Immobilisation of humic acids and binding of nitrophenol to immobilised humics

A new method has been developed for the immobilisation of humic acids on si lica. After using 3-aminopropyl-dimethyl-ethoxysilane to prepare aminopropy l silica, humic acids can be irreversibly bound to the aminopropyl silica. The remaining amino groups on the silica are successfully end-capped using a CH3COONa-EDC method. The products have iso-electric points at low pH and are stable in a wide range of pH. The sorption isotherms of paranitrophenol (PNP) onto immobilised Aldrich hu mic acid show that pH and salt concentration do not affect the sorption of PNP at pH<6, but at higher pH values the sorbed amount decreases strongly. The PNP sorption can be described with a competitive Langmuir equation exte nded with electrostatic interactions. The strong decrease in sorption at hi gh pH is due to both the electrostatic repulsion between the negatively cha rged HA and the negative PNP species and the fact that the concentration of the neutral PNP species decreases. (C) 1999 Elsevier Science B.V. All righ ts reserved.