Preparation of poly(aniline-1,8-diaminonaphthalene) and its application as adsorbent for selective removal of Cr(VI) ions

In this paper, poly(aniline-1,8-diaminonaphthalene) (PANDAN) was synthesized by chemical oxidation and characterized by Fourier transform infrared spectroscopy (FTIR), electrophoretic mobility test and X-ray photoelectron spectroscopy (XPS). The adsorption behavior of Cr(VI) onto PANDAN was then examined using batch and fixed-bed column sorption techniques. Cr(VI) adsorption onto PANDAN follows the Freundlish model and the pseudosecond-order kinetic model well. The pH value has considerable impact on the adsorption capacity of the adsorbent, and the maximum adsorption capacity reached 150 mg g−1 at pH 4. PANDAN displays more preferable adsorption toward Cr(VI) in the presence of K+, Ca2+, Mg2+, H2PO4− at greater levels in solution, while increasing SO42− and CO32− to 5 times of the Cr(VI) concentration could slightly decrease the adsorption. It was proposed that Cr(VI) was removed from aqueous solutions through an adsorption-coupled reduction process, in which the PANDAN of reduction state converts to oxidation state and provides protons for the reduction of Cr(VI) to Cr(III). The addition of 1,8-diaminonaphthalene (1,8-DAN) in the copolymer greatly enhanced the amount of amine and secondary amino groups on polymer chains, offering more protons for Cr(VI) reduction and binding sites for resultant Cr(III), thus improving the uptake properties of the copolymer. It was also proved that the adsorbed chromium ions could be effectively desorbed by 1.0 mol L−1 NaOH. Column breakthrough studies were conducted at different flow rate and Cr(VI) concentrations to investigate the applicability of adsorbent. The results suggest that PANDAN is a promising adsorbent for selective removal of Cr(VI) from waste effluents.

► Poly(aniline-1,8-diaminonaphthalene) (PANDAN) was synthesized for Cr(VI) removal.
► The addition of 1,8-DAN in the copolymer enhanced the amount of amine and secondary amino groups.
► Selective removal of Cr(VI) on PANDAN may result from the adsorption-coupled reduction process.
► Conversion of PANDAN from reduction to oxidation state provided protons for the Cr(VI) reduction.
► Column breakthrough tests show that PANDAN is a promising adsorbent for Cr(VI) selective removal.