Restricted fiber contraction during amidoximation process for reinforced-concrete structured nanofiber sphere with superior Sb(V) adsorption capacity.

Abstract Amidoxime-polyacrylonitrile (APAN) nanofiber possesses advantages of adsorbing heavy metals for abundant amidoxime groups. However, it easily suffers from poor mechanical property caused by fiber contraction during amidoximation process. Inspired by high mechanical strength of reinforced concrete, we embedded stiff polylactic acid (PLA) skeletons into PAN matrix to prepare reinforced-concrete structured nanofiber sphere (APAN/PLA NFS) through solution blending. Preparation parameters including polymer concentration and PAN/PLA ratio were optimized as 4.0% and 1:1, and coarse sphere surface, numerous mesopores and large pore volume (19.3 mL/g) were endowed. Scanning electron microscope results showed restricted fiber contraction with nitrile conversion of 58.1%. APAN/PLA NFS showed robust compressive strength of 3.28 MPa with strain of 80%, and X-ray diffraction and differential scanning calorimeter analysis revealed that crystalline PLA reinforced non-crystalline PAN through molecule-level compatibility. Compared with plain APAN sphere, Sb(V) adsorption from water for APAN/PLA NFS showed better performance with superhigh capacity of 949.7 mg/g and fast rate (equilibrium time of 2 h), which was owing to abundant mesopores preserved by PLA skeletons. These findings indicated that PLA was a promising skeletal candidate which could protect APAN from fiber contraction during amidoximation process and could strongly expand adsorption capacity of APAN for heavy metals.