Synthesis of hyperbranched polyamidoamine-modified chitosan aerogel and its efficient adsorption of Cr(VI) from aqueous solution

Here, hyperbranched polyamidoamine (HPAMAM)-functionalized chitosan aerogels (HPCSA) with a porous structure and abundant active sites were prepared via the freeze-drying method. The structure of HPCSA was proven through Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), and mercury intrusion porosimetry (MIP). The kinetic experiments identified that the adsorption process of Cr(VI) by HPCSA followed the pseudo-second-order model, confirming that Cr(VI) adsorption was dominantly controlled by chemisorption. The adsorption isotherm tests followed the Langmuir model and the maximum capacity of Cr(VI) ions was 862.07 mg/g at pH = 3, obviously higher than most reported chitosan-derived adsorbents. The thermodynamic investigation confirmed that the adsorption was spontaneous and random. In addition, after 4 cycles, the adsorption efficiency of HPCSA for Cr(VI) declined from 95.2 to 73.8 %. The primary adsorption mechanism including the caught and reduction of Cr(VI) ions was elucidated via FT-IR, density functional theory (DFT), and XPS.