Sono-assisted synthesis of nanostructured polyaniline for adsorption of aqueous Cr(VI): Effect of protonic acids

• Nanostructured PANIs were prepared by a facile sono-assisted method.
• Protonic acids impacted PANI morphology and molecular structure.
• PANIs varied in Cr(VI) adsorption properties depending on protonic acids.
• A mechanism of electrostatic adsorption followed by Cr(VI) reduction was proposed.

Polyaniline (PANI) nanoparticles and 1D nanostructures were prepared by a facile sono-assisted chemical oxidation method in protonic acids like HCl, surfulamic acid (SA), citric acid (CA), taurine (TA) and neutral deionized (DI) water for removal of aqueous Cr(VI). Results showed that all the prepared PANI nanostructures showed efficient adsorption for Cr(VI), however, their adsorption efficiencies varied depending on the protonic acids and the consequent molecular structures of PANIs. Among them, the PANI-HCl prepared in strong HCl acid showed the highest adsorption capacity, followed in descending order by PANI-SA, PANI-CA, PANI-TA and PANI-DI. The adsorption capacity was correlated well with oxidation state and protonation extent of PANIs. Solution pH had an obvious effect on Cr(VI) adsorption, especially for PANI-TA and PANI-DI. A mechanism of electrostatic adsorption followed by reduction of Cr(VI) to Cr(III) was proposed by analyzing FTIR, zeta potential and XPS spectra of PANIs before and after Cr(VI) adsorption.

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