Synthesis, characterization, adsorption properties and mechanism of gravity-assisted zirconium alginate hydrogel fiber for removal of methylene blue from water

In this study, zirconium alginate hydrogel fiber (ZAHF) with directional structure was prepared by gravity-assisted wet spinning method and its fabrication was confirmed by SEM, EDS, BET, XRD, FTIR and TGA. Compared with alginate materials crosslinked with divalent metal ions, Zr4+ has a strong affinity for hydroxyl groups, which further increases the content of oxygen-containing functional groups in ZAHF. Hydroxyl functional groups are considered to be important in providing adsorption sites, so ZAHF is very competitive in adsorption. Furthermore, the adsorption results shown that the synthesized ZAHF can easily adsorb methylene blue (MB) from water, and has the advantages of fast adsorption speed, large adsorption capacity and easy recycling. ZAHF can adsorb MB in a wide range of pH, and the lower the temperature, the better the adsorption performance. The actual adsorption capacity is up to 1165 mg/g at 25 ℃. Furthermore, the adsorption rate is also fast, with 79% MB quickly removed in 90 min and saturated in 240 min. Meanwhile, the maximum adsorption capacity calculated was reaches 1538 mg/g, which is much higher and faster than other adsorbents. The reusability investigation indicated that over 75% MB can be removed after five cycles. Adsorption process is spontaneous, exothermic, monolayer physical adsorption, adsorption sites on the surface of the adsorbent evenly distributed. Pores fitting, hydrogen bonding and electrostatic interaction were the main adsorption mechanisms. Meanwhile, the molecular dynamics simulation of electron density distribution proven that electrostatic interaction plays an important role in the adsorption process.