Structure-Controlled Synthesis of Sodium Trititanate and Hexatitanate Nanorods and their Adsorption Properties for Ni²⁺and Pb²⁺ Ions from Aqueous Solutions

Phase pure sodium trititanate (Na₂Ti₃O₇) and hexatitanate (Na₂Ti₆O₁₃) nanorods were controllably synthesized using sodium carbonate and titanic acid as sodium and titanium precursors by calcination at 850 °C for 12 h. The adsorption properties of trititanate and hexatitanate nanorods for the removal of heavy metal ions, Ni²⁺ and Pb²⁺ from simulated wastewaters at pH of 3‒7 and 20‒65 °C were investigated. The adsorption of Ni²⁺ and Pb²⁺ ions on sodium trititanate and hexatitanate nanorods are through ion exchange and electrostatic adsorption. The adsorption of Ni²⁺ and Pb²⁺ ions could be well fitted by the pseudo-second order adsorption kinetics and Langmuir adsorption isotherm. Based on the Langmuir adsorption isotherm, the adsorption capacities of naked sodium trititanate nanorods for Ni²⁺ and Pb²⁺ from simulated wastewaters at 20 °C and pH 7 are 104.17 and 89.85 mg∙g^‒1 while the adsorption capacities of naked sodium hexatitanate nanorods are 95.69 and 76.69 mg∙g^‒1, respectively. Sodium trititanate nanorods exhibit higher adsorption capacities for heavy metal ions from wastewaters than sodium hexatitanate nanorods because the former has richer Na⁺ ions for ion exchange with heavy metal ions than the latter. The adsorption processes of Ni²⁺ and Pb²⁺ on sodium trititanate and hexatitanate nanorods are spontaneous. The phase pure sodium titanate nanorods may have practical application for the removal and enrichment of metal ions from wastewaters.