Effect of nitrogen doping and tunable pore structures on arsenic removal Jisun Han, Daegwon Ha and Shinhoo Kang* * Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742, Korea ABSTRACT Nitrogen doped carbons were synthesized by a carbo- nitride derived carbon (CNDC) at various chlorination temperatures. CN73s that have both small micro- and meso- pores with nitrogen functional group, such as pyrrolic-N at the surface of pores, show excellent adsorption ability for the arsenic complex ions. Experimental and theoretical calculation results suggested that pore structure and the types of nitrogen functional groups making the CN73s highly charged significantly influenced the adsorption of arsenic. The small micro-pores(0.7 nm) that pyrrolic-N is placed at the edge of pores are active sites for capturing arsenic complex ions. The small meso-pores provide the diffusion path for arsenic ions and enhance the adsorption kinetics. Keywords: arsenic adsorption, nitrogen doped porous carbon, carbo-nitride derived carbon (CNDC), pore size distribution, nitrogen functional groups 1 INTRODUCTION The arsenic and its compound are highly toxic and some of them are carcinogen. They could spread into ground water through geothermal, mining and industrial activity, and contaminate ground water. A large amount of water resources around the world contain signification concentration of arsenic ranged from 0.5 to 5000 μg/L. To secure drinking water, removal of arsenic is vitally required. Therefore, developing adsorption material and elimination technology became a big global issue and numerous studies are currently underway. The porous carbons, especially carbide derived carbon (CDC), synthesized by a chlorination of various carbides is one of the typical adsorbent materials. CDC has well developed pore structure not only on its surface but also in bulk [1]. Thus, it is widely applied as the substrate for the gas adsorption and the electrochemistry application [2, 3]. Particularly, certain size of micro-pores and small meso- pores are uniformly formed in CDC via controlling experimental factors [4]. It is suitable for small sized gas adsorption such as hydrogen, carbon dioxide. Because micro-pores, which could catch gas molecules via overlapping of interaction force between the pore walls, act as adsorption sites and meso-pores provide the kinetic path to gas molecules enhancing diffusion of gas molecules within the bulk of CDC [5]. Meanwhile, pure porous carbon itself has high stability and is electrically neutralized. Therefore, it has low van der Waals interaction (4 kJ/mol) with gas molecules or electrolytes. To enhance the interaction energy, hetero atom doping is extensively implemented notably the nitrogen. A number of research about nitrogen doped carbons are currently in progress. Thus nitrogen doped carbons are widely applied as adsorbent, electrode for energy storage device and catalyst for electrochemical applications [6, 7]. In this paper, N-doped porous carbon was synthesized by a carbo-nitride derived carbon (CNDC), which is similar to the CDC process. It has both micro-pores and meso- pores which is the advantage of CDC. Furthermore, the nitrogen is successfully doped on edges of CNDC along with pore development. Therefore, aforementioned N- doped porous carbon has the positively charged surface that could enhance the adsorption ability for arsenic ions in water. This material shows outstanding adsorption performance for arsenic compared with other carbon materials. Also, its performance is comparable to metal oxide adsorbents, such as iron oxide, aluminium oxide, commonly used in arsenic removal. We denoted entire samples as CN73s and each sample as CN-X; In CN73s, 73 represents the carbon-to-nitrogen ratio of the Ti(C 7 N 3 ) precursors. X signifies the chlorination temperature. 2 RESULTS AND DISCUSSION Figure 1: N 2 sorption isotherms of CN73s (solid – adsorption, open – desorption) The N 2 sorption isotherms, shown in fig. 1, exhibit the pore structure of CN73s. CN700 have type I isotherm with mild slope of P/P 0 = 0.1~0.5, which represents the development of micro-pores wider than those of pure micro-porous materials like typical CDC. The sorption isotherms of pure CDC usually have sharp hill at low relative pressure and plateau over wide ranges. TiC-CDC, as a typical CDC, have negligible meso-pores but above 275 Materials for Energy, Efficiency and Sustainability: TechConnect Briefs 2015