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

Abstract

Three-dimensional mesoporous lepidocrocite-type layered sodium titanate (LST) was constructed at room temperature by the electrostatic interaction between Ti 1−δ O 2 4δ− nanosheets and Na + ions. The results of a systematic X-ray diffraction investigation manifested the transition from the Ti 1−δ O 2 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, N 2 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.

Lepidocrocite-Type Layered Titanate Nanoparticles as Photocatalysts for H2 Production

“…Layered transition metal oxides (e.g., layered titanates and niobates) consisting of transition metal oxide nanolayers and interlayer exchangeable cations have been widely used for designing green materials/devices such as adsorbents, − solid acid catalysts, − lithium (sodium)-ion batteries − electrocatalysts, photocatalysts, ,,− and dye-sensitized solar cells. − The compositional variations, combined with the ability to accommodate various guest species in the interlayer space, make layered transition metal oxides more attractive. Transition metal oxide nanosheets obtained by exfoliation of the parent layered compounds have attracted attention from both scientific and practical viewpoints owing to their unique physicochemical properties based on the highly anisotropic shape associated with the large accessible surface area. − Aggregation of 2D nanosheets and positively charged species obtained by electrostatic interactions have been used to obtain porous hybrids, − which are useful due to their easily accessible pores for reactants and functional units such as dye sensitizers when compared with well-ordered (densely packed) intercalation compounds.…”

Nanolayer-Constructed TiO(OH)2 Microstructures for the Efficiently Selective Removal of Cationic Dyes via an Electrostatic Interaction and Adsorption Mechanism

“…For instance, ZnCo hydroxide nanostructures, dithiocarbamate-grafted starlike polymer, sulfur codoped TiO 2 nanostructures, and carboxylic acid-terminated carbon nanoflakes have been developed and applied for the selective adsorption of cationic dyes from aqueous solution. In addition, as demonstrated in previous studies, TiO 2 hollow microspheres and TiO 2 -based heterogeneous nano/microstructures such as TiO 2 /MoS 2 , halloysite–TiO 2 –Fe 3 O 4 composites, Ag 2 O-modified TiO 2 -based nanolayers, and layered sodium titanate have been used as adsorbents for the efficient removal of MB from polluted water.…”

Macroporous Aerogels Using High Internal Phase Pickering Emulsions for Adsorption of Dyes

“…4 Among them, the physical adsorption method has the characteristics of fast speed, simple design, strong adaptability, low cost, and environmental friendliness and thus is widely used to treat dye wastewater. 5 Common adsorbents like activated carbon, 6 clay minerals, 7 mesoporous materials, 8 molecular sieves, 9 carbon nanotubes, 10 graphene oxide, 11 and resins 12 have various limitations, such as complex preparation, high cost, and difficulty in recycling. Macroporous aerogels are ideal candidate for the treatment of dye wastewater due to their advantages of low density, high porosity, high specific surface area, high permeability, stable structure, and effect.…”