Synthesis of nanomaterials by microemulsions is a well-established technique that can be used to determine the desired size of particles of many inorganic and organic materials. Membrane preparation from polymerizable microemulsion is a well-known method which received more and more attention in the last 20 years. For the first time, the term microemulsion was used in 1959 by Schulman et al. [1] to identify a transparent dispersion consisting of water, oil, surfactant and alcohol. The microstructure of a microemulsion depends on the composition of the system, e.g. water-in-oil (w/o) droplets at low water content, oil-in-water (o/w) droplets at high water content, and a bicontinuous structure at intermediate water content [2]. Polymerisation, usually, occurs in consequence of the addition of redox or photo-initiators. At intermediate water content the result is a transparent membrane characterised by the presence of water and oil channels interconnected each other. The polymerized microemulsion may be used for all purposes as membranes. By varying the ratio of the components constituting the microemulsion (water, oil, surfactant and cosurfactant) it is possible to control membrane morphology as, for example, size and pore distribution. In this work a commercial surfactant was used as non-polymerizable surfactant; a monomer constituted the oil phase of the microemulsion; a cosurfactant was used to tailor the pore size; water was used as the aqueous phase of the microemulsion and a cross-linker was added to increase the rigidity of the polymer network. Once a clear solution was obtained by mixing all the components, initiators were added to the system under nitrogen atmosphere in order to start the polymerization process. Microemulsion was allowed to polymerize on a commercial ultrafiltration PES membrane. A transparent coating of about 12 µm was, thus, obtained. By adjusting some parameters, such as the concentration of the cosurfactant and the temperature, the optimal conditions for microemulsion preparation and polymerization were found. Preliminary characterization tests were carried out in order to study the performances of prepared coated membranes and to compare them with the uncoated ones. Two model dye compounds (Remazol Brilliant Blue and Acid Red) were used to evaluate membrane color rejection. For coated membranes, a high rejection to both dyes was found (70% for Acid Red and 97% for Remazol Brilliant Blue) with a water permeability of about 2 L/m2 h bar. Salt rejection tests with NaCl and MgSO4 proved the "dense" nature of the prepared membranes as a consequence of the high salts rejection (76% for NaCl and 88% for MgSO4). Further characterization tests are in progress in order to investigate membrane morphology by SEM and to determine membrane cut-off and pore size. Commercial ultrafiltration membranes used as support showed higher water permeability (500 L/m2 h bar ) but they also showed low dyes rejection ( 30% for Acid Red and 50% Remazol Brilliant Blue) due to their more open structure. Our final aim is to produce a very thin nanostructured hydrophilic coating to be used in water purification and in particular in the removal of dyes encountered, for example, in textile wastewater. REFERENCES [1] Schulman, J.H., Stoeckenius, W., Prince, L.M., Mechanism of formation and structure of micro emulsions by electron microscopy, J. Phys. Chem.,1959, 63; 1677-1680. [2] A. Figoli, Synthesis of nanostructured mixed matrix membrane for facilitated gas separation, PhD Thesis, University of Twente (NL), ISBN 90-365-1673-0 Enschede (NL) Acknowlodgment The work is funded by Bionexgen (grant agreement n. CP-FP- 246039-2 ) EU-FP7/project.
Nano-structured membrane to be applied for wastewater treatment
F Galiano;A Figoli;
2013
Abstract
Synthesis of nanomaterials by microemulsions is a well-established technique that can be used to determine the desired size of particles of many inorganic and organic materials. Membrane preparation from polymerizable microemulsion is a well-known method which received more and more attention in the last 20 years. For the first time, the term microemulsion was used in 1959 by Schulman et al. [1] to identify a transparent dispersion consisting of water, oil, surfactant and alcohol. The microstructure of a microemulsion depends on the composition of the system, e.g. water-in-oil (w/o) droplets at low water content, oil-in-water (o/w) droplets at high water content, and a bicontinuous structure at intermediate water content [2]. Polymerisation, usually, occurs in consequence of the addition of redox or photo-initiators. At intermediate water content the result is a transparent membrane characterised by the presence of water and oil channels interconnected each other. The polymerized microemulsion may be used for all purposes as membranes. By varying the ratio of the components constituting the microemulsion (water, oil, surfactant and cosurfactant) it is possible to control membrane morphology as, for example, size and pore distribution. In this work a commercial surfactant was used as non-polymerizable surfactant; a monomer constituted the oil phase of the microemulsion; a cosurfactant was used to tailor the pore size; water was used as the aqueous phase of the microemulsion and a cross-linker was added to increase the rigidity of the polymer network. Once a clear solution was obtained by mixing all the components, initiators were added to the system under nitrogen atmosphere in order to start the polymerization process. Microemulsion was allowed to polymerize on a commercial ultrafiltration PES membrane. A transparent coating of about 12 µm was, thus, obtained. By adjusting some parameters, such as the concentration of the cosurfactant and the temperature, the optimal conditions for microemulsion preparation and polymerization were found. Preliminary characterization tests were carried out in order to study the performances of prepared coated membranes and to compare them with the uncoated ones. Two model dye compounds (Remazol Brilliant Blue and Acid Red) were used to evaluate membrane color rejection. For coated membranes, a high rejection to both dyes was found (70% for Acid Red and 97% for Remazol Brilliant Blue) with a water permeability of about 2 L/m2 h bar. Salt rejection tests with NaCl and MgSO4 proved the "dense" nature of the prepared membranes as a consequence of the high salts rejection (76% for NaCl and 88% for MgSO4). Further characterization tests are in progress in order to investigate membrane morphology by SEM and to determine membrane cut-off and pore size. Commercial ultrafiltration membranes used as support showed higher water permeability (500 L/m2 h bar ) but they also showed low dyes rejection ( 30% for Acid Red and 50% Remazol Brilliant Blue) due to their more open structure. Our final aim is to produce a very thin nanostructured hydrophilic coating to be used in water purification and in particular in the removal of dyes encountered, for example, in textile wastewater. REFERENCES [1] Schulman, J.H., Stoeckenius, W., Prince, L.M., Mechanism of formation and structure of micro emulsions by electron microscopy, J. Phys. Chem.,1959, 63; 1677-1680. [2] A. Figoli, Synthesis of nanostructured mixed matrix membrane for facilitated gas separation, PhD Thesis, University of Twente (NL), ISBN 90-365-1673-0 Enschede (NL) Acknowlodgment The work is funded by Bionexgen (grant agreement n. CP-FP- 246039-2 ) EU-FP7/project.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
