phosphorus chemical industry.     

Development of an Osmium Redox Polymer Mediated Bioanode and Examination of its Performance in Gluconobacter oxydans Based Microbial Fuel Cell

Gluconobacter oxydans (G. oxydans ) cells together with an osmium redox polymer (ORP) [Osmium (2,2’‐bipyridine)2(poly‐vinylimidazole)10Cl]Cl were combined with a glassy carbon paste electrode (GCPE) to form a bioanode for a microbial fuel cell (MFC) based on G. oxydans . Although there are G.oxydans / ORP combined bioanode in the literature, as far as it is known, this system is the first one where G.oxydans /ORP bioanode is combined with a cathode and a MFC is formed. After the optimization of experimental parameters, analytical characteristics of ORP/G. oxydans /GCPE bioanode were investigated. ORP/G. oxydans /GCPE showed two linear ranges for ethanol substrate as 1.0–30 mM (R²=0.902) and 30–500 mM (R²=0.997) and analytical range as 1.0–1000 mM. Limit of detection (3.0 s/m) and limit of quantification (10 s/m) values were calculated as 1.29 mM and 4.30 mM respectively where the RSD value was 1.16 % for n=5. Combining the developed bioanode in the presence of 5.0 mM K₃Fe(CN)₆ mediator with a Pt wire cathode a double compartment MFC was obtained via a salt bridge. G. oxydans /GCPE bioanode based MFC had maximum power density of 0.133 μW cm⁻² (at 33.5 mV), maximum current density as 8.73 μA cm⁻² and OCP value of 156 mV. On the other hand, ORP/G. oxydans /GCPE based MFC showed maximum power density as 0.26 μW cm⁻² (at 46.8 mV), maximum current density as 15.079 μA cm^‐2 and OCP value of 176 mV.     

全酶型乙醇/氧气生物燃料电池的构筑及性能研究

本文以乙醇脱氢酶（ADH）和胆红素氧化酶（BOD）为生物催化剂,以碳纳米管为电极材料,构筑了全酶型乙醇/氧气生物燃料电池. 将乙醇脱氢酶负载于单壁碳纳米管（SWCNT）上,采用亚甲基绿（MG）为NADH的电化学催化剂,实现乙醇的生物电化学催化氧化,制备了生物燃料电池ADH/MG/SWCNT/GC的电极（阳极）. 同时,将胆红素氧化酶固定于单壁碳纳米管上,通过其直接电子转移,实现了氧气的生物电化学催化还原,制得生物燃料电池的BOD/SWCNT/GC阴极. 据此构筑了全酶型的无膜生物燃料电池,在空气饱和40 mmol·L^-1乙醇磷酸缓冲溶液中该电池开路电压为0.53 V,最大输出功率密度为11 μW·cm^-2. 以商品化伏特酒作为燃料,该生物燃料电池最大输出功率为3.7 μW·cm^-2.     

Growth of Fe3O4 Nanorod Arrays on Graphene Sheets for Application in Electromagnetic Absorption Fields

A facial strategy is developed to fabricate a three‐dimensional (3D) Fe₃O₄ nanorod array/graphene architecture, in which Fe₃O₄ nanorods with a length and diameter of about 600 and 100 nm, respectively, are grown on both surfaces of the graphene sheets. The measured electromagnetic parameters show that the 3D architecture exhibits excellent electromagnetic wave‐absorption properties, that is, more than 99 % of electromagnetic wave energy can be attenuated by the 3D architecture if it is added in only 20 wt % of the paraffin matrix, as the thickness of the absorber is in the range from 2.38 to 5.00 mm. The analysis of the electromagnetic (EM) absorption mechanism reveals that the excellent EM absorption properties are related to the special 3D architecture, and therefore, the construction of graphene‐based 3D heteronanostructures is effective in obtaining lightweight EM absorbers with strong absorption properties.     

三维交联石墨烯纳米纤维的合成及储锂性能

以氧化石墨烯为原料, 高温下自组装得到高结晶的三维交联石墨烯纳米纤维. 扫描电子显微镜和透射电子显微镜观测结果表明, 三维石墨烯纳米纤维为实心结构, 直径小于100 nm, 石墨烯片层有序排列卷曲, 具有较高的结晶度. 电化学性能研究结果表明, 该纳米纤维作为锂离子电池负极材料时, 展现出较高的首次库仑效率(72.4%)与储锂容量(0.1C倍率下容量为692.7 mA·h/g)、 良好的倍率性能(20C倍率下容量为373.3 mA·h/g)及优异的循环稳定性(1000次循环后容量保持率为84.1%).     

Synthesis of Pd@graphene oxide framework nanocatalyst with enhanced activity in Heck-Mizoroki cross-coupling reaction

A new method was developed for producing a catalyst involving a Pd nanoparticle (NP) embedded in a graphene oxide framework (Pd@GOF) with ordered macro- and mesoporous structures. First, 5,5′-diamino-2,2′-bipyridine was selected as cross-linking for covalent modification of GO nanosheets to prepare a three-dimensional (3D) framework with interlayer spaces in which well-dispersed and ultra-small Pd NPs in situ grew and embedded the framework. The synthesized nanopores 3D Pd@GOF can act as nanoreactors to help the reaction substrates thoroughly come into contact with the surface of Pd NPs, thereby exhibiting high activity toward the Heck reaction, rarely reported concerning Pd NPs supported on one-side functionalized graphene. The Pd@GOF catalyst can be used 10 times without any significant loss in the catalytic activity, confirming the long-term stability of this catalyst. Therefore, the covalently assembled GOF was proposed as a universal platform for hosting noble metal NPs to construct the desired metal@GOF nanocatalyst with improved activity and stability that can be used in a broad range of practical applications.     

Macroporous composite capacitive bioanode applied in microbial fuel cells

Interfacial electron transfer between electroactive biofilm and the electrode was crucial step for microbial fuel cells(MFCs).A three-dimensional multilayer porous sponge coating with nitrogen-doped carbon nanotube/polyaniline/manganese dioxide(S/N-CNT/PANI/MnO2)electrode has been developed for MFC anode.Here,the S/N-CNT/PANI/MnO2 anode can function as a biocapacitor,able to store electrons generated from the degradation of organic substrate under the open circuit state and release the accumulated electrons upon requirement.Thus,the mismatching of the production and demand of the electricity can be overcome.Comparing with the sponge/nitrogen-doped carbon nanotube(S/N-CNT)bioanode,S/N-CNT/PANI/MnO2 capacitive bioanode displays a strong interaction with the microbial biofilm,advancing the electron transfer from exoelectrogens to the bioanode.The maximum power density of MFC with S/N-CNT/PANI/MnO2 capacitive bioanode is 1019.5 mW/m^2,which is 2.2 and5.8 times as much as that of S/N-CNT/MnO2 bioanode and S/N-CNT bioanode(470.7 mW/m^2 and176.6 mW/m^2),respectively.During the chronoamperometric experiment with 60 min of charging and 20 min of discharging,the S/N-CNT/PANI/MnO2 capacitive bioanode was able to store 10743.9 C/m^2,whereas the S/N-CNT anode was only able to store 3323.4 C/m^2.With a capacitive bioanode,it is possible to use the MFC simultaneously for production and storage of electricity.     

Study of the effect of chemical composition on the surface wettability of three-dimensional graphene foams

The chemical composition obviously affects the surface wettability of a three-dimensional (3D) graphene material apart from its surface energy and microstructure. In the hydrothermal preparation, the heteroatom doping changes the chemical composition and wettability of the 3D graphene material. To realize the controllable surface wettability of graphene materials, aminobenzene sulfonic acid (ABSA) was selected as a typical doping agent for the preparation of nitrogen and sulfur co-doped 3D graphene foam (SNGF) using a hydrothermal method. Different from using o-ABSA or p-ABSA as the dopant, SNGF with tunable surface wettability is obtained only when m-ABSA is used. This result indicates that the substituent position of -SO₃H group in the benzene ring of ABSA is rather important for the tunable wettability. This work provides some theoretical foundations for dopant selection and some new insights in manipulating the properties of 3D graphene foams by adjusting the configuration of dopants.     

High Performance Supercapacitors Based on Mesopore Structured Multiwalled Carbon Nanotubes

A 3D CNT/few layered graphene construct (CNT−FLG) with mesopore structure was fabricated and applied in supercapacitors. The structure was acquired through a two-step method. Firstly, commercial multiwalled carbon nanotubes (MCNTs) were oxidized in a mixed solution of concentrated acid and modified with a couple of long-chain organic ions. Second, the above resultant product was carbonized at a high temperature. The achieved structure offers a 3D interconnected electrically conductive network as well as mesopore structure. It also significantly improves the specific surface area of MCNTs. Result of BET tests showed that the specific surface area of CNT−FLG reached to 2235 m²/g. When acted as electrode materials in a supercapacitor structure, specific capacitance was approximately 531.2 F/g at a current density of 0.8 A/g. At current density of 50 A/g, specific capacitance remained 204.4 F/g. Besides, the capacitance retention was as high as 96.18 % after 10000 cycles at the current density of 5 A/g.     

Multifunctional properties of 3D printed poly(lactic acid)/graphene nanocomposites by fused deposition modeling

In this work, three-dimensional (3D) printing system based on fused deposition modeling (FDM) is used for the fabrication of conductive polymer nanocomposites. This technology consists in the additive multilayer deposition of polymeric nanocomposite based on poly(lactic acid) (PLA) and graphene by means of a in house made low-cost commercial bench-top 3D printer. Further, 3D printed PLA/graphene nanocomposites containing 10 wt% graphene in PLA matrix were characterized for their mechanical, electrical and electromagnetic induction shielding properties of the nanocomposite. Furthermore X-ray computed micro-tomography analyses showed that printed samples have good dimensional accuracy and are significantly closer to the predefined design and the results of scanning electron microscopy (SEM) printed samples showed a uniform dispersion of graphene in PLA matrix The proposed material has uniquely advantageous when implemented in 3D printed structures, because incorporation of multifunctional graphene has been shown to substantially improve the properties of the resulting nanocomposite.     

Biofabrication of a flexible and conductive 3D polymeric scaffold for neural tissue engineering applications; physical,chemical, mechanical,and biological evaluations

Tissue engineering approach aims to overcome the transplant drawbacks and facilitate tissue repair and regeneration. Here, a new conductive, highly porous, and flexible polycaprolactone/gelatin/polypyrrole/graphene 3D scaffolds for nerve tissue repair is presented. A simple and efficient porogen leaching fabrication method is applied to create a 3D network with a pore radius of 3.8 ± 0.7 to 4.2 ± 0.8 μm with an exceptional uniform circular porous structure. The conductivity of the polymeric scaffold without graphene, in wet conditions, was found to be 0.78 ± 0.1 S.m⁻¹ and it increased to 3.3 ± 0.2 S.m⁻¹ for the optimized sample containing 3wt% graphene (G3). Tensile strength was measured at 163 KPa for the base sample (without graphene) and improved to 526 KPa for G3 sample. Following 42 days of incubation in PBS, 32.5% degradation for the base sample (without graphene) was observed. The cell study demonstrated a non-cytotoxic nature of all scaffolds tested and the cells had mostly stretched and covered the surface. Overall, the sum of results presented in this study demonstrate a simple fabrication platform with extraordinary aspects that can be utilized to mimic the native conductive tissue properties, and also because of its flexibility it can easily be rolled into a nerve conduit to fill gaps in nerve tissue regeneration.     

Superelastic,Macroporous Polystyrene‐Mediated Graphene Aerogels for Active Pressure Sensing

Three‐dimensional (3D) graphene‐based polymer/graphene aerogels with excellent mechanical properties are crucial for broad applications. The creation of such polymer/graphene aerogels remains challenging because of the poor dispersion and compatibility of polymer within the graphene matrix. By using the freezing‐directed assembly of graphene under the assistance of surfactant, 3D macroporous polystyrene/graphene aerogels (MPS‐GAs) with lightweight, superelastivity (80 % strain), high strength (80 kPa), and good electrical properties have been achieved in this study. The as‐prepared MPS‐GAs shows excellent electromechanical performance with stable cyclic resilient properties and sensitive resistance responses, thus making the MPS‐GAs promising candidates for applications in actuators, elastic conductors, strain/pressure sensors, and wearable devices.     

Carbon nanostructure-derived polyaniline metacomposites: electrical, dielectric, and giant magnetoresistive properties

Polyaniline (PANI) nanocomposites incorporating different loadings of graphene and various other carbon nanostructures including carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have been synthesized using a surface-initiated polymerization (SIP) method. Transmission electron microscopy (TEM) results indicate that the graphene has been exfoliated into a few layers (typically one, two, and three layers) during polymerization and has been uniformly dispersed in the PANI matrix. The graphene layer dispersion degree is quantified by a free-path spacing measurement (FPSM) method based on the TEM microstructures. The SIP method also demonstrates its feasibility for coating PANI on one-dimensional (1D) CNFs and CNTs without introducing additional surface functional groups. The effects of graphene size, loading level, and surface functionality on the electrical conductivity and dielectric permittivity of their corresponding nanocomposites have been systematically studied. The temperature-dependent conductivity behavior revealed a quasi-3D variable range hopping (VRH) electron transport mechanism for all the nanocomposites. Giant magnetoresistance (GMR) at room temperature is observed in pure PANI, which can be enhanced by the incorporation of a high loading of graphene (5%) due to the π-π stacking-induced efficient electron transport at the PANI/graphene interface. More interestingly, negative permittivity is found in each composite which can be easily tuned by adjusting the filler loading, morphology, and surface functionality.     

From 2D Graphene Nanosheets to 3D Graphene‐based Macrostructures

The combination of exceptional functionalities offered by 3D graphene‐based macrostructures (GBMs) has attracted tremendous interest. 2D graphene nanosheets have a high chemical stability, high surface area and customizable porosity, which was extensively researched for a variety of applications including CO₂ adsorption, water treatment, batteries, sensors, catalysis, etc. Recently, 3D GBMs have been successfully achieved through few approaches, including direct and non‐direct self‐assembly methods. In this review, the possible routes used to prepare both 2D graphene and interconnected 3D GBMs are described and analyzed regarding the involved chemistry of each 2D/3D graphene system. Improvement of the accessible surface of 3D GBMs where the interface exchanges are occurring is of great importance. A better control of the chemical mechanisms involved in the self‐assembly mechanism itself at the nanometer scale is certainly the key for a future research breakthrough regarding 3D GBMs.     

Microchip-based ethanol/oxygen biofuel cell

One of the limitations of lab-on-a-chip technology has been the lack of integrated power supplies for powering various devices on the chip. This research focused on design of a stackable, microchip-based biofuel cell. The biofuel cell is powered by the addition of ethanol through a flow channel to a bioanode. The bioanode contains a micromolded carbon ink anode that has been modified with two layers. The first layer is poly(methylene green), which is an electrocatalyst for NADH oxidation; the second layer is a membrane that contains an immobilized enzyme, alcohol dehydrogenase. Each layer was characterized electrochemically. It was found that the poly(methylene green) layer is kinetically-limited, but when the complete bioanode is formed, the bioanode is diffusion-limited due to slow mass transport of NADH within the modified Nafion membrane. When used relative to an external platinum cathode, the biofuel cell showed maximum open circuit potentials of 0.34 V and maximum current densities of 53.0 +/- 9.1 microA cm(-2). This research demonstrates the feasibility of a microfabricated biofuel cell device.     

Efficient Degradation of Cellulose in Its Homogeneously Aqueous Solution over 3D Metal-Organic Framework/Graphene Hydrogel Catalyst

Catalytic degradation of cellulose to chemicals is an attracting topic today for the conversion of biomass, and the development of novel catalysts is a key point. Since metal-organic frameworks (MOFs) possess uniform, continuous, and permeable channels, they are valuable candidate as catalysts. Here, a new 3D MOF/graphene catalyst was prepared by in situ growth of the zeolitic imidazolate frameworks (ZIF-8) nanoparticles inside the pore of an as-formed 3D reduced graphene oxide (rGO) hydrogel. The ZIF-8/rGO nanocomposite owns both micropores and mesopores with large specific surface area and plenty of acids sites, which is an idea catalyst for biomass degradation. Cellulose was dissolved in alkaline aqueous solution at first, and then it was degraded efficiently over the new catalyst under hydrothermal condition. The conversion reaches 100% while the main products are formic acid with a maximum yield of 93.66%. In addition, the catalyst can be reused with high activity.     

Synergistic Combination of Reductive Covalent Functionalization and Atomic Layer Deposition—Towards Spatially Defined Graphene-Organic-Inorganic Heterostructures

Three-dimensionally (3D) well-ordered and highly integrated graphene hybrid architectures are considered to be next-generation multifunctional graphene materials but still remain elusive. Here, we report the first realization of unprecedented 3D-patterned graphene nano-ensembles composed of a graphene monolayer, a tailor-made structured organophenyl layer, and three metal oxide films, providing the first example of such a hybrid nano-architecture. These spatially resolved and hierarchically structured quinary hybrids are generated via a two-dimensional (2D)-functionalization-mediated atomic layer deposition growth process, involving an initial lateral molecular programming of the graphene lattice via lithography-assisted 2D functionalization and a subsequent stepwise molecular assembly in these regions in the z-direction. Our breakthrough lays the foundation for the construction of emerging 3D-patterned graphene heterostructures.     

Effect of soot microstructure on its ozonization reactivity

Large uncertainty among the measured uptake coefficients of O(3) on soot highlights the importance of the sources and chemical structures of soot samples in this reaction. Soot samples with different microstructures were prepared by combusting n-hexane under controlled conditions. Their reactivities to O(3) were further investigated using in situ Raman spectroscopy. The fuel∕oxygen ratio in the combustion experiments not only affected the diameter of the primary particles, but also influenced the micro-chemical structure of soot. Average diameters of soot particles decreased with the decreasing fuel∕oxygen ratio. Compared to the "fuel-rich" flame soot, the "fuel-lean" flame soot showed lower structural uniformity with higher disordered carbon content at the graphene layer edges (D1 band) and the surface graphene layers (D2 band) and the amorphous carbon content (D3 band). This disordered carbon was identified as the reactive component for the ozonization of both the "fuel-rich" and "fuel-lean" flame soot samples. The kinetics study demonstrated that the disordered carbon at the surface graphene layers was more active than that at the graphene layer edges in one sample, and the reactivity of these two microstructures types to O(3) in the "fuel-rich" flame soot was higher than that in the "fuel-lean" flame soot.     

Mediator‐Free Bioelectrocatalytic Oxidation of Ethanol on an Electrode from Thermally Expanded Graphite Modified by Gluconobacter oxydans Membrane Fractions

We studied bioelectrocatalytic oxidation of ethanol with membrane fractions of Gluconobacter oxydans VKM B‐1280 bacterial cells participating as an electrocatalyst. Material of the electrode was graphene‐like thermally expanded graphite of a high surface area and low resistivity. Membrane fractions were immobilized on the electrode surface by application in chitosan gel to prevent desorption of the biocatalyst. The bioelectrode characteristics were studied by the voltammetric and chronopotentiometric methods. It was shown that electrooxidation of ethanol on the bioanode could proceed both in the mode of direct mediator‐free electrocatalysis and by the mediator mechanism.