Study on the characteristics of nitrogen-doped activated carbon fibers to remove nitrate ions by multi-factor analysis

Abstract

A type of rayon-based commercial activated carbon fibers (ACFs), named as KF1500, was modified by thermal chemical vapor deposition (CVD) method to remove nitrate in aqueous solution. Acetonitrile (vapor) was introduced to dope positive charge nitrogen species on it. The sample was ded as KF-8ST10-8AN20-9.5HT30-8ST30 (8ST10; steam activation at 800 °C with 10 mL water, 8AN20; thermal CVD treatment at 800 °C charging 20 mL acetonitrile, 9.5HT30; annealing at 950 °C for 30 min, 8ST30; steam activation at 800 °C with 30 mL water), obtaining great nitrate adsorption capacity of 0.74 mmol/g in 200 mg/L nitrate solution at pH 3.0. For deeply exploring the adsorption characteristics of this well-modified ACFs, in this study, the pH of point of zero charge (pHpzc) for KF8ST10-8AN20-9.5HT30-8ST30 as well as KF1500 has been explored to further understand the surface charge properties. The results indicated that pHpzc was 7.2 for KF1500 and that for modified ACFs KF-8ST10-8AN20-9.5HT30-8ST30 was about pHpzc 7.0. Effect of solution pH at various initial solution concentrations was also studied, and adsorption isotherms were well fitted by Langmuir model at pH 1.5–8, and adsorption capacity obtained from the fitting was 0.67 mmol/g (R2 = 0.993). In addition, the effect of temperature (15–35 °C) on nitrate adsorption was also tested. Moreover, desorption of nitrate hydrochloric acid solution proceeded for 3 h at pH 3. With the above results, the working condition of quaternary nitrogen (N–Q) and carbon π bond was investigated, and the contribution to nitrate adsorption by N–Q was also defined more clearly which was 22% at least.