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

Abstract

Efficient removal of organic dyes from contaminated water has become a great challenge and urgent work due to increasingly serious environmental problems. Here, we have for the first time prepared nanolayer-constructed TiO­(OH)2 microstructures which can present negative charge by deprotonation of the hydroxyl group to efficiently and selectively remove cationic dyes from aqueous solution through electrostatic interaction and an attraction mechanism. The nanolayer-constructed TiO­(OH)2 microstructures achieve a high adsorption capacity of 257 mg g–1 for methylene blue (MB). The adsorption kinetics, thermodynamics, and isotherms of MB over the TiO­(OH)2 microstructures have been studied systemically. The experimental measurements and corresponding analyses demonstrate that the adsorption process of MB on TiO­(OH)2 microstructures follows a kinetic model of pseudo-second-order adsorption, agrees well with the Langmuir isotherm mode, and is a spontaneous and exothermic physisorption. Fourier transform infrared (FT-IR) spectra confirm that the prepared TiO­(OH)2 microstructures possess hydroxyl group which can deprotonate to present negative charge in solution. Further experimental studies evidently demonstrate that the TiO­(OH)2 microstructures also can remove other cationic dyes with positive charge such as basic yellow 1, basic green 4, and crystal violet but cannot adsorb anionic dye of methyl orange (MO) with negative charge in aqueous solution. The measurements for FT-IR spectra and the adsorption of cationic and anionic dyes evidently reveal that the adsorption of cationic dyes over the TiO­(OH)2 microstructures is achieved by the electrostatic interaction and attraction between TiO­(OH)2 and the dye. This work opens a strategy for the design of new absorbents to efficiently remove organic dyes from aqueous solution through an electrostatic attraction-driven adsorption process.