A crescent-shaped imprinted microgel adsorbent with near-infrared light-responsive performance for selective adsorption of Lead(II)

Smart hydrogel adsorbent with high selectivity and“on–off”switching ability is vital for the effective elimination of heavy metal pollution, but its simple fabrication remains a serious task. To address this, a facile strategy via an oil-in-water-in-oil (O1/W/O2) droplet microreactor was proposed to prepare polydopamine-coated imprinted microgel adsorbents (DMHIIPs) with crescent shape, and then as-prepared smart adsorbent with near-infrared (NIR) light-responsive performance was used to selectively remove lead ions (Pb(II)) from aqueous solution. The critical solution temperature (LCST) of DMHIIPs is 44.2 °C, resulting from the increase of thermal change and decrease of entropy change during swelling. DMHIIPs have high photothermal conversion efficiency and stability, and the temperature of DMHIIPs dispersion (0.5 mg/L) can be rapidly heated to above 50 °C under NIR (808 nm, 1.0 W cm−2) irradiation for 10 min. The adsorption capacity of Pb(II) on DMHIIPs elevates from 128.0 mg g−1 to 135.2 mg g−1, when the solution temperature increases from 20 °C to 40 °C, but this value significantly reduces to 59.2 mg g−1 at 60 °C. Pseudo-second-order can be well described the kinetic results of DMHIIPs, confirming chemisorption is the rate-limiting step. Desorption ratio of DMHIIPs is 36.5% in 30 min under NIR irradiation, and it can be increased to 63.2% When combining NIR irradiation with the using of elution agent. In addition, the obtained DMHIIPs has excellent selectivity coefficient (k) for competitive Cu(II) (7.20), Cd(II) (23.31), and Ni(II) (39.33), respectively. This work demonstrates a new strategy to NIR-responsive imprinted microgel adsorbent provides a new perspective for controlling the adsorption process of heavy metal pollution.