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Zach-Maor A.,Grand Water Research Institute | Semiat R.,Grand Water Research Institute | Shemer H.,Grand Water Research Institute
Journal of Colloid and Interface Science | Year: 2011

A homogeneous layer of nano-sized magnetite particles (<4nm) was synthesized by impregnation of modified granular activated carbon (GAC) with ferric chloride, for effective removal of phosphate. A proposed mechanism for the modification and formation of magnetite onto the GAC is specified. BET results showed a significant increase in the surface area of the matrix following iron loading, implying that a porous nanomagnetite layer was formed. Batch adsorption experiments revealed high efficiency of phosphate removal, by the newly developed adsorbent, attaining maximum adsorption capacity of 435mg PO4/g Fe (corresponding to 1.1mol PO4/mol Fe3O4). It was concluded that initially phosphate was adsorbed by the active sites on the magnetite surface, and then it diffused into the interior pores of the nanomagnetite layer. It was demonstrated that the latter is the rate-determining step for the process. Innovative correlation of the diffusion mechanism with the unique adsorption properties of the synthesized adsorbent is presented. © 2011 Elsevier Inc.


Zach-Maor A.,Grand Water Research Institute | Semiat R.,Grand Water Research Institute | Shemer H.,Grand Water Research Institute
Journal of Colloid and Interface Science | Year: 2011

Phosphate adsorption mechanism by a homogenous porous layer of nano-sized magnetite particles immobilized onto granular activated carbon (nFe-GAC) was studied for both interface and bulk structures. X-ray Photoelectron Spectroscopy (XPS) analysis revealed phosphate bonding to the nFe-GAC predominantly through bidentate surface complexes. It was established that phosphate was adsorbed to the magnetite surface mainly via ligand exchange mechanism. Initially, phosphate was adsorbed by the active sites on the magnetite surface, after which it diffused into the interior of the nano-magnetite layer, as indicated by intraparticle diffusion model. This diffusion process continues regardless of interface interactions, revealing some of the outer magnetite binding sites for further phosphate uptake. Desorption, using NaOH solution, was found to be predominantly a surface reaction, at which hydroxyl ions replace the adsorbed phosphate ions only at the surface outer biding sites. Five successive fix-bed adsorption/regeneration cycles were successfully applied, without significant reduction in the nFe-GAC adsorption capacity and at high regeneration efficiency. © 2011 Elsevier Inc.


Yurum A.,Sabanci University | Kocabas-Atakli Z.T.,Sabanci University | Sezen M.,Sabanci University | Semiat R.,Grand Water Research Institute | Yurum Y.,Sabanci University
Chemical Engineering Journal | Year: 2014

Iron oxide nanoparticles were deposited on activated carbon (AC) with the microwave hydrothermal (MH) treatment technique. The effect of heating duration and AC's oxidation on structural properties were studied. X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), focused ion beam (FIB) microscopy, Brunauer, Emmett and Teller (BET), and porous texture analyses were utilized to characterize iron oxide/AC system. XRD characterization revealed dependence of crystal structure to heating duration. BET and porous texture analyses showed some pore filling in AC, but pore volume increase in iron oxide particles. With the MH technique, porous iron oxide was obtained with a high loading value of 20.27% in just 9. min. Additionally, As(V) adsorption capacity of synthesized materials was studied. As(V) adsorption onto iron oxide deposited supports obeyed Langmuir and pseudo-second order models. Batch adsorption experiments revealed a high efficiency of As(V) removal with the MH synthesized materials. Maximum adsorption capacity was 27.78. mg/g, and for a loading of 0.75. g/L, 99.90% uptake was reached within just 5. min due to the porous nature of iron oxide. Moreover, more than 99.00% of uptake was obtained within the pH range of 6-8. The results suggest that MH synthesized iron oxide particles are promising materials for water treatment. © 2014 Elsevier B.V.


Zelmanov G.,Grand Water Research Institute | Semiat R.,Grand Water Research Institute
Separation and Purification Technology | Year: 2011

The present research describes an adsorption method for cleaning a solution containing chromium (Cr+ 6) contaminants followed by recovery of the adsorbent and the adsorbed material for safe removal or further reuse. The approach for this purification process was made by using agglomerated nanoparticles-based on iron (Fe +3) oxide/hydroxide suspension as an adsorbent. The technology provides an efficient and cost effective method for chromium (Cr+ 6) removal from water. A strong effect was shown of iron (Fe +3) oxide/hydroxide nanoparticles-based concentration and pH level of polluted water on the removal efficiency. This technique achieved residual chromium (Cr+ 6) concentration less than 0.05 ppm which is acceptable by water quality regulations and at least 95-97% regeneration efficiency of the chromium with the proposed adsorbent. The chromium (Cr+ 6) adsorption capacity on the iron (3) oxides particles at equilibrium concentration of 0.05 ppm as Cr in the solution, is about an order of magnitude higher than these values reported in the literature. This technique allows recovery of the adsorbent while production of concentrated chromium (Cr+ 6) solution that may be treated further to obtain chromium contained crystals while recovering the cleaning solution. © 2011 Elsevier B.V. All rights reserved.


Zach-Maor A.,Grand Water Research Institute | Semiat R.,Grand Water Research Institute | Shemer H.,Grand Water Research Institute
Desalination and Water Treatment | Year: 2011

Nano-sized magnetite homogenous porous layer was immobilized onto modified granular activated carbon and used as an adsorbent for copper (Cu (II)) and chromium (Cr(VI)). Batch adsorption experiments revealed high efficiency for both metals removal attaining maximum adsorption capacity of 590 mg/g Fe. Significant difference in the reaction kinetics was found between the two metals suggesting that the magnetite affinity towards the copper was much higher than for chromium. These results were explained by the different mechanism at which the metals were adsorbed by the immobilized magnetite nano-particles layer. It was concluded that initially the metals were adsorbed by the active sites on the magnetite surface, and then diffused into the interior pores of the nano-magnetite layer. It was demonstrated that the latter was the rate-determining step for the process. Fixed-bed continuous experiments revealed the potential to reuse the nFe-GAC through three consecutive sorption and desorption cycles of copper. © 2011 Desalination Publications. All rights reserved.


Zach-Maor A.,Grand Water Research Institute | Semiat R.,Grand Water Research Institute | Shemer H.,Grand Water Research Institute
Adsorption | Year: 2011

Nano-sized magnetite impregnated charcoal granular activated carbon (nFe-GAC) was utilized for the removal of phosphate from aqueous solutions using a fixed bed column. The dynamic of the phosphate adsorption was analyzed using a new approach to the Thomas model based on a two-step differential sorption rate process. The initial adsorption was found to be external mass transfer controlled, while intra-particle diffusion was the predominant mechanism in the latter stage. Consequently, two kinetic coefficients were calculated for each breakthrough curve resulting in an excellent model prediction. By implementing this approach a transition point, at which diffusion becomes the predominant adsorption mechanism, can be accurately determined. The effect of varying parameters, such as feed flow rates, feed pH, initial phosphate concentrations and adsorbent bed height were examined and described using the modified Thomas model. Reaction rates increased with augmentation of the flow rates from 1 to 40 mL/min while the adsorption capacity and transition point decreased. Similar transition points were obtained for initial phosphate concentrations between 10 and 100 mg/L. The unique characteristics of the nFe-GAC were evident as it exhibited very high phosphate adsorption capacity, at a wide range of pH values (4-9) with negligible effect of competing ions and short critical bed depth. © Springer Science+Business Media, LLC 2011.


Shemer H.,Grand Water Research Institute | Semiat R.,Grand Water Research Institute
Desalination | Year: 2011

The effect of halogen based disinfectants including monochloramines (NH2Cl), free chlorine (HOCl/OCl-), and free oxidants (mixture of HOCl/OCl- and HOBr/OBr) on polyamide membrane was studied in synthetic Ocean seawater. Formation and stability of these oxidants were also examined. Permeability and salt rejection of flat sheet polyamide RO membranes following exposure to the halogen based oxidants were compared to the baseline performance of unexposed membranes. The ratio between free chlorine and free bromine was found to depend on the ratio between the bromides, naturally found in seawater, and the added chlorine. Bromide enhanced the degradation of monochloramines but did not affect the stability of free chlorine. All the oxidants damaged the polyamide membranes studied while the free oxidants appeared to be the most aggressive. © 2010 Elsevier B.V.


Zelmanov G.,Grand Water Research Institute | Semiat R.,Grand Water Research Institute
Separation and Purification Technology | Year: 2013

This study relates to an adsorption method process for treating a fluid containing undesired selenium contaminants (Se4+ and Se6+) in order to clean the fluid of the contaminant and develop a process for recovering the adsorbent material. The approach for this purification process was made using iron (Fe3+) oxide/hydroxide nanoparticles sol (NanoFe) as an adsorbent. The technique provides an efficient and cost-effective method for selenium removal from water. A strong effect was shown of iron (Fe 3+) oxide/hydroxide nanoparticles-based concentration and pH level of polluted water on removal efficiency. The exceptional adsorption properties of synthesized NanoFe adsorbent are demonstrated. This technique achieved residual selenium concentration less than 0.01 ppm, which is acceptable by water quality regulations and at least 95-98% regeneration efficiency of the selenium with the proposed adsorbent. The selenium adsorption capacity on the iron(3) oxide particles at an equilibrium concentration of 0.01 ppm as Se in the solution is about one order of magnitude higher than these values reported in the literature. This technique enables the recovery of the adsorbent by producing concentrated selenium solution that may be treated further to obtain selenium-containing crystals while recovering the cleaning solution. © 2012 Published by Elsevier B.V. All rights reserved.


Paz Y.,Grand Water Research Institute | Shemer G.,Grand Water Research Institute
International Journal of Photoenergy | Year: 2011

The preparation, characterization, and performance of an electrophotocatalytic cell, made of low-cost, planar interdigitated electrodes is reported hereby. The operation of the cell under small positive bias was demonstrated by photocatalytically degrading the dye rhodamine 6G in solution as well as by monitoring the degradation of self-assembled monolayer chemisorbed on the TiO2 electrode. Results point out to the importance of activated oxygen species formed in the process and suggest that the short distance between the two electrodes provides a way to utilize the activated oxygen species formed at the negatively biased electrode. © 2011 Guy Shemer and Yaron Paz.


PubMed | Grand Water Research Institute
Type: Journal Article | Journal: Journal of colloid and interface science | Year: 2011

Phosphate adsorption mechanism by a homogenous porous layer of nano-sized magnetite particles immobilized onto granular activated carbon (nFe-GAC) was studied for both interface and bulk structures. X-ray Photoelectron Spectroscopy (XPS) analysis revealed phosphate bonding to the nFe-GAC predominantly through bidentate surface complexes. It was established that phosphate was adsorbed to the magnetite surface mainly via ligand exchange mechanism. Initially, phosphate was adsorbed by the active sites on the magnetite surface, after which it diffused into the interior of the nano-magnetite layer, as indicated by intraparticle diffusion model. This diffusion process continues regardless of interface interactions, revealing some of the outer magnetite binding sites for further phosphate uptake. Desorption, using NaOH solution, was found to be predominantly a surface reaction, at which hydroxyl ions replace the adsorbed phosphate ions only at the surface outer biding sites. Five successive fix-bed adsorption/regeneration cycles were successfully applied, without significant reduction in the nFe-GAC adsorption capacity and at high regeneration efficiency.

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