Development of a novel pullulan/polydopamine composite hydrogel adsorbent for dye removal

Abstract

Polysaccharides with good renewability, excellent biocompatibility and desirable degradation rate are widely applied in the field of wastewater treatment. Herein, we have synthesized a series of novel semi-interpenetrating polymer network (semi-IPN) polysaccharide hydrogels that are comprised of pullulan, polydopamine (PDA) and 1–6-Hexanediol diglycidyl ether (HDE as a cross-linker) via the chemical cross-linking method. The physical and chemical properties of the semi-IPN hydrogels were investigated through Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD), rheological measurement, thermal gravimetric analysis (TGA) and Scanning electron microscope (SEM) images. Furthermore, TGA and SEM suggest that the thermostability and morphologies of gels were obviously affected by the PDA concentration of solution. In brief, the increase of PDA concentration resulted in better thermostability and bigger pore sizes, and the introduction of PDA led to the improvement of swelling performance. Furthermore, the obtained semi-IPN hydrogels exhibited desirable adsorption capacity (107 mg/g) toward Crystal violet. After four cycles of adsorption experiments, the adsorption capacities still maintained 100 mg/g. The Langmuir and pseudo-second-order models were used to explain the adsorption process of hydrogels. Owing to the advantages of cheaper raw materials, non-toxic and harmless and simple preparation process, the obtained pullulan/PDA semi-IPN hydrogel is expected to be the promising candidate for rapid dye removal.