Water shortage along with contamination is being considered a major global challenge owing to rapid population growth and increased manufacturing industries. It is actually estimated that global water demand will increase by over 50% in the coming decades. Therefore, cheap and effective methods for water purification from source to the point of use without a large footprint on the environment are on high demand. Membrane filtration, advanced oxidation, and UV radiation approaches have been proposed for this purpose. Membrane filtration however appear as a cost effective and energy saving technology.
In view of this, fouling is a considerable challenge to the effective use of membrane separation for purification of water. Fouling occurs when there is a buildup of contaminants on and within the surface of the membrane, leading to a loss in the production of clean water and would demand extensive cleaning and eventual replacement. Proteins and natural organic matter are the commonly known foulants. There occurs a significant decline in membrane lifespan and permeability after adsorption of foulants; therefore, membrane replacement is frequently required. For this reason, mitigation of membrane fouling present a major challenge for those working in this industry. Research to develop excellent polymeric membranes for water filtration processes is indeed necessary.
High water flux as well as antifouling capability of hybrid ultrafiltration membranes without injuring their selectivity can be realized through the implementation of functionalized titanium oxide nanotubes as well as polymers. The extensive surface area of sulfonic acid functionalized titanium oxide nanotubes as well as the presence of negatively charged (-SO3H) in the membrane layer provides an extra path for water permeation while controlling the rejection of the foulant in the course of ultrafiltration.
Researchers led by Professor Jenny Lawler at Dublin City University in Ireland synthesized novel polysulfone and sulfonic acid functionalized TiO2 nanotubes hybrid membranes. The authors also measured the water flux of hybrid membranes at varied concentrations. Their research work is published in Chemical Engineering Journal.
The authors prepared antifouling hybrid ultrafiltration membranes using polysulfone as well as sulfonic acid functionalized titanium oxide nanotubes. They first prepared the nanotubes through a coupling reaction. The researchers then prepared hybrid membranes containing sulfonic acid functionalized titanium oxide nanotubes through a non-solvent induced phase separation approach. The hybrid membrane’s antifouling capability was then investigated with bovine serum and humic acid as foulants.
The research team also observed that the changed behavior, surface hydrophobicity, and water uptake improved when the amount of the sulfonic acid functionalized titanium oxide nanotubes was increased. This was referenced to SO3H groups as well as high water absorption ability of the nanotubes. Porosity was also identified to play a key role in increasing and decreasing water flux of hybrid membranes. Antifouling performance of the proposed hybrid membranes in humic acid removal and ultrafiltration of Bovine serum albumin solution was observed to improve with loading amount of the nanotubes.
The membranes also indicated excellent humic acid removal from aqueous solution at low feed concentration of up to 50ppm. In general, their study provides an easy path for enhancing antifouling capability and hydrophobicity of hybrid ultrafiltration membranes without injuring their selectivity.
Ibrahim Hotan Alsohaimi, Mahendra Kumar, Mohammad Saad Algamdi, Moonis Ali Khan, Kieran Nolan, Jenny Lawler. Antifouling hybrid ultrafiltration membranes with high selectivity fabricated from polysulfone and sulfonic acid functionalized TiO2 nanotubes. Chemical Engineering Journal, volume 316 (2017), pages 573–583.
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