title: Adsorption of Pb²⁺, Cd²⁺, Cu²⁺ and Cr³⁺ onto titanate nanotubes: competition and effect of inorganic ions.
abstract: Adsorption of Pb(2+), Cd(2+), Cu(2+) and Cr(3+) from aqueous solutions onto titanate nanotubes (TNTs) in multiple systems was systematically studied. Particular attention was paid to competitive adsorption and the effect of inorganic ions. TNTs showed large adsorption capacity for the four heavy metals, with the mechanism of ion-exchange between metal ions and H(+)/Na(+) located in the interlayers of TNTs. Binary or quaternary competitive adsorption indicated that the adsorption capacity of the four heavy metals onto TNTs followed the sequence of Pb(2+) (2.64 mmol g(-1)) ≫ Cd(2+) (2.13 mmol g(-1)) > Cu(2+) (1.92 mmol g(-1)) ≫ Cr(3+) (1.37 mmol g(-1)), which followed the reverse order of their hydration energies. Moreover, inorganic ions including Na(+), K(+), Mg(2+) and Ca(2+) inhibited the adsorption of heavy metals on TNTs, because they competed for adsorption sites, decreased the activity of heavy metal ions, and promoted the aggregation of TNTs. However, Al(3+) and Fe(3+) generally enhanced adsorption because the resulting hydroxyl-Al/Fe intercalated or coated TNTs could also capture metal ions. Furthermore, minor effect of inorganic ions on adsorption of Pb(2+) resulted from its strong affinity to TNTs. Difficult desorption and small inhibiting effect by Na(+), K(+), Mg(2+) and Ca(2+) on adsorption of Cr(3+) was due to the formed stable complex of HOCr(OTi)₂ ≡ with TNTs. Present study indicated potential applications of TNTs in wastewater treatment for heavy metals.
authors.affiliation: Shenzhen Key Laboratory for Heavy Metal Pollution Control and Reutilization, School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen 518055, China.
authors.forename: Wen
authors.initials: W
authors.lastname: Liu
authors.forename: Ting
authors.initials: T
authors.lastname: Wang
authors.forename: Alistair G L
authors.initials: AG
authors.lastname: Borthwick
authors.forename: Yanqi
authors.initials: Y
authors.lastname: Wang
authors.forename: Xiaochen
authors.initials: X
authors.lastname: Yin
authors.forename: Xuezhao
authors.initials: X
authors.lastname: Li
authors.forename: Jinren
authors.initials: J
authors.lastname: Ni
mesh_terms: D000327:Adsorption; D001667:Binding, Competitive; D002104:Cadmium / Q000302:isolation & purification; D002412:Cations; D002857:Chromium / Q000302:isolation & purification; D003300:Copper / Q000302:isolation & purification; D007854:Lead / Q000302:isolation & purification; D019216:Metals, Heavy / Q000302:isolation & purification*; D046529:Microscopy, Electron, Transmission; D008956:Models, Chemical; D043942:Nanotubes / Q000737:chemistry*; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods
chemical_list: D002412:Cations; D019216:Metals, Heavy; D014874:Water Pollutants, Chemical; D002104:Cadmium; D002857:Chromium; C009495:titanium dioxide; D007854:Lead; D003300:Copper; D014025:Titanium