Microgel-based thermoresponsive membranes for water filtration
Filtration using membrane filters is one of the most commonly used separation techniques. Modern developments are aimed at membranes with tailored separation properties as well as switchability. German scientists have now developed a very simple method for the modification of membranes through the inclusion of microgels. In the journal Angewandte Chemie, they introduce hollow-fiber membranes that demonstrate temperature-dependent flow and retention, thanks to thermoresponsive microgels.
The researchers from RWTH Aachen University and DWI—Leibniz Institute for Interactive Materials used commercially available hollow-fiber membranes used for the ultra- and microfiltration of water. Hollow-fiber filters consist of bundles of fibers made of a semipermeable material with a channel on the inside. The walls of the fibers act as the membrane. In order to modify the membranes, a team led by Matthias Wessling simply filtered microgel suspensions through them. This allowed the microgels to become embedded into the porous structure of the membrane.
A gel is a three-dimensional molecular network that is filled with a liquid. Unlike the liquid in a sponge, the liquid in the gel is tightly bound. Microparticles of a gel are called microgels. The researchers used microgels made of polyvinylcaprolactam that are stable to about 32 °C. Above this temperature, the gel structure collapses, letting the water out.
The hollow-fiber membranes used have an asymmetric pore structure with internal diameters of 30 nm (ultrafiltration) to 200 nm (microfiltration) and external diameters of several micrometers. The fibers can be loaded with the microgels either from the outside in or from the inside out. In the first method the gel particles penetrate partway into the pores and the outside is then coated with microgel. In the second method, gel particles are only found on the interior of the pores, but not in those pores that are very narrow. In both types of fibers, the microgel is so firmly adsorbed that it cannot be washed away either during filtration or back flushing.
The permeability of both types is significantly reduced relative to the untreated membrane, because the microgel makes the pores less accessible. Raising the temperature causes the microgel to shrink, increasing the permeability of the membrane; cooling reverses the effect. This switching mechanism could be an important method for an efficient cleaning of the hollow fiber when high flow rates are needed during a backwashing step at low temperatures.
“The modification of conventional hollow-fiber membranes with stimuli-responsive microgels provides a straightforward and versatile route to design functional membranes with new, tailored properties that allow for regulation of the permeability,” says Wessling. “Varying the chemical structures of the microgels allows for the introduction of specific functionalities into membranes, increasing the efficiency and selectivity of separation processes in water treatment and medical technology. We will further develop this versatile platform by fundamental research within the SFB Functional Microgels and Microgel Systems of the German Research Foundation (DFG).”
About the Author
Matthias Wessling is Alexander von Humboldt Professor at RWTH Aachen. His research aims to integrate selective mass transfer and conversion into micro-, meso- and macroscopic systems. In particular, he focusses on systems with functionalities controlled by tailored interfaces. Macroscopic systems are being analyzed, modeled and developed at his chair for Chemical Engineering at RWTH Aachen University (Aachener Verfahrenstechnik). At DWI, Matthias Wessling focuses on micro- and mesoscopic systems which integrate the basic principles of biological systems. The overall aim is to synthesize interactive materials systems inspired by nature.
Author: Matthias Wessling, RWTH Aachen (Germany), http://www.avt.rwth-aachen.de/
Title: Temperature-Modulated Water Filtration Using Microgel-Functionalized Hollow-Fiber Membranes
Angewandte Chemie International Edition, Permalink to the article: http://dx.doi.org/10.1002/anie.201400316
Matthias Wessling | Angewandte Chemie International Edition
Even plants can be stressed
03.09.2015 | Max-Planck-Institut für Molekulare Pflanzenphysiologie
Research team from Münster develops innovative catalytic chemistry process
03.09.2015 | Westfälische Wilhelms-Universität Münster
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE have developed a highly compact and efficient inverter for use in uninterruptible power...
China's Loess Plateau was formed by wind alternately depositing dust or removing dust over the last 2.6 million years, according to a new report from University of Arizona geoscientists. The study is the first to explain how the steep-fronted plateau formed.
China's Loess Plateau was formed by wind alternately depositing dust or removing dust over the last 2.6 million years, according to a new report from...
The leaves of the lotus flower, and other natural surfaces that repel water and dirt, have been the model for many types of engineered liquid-repelling surfaces. As slippery as these surfaces are, however, tiny water droplets still stick to them. Now, Penn State researchers have developed nano/micro-textured, highly slippery surfaces able to outperform these naturally inspired coatings, particularly when the water is a vapor or tiny droplets.
Enhancing the mobility of liquid droplets on rough surfaces could improve condensation heat transfer for power-plant heat exchangers, create more efficient...
Longer, more severe, and hotter droughts and a myriad of other threats, including diseases and more extensive and severe wildfires, are threatening to transform some of the world's temperate forests, a new study published in Science has found. Without informed management, some forests could convert to shrublands or grasslands within the coming decades.
"While we have been trying to manage for resilience of 20th century conditions, we realize now that we must prepare for transformations and attempt to ease...
A University of Oklahoma astrophysicist and his Chinese collaborator have found two supermassive black holes in Markarian 231, the nearest quasar to Earth, using observations from NASA's Hubble Space Telescope.
The discovery of two supermassive black holes--one larger one and a second, smaller one--are evidence of a binary black hole and suggests that supermassive...
03.09.2015 | Event News
20.08.2015 | Event News
20.08.2015 | Event News
03.09.2015 | Process Engineering
03.09.2015 | Materials Sciences
03.09.2015 | Materials Sciences