Adsorptive Removal of Nitrate from Aqueous Phase Using Steam Activated and Thermal Treated Polyacrylonitrile (PAN) Fiber

Abstract

Approximately three grams of black colored air-stabilized polyacrylonitrile (PAN) fiber, namely PYROMEX (PYR), containing nitrogen element was activated by steam at 800̊C to develop porosity and thermally treated at 900-1000̊C in helium to convert a part of nitrogen species to quaternary nitrogen (N-Q) using various combinations of the steam and thermal treatments in a 25 φinner diameter quartz tube, and adsorption capacity of nitrate anion from aqueous solution was measured. Steam activation at 800̊C by 20 mL water charge and consecutive heat treatment at 950̊C for 30 min (PYR-8ST20-9.5HT30) showed the largest nitrate adsorption capacity of 0.64 mmol/g among all prepared adsorbents. Effect of solution pH on nitrate adsorption was also investigated at the initial nitrate concentrations of 0.85-5.06 mmol/L for PYR-8ST20- 9.5HT30 compared with thermal treated cellulose based ACF at 950̊C for 30 min (KF1500-9.5HT30). The adsorption amount of nitrate on PYR-8ST20-9.5HT30 was always greater than that on KF1500-9.5HT30 at any condition examined in the experiments in spite of specific surface area of PYR-8ST20-9.5HT30 being less than half of KF1500-9.5HT30. Langmuir type adsorption isotherms of nitrate could be applied at pH range from 3 to 6.Maximum adsorption capacities of PYR-8ST20-9.5HT30 and KF1500-9.5HT30 calculated from the isotherms were 0.56-0.72 and 0.50-0.61 mmol/g, respectively, altering the values depending on the solution pH. The higher adsorption capacities could come from the greater amount of nitrogen, particularly quaternary nitrogen (N-Q),and the less oxygen that would work as inhibitor sites for nitrate adsorption, on PYR-8ST20-9.5HT30 than KF1500-9.5HT30.