UV light-driven controlled photodegradation of condensed tannins from larch bark

Abstract

Photocatalytic degradation of condensed tannins is a more efficient and cleaner way than traditional microbial and chemical degradations. In this work, the ultrasonic-assisted UV light-driven controlled degradation of larch tannins was studied, in which the effects of nano-TiO2 dosage and tannin concentrations on the degradation efficiency were investigated systematically. The structure and molecular weight of photocatalytic degradation products were characterized by time-of-flight mass spectrometry, gel permeation chromatography, and infrared spectrum. Results showed that the controlled photocatalytic degradation of condensed tannins could be achieved by controlling the formaldehyde reactivity of the degradation products. The optimized condition was reached when the tannin concentration was 4%, the nano-TiO2 catalyst load was 0.2%, and the degradation time was 5 h. Under these conditions, the condensed tannins of larch bark were mainly degraded to dimers, with formaldehyde reactivity reaching as high as 0.7931. Photocatalytic degradation can be a new method for the degradation of condensed tannins.