M.Sc. (Chemistry) / Zero-valent nanoscale metal, especially iron nanoparticles have attracted significant attention with regards to remediation of organochlorinated compounds in drinking water. For a more rapid and complete dechlorination, a second and usually electronegative element is often added, resulting in the formationof bimetallic nanoparticles. However, in the absence of surfactants,the bimetallic nanoparticles easily aggregate into large particles (if they are not anchored on solid supports) with wide size distributions, thus losing their reactivity. This work reports an in-situ synthesis method of bimetallic nanoparticles immobilized on L-lysine functionalized microfiltration membranes by chemical reduction of metal ions chelated by amine and hydroxyl functional groups of L-lysine on the composite. The immobilization of the nanoparticles on membranes offers many advantages: reduction of particle loss, prevention of particle agglomeration and application under convective flow. The objective of this research wasto produce catalytic filtration membranes for dechlorination of organic compound, PCB-77. This was achieved first by (i) the modification of commercial PVDF to introduce functional groups that render the membrane more hydrophilic and have the ability to capture metal ions through chelation, and secondly (ii) the controlled introduction of catalytic nanoparticles onto the composite membrane surface, anchored through chelation to the surface functional groups. This approach was selected with aview to produce uniform surface distribution of monodispersed bimetallic nanoparticles that are resistant to leaching during the reduction reactions. The modification of the PVDF membrane was achieved by firstly performing an in situ polymerization of acrylic acid followed by covalently bonded L-lysine to the polymerized acrylic acid chains using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC). The Fe ions were introduced to the composite by L-lysine chelation and subsequently reduced to Fe0 with NaBH4, and finally deposition of Ni2+ which later were also reduced to Ni0 with NaBH4. The Fe/Ni bimetallic NPs system was chosen based on its proven ability for the total dechlorination of chlorinated organic compounds. Systematic characterization of the composite was performed using ATR-FTIR, FESEM, EDS, HRTEM, XRD, AFM and Contact Angle measurements. A relatively uniform distribution of Fe/Ni nanoparticles was found in L-lysine/PAA/PVDF membrane. The diameter of Fe/Ni nanoparticles was predominantly within the range 20-30 nm. Furthermore, the mechanism of the catalytic dechlorination of the model compound, PCB 77, was investigated by careful analysis of the reaction products. It is generally known that zero-valent iron undergoes corrosion to provide hydrogen atoms and electrons for the reductive catalytic hydrodechlorination reaction. The second metal in the bimetallic system on the other hand, acts as...

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Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 174-181).

Zugl.: Aachen, Techn. Hochsch., Diss., 2005.

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published_or_final_version / Civil Engineering / Master / Master of Philosophy

Nanofiltration (NF) membranes have been applied successfully for the removal of inorganic and organic pollutants, including micropollutants, from drinking water for the past two decades. However, a complete and quantitative understanding of NF removal mechanisms has yet to be achieved. Quantifying the factors governing solute transport and retention by NF is necessary in order to achieve higher treatment efficiency at a lower cost. The aim of this research was to contribute to the current state of the knowledge of the mechanisms of solute retention and transport by NF membranes. The focus was on evaluating the contribution of solute-solute interactions and solute-membrane interactions on solute removal and transport mechanisms. To the knowledge of the author, at the start of this research there was a lack of understanding of the simultaneous impacts of both interactions on the performance of NF membranes, which renders this research novel. To highlight challenges faced by modern membrane plants and identify inorganic and organic pollutants of interest, a study of water quality in Scotland was carried out. Experiments were performed in dead-end stirred cells using two commercial NF membranes, TFC-SR2 and TFC-SR3 provided by Koch, which were extensively characterized. Radiolabeled Endosulfan (ES, 10 μg/L), manganese (5-1,500 mg/L) and Humic Acids (HA, 5-250 mgC/L) were spiked in synthetic water with background electrolyte (1 mM NaHCO3 and 20 mM NaCl). Calcium (Ca, 2.5 mM) was employed in fouling experiments. The influence of the complexation of solutes with HA on solute retention by NF was for the first time quantified for the solute concentrations employed in this study. It was found that manganese retention was influenced by membrane pore size and charge (solute-membrane interactions) and solute speciation (solute-solute interactions). Complexation of manganese and HA (solute-solute interactions) occurred at alkaline conditions but did not enhance manganese retention. At high pH manganese precipitated as solid MnCO3 and these precipitates achieved high retention (99%), even without the presence of HA. ES retention by NF membrane was controlled by size exclusion (solute-membrane interactions). For the tighter TFC-SR3, whose pore size are smaller than the size of ES, ES retention increased in the presence of HA, while for the looser TFC-SR2, whose pores are bigger than ES diameter, ES retention decreased in the presence of HA. For TFC-SR3 increase of ES retention in the presence of HA was due to size exclusion (solute-membrane interactions) and formation of ES-HA complexes (solute-solute interactions). For TFC-SR2 HA-membrane interactions were dominant with respect to solute-solute interactions, increasing membrane molecular weight cut-off (MWCO) and in turn passage of ES. The influence of pressure (5-15 bar) on ES retention in the presence of HA was systematically investigated. Results showed that ES transport through TFC-SR2 and TFC-SR3 was dominated by convection. For the tighter TFC-SR3 lower permeate flux was responsible for the increase of retention with pressure, while for the looser TFC-SR2 higher permeate flux increased concentration polarisation, decreasing retention with pressure. The presence of HA lowered the permeate flux, resulting in a less pronounced variation of retention with pressure for TFC-SR2 and in constant retention for TFC-SR3. The impact of manganese scaling on the performance of NF membranes was investigated at neutral pH. The effects of inorganic precipitates on flux and solute retention by NF have been so far scarcely studied and the impact of inorganic scaling on micropollutant retention by NF is unknown. Findings from this research indicated that manganese deposits did not foul the membranes but on the contrary enhanced their flux and prevented fouling by HA and Ca. The retention of ES, manganese and HA by membranes through which manganese was previously filtered was found to decrease with respect to solute retention by virgin membranes. Manganese filtration was shown to increase membrane MWCO and hydrophilicity. It was proposed that manganese-membrane interactions caused swelling of the membrane active layer by increasing the membrane free volume. The findings of this research indicated the importance of investigating simultaneously the impacts of solute-solute interactions and solute-membrane interactions to understand and explain transport and removal mechanisms of organic and inorganic contaminants by NF.

The primary focus of the research is to extend the principles of Nanofiltration(NF) to non-aqueous systems using solvent-resistant NF membranes. Several differentlevels of interaction are introduced when organic solvents are used with polymericmembranes and thus quantification of polymer-solvent interactions is critical. Puresolvent permeation studies were conducted to understand the mechanism of solventtransport through polymeric membranes. Different membrane materials (hydrophilic andhydrophobic) as well as different solvents (polar and non-polar) were used for the study.For example, hexane flux at 13 bar through a hydrophobic silicone based NF membranewas ~ 0.6 x 10-4 cm3/cm2. s. and that through a hydrophilic aromatic polyamide based NFmembrane was ~ 6 x 10-4 cm3/cm2. s. A simple model based on a solution-diffusionapproach which uses solvent physical properties (molar volume, viscosity) andmembrane properties (surface energy, etc) is used for correlating the pure solventpermeation through hydrophobic polymeric membranes.Solute transport studies were performed using organic dyes and triglycerides inpolar and non-polar solvents. For example, the rejection of Sudan IV (384 MW organicdye) in n-hexane medium is about 25 % at 15 bar and that in methanol is about –10 % atabout 20 bar for a hydrophobic (PDMS-based) membrane. However, for a hydrophilicpolyamide based NF membrane, the direction of separation is reversed (86 % in methanoland 43 % in n-hexane). From our experimental data with two types of membranes it isclear that coupling of the solute and solvent fluxes cannot be neglected. Two traditionaltransport theories (Spiegler-Kedem and Surface Force-Pore Flow model) that considercoupling were evaluated with literature and our experimental solute permeation data. Amodel based on a fundamental chemical potential gradient approach has been proposedfor explaining solute separation. The model uses solute, solvent and membrane physicalproperties and uses the Flory-Huggins and UNIFAC theories as activity coefficientmodels. This model has been used to obtain a correlation for the diffusion coefficients ofsolutes in hexane through a hydrophobic membrane. This correlation along withconvective coupling can be used to predict separation behavior for different solutes and atdifferent temperatures.