Xu Linfeng, Pan Chengling, Li Sen, Yin Chengjie, Zhu Jinbo, Pan Yusong, Feng Qi
School of Earth and Environment, Anhui University of Science and Technology, Huainan, Anhui 232001, China.
Department of Advanced Materials Science, Faculty of Engineering and Design, Kagawa University, 2217-20 Hayashi-cho, Takamatsu 761-0396, Japan.
Langmuir. 2021 May 18;37(19):6080-6095. doi: 10.1021/acs.langmuir.1c00913. Epub 2021 May 9.
Three-dimensional mesoporous lepidocrocite-type layered sodium titanate (LST) was constructed at room temperature by the electrostatic interaction between TiO nanosheets and Na ions. The results of a systematic X-ray diffraction investigation manifested the transition from the TiO 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, N 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.
通过TiO纳米片与Na离子之间的静电相互作用，在室温下构建了三维介孔纤铁矿型层状钛酸钠（LST）。系统的X射线衍射研究结果表明从TiO纳米片相转变为钛酸盐/二氧化钛相，这确定了作为温度和NaCl浓度函数的相图。此外，利用扫描电子显微镜、电感耦合等离子体质谱、热重和差热分析、N吸附-脱附、拉曼光谱、傅里叶变换红外光谱以及ζ电位分析对LST的物理和化学性质进行了充分表征。此外，批量吸附实验表明，与阴离子染料相比，LST对阳离子染料具有优异的吸附性能和吸附选择性。系统研究了吸附过程中对阳离子染料吸附行为的多种影响因素。此外，通过详细的动力学研究，伪二级动力学模型恰当地描述了阳离子染料的吸附行为，即化学吸附是主要的吸附作用。同时，利用不同的吸附等温线模型处理实验数据，发现阳离子染料在LST上的吸附等温线适合Langmuir等温模型。更重要的是，提出了阳离子染料在LST上吸附的离子交换机制，离子交换反应发生在LST层间1 mol Na离子与溶液中1 mol MB分子之间的化学计量交换。同时，电化学阻抗谱和循环伏安测量验证了LST层间Na离子的高离子电导率导致了优异的吸附性能。最终采用两步酸碱法有效地再生LST吸附剂。这项工作不仅提供了一种具有优异吸附容量和吸附选择性的替代吸附剂，而且对层状钛酸盐吸附机理的研究具有一定的指导意义。
