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.
ASJC Scopus subject areas
- Environmental Chemistry