|M.Sc Student||Lahav Yotam|
|Subject||Stimuli-Induced Surface-Peeling for Fouling Control in|
Membrane-Based Water Production
|Department||Department of Civil and Environmental Engineering||Supervisors||Assistant Professor Guy Ramon|
|Dr. Oz Gazit|
|Full Thesis text|
Rising demand for drinking water has turned membrane-based desalination into an important technology for producing water from impaired sources. Perhaps the greatest challenge in membrane-based desalination is the additional energy consumption due to the effects of fouling and biofouling.
The common paradigm for biofouling control is prevention, e.g., using microbicidal materials (e.g. silver ions coating) or surface modifications (e.g. PEG chains that inhibit bacteria deposition on the surface). The main limitation of the prevention approach is the capability of bacteria to evolve and resist microbicidal elements.
The approach proposed herein is to accept the biofilm formation, but create a "self-cleaning" membrane. The surface to be protected is coated with a disposable particle array that can be removed using an external stimulus and then re-coated by a fresh array. Specifically, the surface will be decorated with covalently attached boronic acid (BA) end groups, here referred to as the linker, able to reversibly bind to diol-functionalized particles. As a model surface for the proof-of-concept, polydimethylsiloxane (PDMS) was chosen, as it is easy to produce and functionalize. In addition, using a simple protocol, a suitable microfluidic device was successfully produced. Silica nanoparticles were used as a high surface area control material.
The PDMS was examined with a confocal microscope using a solution with fluorescent-labeled polystyrene particles, and was shown to provide a good flow environment in a well-sealed device. The particles and the linkers were synthesized with partial success. The first stage of binding the mediator chain 3-glycidyloxypropyltrimethoxysilane (GLYMO) between the surface (silica particles) and the BA was successful. Graphic results from fourier transform infra-red spectroscopy (FTIR) and calculations for results of thermogravimetric analysis mass spectroscopy (TGA-MS) show that there was a good efficiency of binding between the GLYMO and the particles. In addition to the binding of GLYMO to silica particles, contact angle measurements of a modified PDMS showed the successful binding of GLYMO to the surface. The second stage of binding the BA to the GLYMO (for the linkers) was insignificant - no dramatic change of mass was observed between this stage and the previous one. In spite of that, the MS shown that there are traces of BA on the particles, indicating that the procedure is generally working.
An experiment of binding diol and BA was examined with a fluorescent diol molecule called alizarin red S (ARS) and silica particles with BA. It appeared that the ARS was physically adsorbed to the surface and it couldn't be explicitly determined that the bond between the diol and the BA really formed; however, a significant learning process about the diol and BA system was made.
There's still a need to improve the yield of diols on the particles and of the BA on the linkers, after which the binding experiments of the two groups would be more significant and reliable.