Insights into the mechanism involved by electric double layer on phosphate removal of metal-bearing environmental remediation agent: Taking tricalcium aluminate as representative.

Metal-bearing materials are known to be desirable environmental captures for phosphate removal, yet few studies focus on understanding the reaction process, especially formed a special phenomenon, i.e., electric double layer (EDL), which might influence the phosphate removal. To fill in this gap, we fabricated metal-bearing tricalcium aluminate (C3A, Ca3Al2O6) as representative, to remove phosphate and unveil the impact by electric double layer (EDL). Specifically, a preeminent removal capacity of 142.2 mg·g-1 was achieved at the initial phosphate concentration below 300 mg·L-1. Following thorough the characterizations, the process was that the released Ca2+ or Al3+ of C3A formed positive charged stern layer attracted phosphate to generate Ca or Al-precipitation. At high phosphate concentration (>300 mg·L-1), C3A exhibited inferior removal capability for phosphate (<45 mg·g-1), due to the aggregation of C3A particles with low water permeability under the EDL effect, obstructing Ca2+ and Al3+ to release for phosphate removal. In addition, the feasibility application of C3A was evaluated based on response surface methodology (RSM), highlighting its prospective phosphate treatment. This work not only provides a theoretical guidance for the application of C3A to remove phosphate, but also deepens the understand of phosphate removal mechanism by metal-bearing materials, shedding light on environmental remediation.

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

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.

Resource utilization of organic spent adsorbent to prepare three-dimensional sulfate-functionalized layered double oxide for superior removal of azo dye.

Developing superior, rapid, cost-effective adsorbents derived from organic spent adsorbent is an economically sustainable way for purifying azo dye wastewater. Herein, we report a precursor-calcination strategy for the recycle of the organic spent adsorbent to a high value-added three-dimensional sulfate-functionalized MgAl-layered double oxide (3S-LDO). Thanks to the unique property of the sulfate group and LDO, 3S-LDO exhibited a superior (4340.71 mg/g) and ultrafast (<1 h) adsorption toward methyl orange (MO, as the representative of azo dye). A thermodynamic study revealed that the reaction process was spontaneous and exothermic. FT-IR, XPS, and XRD results confirmed that the sulfate from 3S-LDO played a vital role in MO removal wherein the S=O bond (with the electrophilic character) from SO42- interacted with the N=N double bond (with rich electron) in MO through the electron donor-acceptor mechanism. And the "memory effect" and surface complexation of 3S-LDO further strengthened the MO adsorption. More importantly, 3S-LDO could work efficiently in a wide pH range and even in the presence of competitive anions (e.g., Cl-, NO3-, and CO32-). Multiple cyclic runs and selective tests demonstrated the excellent reusability and explicit selectivity of 3S-LDO. This work not only provides a prospective sulfate-functionalized adsorbent from organic waste for rapid azo dye removal from wastewater but also achieves the high value-added utilization of organic waste.