SLIP VELOCITY IN PULSED DISC AND DOUGHNUT EXTRACTION COLUMN

In the present work, slip velocity has been measured in a 76 mm diameter pulsed disc and doughnut extraction column for four different liquid-liquid systems. The effects of operating variables including pulsation intensity and dispersed and continuous phase flow rates on slip velocity have been investigated. The existence of three different operational regimes, namely mixersettler, transition, and emulsion regimes, was observed when the energy input was changed. Empirical correlations are derived for prediction of the slip velocity in terms of operating variables, physical properties of the liquid systems, and column geometry for different regimes. Good agreement between prediction and experiments was found for all operating conditions that were investigated

ZnO quantum dots-graphene composites: Formation mechanism and enhanced photocatalytic activity for degradation of methyl orange dye

The current study demonstrates homogenous decorating of zinc oxide quantum dots (QDs) onto graphene oxide (GO) surface via simple chemical method. The AFM image exhibited that the prepared graphene was 0.8 nm thick and hence practically monolayer. Average size of the ZnO QDs was estimated by transmission electron microscopy around 3 nm. Instrumental and chemical analyses demonstrated formation of a strong bond between ZnO QDs and GO, through C-O-Zn and C-Zn bridges. The UV-visible spectra displayed that the introduction of graphene sheets to ZnO QDs resulted in higher absorption intensity of UV as well as widening of adsorption window toward visible light for ZnO-Graphene due to chemical bond between ZnO QDS and graphene surface. Results showed that adding of graphene up to 30% can improve resistance of ZnO against acids however for keeping the activity of catalyst, the recommended pH is near neutral (pH approximate to 6-7.2). In addition, the presence of graphene on the surface of the ZnO could significantly suppress the photocorrosion effect. The ZnO-Graphene hybrids indicated enhanced photocatalytic activity for degradation of methyl orange (MO) with the following order: ZnO-5% Graphene > ZnO-10% Graphene > ZnO QDs > ZnO30%-Graphene. This enhancement of photocatalytic activity may be attributed to the extended absorption of visible light, reducing of electronehole recombination rate, and adsorption of MO molecules onto the huge surface area of graphene, where they are kept at vicinity of ZnO for decomposition. (C) 2015 Elsevier B.V. All rights reserved

Magnetite nanoparticles embedded on reduced graphene oxide as an anode material for high capacity and long cycle-life Li-ion battery

A facile and cost-effective method was developed for the synthesis of "magnetite/reduced graphene oxide" nanocomposite, as an anode material for lithium-ion batteries. The fabricated composite was characterized by different instrumental analyses including XRD, Raman, XPS, SEM, TEM, and FTIR, as well as various electro-chemical (i.e. battery) tests. Such broad examination revealed the structure of the prepared material and its electrochemical behavior. It was found that the fabricated composite has a number of advantages over the currently utilized electrode materials such as cost efficiency, high Li ion storage (2528 mAh/g at 0.05 A/g at 1st discharge), cycle stability of 986 mAh/g over 100 cycles at a current density of 0.1 A/g, and eventually Coulombic efficiency of about 100 %. In comparison, the reduced graphene oxide (rGO) shows inferior per-formances, such as a constant capacity of 462 mAh/g, and a slower kinetics of the ion storage. Consequently, the synthesized low-cost anode material seems to be an attractive candidate for development of the next-generation energy-storage devices, used in electrical vehicles, and portable electronic instruments

Synthesis of “L-cysteine–graphene oxide” hybrid by new methods and elucidation of its uptake properties for Hg(II) ion

<p>This study introduces two new, simple, and scalable methods for synthesis of “cysteine–graphene oxide” hybrid, namely nucleophilic and covalent methods. Produced adsorbents could uptake 500 and 600 mg Hg²⁺/g, respectively, which are larger than capacities of most of the commercial adsorbents. By means of different instrumental techniques, chemical structures of the obtained graphene products were disclosed, and two pertinent mechanisms for their formations were suggested. Time for attaining uptake equilibrium for nucleophilic/covalent samples was 30 min/150 min, and kinetics was controlled by liquid film resistance/chemical reaction mechanisms, respectively. High selectivity and good regenerability are other key features of the prepared adsorbents.</p

Modeling and Process Design of Intraparticle Adsorption in Single-Stage and Multistage Continuous Stirred Reactors: An Analytical Kinetics Approach

Continuous adsorption in stirred reactors in the form of carbon in pulp (CIP) and resin in pulp (RIP) is an established process for the extraction of gold and uranium. Under the circumstance of intraparticle diffusion resistance, CIP and RIP have been accurately modeled by the Boyd’s series (reversible adsorption) and shrinking core model (irreversible adsorption). The present study, in its first part, introduces an analytical formula that most closely approximates both models. Using such formula, the study addresses a basic algorithm for optimization of single-stage continuous adsorption systems through linking of the major process variables. Furthermore, this study is devoted to developing an “analytical kinetics approach” for the design of multistage CIP and RIP processes via application of Glauekauf’s multiple series. Advantages of the new approach over the McCabe–Thiele “Equilibrium Approach” are (1) the incorporation of the kinetics and equilibrium into one unified model, and (2) accurate determination of the number of stages, reactor size, and optimum operational conditions

Comparative Study on Adsorption of Iodine Vapor by Silica-Supported Cu Nanoparticles and Micronized Copper

The current study is aimed at comparison of adsorption behaviors of silica-supported Cu nanoparticles (Si–N–Cu) and micrometric copper powder (Mi-Cu) for uptake of iodine vapor. The Si–N–Cu was synthesized by the decomposition of aqueous Cu­(NO₃)₂ solution at supercritical condition, followed by reduction of the sample by H₂–N₂ mixture. The Si–N–Cu sample with 29.4 nm Cu particles adsorbed 95% of I₂ at partial pressure 10^–5 bar in 1 h, while the 1 μm Mi-Cu adsorbed 51% of iodine in 6 h, indicating higher yield and faster kinetics of the nanometric sample. Theoretical analysis revealed the existence of a strong thermodynamic size effect in the Cu–I₂ reaction system, so that molar |Δ<i>G</i>| for 2 nm Cu particles was 2.5 times larger than |Δ<i>G</i>| for 1 μm particles. For the Mi-Cu, kinetics obeyed a three-dimensional diffusion model, while in the case of Si–N–Cu, diffusion did not play any role in the kinetics. Apparently, no passivation mechanism was operative in the iodination

ZnO quantum dots-graphene composites: Formation mechanism and enhanced photocatalytic activity for degradation of methyl orange dye

The current study demonstrates homogenous decorating of zinc oxide quantum dots (QDs) onto graphene oxide (GO) surface via simple chemical method. The AFM image exhibited that the prepared graphene was 0.8 nm thick and hence practically monolayer. Average size of the ZnO QDs was estimated by transmission electron microscopy around 3 nm. Instrumental and chemical analyses demonstrated formation of a strong bond between ZnO QDs and GO, through C-O-Zn and C-Zn bridges. The UV-visible spectra displayed that the introduction of graphene sheets to ZnO QDs resulted in higher absorption intensity of UV as well as widening of adsorption window toward visible light for ZnO-Graphene due to chemical bond between ZnO QDS and graphene surface. Results showed that adding of graphene up to 30% can improve resistance of ZnO against acids however for keeping the activity of catalyst, the recommended pH is near neutral (pH approximate to 6-7.2). In addition, the presence of graphene on the surface of the ZnO could significantly suppress the photocorrosion effect. The ZnO-Graphene hybrids indicated enhanced photocatalytic activity for degradation of methyl orange (MO) with the following order: ZnO-5% Graphene > ZnO-10% Graphene > ZnO QDs > ZnO30%-Graphene. This enhancement of photocatalytic activity may be attributed to the extended absorption of visible light, reducing of electronehole recombination rate, and adsorption of MO molecules onto the huge surface area of graphene, where they are kept at vicinity of ZnO for decomposition. (C) 2015 Elsevier B.V. All rights reserved