Participation of Strong H-Bonding to Acidic Groups Contributes to the Intense Sorption of the Anionic Munition, Nitrotriazolone (NTO) to the Carbon, Filtrasorb 400.

5-Nitro-1,2-dihydro-3H-1,2,4-triazin-3-one ("nitrotriazolone," NTO) is an insensitive munition compound used in modern weaponry. It poses a potential threat to soil and water quality at relevant sites due to its physical properties that cause high mobility in the environment. NTO is polar and predominantly monoanionic (NTO) at environmental pH (p = 3.64 and p = 11.06; determined by two independent methods in this study). Nevertheless, NTO sorbs strongly to the carbon, Filtrasorb 400 (Freundlich coefficient = 1.26 × 10 L μmol kg at pH 9.5). We present evidence that sorption is contributed by the interaction of NTO with functional groups of similar acidity on the carbon to form exceptionally strong, negative charge-assisted hydrogen bonds, (-)CAHB, written (-N···H···O-[Formula: see text]), where -N is the deprotonated N of NTO, and O-[Formula: see text] represents a deprotonated surface group. Behaviors consistent with (-)CAHB include (1) a "hump" in the pH-sorption profile centered around pH 4, where maximal complexation is expected to occur; (2) an apparent ∼2.4-unit upward shift in p due to the enhanced H-bond strength; (3) the consumption of a proton from water to form the complex; and (4) sorption suppression by competing (-)CAHB-capable solutes. Anion exchange played a minor role. The findings help advance our understanding of weak acids sorption by carbonaceous materials.