Modification of polyacrylonitrile (PAN) by hydroxylamine resulted in polyacrylamidoxime (PANOx), the oxime groups of which are nucleophilic and capable of hydrolyzing esters. PANOx fiber mats with submicrometer fiber diameters ranging from tens to 300 nm were produced by electrospinning a suspension of PANOx blended with PAN (1:1 by weight) in a mixture of N,N-dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO) (85:15 by weight). Catalytic properties of the PANOx nanofibers were tested by the hydrolysis of p-nitrophenyl acetate (PNPA), which mimics toxic organophosphate nerve agents and insecticides. The presence of PANOx fibers significantly accelerated the hydrolysis of PNPA compared to its spontaneous hydrolysis. The rate constants for the hydrolysis (k(1)) and the deacetylation (k(2)) reactions for the fibers were obtained using a proposed kinetic model. The effect of the fiber size on reaction rate indicated that intra-fiber diffusional resistances might limit the accessibility of the oxime catalytic sites in the fibers and affect their catalytic activity. (c) 2007 Elsevier Ltd. All rights reserved.