Spiropyran modified polyvinyl alcohol sponge as a light-responsive adsorbent for the removal of Pb(II) in aqueous solution

Abstract Lead (Pb2+) is notorious for its negative effects on humans and the environment. Herein, a photochromic polyvinyl alcohol sponge (PVA-g-SPC) for light-induced removal of Pb2+ from aqueous solution was developed using 1′-(4′-carboxybutyl) −3′, 3′-dimethyl-6-nitro-spiro [chromene-2, 2′-indoline] (SPC) and polyvinyl alcohol sponge (PVA) by Steglich esterification. Evidence from experiments shows that the maximum adsorption capacity of PVA-g-MCC (formed by PVA-g-SPC under UV irradiation) was calculated to be 5.78 mg g−1 and the PVA-g-MCC has excellent selectivity to Pb2+ in the simulated lead–zinc mine leachate, ascribed to the complexation of MCC and Pb2+. Importantly, Pb2+ can be repelled from the sponge effectively by simple rinsing with water under visible light conditions to achieve the regeneration of the PVA-g-SPC with significant change of the colour in whole process, providing a facile method to determining the separation endpoints of Pb2+ by naked eyes and fully avoiding the secondary contamination caused by chemical desorbent. The adsorption capacity of PVA-g-SPC can maintain over 85% after ten cycles, indicating that the novel light-responsive sponge is a valuable material for Pb2+ removal.