Effects of chemosorbed arsenate groups on the mesoporous titania morphology and enhanced adsorption properties towards Sr(II) cations

Abstract

Mesoporous titania samples modified by sodium arsenate to form arsenate functionalities were synthesized using titanium aqua complex [Ті(ОН2)6]3+·3Cl− and salt Na3AsO4 as precursors. The structure, morphology, and texture of the samples were characterized using XRD, IR spectroscopy, TG-DTA, TEM, and nitrogen adsorption methods. The adsorption properties of the samples located in the aqueous media were analyzed with respect to Sr(II) removal. The modified titania samples have a large specific surface area (up to 405 m2/g) and appropriate pore volume (up to 0.26 сm3/g) with a major contribution of mesopores. The maximum adsorption capacity of modified titania (with 4% of arsenate groups) towards Sr(II) is 262.9 mg/g. It is much smaller for unmodified titania (92.1 mg/g). The equilibrium adsorption isotherms were fitted using the Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models. The results revealed that the adsorption equilibrium data match with the Langmuir isotherm model (R2 > 0.993) that corresponds to the localized adsorption onto uniform surface. The adsorption kinetics fitted well by the pseudo-second-order kinetic model. A possible adsorption mechanism was analyzed. Sr(II) removal can be attributed to = Ti(О2AsОOН) groups located at a mesopore surface of the adsorbents. The materials demonstrate the stability of the degree of the Sr(II) adsorption during ten cycles. Thus, arsenate-modified mesoporous titania could be considered as an effective adsorbent for Sr(II) removal from wastewater.