title: Coadsorption of ciprofloxacin and Cu(II) on montmorillonite and kaolinite as affected by solution pH.
abstract: The coadsorption of ciprofloxacin (Cip) and Cu(II) on montmorillonite and kaolinite was studied between pH 4.0 and 9.5. At pH < 5.0, Cu(2+), Cip(+) and [Cu(II)(Cip(+/-))](2+) were the main species in solution. Between pH 5.0-7.0 [Cu(II)(Cip(+/-))](2+) was the dominant complex species. Above pH 8.0 [Cu(II)(Cip(-))(2)](0) precipitated. The presence of Cu(II) exerted no effect on the Cip sorption onto montmorillonite at low pH, whereas it increased Cip sorption on montmorillonite at pH > 6.0 due to the stronger affinity of Cip-Cu(II) complexes compared to sole Cip(-) or Cip(+/-), or Cip sorption via a Cu(II) bridge increased. In contrast, Cip increased Cu(II) adsorption on montmorillonite at pH < 7.0, whereas it decreased the adsorption of Cu(II) on kaolinite at pH 6.0-8.0. Cip was sorbed onto the kaolinite surface via interaction of carboxyl groups over the entire pH range. At pH 4.0-4.7, Cip(+) sorption onto kaolinite's positively charged surface was more favorable than sorption of Cip-Cu(II) complexes. Batch experiments and FTIR analyses indicated that the coordination between Cip(+/-), Cip(-) and Cu(II) were most likely present on kaolinite surface at pH 7.0. At pH > 8.0, Cu(OH)(2) (s) and [Cu(II)(Cip(-))(2)](0) precipitated out of solution or on the montmorillonite or kaolinite surface, which was not considered evidence for either the sorption of Cip or the adsorption of Cu(II).
authors.affiliation: Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Pei
authors.forename: Xiao-Quan
authors.initials: XQ
authors.lastname: Shan
authors.forename: Jingjing
authors.initials: J
authors.lastname: Kong
authors.forename: Bei
authors.initials: B
authors.lastname: Wen
authors.forename: Gary
authors.initials: G
authors.lastname: Owens
mesh_terms: D000327:Adsorption; D001546:Bentonite / Q000737:chemistry*; D002939:Ciprofloxacin / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007616:Kaolin / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D014865:Waste Disposal, Fluid / Q000379:methods
chemical_list: D001546:Bentonite; D007616:Kaolin; D002939:Ciprofloxacin; D003300:Copper