Surface catalyzed hydrolysis of chloramphenicol by montmorillonite under limited surface moisture conditions

摘要

Phyllosilicates possess high surface acidity under limited surface moisture conditions and are thus able to mediate the abiotic transformation of antibiotics. This route of abiotic transformation has long been ignored given that most of the studies carried out in aqueous phase. In this study, the catalytic performance of cation-exchanged montmorillonites (M~(n+)-Mts) to the hydrolysis of chloramphenicol (CAP) was investigated under different moisture conditions. Montmorillonite exchanged with Fe~(3+) and Al~(3+) show the greatest catalytic activities. Multiple spectroscopic techniques and theoretical calculations indicate that the surface Bronsted- and Lewis-acid properties are sensitive to surface wetting. At lower moisture level (<10%, wt/wt), the strong Bronsted-acid catalysis predominates the hydrolysis of CAP. Attributing to the strong Lewis-acidities, Fe~(3+)-Mt and Al~(3+)-Mt could perform high catalytic activities over a wider moisture range (10-100%, wt/wt). However, such hydrolysis reaction was almost suppressed at water content >400%. In addition, the presence of natural organic matter (NOM, 1%, wt/wt) had little impact on the catalytic activities of Fe~(3+)-Mt and Al~(3+)-Mt. The results of this study highlight the environmental significance of dry surface reaction by clay minerals as an effective abiotic transformation pathway to the elimination of antibiotics in natural field soil, which is commonly partly hydrated.