Fabrication of polyaniline hydrogel: Synthesis, characterization and adsorption of methylene blue

•The PAni hydrogel was synthesized using phytic acid as a dopant and cross-linking agent.•The synthesized PAni hydrogel has a big adsorption capacity for MB.•The pseudo-second-order model is available to describe the adsorption of MB.•The Langmuir model is adaptive for the adsorption of MB.•The adsorbent was a specific adsorbent for the removal of MB. Polyaniline (PAni) hydrogel was synthesized in a facial method by using phytic acid as both dopant and cross-linking agent. Then the fabricated hydrogel was employed as an efficient adsorbent to remove the methylene blue (MB) in an aqueous solution. The as-synthesized PAni hydrogel was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images. The characterization results indicate that the obtained PAni hydrogel has a 3D structure, which is available for the contact between the adsorbent and dye molecules. During the adsorption, the phytic acid provides a large number of anionic phosphate groups as adsorption sites for MB molecules, which induces the high adsorption capacity up to 71.2mg/g. The effects of pH, the PAni hydrogel mass and temperatures on adsorption efficiency were studied in details. Further experimental results indicate the adsorption kinetic fits well with the pseudo-second-order kinetic model. Compared with Freundlich model, Langmuir isotherm model was more acceptable to fit the equilibrium adsorption data. Moreover, the conceivable mechanism of the adsorption was also proposed in this work.