Adsorption kinetics and thermodynamics of hydrophobic natural organic matter (NOM) removal from aqueous solution by multi-wall carbon nanotubes A. Naghizadeh, S. Nasseri, A. M. Rashidi, R. Rezaei Kalantary, R. Nabizadeh and A. H. Mahvi ABSTRACT The objective of this research was to study the efficiency of Multi-Walled Carbon Nanotubes (MWCNTs) for the adsorption of hydrophobic natural organic matter (NOM) from aqueous solution under different operational conditions of contact time, pH, initial concentration of NOM and temperature. MWCNTs were synthesized via chemical vapor deposition (CVD) with average diameter of 10–50 nm. The results illustrated that both as-prepared and functionalized MWCNTs showed high adsorption capacity for the NOM studied. Functionalization of MWCNT affected the surface area and introduced oxygen-containing functional groups to the surface of MWCNT which depressed the adsorption of NOM onto MWCNTs-COOH. The obtained data were studied using Freundlich, Langmuir and BET isotherms; NOM adsorption data had the best conformity to the Freundlich isotherm. Kinetic studies were performed and the adsorption kinetics successfully followed the pseudo-second-order kinetic model. Thermodynamic parameters such as free energy change (ΔG W ), enthalpy change (ΔH W ) and entropy change (ΔS W ) were determined and evaluation of them showed that the adsorption process for NOM is general spontaneous, endothermic and thermodynamically favorable. A. Naghizadeh S. Nasseri (corresponding author) R. Rezaei Kalantary R. Nabizadeh A. H. Mahvi Department of Environmental Health Engineering, School of Public Health and center for Water Quality Research (CWQR), Institute for Environmental Research (IER), Tehran University of Medical Sciences (TUMS), Tehran, Iran E-mail: Nasserise@tums.ac.ir A. M. Rashidi Nanotechnology Research Center, Research Institute of Petroleum Industry (RIPI), Tehran, Iran Key words | adsorption, isotherm, kinetics, natural organic matter, thermodynamic INTRODUCTION Natural organic matter (NOM) is a mixture of chemically complex polyelectrolytes with varying molecular weights, produced mainly from the decomposition of plant and animal residues that are present in all surface and ground- water resources, with concentrations ranging from 0.5 up to 10 mg/L organic carbon. Although it has been demon- strated that NOM is regarded as non-toxic, several problems may arise during purification and distribution of naturally colored groundwaters. NOM can have negative effects on the odor, taste and color of drinking water and can also enhance bacterial regrowth and biofilm formation in drinking water distribution systems. These compounds can also react with disinfectants, as precursors to produce disinfection by-products (DBPs), such as trihalomethanes (THMs) and haloacetic acids (HAAs) which are suspected to be carcinogenic (Summers & Roberts ; Jia et al. ; Genz et al. ; Krasner ). One of the best methods of controlling DBPs formation is to remove the pre- cursor compounds by processes such as adsorption and membrane separation. Because of the complex structure and low concentration of NOM, fully characterizing NOM is very difficult. Thus, to assess the water quality and efficiency of treatment pro- cesses, the use of lumped parameters is required. Hence surrogate parameters, total organic carbon (TOC), dissolved organic carbon (DOC) and ultraviolet absorbance at 254 nm can be used to quantify the concentration of NOM (Crittenden et al. ). 273 © IWA Publishing 2013 Water Science & Technology: Water Supply | 13.2 | 2013 doi: 10.2166/ws.2013.018 Downloaded from https://iwaponline.com/ws/article-pdf/13/2/273/415929/273.pdf by guest on 26 May 2020