This
research investigated
chlorinated byproduct formation at Ti4O7 anodes.
Resorcinol was used as a model organic compound representative of
reactive phenolic groups in natural organic matter and industrial
phenolic contaminants and was oxidized in the presence of NaCl (05
mM). Resorcinol mineralization was >68% in the presence and absence
of NaCl at 3.1 V/SHE (residence time = 13 s). Results indicated that
∼4.3% of the initial chloride was converted to inorganic byproducts
(free Cl2, ClO2
–, ClO3
–) in the absence of resorcinol, and this
value decreased to <0.8% in the presence of resorcinol. Perchlorate
formation rates from chlorate oxidation were 115371 mol m–2 h–1, approximately two orders of
magnitude lower than reported values for boron-doped diamond anodes.
Liquid chromatography–mass spectroscopy detected two chlorinated
organic products. Multichlorinated alcohol compounds (C3H2Cl4O and C3H4Cl4O) at 2.5 V/SHE and a monochlorinated phenolic compound (C8H7O4Cl) at 3.1 V/SHE were proposed as
possible structures. Density functional theory calculations estimated
that the proposed alcohol products were resistant to direct oxidation
at 2.5 V/SHE, and the C8H7O4Cl compound
was likely a transient intermediate. Chlorinated byproducts should
be carefully monitored during electrochemical advanced oxidation processes,
and multibarrier treatment approaches are likely necessary to prevent
halogenated byproducts in the treated water.