Arab J Sci Eng DOI 10.1007/s13369-015-1897-1 RESEARCH ARTICLE - CHEMISTRY Removal of Oxidation Fragments from Multi-walled Carbon Nanotubes Oxide Using High and Low Concentrations of Sodium Hydroxide Khalid I. Kabel 1 · Ahmed A. Farag 1 · Elsayed M. Elnaggar 2 · Abdalrhman G. Al-Gamal 1 Received: 22 December 2014 / Accepted: 6 October 2015 © King Fahd University of Petroleum & Minerals 2015 Abstract Modification of multi-walled carbon nanotubes surface (MWCNT) using the mixture of HNO 3 /H 2 SO 4 is widely employed for MWCNT surface oxidation, but it also leads to shortening and thinning of the CNT layers causing fragmentation. The carbonaceous fragments had adsorbed on the surface is not removed from the sample in conven- tional treatments; however, the addition of NaOH success- fully cleans the oxidized material. In this article, MWCNT was functionalized using HNO 3 /H 2 SO 4 as oxidizing agent and evaluate the impact of using high and low concentrations of NaOH to purify CNT oxide. The presence of oxidized groups as hydroxyl and carboxyl has been demonstrated by FTIR. The thermal stability of MWCNT and MWCNT-O after and before purification was studied by TGA, and the degree of its crystallinity was examined by XRD. The defect degree occurs during the oxidation process was confirmed by Raman spectroscopy. TEM images showed the presence and the absence of wrinkles and the adsorbed carbonaceous fragments. Keywords Oxidation of MWCNT · Effect of NaOH · Carbonaceous fragment removal · MCNT thermal stability · Degree of crystallinity B Khalid I. Kabel drkhalid1977@yahoo.com 1 Department of Petroleum Applications, Egyptian Petroleum Research Institute (EPRI), Nasr City, P.B. 11727, Cairo, Egypt 2 Department of Applied Chemistry, Faculty of Science, Al-Azher University, Cairo, Egypt 1 Introduction The commonly noticed existence of carbon nanotubes (CNT) in 1991 [1] opened new advancement paths because their unique properties, chemical and thermal stability, electronic properties, high-tensile strength, and ultralight weight [2– 6] which are matchless made researcher ot use it in several scientific disciplines such as mechanical, electrical, thermo- mechanical, optical, and sensor applications [7–9]. Multi- walled carbon nanotubes (MWCNTs) can be considered as a series of single-walled carbon nanotubes, i.e., graphene sheets rolled into seamless cylinders, arranged coaxially with regularly increasing the diameter [10]. Saleh and Gupta reported that MWCNTs could enhance the photocatalytic activity [11]. Functionalization of CNT could improve the dispersion as well as promote interfacial bonding with polymers [12]. Oxygen-containing functional groups (hydroxyl, epoxy, car- bonyl, and carboxyl) increase sp 3 carbon hybridization and can be decorated at tube ends, as well as at along the side walls of CNT through a liquid-phase oxidation process. These functionalities promote CNT chemical reactivity and can either directly used for composite [13–15]. Saleh proved that, the extent of oxygen content into the MWCNT’s surface is sensitive to oxidizing agent and the process temperature, while the acidic site increases with increase in the treatment temperature [16]. The most usual method for CNT oxidation is treatment with acidic solutions or oxidizing agents, such as H 2 SO 4 [17], HNO 3 [18], H 2 SO 4 /HNO 3 [19], H 2 O 2 [20], H 2 O 2 / HNO 3 [21], KMnO 4 [22], KMnO 4 /H 2 SO 4 [23] etc. It is a very versatile, efficient and potential use [21, 24, 25]. The most common reagent used for liquid-phase oxidation treat- ment is HNO 3 /H 2 SO 4 [26]. 123