Self-assembly of immobilized titanate films with different layers for heavy metal ions removal from wastewater: Synthesis, modeling and mechanism

In this work, a modified NAH method was developed to synthesize immobilized titanate films with different number of layers by conveniently changing hydrothermal duration. Stable trilayer titanate architectures were first obtained with the middle layer functioning as support for the splitting nanowires during synthesis. A series of characterization methods including SEM, XRD, XPS, TG, FTIR and BET analyses were used to evaluate the properties of these immobilized films. Based on a newly proposed area-based method, the performance of different synthesized films for simultaneous removal of Pb(II), Cu(II) and Cd(II) was systematically investigated and the results exhibited preferential and abundant adsorption of Pb(II) for all the immobilized materials. A multi-potential sorption (MPS) model which combined cation-exchanging and static adsorption was firstly established for modeling the sorption kinetics and the fitting results suggested that the proposed MPS model was precise and reliable. Furthermore, the monolayer adsorption model was utilized to fit the sorption isotherms, which revealed the orientation of adsorbates and endothermic physical interactions. The coordinating mechanisms were further confirmed with the receptor sites derived from deconvoluted XPS O 1s spectra as well as Na 1s spectra and the binding modes were clarified by FTIR and XPS. Finally, compared with traditional dispersive titanate powders, the synthesized titanate films were more convenient for separation and exhibited outstanding heavy metal elimination performance, which could be ascribed to the oriented titanate arrangement on the titanium foils. Overall, the low synthetic consumption, high sorption capacity, satisfying selectivity and convenient operation make the newly developed immobilized multilayer titanate films promising materials for the removal of heavy metal ions from wastewater.