Mechanism for acetone sensing property of Pd-loaded SnO 2 nanofibers prepared by electrospinning: Fermi-level effects Wei Tang • Jing Wang • Qiao Qiao • Zhenghua Liu • Xiaogan Li Received: 23 September 2014 / Accepted: 3 January 2015 / Published online: 21 January 2015 Ó Springer Science+Business Media New York 2015 Abstract Undoped and Pd-loaded SnO 2 nanofibers with various Pd loading concentrations from 1.0 to 2.0 mol% had been synthesized by electrospinning with appropriate annealing process subsequently. The morphologies and nanocrystalline structures of the nanofibers were charac- terized by thermogravimetric analysis–differential scan- ning calorimetry, X-ray diffraction, Fourier transform infrared, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, and N 2 physical adsorption. The sensing properties of undoped and Pd-loaded SnO 2 nanofibers were compared. The gas sensing results showed that 1.5 mol% Pd-loaded SnO 2 nanofibers got a best response to acetone at lower operating temperature of 275 °C among all the Pd-loaded SnO 2 nanofibers. The enhanced acetone response of Pd- loaded SnO 2 nanofibers may be correlated with the ‘‘Fermi- level effects’’ of Pd catalysts. Introduction It is well known that one-dimensional (1D) nanomaterials [1] such as nanotubes [2], nanowires [3], nanobelts [4], and nanorods [5] have attracted intense interest due to the high surface to volume ratio and quantum confinement effects [6]. Among the considerable efforts to fabricate the 1D nanomaterials, electrospinning as an economical and effective technique has attracted wide attention to synthe- size nanofibers by electrostatic stretching [7–10]. As an important sensitive semiconductor oxide with wide band gap, n-type SnO 2 has increasing application in detection of explosive and toxic gases [11–16]. Apart from the distinct advantages including rich source of raw materials, low cost, and diverse sensitive gas species, there are some flaws for SnO 2 -based gas sensors such as poor selectivity and reproducibility. Many methods have been developed to improve the gas sensing properties, including surface modification [17], doping [18], heat treatment [19], and composite approach [20–23]. Among them, additive noble metal catalysts can significantly enhance the sensing properties based on the ‘‘spillover’’ effect of oxygen atoms or reducing gases from the surface. It has been reported that surface modification with noble additives such as Pd [24, 25], Pt [17, 26–28], Ru [29, 30], and Au [31–34] can effectively improve sensitivity and selectivity against reducing gases. The main mechanisms for SnO 2 after sur- face modification are that the detection of a reducing gas depends on charge-transfer, spillover effects, Fermi energy shifts as well as the catalytic oxidation during which the concentration of free electrons of the semiconducting SnO 2 changes [35]. In this paper, Pd-loaded SnO 2 nanofibers were synthe- sized by electrospinning with appropriate calcination treatment. Undoped SnO 2 and Pd-loaded SnO 2 nanofibers with different Pd loading concentrations were fabricated and their gas sensitivities were investigated to examine the effects of Pd loading on the morphologies, structures, and sensing properties of SnO 2 . The results showed that 1.5 mol% Pd-loaded SnO 2 nanofibers got a highest response to acetone at 275 °C. A mechanism had also been proposed in detail to analyze the enhanced response of Pd- loaded SnO 2 . W. Tang  J. Wang (&)  Q. Qiao  Z. Liu  X. Li School of Electronic Science and Technology, Dalian University of Technology, Dalian 116023, China e-mail: wangjing@dlut.edu.cn 123 J Mater Sci (2015) 50:2605–2615 DOI 10.1007/s10853-015-8836-0