Hydrophilization of porous polypropylene membranes by atomic layer deposition of TiO2 for simultaneously improved permeability and selectivity

The uses of porous polypropylene (PP) membranes are limited in water-based separations because of their strong hydrophobicity. To improve the separation performances of polypropylene membranes by hydrophilization, we deposited TiO2 on their pore surface using the atomic layer deposition strategy with and without a pretreatment to the membrane by plasma. The direct deposition without plasma pretreatment led to slightly enhanced hydrophilicity because TiO2 was slowly deposited on the membrane as discrete particles due to the lack of active groups on the bare polypropylene surface. In contrast, after a short exposure to plasma generated in air, oxygen-containing active groups were formed on the membrane and subsequent atomic layer deposition yielded conformal thin layer of TiO2 on the pore walls. The deposited membranes showed remarkably enhanced hydrophilicity and higher deposition cycles led to stronger hydrophilicity. As a consequence of the enhanced hydrophilicity, the permeability and retention of the deposited membrane were simultaneously improved with big amplitudes. For example, an increase in pure water flux of ~60% and a more than doubled retention ratio were obtained by deposition of TiO2 for 150 cycles on the plasma-activated polypropylene membrane. Furthermore, the TiO2-deposited membranes showed improved resistance to protein fouling compared to unmodified membranes also because of the enhanced hydrophilicity. Such a hydrophilization strategy of plasma pretreatment and subsequent atomic layer deposition of metal oxides is expected to be also effective in the upgrading of performances of other membranes with inert surfaces.

[1]  K. Choo,et al.  Hydrophilic modification of polypropylene microfiltration membranes by ozone-induced graft polymerization , 2000 .

[2]  Robin H. A. Ras,et al.  Inorganic hollow nanotube aerogels by atomic layer deposition onto native nanocellulose templates. , 2011, ACS nano.

[3]  Steven M. George,et al.  Improved Functionality of Lithium‐Ion Batteries Enabled by Atomic Layer Deposition on the Porous Microstructure of Polymer Separators and Coating Electrodes , 2012 .

[4]  M. Ritala,et al.  Surface modification of thermoplastics by atomic layer deposition of Al2O3 and TiO2 thin films , 2008 .

[5]  Zhi‐Kang Xu,et al.  Surface modification of polypropylene microfiltration membranes by graft polymerization of N-vinyl-2-pyrrolidone , 2004 .

[6]  Zhi-Kang Xu,et al.  Flux enhancement for polypropylene microporous membrane in a SMBR by the immobilization of poly(N-vinyl-2-pyrrolidone) on the membrane surface , 2006 .

[7]  Yong Wang,et al.  Precise pore size tuning and surface modifications of polymeric membranes using the atomic layer dep , 2011 .

[8]  Li-ping Zhu,et al.  Preparation and properties of poly(ethylene oxide) gel filled polypropylene separators and their corresponding gel polymer electrolytes for Li-ion batteries , 2011 .

[9]  C. Schroën,et al.  Membrane modification to avoid wettability changes due to protein adsorption in an emulsion/membrane bioreactor. , 1993 .

[10]  Zhi-Kang Xu,et al.  Microporous polypropylene hollow fiber membrane: Part I. Surface modification by the graft polymerization of acrylic acid , 2002 .

[11]  W. Jin,et al.  Atomic layer deposition of alumina on porous polytetrafluoroethylene membranes for enhanced hydrophilicity and separation performances , 2012 .

[12]  Zhi‐Kang Xu,et al.  Covalent attachment of phospholipid analogous polymers to modify a polymeric membrane surface: a novel approach. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[13]  J. Jur,et al.  Temperature-dependent subsurface growth during atomic layer deposition on polypropylene and cellulose fibers. , 2010, Langmuir : the ACS journal of surfaces and colloids.

[14]  Yong Wang,et al.  PVDF membranes with simultaneously enhanced permeability and selectivity by breaking the tradeoff effect via atomic layer deposition of TiO2 , 2013 .

[15]  Changsheng Zhao,et al.  Polymeric pH-sensitive membranes—A review , 2011 .

[16]  A. Angelova,et al.  Scanning Force Microscopy and Wetting Study of the Surface Modification of a Polypropylene Membrane by Means of Langmuir-Blodgett Film Deposition , 1995 .

[17]  J. Jur,et al.  Surface and sub-surface reactions during low temperature aluminium oxide atomic layer deposition on fiber-forming polymers , 2010 .

[18]  Zhi-Kang Xu,et al.  Surface modification of polypropylene microporous membrane to improve its antifouling property in MBR: CO2 plasma treatment , 2005 .

[19]  G. Parsons,et al.  Quantitative in situ infrared analysis of reactions between trimethylaluminum and polymers during Al2O3 atomic layer deposition , 2012 .

[20]  Jiaqiu Wang,et al.  pH Sensitive polypropylene porous membrane prepared by grafting acrylic acid in supercritical carbon dioxide , 2004 .

[21]  C. Wan,et al.  Conductivity Study of Porous Plasticized Polymer Electrolytes Based on Poly(vinylidene fluoride) A Comparison with Polypropylene Separators , 2000 .

[22]  Shih-Hsiung Chen,et al.  Preparation and characterization of plasma-modified PTFE membrane and its application in direct contact membrane distillation , 2011 .

[23]  Myung-Hyun Ryou,et al.  Mussel‐Inspired Polydopamine‐Treated Polyethylene Separators for High‐Power Li‐Ion Batteries , 2011, Advanced materials.

[24]  Zhi‐Kang Xu,et al.  Surface modification of polypropylene microfiltration membranes by the immobilization of poly(N-vinyl-2-pyrrolidone): a facile plasma approach , 2005 .

[25]  Zhi‐Kang Xu,et al.  Surface Modification of Microporous Polypropylene Membranes by Plasma-Induced Graft Polymerization of α-Allyl Glucoside , 2003 .

[26]  Mato Knez,et al.  Greatly Increased Toughness of Infiltrated Spider Silk , 2009, Science.

[27]  Jaegab Lee,et al.  Formation of TiO2 and ZrO2 Nanotubes Using Atomic Layer Deposition with Ultraprecise Control of the Wall Thickness , 2004 .

[28]  Fengbao Zhang,et al.  Bilirubin removal by Cibacron Blue F3GA attached nylon-based hydrophilic affinity membrane , 2003 .

[29]  G. Parsons,et al.  Making inert polypropylene fibers chemically responsive by combining atomic layer deposition and vapor phase chemical grafting , 2011, Nanotechnology.

[30]  M. Ritala,et al.  Radical Enhanced Atomic Layer Deposition of Titanium Dioxide , 2007 .

[31]  Jia-shan Gu,et al.  Surface modification of polypropylene macroporous membrane by marrying RAFT polymerization with click chemistry , 2012 .

[32]  Yong Wang,et al.  Plasma activation of porous polytetrafluoroethylene membranes for superior hydrophilicity and separation performances via atomic layer deposition of TiO2 , 2013 .

[33]  Zhi-Kang Xu,et al.  Surface engineering of macroporous polypropylene membranes , 2009 .

[34]  S. George.  Atomic layer deposition: an overview. , 2010, Chemical reviews.

[35]  Yong Wang,et al.  Highly ordered TiO2 nanostructures by sequential vapour infiltration of block copolymer micellar films in an atomic layer deposition reactor , 2013 .

[36]  S. George,et al.  Nucleation and Growth during Al2O3 Atomic Layer Deposition on Polymers , 2005 .

[37]  W. Jin,et al.  Highly porous metal oxide networks of interconnected nanotubes by atomic layer deposition. , 2012, Nano letters.