pH-responsive magnetic graphene oxide/poly(NVI-co-AA) hydrogel as an easily recyclable adsorbent for cationic and anionic dyes

pH-responsive magnetic graphene oxide/poly(N-vinylimidazole-co-acrylic acid) hydrogel (MGO/PNA) was synthesized by random copolymerization of N-vinylimidazole (NVI) and acrylic acid (AA) in the presence of ethylenediamine-modified magnetic graphene oxide (MGO). The resulting hydrogel was systematically characterized by mean of Fourier transform infrared spectrometer, X-ray photoelectron spectroscopy, Raman spectrum, Thermogravimetric analysis, and Scanning electron microscope. The swelling percentage of the hydrogel attained the extremely high value at pH = 2 and pH = 12. The resulting MGO/PNA was used as an easily recyclable adsorbent to remove cationic and anionic dyes, and the effects of solution pH, adsorption time, adsorption temperature, and initial concentration on the adsorption process were systematically investigated. The maximum theoretical adsorption capacities of methyl violet (MV), methylene blue (MB), tartrazine (TZ), and amaranth (AR) were 609.8, 625.0, 613.5 and 609.8 mg/g, respectively. The adsorption behaviors of the hydrogel conformed to Langmuir isothermal model and pseudo-second-order model. The mechanism analysis indicated that the addition of Fe3O4 into the hydrogel not only endowed MGO/PNA with easily recyclable characteristic, but also improved the adsorption capacity of the hydrogel to some degree. MGO/PNA hydrogel could maintain good adsorption effect after five adsorption-desorption cycles, so the hydrogel might have the wide application prospect in adsorption science and technology area.