Influence of catechin on precipitation of aluminum hydroxide

Abstract

Polyphenols (catechins) are vital biomolecules in tea plants, Camellia sinensis, which are well adapted to acid soils with high availability of phytotoxic Al species. Since the mechanism of Al resistance in tea plants by catechin remains obscure, this study investigates the influence of catechin on aluminum transformation. It is found that the pH of the suspensions decreased with aging. The hydrolytic precipitates of Al were subjected to surface area, X-ray diffraction (XRD), Fourier-transform infrared absorption spectroscopy (FT-IR), transmission electron microscopy (TEM), thermal, and chemical analyses. At the initial Al concentration of 2 × 10 − 2 M sample, in the absence of catechin for 180-d aging, only 59.7% of the Al is remained in the filtrate, including readily, moderately extractable and nonextractable fractions. However, in the presence of catechin, above 70.5% of the Al is present in the filtrate. The readily, moderately extractable and nonextractable Al fractions with 8-quinolinolate method are decreased with increasing concentrations of catechin after 180-d aging. Specific surface area of the Al precipitates increases with increasing concentrations of catechin. In the absence of catechin, the Al precipitates with prolonged aging are mostly crystalline gibbsite. X-ray diffraction analysis and TEM observations also show the structural distortion within the hydrolytic precipitates of Al in the presence of catechin. FT-IR spectra show that catechin substantially inhibits the formation of crystalline aluminum hydroxides. X-ray noncrystalline to poor-ordered hydrolytic reaction products of Al are formed in the presence of catechin. TEM images also show that the Al precipitates form under the perturbation of catechin are fine, shapeless and hollow colloids that are deformed and aggregated. Thermal analysis shows that the hydrolytic reaction products of Al lost their structural water gradually when catechin concentration is raised from 0 M (control) to 4.0 × 10 − 3 M, indicating that greater structural disorder occurs with increasing catechin concentration in the Al systems.