Hydroxyl radical formation during ozonation of multiwalled carbon nanotubes: performance optimization and demonstration of a reactive CNT filter.
We explored factors influencing hydroxyl radical (•OH) formation during ozonation of multiwalled carbon nanotubes (MWCNTs) and assessed this system's viability as a next-generation advanced oxidation process (AOP). Using standard reactivity metrics for ozone-based AOPs (RCT values), MWCNTs promoted •OH formation during ozonation to levels exceeding ozone (both alone and with activated carbon) and equivalent to ozone with hydrogen peroxide. MWCNTs oxidized with nitric acid exhibited vastly greater rates of ozone consumption and •OH formation relative to as-received MWCNTs. While some of this enhancement reflects their greater suspension stability, a strong correlation between RCT values and surface oxygen concentrations from X-ray photoelectron spectroscopy suggests that surface sites generated during MWCNT oxidation promote •OH exposure. Removal of several ozone-recalcitrant species [para-chlorobenzoic acid (p-CBA), atrazine, DEET, and ibuprofen] was not significantly inhibited in the presence of radical scavengers (humic acid, carbonate), in complex aquatic matrices (Iowa River water) and after 12 h of continuous exposure of MWCNTs to concentrated ozone solutions. As a proof-of-concept, oxidized MWCNTs deposited on a ceramic membrane chemically oxidized p-CBA in a flow through system, with removal increasing with influent ozone concentration and mass of deposited MWCNTs (in mg/cm2). This hybrid membrane platform, which integrates adsorption, oxidation, and filtration via an immobilized MWCNT layer, may serve as the basis for future novel nanomaterial-enabled technologies, although long-term performance trials under representative treatment scenarios remain necessary.
†Department of Civil and Environmental Engineering, University of Iowa, 4105 Seamans Center, Iowa City, Iowa 52242, United States.
Rebekah
R
Oulton
†Department of Civil and Environmental Engineering, University of Iowa, 4105 Seamans Center, Iowa City, Iowa 52242, United States.|‡Henry B. Tippie School of Management, University of Iowa, 108 Pappajohn Business Building, Suite 160, Iowa City, Iowa 52242, United States.
Jason P
JP
Haase
§Department of Chemical and Biochemical Engineering, University of Iowa, 4133 Seamans Center, Iowa City, Iowa 52242, United States.
Sara
S
Kaalberg
§Department of Chemical and Biochemical Engineering, University of Iowa, 4133 Seamans Center, Iowa City, Iowa 52242, United States.
Connor T
CT
Redmond
∥Department of Chemical and Environmental Engineering, University of California, Riverside A220 Bourns Hall, Riverside, California 92521, United States.
Michael J
MJ
Nalbandian
†Department of Civil and Environmental Engineering, University of Iowa, 4105 Seamans Center, Iowa City, Iowa 52242, United States.|§Department of Chemical and Biochemical Engineering, University of Iowa, 4133 Seamans Center, Iowa City, Iowa 52242, United States.
David M
DM
Cwiertny
D002254:Carbonates / Q000737:chemistry; D002723:Chlorobenzoates / Q000032:analysis; D004777:Environment; D005374:Filtration / Q000295:instrumentation*; D006812:Humic Substances / Q000032:analysis; D017665:Hydroxyl Radical / Q000737:chemistry*; D007484:Iowa; D008855:Microscopy, Electron, Scanning; D037742:Nanotubes, Carbon / Q000737:chemistry*; D010084:Oxidation-Reduction; D010126:Ozone / Q000737:chemistry*; D045483:Rivers / Q000737:chemistry; D013499:Surface Properties; D013535:Suspensions
D002254:Carbonates; D002723:Chlorobenzoates; D006812:Humic Substances; D037742:Nanotubes, Carbon; D013535:Suspensions; D017665:Hydroxyl Radical; D010126:Ozone; C040768:4-chlorobenzoic acid