A thermally stabilized polyacrylonitrile (PAN) fiber was activated with sodium carbonate (Na2CO3) at 800 °C (PYR-8SC1) followed by annealing at 950 °C (PYR-8SC1-9.5HT30) to remove negatively charged surface oxygen and supplied for adsorption of nitrate in aqueous solution from acidic to weak basic range. Nitrogen adsorption-desorption analysis was conducted to examine the textural properties of PYR-8SC1-9.5HT30 sample comparing with the non-annealing sample of PYR-8SC1. Elemental analysis was performed to know the content of nitrogen and oxygen in the samples and X-ray photoelectron spectroscopy (XPS) was also applied to determine the amount of quaternary nitrogen (N-Q) species favorable for the nitrate adsorption. PYR-8SC1-9.5HT30 exhibited a stable high adsorption capacity in a wide equilibrium solution pH (pHe) range, particularly around neutral pHe, whereas PYR-8SC1 worked well only in acidic condition at pHe close to 3 or lower. Maintaining high adsorption capacities of nitrate on PYR-8SC1-9.5HT30 could be caused by not only surface exposure of positively charged graphitic N-Q species, but also the presence of positively charged oxygen and the absence of negatively charged pyridine N-oxide (N-X) and the other negatively charged nitrogen and oxygen species that might hinder the nitrate adsorption onto the surface of PAN activated carbon fiber (ACF).
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