Nucleobase-mediated hydrogen bonding crosslinked highly sulfonated poly (ether ether ketone) electrodialysis membranes for efficient waste acid recovery

Electrodialysis is a promising technology for waste acid recovery with the advantages of low energy consumption and high efficiency. In this work, two nucleobase-modified highly sulfonated poly(ether ether ketone) with adenine (SPEEK-50A) and thymine (SPEEK-50T) were successfully synthesized. Then, a series of blending SPEEK50Ax/50Ty x /50T y membranes with varying molar ratios of these two functionalized SPEEKs were fabricated by solution casting. The hydrogen bonding crosslinked structure of 'A-T base pairs', as well as the acid-base interactions between the incorporated nucleobases and SO3H 3 H groups of the polymer backbone, not only enhanced the mechanical properties and thermal stability of the blending membranes, but more importantly, it successfully addressed the over-swelling issue of highly sulfonated SPEEK membrane. The SPEEK-50Ax/50Ty x /50T y membranes exhibited tensile strengths between 59.3 and 72.3 MPa, which is 2.2-2.6 times that of the pristine SPEEK membrane. And the water uptake of the blending membranes reduced from 116 % to 14.6-19.2 %, while the swelling ratio decreased from 27.1 % to 5.86-6.60 %. The proton affinity of the multiple basic N atoms in nucleobases, as well as the 'A-T base pairs' hydrogen bonding network and acid-base interactions between nucleobases and SO3H 3 H groups, all can serve as effective proton transport channels. Additionally, the charge repulsion effect of protonated nucleobases and the crosslinking structure is beneficial to the permselectivity. Therefore, the fabricated blending SPEEK-50Ax/50Ty x /50T y membranes exhibited superior H+ + flux (1.66-1.73 mmol m- 2 s- 1 ) and enhanced H+/Fe2+ + /Fe 2+ permselectivity (40.3-43.2). The SPEEK-50A0.5/50T0.5 0.5 /50T 0.5 membrane demonstrated a H+ + flux of 1.70 mmol m- 2 s- 1 and a H+/Fe2+ + /Fe 2+ permselectivity of 43.2, which is 2.8 times that of the pristine SPEEK membrane, surpassing both commercially available and recently reported membranes. Therefore, the nucleobase-modified blending SPEEK-50Ax/50Ty x /50T y membranes might be potential candidates for the efficient recovery of acid from pickling wastewater.