Preparation and characterization of MOF-PES ultrafiltration membranes Arcadio Sotto, 1 Gisela Orcajo, 1 Jes  us Mar  ıa Arsuaga, 1 Guillermo Calleja, 1 Junkal Landaburu-Aguirre 2 1 Department of Chemical and Environmental Technology, Rey Juan Carlos University, Madrid, Spain 2 Mass and Heat Transfer Process Laboratory, Department of Process and Environmental Engineering, P.O. Box 4300, FI-90014, University of Oulu, Finland Correspondence to: A. Sotto (E - mail: arcadio.sotto@urjc.es) ABSTRACT: Fouling is one of the main disadvantages of membrane processes. Fouling can be mitigated by incorporating inorganic particles into the membrane. Composite membranes containing the inorganic fillers show higher pore size, porosity, and hydrophilic character than the neat PES membrane, which contributes to a better permeability. In this research, PES ultrafiltration membranes are prepared using both commercial and synthesized metal-organic framework materials (MOF) as well as ZnO particles as fillers. Among the different fillers used, MOF particles produce a better effect on the permeability of the membrane than ZnO particles. The synthesized Zn/Co-MOF-74-type materials have good structural stability in the polymeric matrix and the MOF-PES membrane main- tains its performance after a series of cycles of BSA water solution. Tested MOF-PES membrane also shows higher BSA rejections and permeate flux than the neat PES membrane, demonstrating that it is possible to enhance the flux without losing the selectivity of the membrane. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41633. KEYWORDS: porous materials; properties and characterization; surfaces and interfaces; polycarbonates Received 24 July 2014; accepted 14 October 2014 DOI: 10.1002/app.41633 INTRODUCTION Membrane fouling is one the main disadvantages of the pressure-driven membrane processes applied to wastewater treatment. 1 Membrane fouling can be caused by mineral precip- itation, 2 attachment of colloids and dissolved organics 3,4 and growth of microbes on the membrane surface. 5 As a conse- quence, permeate flux is reduced and salt passage through the membrane increases, decreasing the overall membrane process performance. As a consequence the membrane efficiency is reduced, being the water recovery level below the optimum. In addition, both the energy demand and the overall operational cost of the process increase. 6 These fouling mechanisms can be reversible or irreversible. Reversible fouling is caused by the for- mation of a cake layer (deposition) or concentration polariza- tion (gel formation) of materials at the membrane surface. They can be removed by an appropriate physical washing such as backwashing or surface washing. Irreversible fouling, however, is caused by permanent adsorption and/or pore blockage by spe- cies present in the liquid. In order to improve the fouling tend- ency of membranes, research studies have focused on the introduction of hydrophilic layers, the reduction of surface roughness and the improvement of surface charge. 7 Another important development in antifouling pressure-driven mem- branes is the incorporation of nanoscale inorganic particles into the membrane. The use of nanoparticles in the synthesis of membranes can improve their performance by decreasing the degree of membrane fouling, and therefore increasing the per- meate flux. 8,9 The hydrophobicity of both organic pollutants and the membrane surface (polymeric material) favors the pres- ence of hydrophobic interactions in the surface-pollutant inter- face, which promotes the formation of a fouling layer onto the membrane surface and in the inner pore walls of the membrane structure. 10 The addition of hydrophilic fillers into the mem- brane composition mitigates the formation and progress of fouling phenomena taking into account the hydrophilic charac- ter of nanomaterials proposed as dopants. 11 Among these nano- materials, TiO 2 , SiO 2, ZrO 2, Al 2 O 3 , and Ag were found to improve anti-fouling performance of membranes. The increased hydrophilic character of the membranes containing Al 2 O 3 , reduces the chance of absorbing hydrophobic matter, 12 thus preventing colloidal and organic fouling. Membranes combined with silver benefit from the bactericidal activity of silver nano- particles. Silver composite thin films have a less compact struc- ture and a rougher surface than the pure polyamide films. These membranes were shown to have a great anti-biofouling performance, but the release of silver is likely to influence the long-lasting antibacterial and biofouling resistant performance. 13 The environmental risk associated to the use of nanomaterials and the integrity of membrane functions are additional issues associated to the use of nanoparticles in aqueous environments. 14 V C 2014 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2015, DOI: 10.1002/APP.41633 41633 (1 of 9)