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

Sterile batch experiments were conducted to investigate the effects of pH, dissolved O2 concentration, and reaction time on interaction of 0.1 mM 14C-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/ O2). However, a significant increase in sorption of 14C 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 O2, 1-naphthol transformation and removal were negligible even after 7 d reaction time. Therefore, sorption of 14C labeled compound is due to a stronger interaction between the naphthol oxidation product and Al(OH)3(s). 13C CPMAS NMR spectra of 1,4-13C-labeled 1-naphthol reacted with Al(OH)3(s) showed a chemical shift change at the C4 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.