title: Removal of oil droplets from contaminated water using magnetic carbon nanotubes.
abstract: Water contaminated by oil and gas production poses challenges to the management of America's water resources. Here we report the design, fabrication, and laboratory evaluation of multi-walled carbon nanotubes decorated with superparamagnetic iron-oxide nanoparticles (SPIONs) for oil-water separation. As revealed by confocal laser-scanning fluorescence microscopy, the magnetic carbon nanotubes (MCNTs) remove oil droplets through a two-step mechanism, in which MCNTs are first dispersed at the oil-water interface and then drag the droplets with them out of water by a magnet. Measurements of removal efficiency with different initial oil concentration, MCNT dose, and mixing time show that kinetics and equilibrium of the separation process can be described by the Langmuir model. Separation capacity qt is a function of MCNT dose m, mixing time t, and residual oil concentration Ce at equilibrium: [Formula in text] where qmax, kw, and K are maximum separation capacity, wrapping rate constant, and equilibrium constant, respectively. Least-square regressions using experimental data estimate qmax = 6.6(± 0.6) g-diesel g-MCNT(-1), kw = 3.36(± 0.03) L g-diesel(-1) min(-1), and K = 2.4(± 0.2) L g-diesel(-1). For used MCNTs, we further show that over 80% of the separation capacity can be restored by a 10 min wash with 1 mL ethanol for every 6 mg MCNTs. The separation by reusable MCNTs provides a promising alternative strategy for water treatment design complementary to existing ones such as coagulation, adsorption, filtration, and membrane processes.
authors.affiliation: Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556, USA.
authors.forename: Haitao
authors.initials: H
authors.lastname: Wang
authors.forename: Kun-Yi
authors.initials: KY
authors.lastname: Lin
authors.forename: Benxin
authors.initials: B
authors.lastname: Jing
authors.forename: Galyna
authors.initials: G
authors.lastname: Krylova
authors.forename: Ginger E
authors.initials: GE
authors.lastname: Sigmon
authors.forename: Paul
authors.initials: P
authors.lastname: McGinn
authors.forename: Yingxi
authors.initials: Y
authors.lastname: Zhu
authors.forename: Chongzheng
authors.initials: C
authors.lastname: Na
mesh_terms: D003911:Dextrans / Q000737:chemistry; D060328:Magnetic Phenomena; D058185:Magnetite Nanoparticles / Q000737:chemistry; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000648:ultrastructure; D009821:Oils / Q000302:isolation & purification*; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*
chemical_list: D003911:Dextrans; D058185:Magnetite Nanoparticles; D037742:Nanotubes, Carbon; D009821:Oils; D014874:Water Pollutants, Chemical; D014867:Water; C065507:ferumoxides