High-efficiency water purification for methyl orange and lead(II) by eco-friendly magnetic sulfur-doped graphene-like carbon-supported layered double oxide

Highlights: • Magnetic sulfur-doped graphene-like carbon-supported layered double oxide (MG/S-LDO) was prepared. • The MG/S-LDO exhibited an ultrafast and superior methyl orange (MO) and Pb²⁺ removal. • Sulfur functionalization played a vital role in MO and lead removal. • LDO with "memory effect" and released ions benefited for MO and Pb²⁺ removal as well. Traditional disposal techniques for the spent layered adsorbents after capturing organics suffer from intractable obstacles, such as resource waste and secondary pollution. To address this diploma, we here developed the "resource-utilization" strategy, i.e., converting the organic layered double hydroxide (as representative) to magnetic sulfur (S)-doped graphene-like carbon-supported layered double oxide (MG/S-LDO) to be reutilized in water purification. The as-prepared MG/S-LDO exhibited outstanding remediation ability toward methyl orange (MO) and lead(II), with the adsorption capacity of 1456 and 656 mg g⁻¹, respectively. Specifically, the residue concentration of Pb²⁺ was reduced to 0.15 mg L⁻¹ within 1 h, which met the discharge limit of the secondary industrial wastewater. MG/S-LDO could also maintain the preeminent adsorption capability under various interferences (such as wide pH and co-existing ions), even in the authentic water matrices. The removal mechanisms were systematically investigated to unveil that MO removal was dominated by metal-complexation, "memory effect", and π-π electron donor–acceptor (EDA). While for Pb²⁺ removal, besides the released OH^- from LDO as precipitate agent, the vacancy defect resulting from the S doping played a crucial role in electron interaction between Pb²⁺ and S-doped graphene. Additionally, the MG/S-LDO was further confirmed as an eco-friendly adsorbent with excellent reusability via the acute toxicity tests using green algae and multiple cycle experiments. This work provides a novel resource-utilization strategy for organic layered wastes to construct the functional eco-friendly materials in wastewater purification realm.