Virus-sized colloid transport in a single pore: Model development and sensitivity analysis

A mathematical model is developed to simulate the transport and deposition of virus-sized colloids in a cylindrical pore throat considering various processes such as advection, diffusion, colloid-collector surface interactions and hydrodynamic wall effects. The pore space is divided into three different regions, namely, bulk, diffusion and potential regions, based on the dominant processes acting in each of these regions. In the bulk region, colloid transport is governed by advection and diffusion whereas in the diffusion region, colloid mobility due to diffusion is retarded by hydrodynamic wall effects. Colloid-collector interaction forces dominate the transport in the potential region where colloid deposition occurs. The governing equations are non-dimensionalized and solved numerically. A sensitivity analysis indicates that the virus-sized colloid transport and deposition is significantly affected by various pore-scale parameters such as the surface potentials on colloid and collector, ionic strength of the solution, flow velocity, pore size and colloid size. The adsorbed concentration and hence, the favorability of the surface for adsorption increases with: (i) decreasing magnitude and ratio of surface potentials on colloid and collector, (ii) increasing ionic strength and (iii) increasing pore radius. The adsorbed concentration increases with increasing Pe, reaching a maximum value at Pe = 0.1 and then decreases thereafter. Also, the colloid size significantly affects particle deposition with the adsorbed concentration increasing with increasing particle radius, reaching a maximum value at a particle radius of 100 nm and then decreasing with increasing radius. System hydrodynamics is found to have a greater effect on larger particles than on smaller ones. The secondary minimum contribution to particle deposition has been found to increase as the favorability of the surface for adsorption decreases. The sensitivity of the model to a given parameter will be high if the conditions are favorable for adsorption. The results agree qualitatively with the column-scale experimental observations available in the literature. The current model forms the building block in upscaling colloid transport from pore scale to Darcy scale using Pore-Network Modeling. (C) 2014 Elsevier By. All rights reserved.

Solar driven Adsorption Desalination system

Desalination is one of the most traditional processes to generate potable water. With the rise in demand for potable water and paucity of fresh water resources, this process has gained special importance. Conventional thermal desalination processes involves evaporative methods such as multi-stage flash and solar distils, which are found to be energy intensive, whereas reverse osmosis based systems have high operating and maintenance costs. The present work describes the Adsorption Desalination (AD) system, which is an emerging process of thermal desalination cum refrigeration capable of utilizing low grade heat easily obtainable from even non-concentrating type solar collectors. The system employs a combination of flash evaporation and thermal compression to generate cooling and desalinated water. The current study analyses the system dynamics of a 4-bed single stage silica-gel plus water based AD system. A lumped model is developed using conservation of energy and mass coupled with the kinetics of adsorption/desorption process. The constitutive equations for the system components viz. evaporator, adsorber and condenser, are solved and the performance of the system is evaluated for a single stage AD system at various condenser temperatures and cycle times to determine optimum operating conditions required for desalination and cooling. (C) 2013 P. Dutta. Published by Elsevier Ltd.

Development, in vitro and in vivo characterization of zoledronic acid functionalized hydroxyapatite nanoparticle based formulation for treatment of osteoporosis in animal model

We investigated the potential of using novel zoledronic acid (ZOL)-hydroxyapatite (HA) nanoparticle based drug formulation in a rat model of postmenopausal osteoporosis. By a classical adsorption method, nanoparticles of HA loaded with ZOL (HNLZ) drug formulation with a size range of 100-130 nm were prepared. 56 female Wistar rats were ovariectomized (OVX) or sham-operated at 3 months of age. Twelve weeks post surgery, rats were randomized into seven groups and treated with various doses of HNLZ (100, 50 and 25 mu g/kg, intravenous single dose), ZOL (100 mu g/kg, intravenous single dose) and HA nanoparticle (100 mu g/kg, intravenous single dose). Untreated OVX and sham OVX served as controls. After three months treatment period, we evaluated the mechanical properties of the lumbar vertebra and femoral mid-shaft. Femurs were also tested for trabecular microarchitecture. Sensitive biochemical markers of bone formation and bone resorption in serum were also determined. With respect to improvement in the mechanical strength of the lumbar spine and the femoral mid-shaft, the therapy with HNLZ drug formulation was more effective than ZOL therapy in OVX rats. Moreover, HNLZ drug therapy preserved the trabecular microarchitecture better than ZOL therapy in OVX rats. Furthermore, the HNLZ drug formulation corrected increase in serum levels of bone-specific alkaline phosphatase, procollagen type I N-terminal propeptide, osteocalcin, tartrate-resistant acid phosphatase 5b and C-telopeptide of type 1 collagen better than ZOL therapy in OVX rats. The results strongly suggest that HNLZ novel drug formulation appears to be more effective approach for treating severe osteoporosis in humans. (C) 2014 Elsevier B.V. All rights reserved.

SIMULATION STUDY OF THE ADSORPTION DYNAMICS OF CYLINDRICAL SILICA GEL PARTICLES

The paper presents a simulation study of loose cylindrically shaped particles packed within a copper plate and aluminum fins. The model presented solves coupled heat and mass transfer equations using the finite volume method based on ANSY S FLUENT medium. Three different arrangements of cylindrical particles are considered. The model is validated with experimental data. It is found that the arrangements which represented monolayer configurations are only marginally better in heat transfer and uptake efficiency than the tri-layer configuration in the presence of fins. However, there is an appreciable difference in the uptake curve between monoand tri-layer configurations in the absence of fins. Finally, it is found that the fin pitch also plays an important role in determining the time constant for the adsorber design.

Ag-doped hydroxyapatite as efficient adsorbent for removal of Congo red dye from aqueous solution: Synthesis, kinetic and equilibrium adsorption isotherm analysis

In the present study a versatile and efficient adsorbent with high adsorption capacity for adsorption of Congo red dye in aqueous solution at ambient temperature without adjusting any pH is presented over the Ag modified calcium hydroxyapatite (CaHAp). CaHAp and Ag-doped CaHAp materials were synthesized using facile aqueous precipitation method. The physico-chemical properties of the materials were determined by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Transmission electron microscopy (TEM), UV-Visible spectroscopy, N-2 physisorption and acidity was determined by n-butylamine titration and pyridine adsorption methods. XRD analysis confirmed all adsorbents exhibit hexagonal CaHAp structure with P6(3)/m space group. TEM analysis confirms the rod like morphology of the adsorbents and the average length of the rods were in the range of 40-45 nm. Pyridine adsorption results indicate increase in number of Lewis acid sites with Ag doping in CaHAp. Adsorption capacity of CaHAp was found increased with Ag content in the adsorbents. Ag (10): CaHAp adsorbent showed superior adsorption performance among all the adsorbents for various concentrations of Congo red (CR) dye in aqueous solutions. The amount of CR dye adsorbed on Ag (10): CaHAp was found to be 49.89-267.81 mg g(-1) for 50-300 ppm in aqueous solution. A good correlation between adsorption capacity and acidity of the adsorbents was observed. The adsorption kinetic data of adsorbents fitted well with pseudo second-order kinetic model with correlation coefficients ranged from 0.998 to 0.999. The equilibrium adsorption data was found to best fit to the Langmuir adsorption isotherm model. (C) 2015 Elsevier Inc. All rights reserved.

Performance evaluation of a two-stage silica gel plus water adsorption based cooling-cum-desalination system

The first objective of this paper is to show that a single-stage adsorption based cooling-cum-desalination system cannot be used if air cooled heat rejection is used under tropical conditions. This objective is achieved by operating a silica gel + water adsorption chiller first in a single-stage mode and then in a 2-stage mode with 2 beds/stage in each case. The second objective is to improve upon the simulation results obtained earlier by way of empirically describing the thermal wave phenomena during switching of operation of beds between adsorption and desorption and vice versa. Performance indicators, namely, cooling capacity, coefficient of performance and desalinated water output are extracted for various evaporator pressures and half cycle times. The improved simulation model is found to interpret experimental results more closely than the earlier one. Reasons for decline in performance indicators between theoretical and actual scenarios are appraised. (C) 2015 Elsevier Ltd and IIR. All rights reserved.

Surface Stress Induced By Adatoms Adsorption On Solid Surfaces

Based on the statistical thermodynamics theory, a theoretical model of adsorbate induced surface stress of adatoms adsorption on solid surface is presented. For the low coverage, the interaction between the adsorbed molecules is entirely negligible and the adsorption induced surface stress is found to be the function of the coverage and the adsorption energy change with strain. For the high coverage, the adsorbate-adsorbate interaction contributes to the adsorption-induced surface stress effectively. In the case of carbon adsorption on the Ni(100) surface, the value of 0.5 is obtained as a characteristic coverage to decide whether to take the interaction between the adsorabtes into consideration and the results also show that the adsorption induces a compressive surface stress.

Quantum Monte Carlo study of the CO interaction with a dimer model surface for Cr(110)

The chemisorption of CO on a Cr( 110) surface is investigated using the quantum Monte Carlo method in the diffusion Monte Carlo (DMC) variant and a model Cr2CO cluster. The present results are consistent with the earlier ab initio HF study with this model that showed the tilted/ near-parallel orientation as energetically favoured over the perpendicular arrangement. The DMC energy difference between the two orientations is larger (1.9 eV) than that computed in the previous study. The distribution and reorganization of electrons during CO adsorption on the model surface are analysed using the topological electron localization function method that yields electron populations, charge transfer and clear insight on the chemical bonding that occurs with CO adsorption and dissociation on the model surface.

Adsorption of Pb(II) and Cu(II) on α-quartz from aqueous solutions: influence of pH, ionic strength, and complexing ligands

Adsorption of aqueous Pb(II) and Cu(II) on α-quartz was studied as a function of time, system surface area, and chemical speciation. Experimental systems contained sodium as a major cation, hydroxide, carbonate, and chloride as major anions, and covered the pH range 4 to 8. In some cases citrate and EDTA were added as representative organic complexing agents. The adsorption equilibria were reached quickly, regardless of the system surface area. The positions of the adsorption equilibria were found to be strongly dependent on pH, ionic strength and concentration of citrate and EDTA. The addition of these non-adsorbing ligands resulted in a competition between chelation and adsorption. The experimental work also included the examination of the adsorption behavior of the doubly charged major cations Ca(II) and Mg(II) as a function of pH.

The theoretical description of the experimental systems was obtained by means of chemical equilibrium-plus-adsorption computations using two adsorption models: one mainly electrostatic (the James-Healy Model), and the other mainly chemical (the Ion Exchange-Surface Complex Formation Model). Comparisons were made between these two models.

The main difficulty in the theoretical predictions of the adsorption behavior of Cu(II) was the lack of the reliable data for the second hydrolysis constant(*β_2) The choice of the constant was made on the basis of potentiometric titratlons of Cu^(2+)

The experimental data obtained and the resulting theoretical observations were applied in models of the chemical behavior of trace metals in fresh oxic waters, with emphasis on Pb(II) and Cu(II).

A comprehensive study of lysozyme adsorption using dual polarization interferometry and quartz crystal microbalance with dissipation.

Protein adsorption plays a crucial role in biomaterial surface science as it is directly linked to the biocompatibility of artificial biomaterial devices. Here, elucidation of protein adsorption mechanism is effected using dual polarization interferometry and a quartz crystal microbalance to characterize lysozyme layer properties on a silica surface at different coverage values. Lysozyme is observed to adsorb from sparse monolayer to multilayer coverage. At low coverage an irreversibly adsorbed layer is formed with slight deformation consistent with side-on orientation. At higher coverage values dynamic re-orientation effects are observed which lead to monolayer surface coverages of 2-3 ng/mm² corresponding to edge-on or/and end-on orientations. These monolayer thickness values ranged between 3 and 4.5 nm with a protein density value of 0.60 g/mL and with 50 wt% solvent mass. Further increase of coverage results formation of a multilayer structure. Using the hydration content and other physical layer properties a tentative model lysozyme adsorption is proposed.

A comprehensive study of lysozyme adsorption using dual polarization interferometry and quartz crystal microbalance with dissipation

Protein adsorption plays a crucial role in biomaterial surface science as it is directly linked to the biocompatibility of artificial biomaterial devices. Here, elucidation of protein adsorption mechanism is effected using dual polarization interferometry and a quartz crystal microbalance to characterize lysozyme layer properties on a silica surface at different coverage values. Lysozyme is observed to adsorb from sparse monolayer to multilayer coverage. At low coverage an irreversibly adsorbed layer is formed with slight deformation consistent with side-on orientation. At higher coverage values dynamic re-orientation effects are observed which lead to monolayer surface coverages of 2-3 ng/mm2 corresponding to edge-on or/and end-on orientations. These monolayer thickness values ranged between 3 and 4.5 nm with a protein density value of 0.60 g/mL and with 50 wt% solvent mass. Further increase of coverage results formation of a multilayer structure. Using the hydration content and other physical layer properties a tentative model lysozyme adsorption is proposed. © 2012 Elsevier Ltd.

Studies on the adsorption equilibrium and kinetics of pentachlorophenol on suspended particulate matter of Donghu Lake water

In this paper, the adsorption equilibrium and kinetic behaviors of pentachlorophenol (PCP) on suspended particulate matter (SPM) in Donghu Lake water were investigated. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and their constants were evaluated. The results indicated that the adsorption of PCP on Donghu Lake SPM followed the Freundlich isotherm. Furthermore, the first order Lagergren rate equation and the pseudo-second order rate equation were used to describe the kinetic behaviors of PCP adsorption on Donghu Lake SPM, the rate constants were determined, and the kinetic process of the adsorption of PCP on Donghu Lake SPM followed the second order kinetic model.

Hydrodynamics in an expanded bed of large size ion-exchange resin, and natural product adsorption

Successful applications of expanded bed adsorption (EBA) technology have been widely reported in the literature for protein purification. Little has been reported on the recovery of natural products and active components of Chinese herbal preparations using EBA technology. In this study, the hydrodynamic behavior in an expanded bed of cation resin, 001 x 7 Styrene-DVB, was investigated. Ephedrine hydrochloride (EH) was used as a model natural product to test the dynamic binding capacity (DBC) in the expanded bed. EBA of EH directly from a feedstock containing powdered herbs has also been investigated. These particles are different from commercially available expanded bed adsorbents by virtue of their large size (20S to 1030 gm). When the adsorbent bed is expanded to approximately 1.3 to 1.5 times its settled bed height, the axial liquid-phase dispersion coefficient was found to be of the order 10(-5) m(2) s(-1), which falls into the range 1.0 x 10(-6) to 1.0 X 10(-5) m(2) s(-1) observed previously in protein purification. Because of the favorable column efficiency (low axial dispersion coefficient), the recovery yield and purification factor values of EH directly from a feedstock reached 86.5% and 18, respectively. The results suggest that EBA technology holds promise for the recovery of natural products and active components of Chinese herbal preparations.

A surface kinetics model for the growth of Si1-xGex by UHV/CVD using SiH4/CeH4

The surface reaction mechanism of Si1-xGex/Si growth using SiH4 and GeH4 in UHV/CVD system was studied. The saturated adsorption and desorption of SiH4 from Si(1 0 0) surface was investigated with the help of TPD and RHEED, and it was found that all the 4 hydrogen atoms of one SiH4 molecule were adsorbed to the Si surface, which meant that the dissociated adsorption ratio was proportional to 4 power of surface vacancies. The analysis of the reaction of GeH4 was also done. A new surface reaction kinetic model on Si1-xGex/Si epitaxial growth under UHV conditions by SiH4/GeH4 was proposed based on these studies. The predictions of the model were verified by the experimental results. (C) 2000 Elsevier Science B.V. All rights reserved.

Synthesis and characterization of carbon black supported Pt-Ru alloy as a model catalyst for fuel cells

A set of bimetallic Pt-Ru catalysts prepared by co-impregnation of carbon black with ruthenium(III) chloride hydrate and hydrogen hexachloroplatinate(IV) hydrate were investigated by temperature-programmed reduction (TPR), chemisorption of hydrogen, transmission electron microscopy (TEM), microcalorimetry of adsorbed CO and a structure-sensitive reaction (n-hexane conversion). The results showed that the volumetric capacities for CO and H-2 adsorption is influenced in the bimetallic Pt-Ru catalysts by the formation of a Pt-Ru alloy. The n-hexane reaction revealed that the reaction mechanism for the pure Pt catalyst mainly occurs via cyclic isomerization and aromatization due to the presence of bigger Pt surface ensembles, whereas the Pt-Ru catalysts exhibited predominantly bond-shift isomerization by the diluting effect of Ru metal addition. The differential heats of CO chemisorption on Pt-Ru catalysts fell between the two monometallic Pt and Ru catalysts extremes. (C) 2004 Elsevier B.V. All rights reserved.