Air filtration efficiency and pressure drop of nanofibrous filter media based on polyacrylonitrile (PAN) nanofibers with and without TiO2 nanoparticles were evaluated. The nanofibrous filter media were fabricated by covering a cellulose substrate with varying masses of PAN fiber or PAN/TiO2 hybrid nanofiber. Capillary flow porometry tests revealed that the hybrid nanofibrous filter media showed larger pore size and broader pore size distribution than their counterpart pure PAN nanofibrous filter media. The pressure drop of the filter media covered with the PAN/TiO2 hybrid nanofibers (0.5 g/ft(2)) was 4 times less than that of the counterpart filter media at an air velocity of 80 cm/s. Despite less fiber coverage density on the cellulose substrate and a greatly reduced pressure drop, the filtration efficiency of the nanofibrous filter media made with PAN/TiO2 hybrid fibers was found to be much greater than that of those made with just pure PAN fibers, especially for smaller particles in the range 0.1-0.5 mu m. These results might be influenced by the added electric charge caused by the insertion of TiO2 nanoparticles in the fibers. Therefore, the improvement of two important features, enhanced filtration efficiency and reduced pressure drop can be simultaneously achieved through the use of polymer/TiO2 hybrid nanofibrous filter media. This holds promise for facile development of energy-saving, high performance filters. (C) 2013 Elsevier Ltd. All rights reserved.