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Adsorption Time (adsorption + time)
Selected AbstractsGlassy Carbon Electrodes Modified with Multiwall Carbon Nanotubes Dispersed in PolylysineELECTROANALYSIS, Issue 15 2008Yamile Jalit Abstract We report the analytical performance of glassy carbon electrodes (GCE) modified with a dispersion of multiwall carbon nanotubes (MWCNT) in polylysine (Plys) (GCE/MWCNT-Plys). The resulting electrodes show an excellent electrocatalytic activity towards different bioanalytes like ascorbic acid, uric acid and hydrogen peroxide, with important decrease in their oxidation overvoltages. The dispersion of 1.0,mg/mL MWCNT in 1.0,mg/mL polylysine is highly stable, since after 2 weeks the sensitivity for hydrogen peroxide at GCE modified with this dispersion remained in a 90% of the original value. The MWCNT-Plys layer immobilized on glassy carbon electrodes has been also used as a platform to build supramolecular architectures by self-assembling of polyelectrolytes based on the polycationic nature of the polylysine used to disperse the nanotubes. The self-assembling of glucose oxidase has allowed us to obtain a supramolecular multistructure for glucose biosensing. The influence of glucose oxidase concentration and adsorption time as well as the effect of using polylysine or MWCNT-Plys as polycationic layers for further adsorption of GOx is also evaluated. [source] The removal of colour, carotene and acidity from crude olive oil by using sepioliteINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 3 2007Mehmet U, urlu Summary The capacity of sepiolite to adsorb colouring matters in olive oil was studied. The effects of adsorption time, temperature and solid:liquid ratio were selected as parameters. The effect of bleaching of olive oil was evaluated for determining the % free fatty acid (FFA), % bleachability and residual carotene by using both thermally activated sepiolite (AS) and acid-activated sepiolite (AAS). Results reveal that thermally acid-activated sepiolite was more efficient than thermally activated sepiolite. The adsorption equilibriums of carotene and FFA on AS and AAS were described by the Freundlich models. A higher adsorption coefficient (K) was observed for AAS (Kcarotene = 2.73 × 10,3mgg,1, KFFA = 0.98mgg,1) compared to AS (Kcarotene = 2.63 × 10,7mgg,1, KFFA = 0.21mgg,1). Moreover, the rate constants obtained for carotene and colour by using AAS (kcolor = 0.0241 min,1, kcarotene = 0.0217min,1) were higher than that of AS (kcolor = 0.01min,1, kcarotene = 0.0165min,1). [source] Preconcentration and matrix elimination for the determination of Pb(II), Cd(II), Ni(II), and Co(II)by 8-hydroxyquinoline anchored poly(styrene-divinylbenzene) microbeadsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008Hakan A Abstract Poly(styrene-divinylbenzene), PS-DVB, microbeads were modified with 8-hydroxyquinoline (8-HQ) following nitration, reduction of NO2 to NH2, and conversion of NH2 to diazonium salt. Characterization of pristine, NO2, NH2, NN+Cl,, and 8-QH functional groups modified microbeads was made by Fourier transform-infrared spectrometry (FTIR) and porosimetry. Total reflectron-X-ray florescence spectrometer (TXRF) was used to test the affinity of the 8-HQ modified microbeads to toxic metal ions. 8-HQ-modified microbeads were used to examine the adsorption capacity, recovery, preconcentration, and the matrix elimination efficiency for Pb(II), Cd(II), Ni(II), and Co(II) ions as a function of changing pH, initial metal-ion concentrations, and also equilibrium adsorption time of the studied metal ions. Preconcentration factors for the studied toxic metal ions were found to be more than 500-fold and recovery between 93.8% and 100.6%. Ultratrace toxic metal-ion concentrations in sea water were determined easily by using modified microbeads. Reference sea-water sample was used for the validation of the method, and it was found that recovery, preconcentration, and the matrix elimination were performed perfectly. For the desorption of the toxic metal ions, 3M of HNO3 was used and desorption ratio shown to be more than 96%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Optimization and analysis of nickel adsorption on microwave irradiated rice husk using response surface methodology (RSM)JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2009Magesh Ganesa Pillai Abstract BACKGROUND: The removal of heavy metals using adsorption techniques with low cost biosorbents is being extensively investigated. The improved adsorption is essentially due to the pores present in the adsorbent. One way of improving the porosity of the material is by irradiation of the precursor using microwaves. In the present study, the adsorption characteristics of nickel onto microwave-irradiated rice husks were studied and the process variables were optimized through response surface methodology (RSM). RESULT: The adsorption of nickel onto microwave-irradiated rice husk (MIRH) was found to be better than that of the raw rice husk (RRH). The kinetics of the adsorption of Ni(II) from aqueous solution onto MIRH was found to follow a pseudo-second-order model. Thermodynamic parameters such as standard Gibbs free energy (,G°), standard enthalpy (,H°), and standard entropy (,S°) were also evaluated. The thermodynamics of Ni(II) adsorption onto MIRH indicates that it is spontaneous and endothermic in nature. The response surface methodology (RSM) was employed to optimize the design parameters for the present process. CONCLUSION: Microwave-irradiated rice husk was found to be a suitable adsorbent for the removal of nickel(II) ions from aqueous solutions. The adsorption capacity of the rice husk was found to be 1.17 mg g,1. The optimized parameters for the current process were found as follows: adsorbent loading 2.8 g (100 mL),1; Initial adsorbate concentration 6 mg L,1; adsorption time 210 min.; and adsorption temperature 35 °C. Copyright © 2008 Society of Chemical Industry [source] Interfacial and foaming characteristics of milk whey protein and polysaccharide mixed systemsAICHE JOURNAL, Issue 4 2010Adrián A. Perez Abstract Protein-polysaccharide (PS) interactions find many applications in food engineering and new foam formulations. In this article, we have studied the effect of anionic nonsurface active PSs [sodium alginate (SA) and lambda-carrageenan (,-C)] in aqueous solution on interfacial and foaming characteristics of milk whey proteins [whey protein concentrate (WPC) and whey protein isolate (WPI)]. Whey protein concentration (1.0% wt), temperature (20°C), pH (7), and ionic strength (0.05 M) of the aqueous media were kept constant, while PS influence was evaluated within a 0.0,1.0% wt concentration range. The dynamic properties (dynamics of adsorption and surface dilatational properties) of WPC/PS and WPI/PS adsorbed films were considered in order to correlate the foaming characteristics of the biopolymer mixed systems. Foaming characteristics of the biopolymer mixed systems depended on the PS relative concentration in the aqueous phase and on the whey protein-PS interactions in solution and at the air,water interface. Dynamic surface properties of the adsorbed films at short adsorption time had a significant effect on foaming capacity. For a particular system, the overall foam destabilization (foam half-life time) and the individual destabilization processes (drainage, disproportionation, and bubble coalescence) depend on the nature of the PS, its relative bulk concentration, and whey protein-PS interactions in the vicinity of the air,water interface. The viscosity of the aqueous phase has an effect on the rate of drainage while the rate of disproportionation/collapse is more dependent on the interfacial characteristics of the adsorbed film. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Design of a two-step pulsed pressure-swing adsorption-based oxygen concentratorAICHE JOURNAL, Issue 2 2010V. Rama Rao Abstract A two-step pulsed pressure-swing adsorption (PPSA) process has been modeled to assess the extent to which an oxygen concentrator might be miniaturized for medical applications. The process consists of a single bed of packed adsorbent particles that is alternately pressurized and depressurized at the feed end. An enriched oxygen product is withdrawn at ambient pressure from the product end when the bed is pressurized at the feed end. The product end remains closed during depressurization. The model development addresses the manner in which axial dispersion enters into the describing equations and the formulation of proper boundary conditions, both of which have not been handled rigorously in some prior modeling studies. The describing equations are solved using COMSOL® Multiphysics software. The effect on the performance of the adsorption time, desorption time, bed length, particle diameter, and imposed pressure drop across the bed have been investigated. An interesting novel result is that for a chosen particle size, bed length, and applied pressure drop, there is an optimum combination of adsorption and desorption times that maximizes the product purity. The results suggest that there are operating windows for both 5A and partially Ag-exchanged Li-substituted 13X zeolite adsorbents wherein the product oxygen purity is greater than 90%. At a given product flow rate within this operating window, the extent of miniaturization is limited by the (maximum) cycling frequency that is practically achievable. Sizing of an oxygen concentrator for personal medical applications is also discussed. A principal conclusion is that a compact oxygen concentrator capable of producing a highly oxygen-enriched product is possible using commercially available adsorbents and implementable operating conditions. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] | ||||||||||