Adsorption and photocatalytic degradation of bilirubin on hydroxyapatite coatings with nanostructural surface

Bilirubin produced from hemoglobin metabolism and normally conjugated with albumin is a kind of lipophilic endotoxin, and can cause various diseases when its concentration is high. Bilirubin adsorption on nanostructural hydroxyapatite coatings was investigated using quartz crystal microbalance (QCM) technique, and factors affecting its adsorption such as bilirubin concentration and thickness of hydroxyapatite coatings were discussed in detail. The adsorption kinetic parameter estimated from the in situ frequency measurement is about 3.59 x 10(7) M(-1). With the present method, the photocatalytic degradation of adsorbed bilirubin under UV irradiation was investigated and discussed as well, and a photocatalytic mechanism has been proposed. The obtained information suggests that QCM is a useful method for monitoring the adsorption/degradation behavior of bilirubin on nanostructural hydroxyapatite coatings, and that nanostructural hydroxyapatite coatings which is used as adsorbent for the removal of bilirubin can be photochemically regenerated due to the degradation of adsorbed bilirubin. (C) 2008 Elsevier B.V. All rights reserved.