Surface-functionalization of hydrogen titanate nanowires for efficiently selective adsorption of methylene blue

Polydopamine coated hydrogen titanate nanowires (PDA-HTN) are prepared via dopamine self-polymerization. The obtained PDA-HTN is a cheap adsorbent for selective adsorption of methylene blue (MB). The adsorption characteristics of PDA-HTN are studied from three aspects: isotherm, kinetics and thermodynamics. Date show that PDA-HTN adsorbs MB spontaneously, and the adsorption process is agreement with the fitting results of Langmuir and pseudo-second-order model. PDA-HTN is used to selectively adsorb MB from dye mixtures, the removal rate of MB can reach as high as 99.8% and adsorption capacity can reach 241.3 mg g−1. PDA-HTN can be used to adsorb MB in 0.5 mol L−1 NaCl solution, and the increase of ionic concentration in NaCl solution will improve the adsorption performance of PDA-HTN for MB, because salt ions will induce the dimerization of MB. PDA-HTN exhibits excellent cyclic adsorption property, the removal rate of MB remains above 97.7% after 12 cycles of adsorption-desorption. The adsorption is explained by cooperative effects of π–π stacking, electrostatic interaction, 1,4–Michael addition reaction and hydrogen bonding. Compared to the pristine HTN, the adsorption capacity of PDA-HTN for MB is greatly increased. In addition, PDA-HTN can also be used to remove other cationic dyes, and its adsorption capacity for basic yellow 1 (BY1) and crystal violet (CV) is 586.7 mg g−1 and 865.1 mg g−1, respectively.