posted on 2016-02-21, 16:17authored byGuandao Gao, Chad D. Vecitis
Electrochemical filtration with anodic carbon nanotube
(CNT) networks
is reported to be effective for chemical and microbiological water
treatment. Here, we investigate how CNT doping affects the electrochemical
filtration performance toward the remediation of aromatic wastewaters.
Purified and well-characterized undoped (C-CNT), boron-doped (B-CNT),
and nitrogen-doped (N-CNT) anodic carbon nanotube networks are challenged
with aqueous phenol in a sodium sulfate electrolyte. Steady-state
current and effluent total organic carbon (TOC) measurements are utilized
to evaluate the oxidative performance as a function of voltage and
electrolysis time. In terms of steady-state TOC removal, at an applied
voltage of 3 V all three anodic CNT networks are able to remove approximately
7 to 8 mgC L–1 of the influent TOC within the ∼1
s liquid residence time of the electrochemical filter. The anodic
CNT networks are partially passivated over the 5 h electrolysis time
with the B-CNT network displaying the least passivation. The extent
of passivation was observed to be inversely correlated to the CNT
work function. SEM, XPS, and TGA of the electrolyzed CNT networks
are used to identify the two primary passivation mechanisms of electrochemical
phenols polymerization and electrochemical electrolyte precipitation.
In agreement with chronoamperometry results, the B-CNT network has
the lowest extent of passivating polymer and precipitate formation.
The precipitant is determined to likely be sodium persulfate or carbonate
and is removed with a simple acidic water wash. The polymer is determined
to likely be polyphenylene oxide and is partially removed with the
wash. All three anodic CNT networks display potential for energy efficient
electrochemical filtration of aromatic wastewaters and the B-CNT are
determined to be the most resistant to passivation.