Browsing by Author "Roam, GD"

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Adsorption characteristics of dichlorvos onto hydrous titanium dioxide surface
(1996-07-01)
Lu, MC
;
Roam, GD
;
Chen, JN
;
Huang, CP
;
環境工程研究所
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
Photocatalytic mineralization of toxic chemicals with illuminated TiO2
(1995)
Lu, MC
;
Roam, GD
;
Chen, JN
;
Huang, CP
;
環境工程研究所
Photocatalytic oxidation process can be an effective method for the removal of toxic organic compounds from dilute aqueous solutions. Three toxic compounds, namely, dichlorvos (an insecticide), propoxur (an insecticide), and 2, 4-D (a herbicide), were used as the model compounds for the mineralization experiments. Total organic carbon measurements were used to measure the extent and the rate of the mineralization of these toxic chemicals. Additionally, ions such as chloride, phosphate and ammonia were also measured during the photomineralization reaction. Results show that the photocatalytic system is effective in mineralizing these pesticides. Both pH and the initial concentration of the organic compounds affect the mineralization reaction. The mineralization reaction is favored under an acid condition and increases with increasing initial organic concentration. The initial rate of the photomineralization reaction can be described by a Langmuir-Hinshelwood expression.