Mixed matrix membranes (MMMs) comprising polysulfone (PSF) Udel (R) P-1700 and 30 wt% carbon molecular sieve (CMS) particles (<25 mu m) have been fabricated and characterized. CMS particles were treated in poly(vinyl pyrrolidone) kollidone 15 (PVP K-15) sizing bath solution (1-10 wt% in isopropanol) prior to embedment into the matrix solution to improve matrix-sieve interfacial adhesion. This study investigated the effects of CMS sizing with PVP K-15 on the morphology and the gas separation performance of PSF-CMS MMMs. The fabricated MMMs were characterized using TGA, DSC, FESEM, ATR-FTIR and single gas permeation test using high purity O-2 and N-2. A dramatic improvement in CMS-PSF adhesion was observed using FESEM micrographs upon incorporation of PVP K-15-sized CMS particles. ATR-FTIR results suggest the occurrence of intermolecular interaction between PVP K-15 sizing layer on the outer surface of CMS particles and PSF matrix. A substantial recovery of separation performance was achieved whereby the PSF-PVP-sized CMS MMM exhibited 1.7 times higher O-2/N-2 selectivity compared to that of unmodified MMM. (c) 2007 Elsevier B.V. All rights reserved.