?RYU K M, ZHANG D H, ZHOU C W. High performance metal oxide nanowire chemical sensors with integrated micro machined hotplates [J]. Appl Phys Lett, 2008, 92:093111(1–3). [2]? HUANG S Z, LIN W, CHEN W Z, et al. Gas sensitivity of indium oxide [J]. Nonferrous Met Soc China , 2009, 19(B09): 80–82. [3]? DOINA L, MICHAEL S, ANITA L S. Catalytic properties of oxide nanoparticles applied in gas sensors [J]. Top Catal, 2007, 45(1–4): 105–109. [4]? MAKHIJA K K, RAY A, PATEL R M. Indium oxide thin film based ammonia gas and ethanol vapour sensor [J]. Bull Mater Sci, 2005, 28(1): 9–17. [5]? ZHAN Z L, XU J Q, JIANG D G. State of In2O3 based gas sensors [J]. J Transducer Technol, 2003, 22(3): 1–3. [6] ?XU PC, CHENG Z X, PAN Q Y, et al. High aspect ratio In2O3 nanowires: Synthesis, mechanism and NO2 gas sensing properties [J]. Sens Actuators B: Chem, 2008, 130(2): 802–808. [7] ?LIU A Y, WANG J, LI Z. Preparation of In2O3 nanwires by sol–gel template technology and their gas sensing property [J]. Nanosci Nanotechnol, 2010, 7(5): 61–64. [8] ?VARGHESE O K, KICHAMBRE P D, GONG D, et a1. Gas sensing characteristics of multi-wall carbon nanotubes [J]. Sens Actuators B: Chem, 2001, 81(1): 32–41. [9] ?WANG W D, PHILIPPE S, PHILIPPE K, et a1. Visible light photodeg- radation of phenol on MWNT–TiO2 composite catalysts prepared by a modified sol–gel method [J]. J Mol Catal A: Chem, 2005, 235(1–2): l94–l99. [10] ?ZHANG B, FU R W, ZHANG M Q, et a1. Preparation and characterization of gas sensitive composites from multi-walled carbon nanotubes/polystyrene [J]. Sens Actuators B: Chem, 2005, 109(2): 323– 328. [11] ?LI L, PAN Q Y, CHENG Z X, et a1. NH3 sensing properties of CNT–WO3 sensors [J]. J Inorg Mater, 2006, 21(1): 151–156. [12] ?KANG S Z, CUI Z Y, MU J. Electrical property of tin oxide doped with multi-walled carbon nanotubes [J]. J Dispersion Sci Technol, 2007, 28(4): 569–571. [13] ?SUN X, FANG H T, YU H L, et a1. Room-temperature hydrogen sensing properties of SnO2 coated multi-walled carbon nanotubes [J]. New Carbon Mater, 2010, 25(3): 218–224.