Surface chitosan-grafting modification of polyimide fibers for cobalt ion adsorption

Chitosan (CTS) is widely used to treat wastewater's heavy metal and organic matter pollution. When used as an adsorbent, it can be prepared into different forms, such as microspheres, gels, and fibers. However, CTS has certain drawbacks, including a propensity to swell, low acid resistance, and poor mechanical characteristics. Polyimide (PI) has good acid resistance and recyclability. This study focused on the surface CTS-grafting modification of PI fibers for cobalt ion adsorption. The morphological changes of the resultant CTS-grafted PI fibers (PICTS fibers) during functionalization were investigated by scanning electron microscopy and atomic force microscopy, and their structural and chemical changes were characterized by using X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and static contact angle measurement. The PICTS fibers could fit the Langmuir isotherm model to yield a maximum adsorption capacity of 46.04mgg-1, and its thermodynamic fitting indicated that the adsorption process was a heat-absorbing reaction. The PICTS fibers demonstrated good cycling performance and stable tensile strength in the adsorption-desorption cycling experiments. In the third cycle experiment, the PICTS fibers maintained an adsorption rate of 89.13% and tensile strength of 89.14%. Through grafting CTS onto the PI fibers, the low acid resistance of CTS was significantly enhanced. The PICTS fibers could also be recycled, generating a novel notion for cobalt recycling.