Phosphate Ion Adsorption Properties of PAN-Based Activated Carbon Fiber Prepared with Na2CO3 Activation

The main objective of this study was to evaluate the efficiency of Na2CO3 activation and to examine polyacrylonitrile-based activated carbon fibers (PAN-ACFs) for phosphate ion adsorption in aqueous solution. PAN-ACFs were prepared by Na2CO3 activation (Na2CO3/PAN-CF weight ratio of 1–3) at 800°C and then heat treatment at 950°C under N2 gas flow using a horizontal furnace. The batch adsorption results on the effects of Na2CO3 impregnation ratio showed that equilibrium adsorption capacities were more than 0.2 mmol/g at the initial phosphate ion concentration of 3 mmol/L, especially the PAN-ACF prepared with N2CO3/PAN-CF weight ratio of 1 had the highest capability (0.27 mmol/g). This result was also supported by the characterization data, such as specific surface area (2600 m2/g) and quaternized-nitrogen (N-Q) content (1.6 wt %) for adsorption site calculated from the experimental N2 adsorption-desorption isotherm at –196°C and N1s spectra using XPS, respectively. The experimental data of optimized PAN-ACF for phosphate ion adsorption were well fitted to both Langmuir adsorption isotherms and pseudo-second-order kinetic model with high correlation coefficients of 0.96 and 0.98, respectively. The calculated maximum adsorption capacity was 0.7 mmol/g and the adsorption process reached equilibrium within 1 h, indicating that PAN-ACF has great adsorption ability as a carbonaceous material compared to other adsorbents. The solution pH influenced phosphate ion adsorption as well, and the most suitable pH for adsorption amount was around 6. As for regeneration performance, PAN-ACF still remained more than 90% adsorption amount of the fresh one at the first and second cycles after rejuvenation treatment using 1 mol/L HCl as desorption solution, indicating great reuse performance.