Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/synmet Investigation of optical and dispersion parameters of electrospinning grown activated carbon nanofiber (ACNF) layer K. Dincer a , B. Waisi b,c , G. Önal a , N. Tuğluoğlu d, ⁎ , J. McCutcheon b , Ö.F. Yüksel e a Department of Mechanical Engineering, Faculty of Engineering, Selcuk University, Konya 42075, Turkey b Chemical & Biomolecular Engineering Department, Faculty of Engineering, University of Connecticut, Storrs, CT 06269, USA c Department of Chemical Engineering, Faculty of Engineering, Baghdad University, Baghdad, Iraq d Department of Energy Systems Engineering, Faculty of Engineering, Giresun University, Giresun 28200, Turkey e Department of Physics, Faculty of Science, Selçuk University, Konya 42075, Turkey ARTICLE INFO Keywords: Activated carbon nanofiber Electrospinning UV–vis-NIR spectrum Optical band gap Optical constants Dispersion parameters ABSTRACT Activated carbon nanofiber (ACNF) layers are prepared by electrospinning method. We have investigated the optical properties of ACNF layer using UV–vis-NIR spectrophotometer. The optical constants such as refractive index, extinction coefficient and dielectric constants were evaluated using reflectance and transmittance spectra for ACNF layer. The optical energy gap of ACNF layer was determined as 1.07 eV. The refractive index dispersion of ACNF layer was analyzed by using the single oscillator model proposed by Wemple and DiDomenico. The dispersion parameters such as oscillator energy and dispersion energy values of ACNF layer were determined. Several dispersion parameters such as optical dielectric constant at higher frequency, lattice dielectric constant, oscillator average wavelength, oscillator average strength and the ratio of carrier concentration to the effective mass were also determined by analysis of refractive index dispersion. Furthermore, the optical conductivity of ACNF layer was evaluated from the analysis of optical dielectric constants. 1. Introduction Among the carbon nanostructures (e.g., graphenes, carbon nano- tubes (CNTs), carbon nanofibers (CNFs), activated carbon nanofibers (ACNFs), and C60), graphenes present new opportunities in photo- catalysis and photovoltaic (PV) conversion by the hybrid structures with a variety of nanomaterials, due to their beneficial electrical con- ductivity, a major specific surface area, and ideal charge carrier mo- bility [1,2]. Ultra fast photoresponses and new optical functionalities have been achieved with semiconductor nanowires/nanorods grown on the few layer graphene (FLG) and single layer (SLG) substrates for multifunctional optoelectronic device applications [3,4]. CNTs are known as excellent light absorbers [5]. Also, CNTs have excellent ad- vantages in chemical stability, thermal and electric conductivity. The use of CNTs has been recommended for diverse applications such as components of PV devices, energy storage devices, chemical sensors, actuators, and metrology-probe tips [6,7]. Carbon nanofibers (CNFs) have received much attention due to their various potential applica- tions such as rechargeable battery [8], hydrogen storage [9], electrode materials in electrochemical capacitor cells [10], gate materials in na- noelectronics [11], etc. B. Réti et al. reported that the CNFs also play a role in extending the absorption edge and enhancing photoelectric activities. This unique nanostructures hold great promise for potential applications in solar cells because of their excellent optical and elec- tronic transport properties [12]. Recently, activated carbon nanofibers (ACNFs) have attracted con- siderable attention because of their various applications, such as energy storage devices, capacitors [13] or lithium ion second batteries [14]. Nowadays, these carbons are produced from precursors, such as poly(L- lactic acid) (PLLA) [15], polyacrylonitrile (PAN)-based fibers [16], rayon-based fibers [17], etc. Amongest the different fabrication methods of carbon nanofibers [18–20], electrospinning method is still the dominant technique for the production of large amounts of nano- fibers [20]. Electrospinning method is a simple technique for producing nanofibers from organic polymers and inorganic oxide materials. ACNF has been fabricated by the electrospinning approach followed by sub- sequented heat treatment steps. Because the diameter of the prepared electrospun nanofibers ranges from sub-microns to nanometers scales, this type of material should display various effective benefits such as remarkable mechanical properties, excellent porosity and high specific surface area [21–23]. In earlier work of our other group, they have reported the perfor- mances of nanofiber and nanofiber/nanoparticles on proton exchange membrane (PEM) fuel cell [24] and the use of ACNF in microbial fuel https://doi.org/10.1016/j.synthmet.2018.01.008 Received 31 July 2017; Received in revised form 10 December 2017; Accepted 23 January 2018 ⁎ Corresponding author. E-mail address: tugluo@gmail.com (N. Tuğluoğlu). Synthetic Metals 237 (2018) 16–22 0379-6779/ © 2018 Elsevier B.V. All rights reserved. T