Pyridinic nitrogen (N-6) in flame resistant polyacrylonitrile (PAN) fiber was converted to positively charged quaternary nitrogen (N-Q) of methyl pyridine using methyl iodide at 40°C to prepare carbon fiber adsorbents to remove a negatively charged pollutant of nitrate from aqueous solution. The prepared PAN fiber adsorbent could uptake nitrate above 0.3 mmol/g from 3 mmol/L nitrate solution, whereas only 0.03 mmol/g of nitrate was captured with the unmodified PAN fiber. Some reaction conditions for methylation were examined to maximize nitrate and above 0.6 mmol/g of nitrate adsorption could be achieved at equilibrium solution pH (pH_e) 3. Langmuir adsorption isotherm could be applied to the nitrate adsorption at solution pH_e 3 and calculated adsorption affinity (K_e) and capacity (X_m) of nitrate were 0.24 L/mmol and 2.39 mmol/g, respectively, for the optimum prepared conditions for the adsorbent. Influence of pH_e on nitrate adsorption was also inspected for the modified PAN adsorbent and above 0.3 mmol/g at pH_e 1-3 was maintained and above 0.15 mmol/g in a constant value at pH_e 6-10 under standard conditions indicating that 0.15 mmol/g or greater number of quaternary nitrogen (N-Q) might be exposed to the PAN surface. XPS N1s analysis and Boehm titration support the presence of N-Q species on the modified PAN sample to adsorb nitrate.

ε-Poly-L-lysine (PL) is a natural polymer bearing a key amino group that provides it with a cationic nature, high reactivity in water, and consequent broad applicability. Here we prepared a guanidinylated PL (GPL) exhibiting an enhanced cationic nature by guanidinylation of the amino group with 1-amidinopyrazole hydrochloride (AP) and trimethylamine (TEA) (AP-TEA system). In the AP-TEA system using 3 eq of AP for 2 days at room temperature, a GPL with the degree of guanidinylation (DG) of 100% was achieved. The DG value could be controlled by the AP amount. The lower acidity of the GPL relative to PL was confirmed by pH titration; the reduced acidity resulted in enhanced antibacterial activity of the GPL under an alkaline condition (pH 8.0 and 9.0).