Mechanism of Vegetable Extracts on Preventing the Oxidation of Chrome(Ⅲ)

摘要

To explore the mechanism whereby hydrolysable tannins and the monomers hydrolysed from hydrolysable tannins in preventing Cr(III) from oxidising into Cr(VI), we selected Valonia, Tara, plus monomers including gallic acid and ellagic acid as test samples to evaluate their complexing ability, reducibility, antioxidation ability and impact on preventing Cr(III) from oxidising into Cr(VI) as well as the relationship between their abilities and impact. With total phenolic value taken as a measurement basis, we took the equivalent quantity of every material based on its total phenolic value, and tested the effect on the same amount of Cr(III) and with the Folin-phenol method to total the number of the active phenolic groups, then we inferred the binding ability from the phenolic group activity. The complexation ability was determined by measuring the decrease of the phenolic value during a given interval in a system where we mixed every material with chrome powder and found the reducibility by using the absorbency method of K3Fe(CN)(6) reduction, and analysed the antioxidation ability by DPPH. These abilities are major influential elements in preventing Cr(III) from oxidising into Cr(VI). The relationship between parameters was discovered. The main results were: generally speaking, that the complexing ability of these materials, in order from great to small, is in the order: ellagic acid, Tara, Valonia and gallic acid, which accords with their abilities to prevent Cr(III) from oxidation into Cr(VI) to a large extent. The reducibility and antioxidation effect of these materials from large to small is in the order: ellagic acid>gallic acid>Tara>Valonia, and this has a positive affect on preventing Cr(III) from oxidation into Cr(VI) to quite a large extent, However, the order of reducibility and antioxidation doesn't accord with the order of ability to prevent Cr(III) from oxidising into Cr(VI).