Delivered by Ingenta to: Sedong Kim IP: 203.255.53.204 On: Thu, 02 Nov 2017 06:54:28 Copyright: American Scientific Publishers Copyright © 2018 American Scientific Publishers All rights reserved Printed in the United States of America Article Journal of Nanoscience and Nanotechnology Vol. 18, 645–650, 2018 www.aspbs.com/jnn Surface Modification of Graphene Nanoparticles by Acid Treatment and Grinding Process A. K. M. Mahmudul Haque 1 , Sedong Kim 1 , Junhyo Kim 2 , Jungpil Noh 1 , Sunchul Huh 1 , Byeongkeun Choi 1 , Hanshik Chung 1 , and Hyomin Jeong 1 ∗ 1 Department of Energy and Mechanical Engineering, Gyeongsang National University, Institute of Marine Industry, Cheondaegukchi-Gil 38, Tongyeong, Gyeongnam 650-160, South Korea 2 Department of Marine Engineering, Mokpo National Maritime University, Haeyangdaehang-Ro 91, Mokpo-si, Jeollanam-do, 58628, Republic of Korea Surface modification is necessary to decrease graphene’s (GN) stacking process and increase its advantageous properties. In this study, the effects of acid treatment and grinding processes on the structural integrity of GN have been studied. Morphological and structural characteristics of mod- ified GN were investigated by field emission scanning electron microscopy, transmission electron microscopy, gas Pycnometer, particle size analyzer, X-ray diffractometer, UV-Vis spectroscopy and thermal conductivity measurement system which expose some strong evidences of the effects of purification and grinding process on GN nanoparticles in order to get GN based better nanofluid dispersed in water which gives 1.66% and 3.38% enhancement of thermal conductivity at 20  C and at 40  C respectively compared to that of DW in this experiment. Keywords: Acid Treatment, Absorbance, Grinding, Graphene, Thermal Conductivity. 1. INTRODUCTION To date, the researchers of nano-science field have demon- strated the advantages of nanofluids compared to those flu- ids containing millimeter or micrometer size particles. 1–11 And, graphene (GN) nanoparticles, a single atom-thick sheet of hexagonally arrayed sp 2 -bonded carbon atoms, 12 have attracted much attention due to their extraordi- nary features such as high electron mobility, 13 excel- lent mechanical, chemical and thermal properties 14 and twice particular surface area compared with SWCNTs. 15 Besides, the single-layer graphene flake is a 0 eV bandgap semiconductor with a width up to ∼50 m and thick- ness of 0.34 nm 16 as well as having extremely high ther- mal conductivity of about 5000 W/m · K. 17 18 Because of these properties, GN is used in a wide range of appli- cations including transparent conductive films, organic photovoltaic (PV) cells, field-effect transistor devices, ultra sensitive sensors, polymer composite materials, elec- tromechanical systems, hydrogen storage, energy conver- sion and storage, batteries, solar cells and drug delivery ∗ Author to whom correspondence should be addressed. systems. 19–22 However, the dispersing of GN in base fluid water is difficult due to its  – interactions 23 where GN tends to agglomerate and restack through  – and van der Waals interactions resulting indigent dispersion and infe- rior properties. In this study, acid treatment and a grinding process by a planetary ball mill are applied to enhance the dis- persibility of GN nanoparticles in base fluid distilled water. Acid treatment is done in order to purify and oxidize the GN nanoparticles, and grinding process is applied to decrease the particle size and increase the specific sur- face area of GN nanoparticles. The objective of this study was two-fold: (I) to observe the effect of acid treatment on the surface of GN nanoparticles; (II) to observe the effect of wet grinding on the acid treated purified GN nanoparticles in order to get better dispersed nanofluid with relatively higher thermal conductivity compared to that of raw GN nanoparticles. In this regard, Raman spectral analysis (Section 3.1), morphological analysis by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) (Section 3.2), particle size and density measurement (Section 3.4), X-ray diffraction (XRD) analysis (Section 3.3), absorbance by J. Nanosci. Nanotechnol. 2018, Vol. 18, No. 1 1533-4880/2018/18/645/006 doi:10.1166/jnn.2018.13928 645