Synthesis of three-dimensional graphene architectures by using an environmental-friendly surfactant as a reducing agent

Polyvinylpyrrolidone (PVP) modified reduced graphene aerogel (PVP-GA) was prepared through hydrothermal reduction and chemical reduction of graphene oxide (GO) in the presence of PVP. The structure of PVP-GA was characterized using XRD, FTIR, SEM, TEM and BET specific surface area. The results showed that GO was reduced effectively in the presence of PVP and the PVP molecules were absorbed onto the basal plane of reduced graphene oxide (rGO) through non-covalent interactions. The preparation process was carried out in aqueous media at 120 °C for 10 h without using any toxic reducing agent, thereby making it a facile, environmental-friendly and economical approach for the synthesis of a three-dimensional (3D) interconnected graphene macrostructure. The as-prepared monolithic 3D graphene exhibits a loose and high porous structure, which may find potential applications for adsorbent, shock absorber, catalyst carrier and hydrogen storage materials. In addition, it confirmed that simultaneous hydrothermal reduction and chemical reduction routes would be of value for preparing 3D nonporous graphene-based materials via the use of cheap and environmentally-friendly PVP as a reducing agent.     

An operation control strategy for a virtual pumped storage system based on a linear motor

储能技术是智能电网的关键技术之一，对新能源大规模并网消纳、实现"两个替代"、完成能源结构转型具有重要意义。根据热力学原理分析，等温压缩空气储能技术在理论上具有更高的效率，因此提出了基于等温压缩空气储能原理的虚拟抽水蓄能系统，以及适用于该系统稳定运行的恒功率运行控制策略和适用于电力系统对储能电站功率可调控需求的功率调整运行控制策略，采用基于SVPWM的磁场定向矢量控制方法，借助MATLAB/SIMULINK平台，研究其基于直线电机的系统运行控制策略，通过仿真验证控制策略的可行性。     

Effect of pharmaceutical agent degradation on axonal transport drug delivery: An analytical solution for a transient situation

This paper is motivated by recent experimental research that demonstrated pharmacological efficiency of axonal transport drug delivery. The purpose is to develop a model of this process and to study how the rate of destruction of pharmaceutical agent complexes (PACs) affects their transport in the axon. The model includes two populations of PACs: PACs in the state when they are driven retrogradely (from the axon terminal toward the neuron soma) by dynein motors and PACs residing in the accumulated state (but can still be re-released to the dynein-driven state). The coupling between the kinetic states is accounted for by first-order reactions. Utilizing Laplace transform, analytical solutions for concentrations of these two populations of PACs are obtained. The effect of PAC destruction is investigated for different values of other parameters. It is shown that the shapes of the waves describing the PAC concentrations can be significantly affected by transport parameters.     

Novel nanocomposite membranes based on PBI and doped-perovskite nanoparticles as a strategy for improving PEMFC performance at high temperatures

In this work, Sr²⁺ dopant effects of Ba_0.9Sr_0.1TiO₃ and La_0.9Sr_0.1CrO_3-δ doped-perovskite nanoparticles on increasing proton conductivity, fuel cell performance, and mechanical and thermal stability of polybenzimidazole-based nanocomposite membranes were studied. The Sr²⁺ dopant creates cation vacancies in Ba_0.9Sr_0.1TiO₃ doped-perovskite nanoparticles and oxygen vacancies in La_0.9Sr_0.1CrO_3-δ doped-perovskite nanoparticles. The oxygen vacancies, which decrease columbic repulsion between protons and positive ions, have a more important role than the cation vacancies. They provide high surface area and high interfacial interaction between La_0.9Sr_0.1CrO_3-δ doped-perovskite nanoparticles, phosphoric acid, and polybenzimidazole for proton transfer and increase the proton conductivity of the nanocomposite membranes. In addition, the results of relative humidity effects showed that the ordered arrangement of oxygen vacancies of the La_0.9Sr_0.1CrO_3-δ doped-perovskite nanoparticles creates a specific pathway in the nanocomposite membranes for increasing proton transfer in the presence of relative humidity. Furtheremore, at phosphoric acid doping level of 13 mol phosphoric acid per monomer unit, proton conductivity of the nanocomposite membranes containing 8 wt.% La_0.9Sr_0.1CrO_3-δ doped-perovskite nanoparticles was obtained as 126 mS cm^-1 at 180°C and 6% relative humidity. The nanocomposite membrane showed the best performance and the power density of 0.62 W cm^-2 at 180°C and 0.5 V.     

An improvement on the efficiency of a single rotor transonic compressor by reducing the shock wave strength on the blade suction surfaces

It is well known that increasing the rotational velocity is an effective way to increase the total pressure ratio. With increasing flow velocity especially under the condition of transonic flow in the supersonic region, where exist strong shock waves, the shock wave loss becomes main and important. Simultaneously, there occurs boundary layer separation due to the shock wave / boundary layer interaction. In the present paper the transonic compressor blades were studied and analyzed to find a proper and simple way to reduce the shock wave loss by optimizing the suction surface configuration or controlling the gradient of isentropic Mach number on the suction surface. A Navier-Stokes solver combined with a modified design algorithm was developed and used. The NASA single rotor for transonic flow compressor was served as a numerical example to show the effectiveness of this method. Two cases for both original and modified rotors were analyzed and compared.     

Bio-hydrogen production based on catalytic reforming of volatiles generated by cellulose pyrolysis: An integrated process for ZnO reduction and zinc nanostructures fabrication

The paper presents a process of cellulose thermal degradation with bio-hydrogen generation and zinc nanostructures synthesis. Production of zinc nanowires and zinc nanoflowers was performed by a novel processes based on cellulose pyrolysis, volatiles reforming and direct reduction of ZnO. The bio-hydrogen generated in situ promoted the ZnO reduction with Zn nanostructures formation by vapor-solid (VS) route. The cellulose and cellulose/ZnO samples were characterized by thermal analyses (TG/DTG/DTA) and the gases evolved were analyzed by FTIR spectroscopy (TG/FTIR). The hydrogen was detected by TPR (Temperature Programmed Reaction) tests. The results showed that in the presence of ZnO the cellulose thermal degradation produced larger amounts of H₂ when compared to pure cellulose. The process was also carried out in a tubular furnace with N₂ atmosphere, at temperatures up to 900 °C, and different heating rates. The nanostructures growth was catalyst-free, without pressure reduction, at temperatures lower than those required in the carbothermal reduction of ZnO with fossil carbon. The nanostructures were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The optical properties were investigated by photoluminescence (PL). One mechanism was presented in an attempt to explain the synthesis of zinc nanostructures that are crystalline, were obtained without significant re-oxidation and whose morphologies are dependent on the heating rates of the process. This route presents a potential use as an industrial process taking into account the simple operational conditions, the low costs of cellulose and the importance of bio-hydrogen and nanostructured zinc.     

Efficient oxygen reduction in a microbial fuel cell based on carbide-derived carbon electrode synthesized using thiourea as the single source of electroconductive heteroatoms and graphitic carbon

A novel one step method was developed to dope nitrogen (N), sulfur (S) and carbon (C) in the Fe nanoparticles-dispersed carbon nanofibers (CNFs) grown over carbide-derived carbon (CDC), using thiourea as the single source of N, S and C. The synthesized N/S-Fe-CNF/CDC electrode was successfully used in a microbial fuel cell (MFC). When tested as the oxygen reduction reaction (ORR) catalyst, the electrode achieved a high current density (2.261 ± 0.002 mA/cm²), high OCP (0.611 ± 0.005 V), high stability upto 400 cycles, response time of ∼11 s, electron transfer number in the range 3.73–4.03, and Tafel slopes of −0.0627 and −0.183 V/dec at low and high current densities, respectively. A first order kinetics and a 4e⁻ pathway were deduced from the ORR analysis. Notably, the fabricated MFC based on the prepared electrode produced a high current density of 1.3887 ± 0.002 mA/cm², high OCP of 0.626 ± 0.005 V and maximum power density of 0.238 ± 0.002 mW/cm², attributed to the synergistic effects of heteroatoms, Fe nanoparticles, and CNFs.     

A new insight for photocatalytic hydrogen production by a Cu/Ni based cyanide bridged polymer as a co-catalyst on titania support in glycerol water mixture

A two dimensional Cu/Ni based coordination polymer [{Cu^II(4,4ʹ-dipy)₂}{Ni(CN)₄}]_n·0.7(C₂H₆O₂)·1.6(H₂O) (CP-1) (4,4ʹ-dipy = 1,3-di (4-pyridyl)propane) has been demonstrated as a potential co-catalyst on TiO₂ support for hydrogen evolution under UV light. CP-1/TiO₂ composite exhibits considerable hydrogen production in comparison with the pristine CP-1 and TiO₂ (P25), highlighting that the photocatalytic performance is significantly related with the good separation of photo generated e⁻/h⁺ pairs. Different wt. % (2.5, 5 and 7.5%) of CP-1 in CP-1/TiO₂ composites were tested for photocatalytic hydrogen production in 5 vol % glycerol/water mixture. The 5 wt % CP-1/TiO₂ composite displayed the greatest hydrogen production of 9.2 mmolh⁻¹g⁻¹. The concealed mechanism is divulged on the behalf of results obtained by cyclic voltammetry, photoluminescence and diffused reflectance/UV-visible studies which demonstrate that upon irradiation of UV light, electrons transfer from TiO₂ conduction band to CP-1. CP-1 not only grabs the conduction band electrons of titania but also performes as a co-catalyst to reduce the protons into hydrogen. These results are anticipated to direct the forthcoming advancement in creating proficient, cheap semiconductor photocatalysts for solar hydrogen production.