Sorting semiconducting single walled carbon nanotubes by poly(9,9-dioctylfluorene) derivatives and application for ammonia gas sensing

© 2015 Elsevier Ltd. All rights reserved. In this work, we investigated the ability of several poly(9,9-dioctylfluorene) (PFO) derivatives to selectively separate semiconducting single-walled carbon nanotube (sc-SWCNT) from commercial arc discharge SWCNTs. The results illustrated that the separation efficiency of PFO derivatives and the stability of sc-SWCNT inks increased with the sizes of conjugated systems in subunits. The relative height of sc-SWCNTs peaks and the shelf life of sc-SWCNT inks can be up to 0.71 and 5 months when being sorted by poly{(9,9-dioctylfluorene)-2,7-diyl-alt-[3,6-dithiene-2-yl-2,5-di(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4-dione-5,5″-diyl} (PF8-DPP). Electrical properties of thin film transistors (TFTs) and sensors based on PF8-DPP-sorted sc-SWCNTs were also investigated. Printed TFTs showed excellent performance with on/off ratios of 106, effective mobility of 22.6 cm2 V-1s-1, subthreshold swing of 178 mV/dec and small hysteresis at low operating voltage. PF8-DPP-sorted sc-SWCNTs were used as sensing material for selectively detecting ammonia gas at room temperature. Upon exposure to 0.6% NH3 at room temperature, the ammonia sensors based on sorted sc-SWCNTs exhibited high sensitivity (ΔR/Ro ∼ 54.4%), fast response (30 s) and good stability. The desorption rate of NH3 from carbon nanotube surface can be controlled by tuning the voltage of heating resistor integrated into the platforms, and excellent reversibility can be achieved within 1 min at applied voltage of 1.5 V.