Visualized Fibrous Adsorbent Prepared by the Microwave-Assisted Method for Both Detection and Removal of Heavy Metal Ions

In the present study we synthesized a dual-functionalized material by incorporating a chromophore, 4-(2-pyridylazo)-resorcinol (PAR), onto polyacrylonitrile (PAN) fiber by microwave (MW) irradiation; the produced material was labeled PAN_MW-PAR. Compared with conventional methods, MW irradiation exhibits superior advances in reaction time and grafting rate of surface modification, further resulting in satisfactory colorimetric and adsorption properties. A systematic study has been implemented to analyze the detection and removal ability for heavy metal ions, including Hg²⁺, Cu²⁺, Pb²⁺, and Ni²⁺. Results demonstrated that PAN_MW-PAR fibers possess impressive colorimetric sensitivity (red-to-black color change) and high adsorption capacity for these metal ions, especially for Hg²⁺. Thus, these fibers present excellent potential as optical sensors and adsorbent for heavy metal contaminants. At low pH, the PAN_MW-PAR fibers showed selective detection ability for Hg²⁺, and the detection limit can be obtained at 35 μg/L. Adsorption of heavy metal ions followed pseudo-second-order kinetics and Langmuir isotherms. X-ray photoelectron spectroscopy provided insights into the interaction mechanism between heavy metal ions and PAN_MW-PAR fibers. PAN_MW-PAR fibers can be feasibly regenerated with EDTA and still exhibited high sensitivity and adsorption affinity for heavy metal ions after 10 cycles of reuse. The proposed fibers present a cost-effective material that can be considered an alternative for effective detection and removal of toxic metal ions from water.