Waste treatment by waste: High-value utilization of superabsorbent polymer in disposable diapers as efficient adsorbent for heavy metal.

[Display omitted] • High-value utilization of SAPs in used disposable diapers. • Synthesis of the proposed adsorbent is green, facile, and cost-effective. • The proposed adsorbent is the first modified-SAP-based one reported to date. • The proposed adsorbent shows superior adsorption capacity towards Cr(VI) The consumption of disposable diaper has increased drastically over the past decades in virtue of its cost effectiveness, user-friendly nature, and excellent skin compatibility. Nevertheless, used disposable diapers are typically fed to landfills with no treatment. This is a huge threat to the environment as superabsorbent polymer (SAP) in disposable diapers are essentially non-degradable under natural conditions. Unfortunately, recycling of SAP remains extremely challenging owing to its crosslinked network structure and ultra-high water absorption capacity. In this study, we propose a novel route for high-value utilization of SAP in used disposable diapers in a 'waste treatment by waste' manner. Specifically, the SAP was modified by polyethyleneimine (PEI) in a facile way (grafting and crosslinking under mild conditions) to develop the SAP-PEI, which is, to the best of our knowledge, the first modified-SAP-based adsorbent reported to date. The results demonstrated that the as-prepared SAP-PEI was superior to most low-cost adsorbents in terms of maximum adsorption capacity towards Cr(Ⅵ) (527.52 mg/g). Meanwhile, adsorption isotherms and kinetics revealed that Cr(Ⅵ) adsorption by the SAP-PEI can be effectively described by the pseudo-second-order model and the Langmuir model. Meanwhile, electrostatic attraction plays a key role in Cr(VI) adsorption by the SAP-PEI, and Cr(VI) are partially reduced to Cr(Ⅲ) in this process. Additionally, the SAP-PEI exhibited excellent reusability as its Cr(VI) removal efficiency decreased by less than 5 % after seven cycles. Overall, the SAP-PEI is a high-performance adsorbent and its application in removal of heavy metals such as Cr(VI) serves as a green and cost-effective approach for high-value utilization of SAP in used disposable diapers. [ABSTRACT FROM AUTHOR]