Apple – biomorphic synthesis of porous ZnO nanostructures for glucose direct electrochemical biosensor

Biomorphic porous ZnO nanostructures were successfully synthesized via an aqueous sol–gel soaking process using pieces of apple flesh and skin as templates and employed for glucose direct electrochemical biosensor. The structure and morphology of ZnO nanostructures were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). By modifying glassy carbon electrode with the biomorphic ZnO nanostructures and Nafion, two glucose biosensors were constructed and their direct electrochemistry of glucose oxidase (GOD) was successfully investigated by cyclic voltammetry (CV). The biomorphic porous ZnO nanostructures using apple skin template (S-ZnO) were more effective in facilitating the electron transfer of immobilized GOD than that of using flesh apple template (F-ZnO). This may be a result of the unique morphology and smaller average crystallite size of the S-ZnO nanostructure. GOD immobilized on Nafion-porous S-ZnO nanostructure composite display direct, reversible, and surface-controlled redox reaction with a detection limit of 10 μM, a response time of 7 s, high sensitivity of 23.4 μA/mM cm² and a fast heterogeneous electron transfer rate with a rate constant (k_s) of 3.9 s^?1. It was found that S-ZnO significantly has improved the direct electron transfer between GOD and glassy carbon electrode with good stability and reproducibility.     

A fuzzy based threshold policy for a single server retrial queue with vacations

In this paper we deal with a single server retrial queue with vacations. The server serves the customers until the system becomes empty, then it takes a vacation. The system consists of two types of costs. The blocking cost is considered whenever a customer is blocked either because of the server is busy or off. There is also a cost each time the server is turned on. The problem is to find an effective policy for turning on the dormant server. We propose a Fuzzy Based Threshold Policy (FBTP) to control the server, substitute for conventional threshold policies. The FBTP is based on four input parameters, an inference stage and it is tuned up using a stochastic List Based Threshold Accepting (LBTA) algorithm. Simulation models are developed to validate the fuzzy controller. Numerical experiments are provided to show that the proposed method is superior to crisp threshold policies.     

LDH(Mg/Al:2)@montmorillonite nanocomposite as a novel anion-exchanger to adsorb uranyl ion from carbonate-containing solutions

Journal of Radioanalytical and Nuclear Chemistry - A layered double hydroxide@montmorillonite nanocomposite (LDH@MMT) was synthesized by the coating of growing LDH layers onto the MMT surface...     

Effect of mass transfer limitations on catalyst performance during reduction and carburization of iron based Fischer-Tropsch synthesis catalysts

Existence of intraparticle mass transfer limitations under typical Fischer-Tropsch synthesis has been reported previously,but there is no suitable study on the existence of intraparticle diffusion limitations under pretreatment steps (reduction and activation) and their effect on catalytic performance for iron based catalysts.In this study,Fe-Cu-La-SiO2 catalysts were prepared by co-precipitation method.To investigate the intraparticle mass transfer limitation under reduction,activation and reaction steps,and its effect on catalytic performance,catalyst pellets with different sizes of 6,3,1 and 0.5 mm have been prepared.All catalysts were calcined,pretreated and tested under similar conditions.The catalysts were activated in hydrogen (5%H2in N2) at 450℃ for 3 h and exposed to syngas (H2/CO=1) at 270℃ and atmospheric pressure for 40 h.Afterwards,FTS reaction tests were performed for approximately 120 h to reach steady state conditions at 290℃,17 bar and a feed flow (syngas H2/CO=1) rate of 3 L/h (STP).Using small pellets resulted in higher CO conversion,FT reaction rate and C5+ productivity as compared with larger pellets.The small pellets reached steady state conditions just 20 h after starting the reaction.Whereas for larger pellets,CO conversion,FT reaction rate and C5+ productivity increased gradually,and reached steady state and maximum values after 120 h of operation.The results illustrate that mass transfer limitations exist not only for FTS reaction but also for the reduction and carburization steps which lead to various phase formation through catalyst activation.Also the results indicate that some effects of mass transfer limitations in activation step,can be compensated in the reaction step.The results can be used for better design of iron based catalyst to improve the process economy.     

Chlorofluorofullerenes (CFFs)

We have applied density functional theory calculations to devise stable arrangements of chlorofluorofullerenes (CFFs). In the case of C₆₀ClF and C₆₀Cl₂F₂, an extensive isomer search shows that the most stable configurations are those with two halogens located on the corannulene-like structure. In general, 1,2-adduct is more stable than 1,4-adduct and 1,2 addition across 6–6 bonds is more stable than 1,2 addition across 5–6 bonds. The formation of a CFF from chlorofullerene is exothermic while chlorination of a fluorofullerene is endothermic. For C₆₀Cl_18-3nF_3n (n = 0, 1, 2, 3, 4, 5, and 6), the binding energies decrease as the number of Cl atoms increases and the energy differences between isomers with the same formula are small. The ¹³C NMR patterns of C₆₀Cl_18-3nF_3n (n = 0, 1, 2, 3, 4, 5, and 6) are divided into two parts: δ_iso values of chlorinated and fluorinated carbons shift to low field and appear in the range of 65.1–100.2 and 84.5–97.4 ppm; two peaks related to C sites on the cyclohexatriene pole and the flattened equatorial belt separating the two hemispheres appear at 120.2–123.4 and 125.8–129.1 ppm, respectively. Negative nucleus independent chemical shift (NICS) in interior positions of rings or cages indicates the presence of induced diatropic ring currents which suggests that cyclohexatriene poles can be considered as benzenoid fragments. NICS yields minor value (?2.7 ppm) at the ring center of polar pentagons of C₆₀Cl₁₀F₁₀, and significantly negative values in the cage center.     

Direct electron transfer and biocatalytic activity of iron storage protein molecules immobilized on electrodeposited cobalt oxide nanoparticles

Ferritin was immobilized on a glassy carbon electrode with electrodeposited cobalt oxide nanoparticles, and its direct electron transfer behavior was studied. It exhibits a pair of redox peaks due to direct electron transfer between ferritin and the nanoparticles. Electrochemical parameters including the formal potential (E^0??), the charge transfer coefficient (??), and the apparent heterogeneous electron transfer rate constant (k_s) were determined. The sensor displays excellent biocatalytic activity in terms of reduction of hydrogen peroxide, and this was applied to electrochemical sensing of hydrogen peroxide.

Oxidative Coupling of Methane over Lithium Doped （Mn＋W）/SiO2 Catalysts

Modification and performance of Li induced silica phase transition of (Mn W)/SiO2 catalyst, under reaction conditions of oxidative coupling of methane (OCM), have been investigated employing textural characterizations and redox studies. Stability and precrystalline form of fresh Li induced silica phase transition catalyst depend on the Li loading. A catalyst, with high lithium loading, destabilizes on OCM stream. This destabilization is not due to Li evaporation at OCM reaction conditions.α-cristobalite is proposed to be an intermediate in the crystallization of amorphous silica into quartz in the Li-induced silica phase transition process. However, the type of crystalline structure was found to be unimportant with regard to the formation of a selective catalyst. Metal-metal interactions of Li-Mn, Li-W and Mn-W, which are affected during silica phase crystallization, are found to be critical parameters of the trimetallic catalyst and were studied by TPR. Role of lithium in Li doped (Mn W)/SiO2 catalyst is described as a moderator of the Mn-W interaction by involving W in silica phase transition. These interactions help in the improvement of transition metal redox properties, especially that of Mn, in favor of OCM selectivity.