Effective Adsorption/Reduction of Cr(VI) Oxyanion by Halloysite@Polyaniline Hybrid Nanotubes

Tianzhu Zhou; Cuiping Li; Huiling Jin; Yangyang Lian; Wenmei Han

doi:10.1021/acsami.6b14079

Effective Adsorption/Reduction of Cr(VI) Oxyanion by Halloysite@Polyaniline Hybrid Nanotubes

ACS Appl Mater Interfaces. 2017 Feb 22;9(7):6030-6043. doi: 10.1021/acsami.6b14079. Epub 2017 Feb 7.

Authors

Tianzhu Zhou¹, Cuiping Li¹, Huiling Jin¹, Yangyang Lian¹, Wenmei Han¹

Affiliation

¹ School of Chemical Science and Technology, Key Laboratory of Medicinal Chemistry for Natural Resource, Ministry of Education, Yunnan University , Kunming 650091, China.

PMID: 28121121
DOI: 10.1021/acsami.6b14079

Abstract

Halloysite@polyaniline (HA@PANI) hybrid nanotubes are synthesized by the in situ chemical polymerization of aniline on halloysite clay nanotubes. By facilely tuning the dopant acid, pH, and apparent weight proportion for aniline (ANI) and halloysite (HA) nanotubes in the synthesis process, PANI with tuned oxidation state, doping extent, and content are in situ growing on halloysite nanotubes. The reaction system's acidity is tuned by dopant acid, such as HCl, H₂SO₄, HNO₃, and H₃PO₄. The adsorption result shows the fabricated HA@PANI hybrid nanotubes can effectively adsorb Cr(VI) oxyanion and the adsorption ability changes according to the dopant acid, pH, and apparent weight proportion for ANI and HA in the synthesis process. Among them, the HA@PANI fabricated with HCl as dopant acid tuning the pH at 0.5 and 204% apparent weight proportion for ANI and HA (HP/0.5/204%-HCl) shows the highest adsorption capacity. The adsorption capacity is in accordance well with the doping extent of PANI in HA@PANI. Furthermore, when HP/0.5/204%-HCl is redoped with HNO₃, H₂SO₄, and H₃PO₄, the adsorption capacity declines, implying the dopant acid in the process of redoping exhibits a marked effect on Cr(VI) oxyanion adsorption for the HA@PANI hybrid nanotubes. HP/0.5/204%-HCl and HP/0.5/204%-H₃PO₄ have demonstrated good regenerability with an above 80% removal ratio after four cycles. Moreover, the HA@PANI adsorbent has better sedimentation ability than that of pure PANI. The adsorption behavior is in good agreement with Langmuir and pseudo second-order equations, indicating the adsorption of HA@PANI for Cr(VI) oxyanion is chemical adsorption. FT-IR and XPS of HA@PANI after Cr(VI) oxyanion adsorption indicate that the doped amine/imine groups (-NH⁺/═N⁺- groups) are the main adsorption sites for the removal of Cr(VI) oxyanion by electrostatic adsorption and reduction of the adsorbed Cr (VI) oxyanion to Cr(III) simultaneously.

Keywords: Cr(VI) oxyanion adsorption; Cr(VI) oxyanion reduction; dopant acid; halloysite nanotube; polyaniline.