Efficient Heavy Metal Removal from Water by Polydopamine Confined ZrO₂ Nanocrystals with Improvements in Nanoparticles Utilization and Ion Diffusion

Abstract

Nanocomposites for purification of trace heavy metal to the μg/L level remain a hard task and pressing matter, which is mainly challenged by their stable small size (<10 nm) formation and slow ion diffusion. To overcome these problems, we designed an engineered sub-10 nm nanocomposite with exceptional performances in heavy metal removal, e.g., Pb. It relies on a cooperative adsorption, originating from the fixation of charged SO3H groups and in situ external surface deposition of sub-10 nm ZrO2 nanocrystals over a polydopamine (PDA) layer. Not only does the PDA interface favor the formation of stable and active sub-10 nm ZrO2 nanocrystals, but also the external growth of nano-ZrO2 on the PDA layer further maximizes Zr utilization and shortens the heavy metal diffusion distance. In addition, the charged SO3H groups of the matrix can drive trace heavy metal ions from the bulk solution to the vicinity of absorbents with several orders of magnitude enrichment (∼31000 times), significantly increasing the interaction possibility between the sub-10 nm ZrO2 nanocrystals and the target heavy metals. These hybrid adsorbents exhibited superior selectivity with a distribution coefficient of 10500 mL/g, wide solution pH usage (∼2.0–7.0), rapid kinetics, and satisfactory filtration performances (>99.5% removal) in Pb removal. A remarkable capacity of ∼7240 L water/kg sorbent with low effluent (∼1 μg/L) was achieved in the treatment of the contaminated river stream, and the saturated adsorbents can be regenerated and reused with a negligible capacity loss. Our work therefore presents a new concept and benchmark for the lead(II) adsorbent and brings a new perspective for mitigating the problem of diverse heavy metal contamination.