Polymeric mesocomposite membranes were prepared via wet phase inversion processes by incorporating surfactara-templatecl mesoporous silica particles, denoted MSP-1, into polysulfone matrices formed with and without PEG as a molecular porogen. Transmission electron microscopy and N-2 adsorption-desorption measurements showed higher surface area (354 m(2)/g), smaller average pore size (53 nm), and larger pore volume (2.92 cm(3)/g) with a narrower pore size distribution (26 nm width at half-maximum) for surfactant-templated mesoporous silica particles compared to those of precipitated commercially available mesoporous silica, HiSil. The distinct morphological changes induced by PEG and by MSP-1 were redundant from the membrane performance point of view as they translated into similar performance gains that were not additive, pointing to the potential use of mesoporous additive as an alternative porogen. The higher hydrophilicity and unique structural features of MSP-1 resulted in enhanced performance of the prepared membranes compared to MSP-free controls and HiSil-based mesocomposites. Mechanical properties of mesocomposites and neat polysulfone membranes were comparable. Electron microscopy coupled with flux and rejection measurements were used to investigate the influence of polymer content, MSP loading, and the presence of porogen on the structure and separation properties of mesocomposite membranes. Mesocomposite membranes showed increased water flux and dextran rejection. For ultrafiltration membranes the figure of merit, operationally-defined as the product of water flux and rejection of 12 kDa dextran, increased by the factor of 2.8 (for membranes cast with a porogen) and 6.3 (in the absence of porogen) upon incorporation of the mesoporous additive at the loading of 10 wt%. Enhancement factors were 3.7 and 11.2 for less permeable membranes cast from mixtures with higher (20 wt%) polymer content. Fouling tests with humic acid solutions demonstrated that mesocomposite membranes experienced lower flux decline and showed higher rejections. (C) 2013 Elsevier B.V. All rights reserved,