Oxidized-sulfonated multi-walled carbon nanotube/hydroxyapatite hybrid particles: Synthesis and characterization Kaio A.B. Pereira a , Sibele P. Cestari a , Roberto P. Cucinelli Neto a , Katharina R.M. Macedo a , Luis C. Mendes a, * a Universidade Federal Do Rio de Janeiro, Instituto de Macromomol eculas Professora Eloisa Mano, Centro de Tecnologia, Bloco J, Cidade Universit aria, 21941-598, Rio de Janeiro, Brazil ARTICLE INFO Keywords: Carbon nanotube Sulfonation Oxidation Hydroxyapatite Hybrid particle ABSTRACT To ensure polarity and to improve dispersibility for future application in polymer nanocomposite CNT was modified by sulfonitric mixture with molar ratio H 2 SO 4 :HNO 3 5.50:1.43, at 110  C, under stirring, for 3 h. The product labeled as oCNT was reacted with hydroxyapatite (HAp) at 2:1 oCNT:HAp mass ratio. Infrared spectra of oCNT and oCNT-HAp were different of the parent reagents. Crystallographic structure of CNT and oCNT was partially altered owing to the acid attack and reaction with HAp, respectively. Thermogravimetry indicated that HAp thermal behavior of was changed in the oCNT-HAp. By oCNT-HAp time decay curves were deduced that an effective chemical bond between oCNT and HAp occurred. The SEM/EDX analyses disclosed that oCNT disag- gregation and the surface chemical reaction between oCNT and HAp. EDX revealed oxygen and sulfur in the oCNT and oCNT-HAp indicating that in some extent both oxidation and sulfonation of aromatic ring occurred. The hybrid particle is constituted by 70 and 30% of oCNT and HAp, respectively. 1. Introduction The development of nanometric materials has attracted industrial and scientific attention owing to their wide and feasible applications [1,2]. Since their discovery in 1991, carbon nanotubes (CNTs) have been investigated due to their highlighted mechanical, physico-chemical and biological properties, amongst others. This set of characteristics makes them a promising material for use in several areas [3,4]. Baddour and Briens summarized the advantages and disadvantages of three pathways to produce CNTs [5]. The arc discharge and chemical vapor deposition methods produce multi-walled carbon nanotubes (CNT). According to Rafique and Iqbal, among the manufacturing methods, the chemical vapor disposition (CVD) is understood as the most promising owing to technical and economic aspects [6]. With multiple and marked proper- ties, the carbon nanotubes present superior performance in nano- composites when compared to traditional materials such as carbon black and ultra fine metal powders [7]. Sharma et al. reported the CNTs syn- thesis by arc-discharge and chemical vapor deposition method and their characterizations [8]. The functionalization through acid treatment assisted the dispersion in water. About the CNTs carbon graphitization degree, the Raman spectroscopy has been used by ratio estimation between the D (1342 cm 1 ) and G (1572 cm 1 ) while G 0 band at 2738 cm 1 revealed the purity degree [9]. The chemical inertia, biocompatibility and antimicrobial characteristics candidate them to medical applications such as bone tissue cell [10–12]. The hydroxyapatite (HAp) is a bioceramic material which either at micrometric or nanometer scale presents high surface area and low density [13]. There are reports concerning limitation to mechanical properties [14–16], which resembles the chemical and crystallographic properties of apatite in the human skeletal system; due to the increase of incidence of bone lesions, the search as bone tissue has been growing [17]. Owing to the biocompatibility and bioactivity, there have been efforts to use HAp as bone substitute or for general applications in biomedicine - such as bone filling, orthopedic or dental implants, tissue repair, drug delivery system, protein segregation and chromatographic column for biomolecules fractionation [1,18–20]. Mostly applied in or- thopedic treatments, the HAp improves the affinity of the implants with the rigid tissue and accelerates the formation of bone apatite [14,21]. Recently, improvements in fracture and wear resistance as well as in- crease of osteoblastic cells proliferation were reported [13,22,23]. In order to overcome some HAp shortcoming such as brittleness and low wear resistance its modification with CNTs has been studied [24–27]. * Corresponding author. E-mail address: lcmendes@ima.ufrj.br (L.C. Mendes). Contents lists available at ScienceDirect Journal of Solid State Chemistry journal homepage: www.elsevier.com/locate/jssc https://doi.org/10.1016/j.jssc.2019.120924 Received 3 June 2019; Received in revised form 9 July 2019; Accepted 22 August 2019 Available online 27 August 2019 0022-4596/© 2019 Elsevier Inc. All rights reserved. Journal of Solid State Chemistry 279 (2019) 120924