Adsorptive Removal of Nitrate from Aqueous Solution Using Nitrogen Doped Activated Carbon

Abstract

Activated carbon (AC) has been widely applied for adsorptive removal of organic contaminants from aqueous phase, but not for ionic pollutants. In this study, nitrogen doped AC was prepared to increase the adsorption capacity of nitrate from water. AC was oxidized with (NH 4 ) 2 S 2 O 8 solution to maximize oxygen content for the first step, and then NH 3 gas treatment was carried out at 950°C to aim at forming quaternary nitrogen (N-Q) species on AC surface (Ox-9.5AG). Influence of solution pH was examined so as to elucidate the relationship between surface charge and adsorption amounts of nitrate. The results showed that Ox-9.5AG exhibited about twice higher adsorption capacity than non-treatment AC at any initial nitrate concentration and any equilibrium solution pH (pH e ) investigated. The more decrease in pH e value, the more adsorption amount of negatively charged nitrate ion, because the surface charge of AC and Ox-9.5AG could become more positive in acidic solution. The oxidation and consecutive ammonia treatments lead to increase in nitrogen content from 0.35 to 6.4% and decrease in the pH of the point of zero charge (pH pzc ) from 7.1 to 4.0 implying that positively charged N-Q of a Lewis acid was created on the surface of Ox-9.5AG. Based on a Langmuir data analysis, maximum adsorption capacity attained 0.5-0.6 mmol/g of nitrate and adsorption affinity was 3.5-4.0 L/mmol at pH e 2.5 for Ox-9.5AG.

Adsorption of nitrate from aqueous phase onto nitrogen-doped activated carbon fibers (ACFs)

“…− /L). The equilibrium solution pH (pH e ) was adjusted to about 3 by use of 0.1 M HCl solution, because maximum adsorption amounts of nitrate could be always observed at pH e 3, in which differences in adsorption capacities were easily distinguished among adsorbents [10][11][12]. The solution pH was measured with portable pH meter, HORIA model D-51.…”

“…In our previous study, oxidized activated carbons (ACs) and activated carbon fibers (ACFs) were successfully prepared to reduce the concentration of cationic contaminants as Pb(II), Cd(II), Ni(II) and other heavy metal ions in aqueous phase [7,8]. However, development of carbonaceous adsorbents to uptake anionic pollutants as As(III), Cr(VI), phosphate, nitrate, etc., are still a challenging study, because adsorption capacities are far below compared to ion-exchange resin [9,10]. In our preliminary study, nitrogen doping was repeatedly carried out using various procedures to increase the adsorption capacities of anions.…”

“…In our preliminary study, nitrogen doping was repeatedly carried out using various procedures to increase the adsorption capacities of anions. At first, oxidized ACs were treated with ammonia to efficiently enhance the adsorption capacity of nitrate [10]. Next melamine form was used as a starting material for carbonization and methylation of nitrogen elements using methyl iodide for pyridinic (N-6) and pyrrolic (N-5) type nitrogen to yield quaternary nitrogen (N-Q) on carbonized melamine for the nitrate removal [11].…”

Effect of Salinity and PH on the Industrial Effluent Treatment by Activated Carbon: Modeling of the Kinetic Adsorption and Equilibrium Isotherms

“…At high pH, OH ions would compete with the phenol molecules for sorption sites. Sorption of excess of OH ions could convert an initial positively charged surface of activated carbon into a negatively charged surface resulting repulsion of negatively charged phenoxide ions and adsorption decreased (Machida et al, 2016). The effect of pH on the removal of the phenol and PHBA using AC S23 is presented in Figure 5.…”

Nitrate Ion Adsorption Characteristics of Activated Carbon Fibers with and without Quaternary Nitrogen Effective for Anion Adsorption

“…11) Activated carbon fibers (ACFs) are porous and have been widely used for the adsorption of organic pollutants in water. 12) However, ACFs are hydrophobic and not suitable for removing nitrate ions, but there is still a room for improvement. In the present study, various modifications such as chemical activation and heat treatment were performed to improve the adsorption performance of nitrate ions.…”