Electrostatic Self-Assembly Synthesis of Three-Dimensional Mesoporous Lepidocrocite-Type Layered Sodium Titanate as a Superior Adsorbent for Selective Removal of Cationic Dyes via an Ion-Exchange Mechanism

Linfeng Xu; Chengling Pan; Sen Li; Chengjie Yin; Jinbo Zhu; Yusong Pan; Qi Feng

doi:10.1021/acs.langmuir.1c00913

Electrostatic Self-Assembly Synthesis of Three-Dimensional Mesoporous Lepidocrocite-Type Layered Sodium Titanate as a Superior Adsorbent for Selective Removal of Cationic Dyes via an Ion-Exchange Mechanism

Langmuir. 2021 May 18;37(19):6080-6095. doi: 10.1021/acs.langmuir.1c00913. Epub 2021 May 9.

Authors

Linfeng Xu^{1

2}, Chengling Pan¹, Sen Li², Chengjie Yin³, Jinbo Zhu³, Yusong Pan³, Qi Feng²

Affiliations

¹ School of Earth and Environment, Anhui University of Science and Technology, Huainan, Anhui 232001, China.
² Department of Advanced Materials Science, Faculty of Engineering and Design, Kagawa University, 2217-20 Hayashi-cho, Takamatsu 761-0396, Japan.
³ Department of Materials Science and Engineering, Anhui University of Science and Technology, Huainan, Anhui 232001, China.

PMID: 33969686
DOI: 10.1021/acs.langmuir.1c00913

Abstract

Three-dimensional mesoporous lepidocrocite-type layered sodium titanate (LST) was constructed at room temperature by the electrostatic interaction between Ti_1-δO₂^4δ- nanosheets and Na⁺ ions. The results of a systematic X-ray diffraction investigation manifested the transition from the Ti_1-δO₂^4δ- nanosheets phase to the titanate/titania phase, which determined a phase diagram as a function of the temperature and NaCl concentration. In addition, scanning electron microscopy, inductively coupled plasma-mass spectrometry, thermogravimetric and differential thermal, N₂ adsorption-desorption, Raman spectroscopy, Fourier transform infrared spectroscopy, as well as ζ-potential analyses were utilized for adequate characterization of the LST physical and chemical properties. Furthermore, batch adsorption experiments demonstrated that LST had superior adsorption property and adsorption selectivity toward cationic dyes compared to those of anionic dyes. A multifarious influencing effect on the cationic dye adsorption behavior during the adsorption process was systematically investigated. Moreover, the pseudo-second-order kinetic model felicitously depicted the cationic dye adsorption behavior through an elaborate kinetic study, namely, chemisorption was the main adsorption action. Meanwhile, different adsorption isotherm models were utilized to process the experimental data, uncovering that the adsorption isotherms of cationic dyes on LST were suitable for a Langmuir isothermal model. More importantly, an ion-exchange mechanism was proposed for the cationic dye adsorption on LST, and the ion-exchange reaction occurred with a stoichiometric exchange between 1 mol of Na⁺ ions in the LST interlayer and 1 mol of MB molecules in the solution. In parallel, the electrochemical impedance spectroscopy and cyclic voltammogram measurements verified that the high ionic conductivity of Na⁺ ions in the LST interlayer resulted in a superior adsorption property. A two-step acid-base procedure was ultimately adopted to effectively regenerate LST adsorbent. This work provides not only an alternative adsorbent with superior adsorption capacity and adsorption selectivity but also some guiding significance for research on the adsorption mechanism of layered titanates.