Mechanistic implications of the effect of TiO2 accessibility in TiO2-SiO2 coatings upon chlorinated organics photocatalytic removal in water.
The photocatalytic removal rates r of dichloroacetic acid (DCAA), 4-chlorobenzoic acid (4-CBA) and 4-chlorophenol (4-CP) in water were compared for TiO2 samples used either as a powder or as a coating on a fiber glass tissue, SiO2 being the binder. From SEM-EDX measurements it was deduced that SiO2 prevails over TiO2 in the coating top layers and 18O2-Ti16O2 isotopic exchange showed that the accessibility of O2 to TiO2 was markedly reduced when TiO2 was thus coated. The unfavorable effect of the restricted TiO2 accessibility on r was drastic for DCAA, much less pronounced for 4-CBA, and still smaller for 4-CP. It is inferred that DCAA can be attacked only when it directly interacts with TiO2, whereas 4-CP can also react within the near-TiO2 surface water layers. The 4-CBA intermediate behavior is in line with the structural similarities of 4-CBA with DCAA and 4-CP.
Enriquez
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Laboratoire Photocatalyse, Catalyse et Environnement, CNRS UMR IFoS, Ecole Centrale de Lyon, 069134 Ecully Cedex, France.
Beaugiraud
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Pichat
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D002384:Catalysis; D002723:Chlorobenzoates / Q000737:chemistry / Q000302:isolation & purification*; D002733:Chlorophenols / Q000737:chemistry / Q000302:isolation & purification*; D004396:Coloring Agents / Q000737:chemistry*; D003999:Dichloroacetic Acid / Q000737:chemistry / Q000302:isolation & purification*; D010777:Photochemistry; D012388:Root Canal Irrigants / Q000737:chemistry / Q000302:isolation & purification*; D012822:Silicon Dioxide / Q000737:chemistry; D014025:Titanium / Q000737:chemistry*; D014873:Water Pollutants / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*
D002723:Chlorobenzoates; D002733:Chlorophenols; D004396:Coloring Agents; D012388:Root Canal Irrigants; D014873:Water Pollutants; C009495:titanium dioxide; C029107:4-chlorophenol; D012822:Silicon Dioxide; D003999:Dichloroacetic Acid; D014025:Titanium; C040768:4-chlorobenzoic acid