Adsorption characteristics of dichlorvos onto hydrous titanium dioxide surface

Adsorption of dichlorvos (2,2-dichlorovinyl-o,o-dimethl phosphate) onto hydrous TiO2 from water was evaluated in the laboratory using a batch reactor. The presence of organic solvents resulted in a decreasing dichlorvos adsorption on TiO, surface. These data were used to assess a cosolvent model. Decreased adsorption of dichlorvos was observed at an initial pH of 4 with increasing ionic strength. The inhibitory adsorption is attributed to the blockade of surface sites by electrolytes. In addition, electrolytes play an important role on the pa-dependent dichlorvos adsorption. It is suggested that at pH < pH(pzc) (point of zero charge), dichlorvos adsorption is inhibited because electrolytes compete with dichlorvos fbr surface sites. At pH > pH(pzc) the adsorption density of dichlorvos decreases with increasing solution pH due to the decrease of surface group, TiOH, on the TiO2 surface. The variation of adsorption density with temperature over the range 10 degrees-40 degrees C has been investigated. Results show that the reaction is controlled by enthalpy. The adsorption of dichlorvos onto the TiO2 surface is primarily brought about by hydrogen bonding. Copyright (C) 1996 Elsevier Science Ltd