Analysis of chitin particle size on maximum power generation, power longevity, and Coulombic efficiency in solid-substrate microbial fuel cells

Microbial fuel cells (MFCs) produce bioelectricity from a wide variety of organic and inorganic substrates. Chitin can be used as a slowly degrading substrate in MFCs and thus as a long-term fuel to sustain power by these devices in remote locations. However, little is known about the effects of particle size on power density and length of the power cycle (longevity). We therefore examined power generation from chitin particles sieved to produce three average particle sizes (0.28, 0.46 and 0.78 mm). The longevity increased from 9 to 33 days with an increase in the particle diameter from 0.28 to 0.78 mm. Coulombic efficiency also increased with particle size from 18% to 56%. The maximum power density was lower for the largest (0.78 mm) particles (176 mW m⁻²), with higher power densities for the 0.28 mm (272 mW m⁻²) and 0.46 mm (252 mW m⁻²) particle sizes. The measured lifetimes of these particles scaled with particle diameter to the 1.3 power. Application of a fractal dissolution model indicates chitin particles had a three-dimensional fractal dimension between 2 and 2.3. These results demonstrate particles can be used as a sustainable fuel in MFCs, but that particle sizes will need to be controlled to achieve desired power levels.     

CO2 reforming of CH4 over nanocrystalline zirconia-supported nickel catalysts

Mesoporous nanocrystalline zirconia with high-surface area and pure tetragonal crystalline phase has been prepared by the surfactant-assisted route, using Pluronic P123 block copolymer surfactant. The synthesized zirconia showed a surface area of 174 m² g⁻¹ after calcination at 700 °C for 4 h. The prepared zirconia was employed as a support for nickel catalysts in dry reforming reaction. It was found that these catalysts possessed a mesoporous structure and even high-surface area. The activity results indicated that the nickel catalyst showed stable activity for syngas production with a decrease of about 4% in methane conversion after 50 h of reaction. Addition of promoters (CeO₂, La₂O₃ and K₂O) to the catalyst improved both the activity and stability of the nickel catalyst, without any decrease in methane conversion after 50 h of reaction.     

Microwave‐assisted hydrodistillation of essential oil from Zataria multiflora Boiss

Microwave‐assisted hydrodistillation (MAHD) has recently gained attention for the extraction of essential oils. A concern with the use of MAHD is the possibility of sample deterioration during the extended exposure to microwave irradiation. In this study, MAHD was applied as a new and green technology for the extraction of essential oil from Zataria multiflora Boiss. (Shirazi thyme) aerial parts. Superior results were obtained with the proposed method in terms of extraction time [1 h vs. 4 h in hydrodistillation (HD)] for an essential oil recovery of 3.66 and 3.44%, respectively. Images obtained from thyme leaves using scanning electron microscopy indicated a sudden eruption of essential oil glands undergoing MAHD. GC‐MS analysis of the essential oils did not indicate any new or missing compounds in the essential oil obtained by MAHD in comparison with that by HD. Therefore, a microwave oven can be safely used for the extraction of essential oil from Shirazi thyme.     

Application of ionic liquids as an electrolyte additive on the electrochemical behavior of lead acid battery

Ionic liquids (ILs) belong to new branch of salts with unique properties which their applications have been increasing in electrochemical systems especially lithium-ion batteries. In the present work, for the first time, the effects of four ionic liquids as an electrolyte additive in battery's electrolyte were studied on the hydrogen and oxygen evolution overpotential and anodic layer formation on lead–antimony–tin grid alloy of lead acid battery. Cyclic and linear sweep voltammetric methods were used for this study in aqueous sulfuric acid solution. The morphology of grid surface after cyclic redox reaction was studied using scanning electron microscopy. The results show that most of added ionic liquids increase hydrogen overpotential and whereas they have no significant effect on oxygen overpotential. Furthermore ionic liquids increase antimony dissolution that might be related to interaction between Sb³⁺ and ionic liquids. Crystalline structure of PbSO₄ layer changed with presence of ionic liquids and larger PbSO₄ crystals were formed with some of them. These additives decrease the porosity of PbSO₄ perm selective membrane layer at the surface of electrode. Also cyclic voltammogram on carbon–PbO paste electrode shows that with the presence of ionic liquids, oxidation and reduction peak current intensively increased.     

Optimal design of engineered gas adsorbents: Pore-scale level

This study presents an optimization methodology and results for the structure of gas adsorbents at a pore level by evaluating the effect of pore geometry, size and overall adsorbent porosity on ultimate working capacity of adsorbents used in pressure swing adsorption (PSA) processes. Three model pore network topologies are studied: parallel, grid-like and branched structures. These are “near” optimal structures for an adsorbent particle and their relative performance is compared in a two-step PSA cycle. The macropore network of such structured adsorbents is optimized through maximization of an objective function i.e. working capacity WC, defined as the number of moles adsorbed per unit volume of slab. Molecular and Knudsen diffusion are considered as the sole transport mechanisms in the macropore channels. An unexpected finding of this optimization technique is that the branched structure with a porosity of less than 50% represents an optimum structure with highest working capacity for the system considered. Furthermore, for faster cycles the advantage of branched structures is more obvious, reflecting the advantages of the pore network in facilitating diffusion more efficiently than other structures. A macropore channel density (defined as the density of macropores per metre of external surface) of below 10 is suggested for optimum performance for both “fast” and “slow” PSA cycles. The theoretical results of this study will be used as a priori results for the design of adsorbents at the macro-scale (bed) level.     

Implementing the homotopy continuation method in a hybrid approach to solve the kinematics problem of spatial parallel robots

In this paper, first the application of homotopy continuation method (HCM) in numerically solving kinematics problem of spatial parallel manipulators is investigated. Using the HCM the forward kinematics problem (F-Kin) of a six degrees of freedom (DOFs) 6–3 Stewart platform and the inverse kinematics problem (I-Kin) of a 3-DOF 3-PSP robot are solved. The governing equations of the kinematics problems of the robots are developed and embedded in the homotopy continuation function. The HCM is utilized in order to solve the nonlinear system of equations derived from the kinematics analysis of the robots. Then, to represent the real case application an initial guess far from the correct answer is selected. It is shown that, comparing with the Newton–Raphson method (NRM), the F-Kin calculation time for the Stewart robot is decreased by 43%. Therefore, using the HCM a hybrid method is suggested to solve the F-Kin of the Stewart robot. Furthermore, the HCM, as an innovative method, relieves other downsides of the conventional numerical methods, including a proper initial guess requirement as well as the problems of convergence.     

Sn-adopted fullerene $$(\hbox {C}_{60})$$ nanocage as acceptable catalyst for silicon monoxide oxidation

In recent years, the discovery of metal catalysts for the oxidation of silicon monoxide (SiO) has become extremely important. In first step, the Sn adoption of fullerene (\(\hbox {C}_{60})\) was investigated and then activation of surface of \(\hbox {Sn-C}_{60}\) via \(\hbox {O}_{2}\) molecule was examined. In second step, the SiO oxidation on surface of \(\hbox {Sn-C}_{60}\) via Langmuir Hinshelwood (LH) and Eley Rideal (ER) mechanisms was investigated. Results show that \(\hbox {O}_{2}\hbox {-Sn-C}_{60}\) can oxidize the SiO molecule via \(\hbox {Sn-C}_{60}\hbox {-O-O}^{*} + \hbox {SiO}\rightarrow \hbox {Sn-C}_{60}\hbox {-O-O}^{*}\hbox {-SiO} \rightarrow \hbox {Sn-C}_{60}\hbox {-O}^{*} + \hbox {SiO}_{2}\) and \(\hbox {Sn-C}_{60}\hbox {-O}^{*} + \hbox {SiO}\rightarrow \hbox {Sn-C}_{60} + \hbox {SiO}_{2}\) reactions. Results show that SiO oxidation via the LH mechanism has lower energy barrier than ER mechanism. Finally, \(\hbox {Sn-C}_{60}\) is an acceptable catalyst with high performance for SiO oxidation in normal temperature.     

Ni Catalysts Supported on Mesoporous Nanocrystalline Magnesium Silicate in Dry and Steam Reforming Reactions

Mesoporous nanocrystalline MgSiO₃ with high surface area was synthesized by a hydrothermal method and employed as support in dry and steam reforming of methane. Ni/MgSiO₃ catalysts were prepared by an impregnation method and characterized by different techniques. N₂ adsorption analysis indicated that addition of nickel shifted the pore size distributions to smaller sizes. Temperature‐programmed reduction analysis revealed that a higher nickel loading enhanced the reducibility of the catalyst. The catalytic performance was improved with increasing the nickel content. The Ni/MgSiO₃ catalyst exhibited high stability in dry reforming but methane conversion declined with time‐on‐stream in the steam reforming reaction. Temperature‐programmed oxidation profiles of spent catalysts indicated that the high amount of carbon deposited on the catalyst surface in dry and steam reforming was assigned to whisker‐type carbon.     

Comparison of Preparation Methods of Iron‐Based Catalysts for High‐Temperature Water‐Gas Shift Reaction

The influence of preparation methods on structural and catalytic properties of the Fe₂O₃‐Cr₂O₃‐CuO catalyst during the high‐temperature water‐gas shift reaction was determined. The prepared samples were characterized by X‐ray diffraction (XRD), Brunauer‐Emmett‐Teller method (BET), and temperature‐programmed reduction (TPR). The results revealed that the type of coprecipitation, i.e., simple, inverse, and differential, had a significant effect on both structural and catalytic properties. The catalyst prepared by the simple precipitation method exhibited higher activity than the catalysts generated by inverse and differential coprecipitation and the commercial catalyst. The types of precipitation agent and iron and chromium precursors were found to have a significant impact on the structural and catalytic features.     

Electrospun core-shell nanofibers based on polyethylene oxide reinforced by multiwalled carbon nanotube and silicon dioxide nanofillers: A novel and effective solvent-free electrolyte for lithium ion batteries

Insertion of conductive fillers into solvent-free polymer electrolytes enhances electrochemical behavior of the electrolyte membranes leading to higher ionic conductivity, lower capacity fading, and so on. Although, the presence of the conductive fillers in the polymer matrixes increases the risk of electrical shorting, herein, polyethylene oxide (PEO)-based core-shell nanofibers were prepared via a simple electrospinning method. In the core-shell electrospun fibers, ethylene carbonate (EC) and lithium perchlorate (LiClO₄) were used as a plasticizer and as a lithium salt, respectively. The core component was enwrapped by the PEO/EC/LiClO₄ shell part incorporated with SiO₂ nanoparticles. Various properties of the fabricated membranes were evaluated by changing the ratio of multiwall carbon nanotubes (MWCNTs) in the core part of the nanofibers. The morphology and core-shell structure of the electrospun fibers were studied by FESEM and TEM images. According to FTIR and XRD results, addition of the EC plasticizer and the fillers into the as-spun fibers increased the fraction of free ions and the amorphous regions. From electrochemical impedance spectroscopy studies, the ionic conductivity enhanced by insertion of the plasticizer molecules and the filler particles into the core-shell structures. The highest ionic conductivities of 0.09 and 0.21 mS.cm⁻¹ were obtained for the free-filler and the filler-loaded nanofibrous membranes, respectively. The prepared mats obeyed the Arrhenius behavior ( R²~1 ). Dielectric studies confirmed the obtained data from the ionic conductivities. Furthermore, the capacity residual was enhanced from 69% to 85% by incorporation of the MWCNTs filler into the core component of the electrospun nanofibers. The presented results may facilitate development of versatile nanofibrous membranes embedded with the conductive fillers as solvent-free electrolytes applicable in lithium-ion batteries.