Sorption enhancement of Cr(VI) from aqueous solution by polyaniline confined in three-dimensional network of composite porous hydrogel

Hexavalent chromium Cr(VI) is a typical harmful pollutant, which is carcinogenic or mutagenic to aquatic animals and humans. In this study, sepiolite/humic acid/polyvinyl alcohol@ polyaniline (SC/HA/PVA@PANI) composite porous hydrogel adsorbent was synthesized by Pickering emulsion template in situ chemical oxidative polymerization for adsorption of Cr(VI) from aqueous solution. The in situ polymerization of aniline at the Pickering emulsion interface and the unique three-dimensional network structure of the hydrogel act as an effective "confinement" for the growth of the polymer. The porous structure of the material acts as a water channel, which effectively accelerates the binding of the adsorbate to the adsorption sites, and significantly improves the adsorption rate and adsorption capacity. The adsorption capacity of PANI for Cr(VI) confined in three-dimensional network of composite porous SC/HA/PVA@PANI hydrogel reached 1180.97 mg/g-PANI, which increased about 27-fold compared the adsorption capacity of pure PANI (43.48 mg/g). It is shown that the experimental design effectively avoids the agglomeration of PANI and improves its potential adsorption performance. In addition, the analysis of FESEM-EDX, FT-IR, and XPS spectra before and after adsorption confirmed that the main adsorption mechanisms of Cr(VI) on SC/HA/PVA@PANI included ion exchange, electrostatic attraction, and redox reaction. In conclusion, SC/HA/PVA@PANI has good stability and excellent adsorption performance, which is a new type of Cr(VI) ion adsorbent with great potential.