Interaction of 1-Naphthol and Its Oxidation Products with Aluminum Hydroxide

Sterile batch experiments were conducted to investigate the effects of pH, dissolved O 2 concentration, and reaction time on interaction of 0.1 mM 14 C-1-hydroxynaphthalene [1-naphthol] with poorly crystalline Al(OH) 3 (s). Negligible (<4%) sorption of 1-naphthol to Al(OH) 3 (s) was observed after 20 h reaction time (conditions − dark, w/ O 2 ). However, a significant increase in sorption of 14 C labeled compound occurred with increasing equilibration time to 7 days, and a clear pH dependent trend emerged. The extent of removal was minimal below pH 6.8, increased sharply over a narrow pH range, and leveled off around pH 8.2. A similar pH-dependent trend was observed for 1-naphthol transformation in controls [no Al(OH) 3 (s)]. In the absence of O 2, 1-naphthol transformation and removal were negligible even after 7 d reaction time. Therefore, sorption of 14 C labeled compound is due to a stronger interaction between the naphthol oxidation product and Al(OH) 3 (s). 13 C CPMAS NMR spectra of 1,4- 13 C-labeled 1-naphthol reacted with Al(OH) 3 (s) showed a chemical shift change at the C 4 position and also the progressive emergence of a new peak attributable to naphthoquinone. Possible mechanisms for interaction of naphthoquinones with Al(OH) 3 (s) include hydrophobic sorption and/or surface complexation. The Al(OH) 3 (s) surface provides a “sink” for irreversible binding of the quinone transformation product.