Construction of 3D Ni2+-Al3+-LDH/γ-Fe2O3-Cd2+-Ni2+-Fe3+-LDH structures and multistage recycling treatment of dye and fluoride-containing wastewater

The construction of three-dimensional (3D) Ni 2+ -Al 3+ -LDH / γ-Fe 2 O 3 - Cd 2+ -Ni 2+ -Fe 3+ -layered double hydroxide (LDH) structures (S1–S6) with magnetic properties and different (γ-Fe 2 O 3 - Cd 2+ -Ni 2+ -Fe 3+ -LDH)/(Ni 2+ -Al 3+ -LDH) ratios were successfully prepared. The effects of these ratios in these 3D LDH constructions on physicochemical properties were investigated using XRD, SEM, VSM, UV–vis, and BET analyses. The specific surface area and band gap of these materials decreased with increased ratio, while the saturation magnetization increased. The synergistic combination of saturation magnetization, adsorption characteristics, and band gap of six sample types were evaluated. S3 samples were used in a multistage recycling treatment study of dye wastewater and fluoride ion (F − )-containing wastewater, effectively degrading methyl orange (MO) due to its high photocatalytic activity. After this, the memory effect of the calcined product (S3, 300 °C) significantly enhanced the migration and diffusion of F − , resulting in a F − adsorption capacity of 49.25 mg/g. The recycling properties of this composite material for photocatalytic degradation and adsorption capabilities for F − removal were evaluated, showing a reduction in efficiency of only 1 % and 8.6 % for degradation of MO and F − removal respectively, with no significant loss of efficiency after 10 cycles. Adsorption experiments and subsequent sample characterization showed that the F − adsorption mechanism of S3 involved ion exchange mechanism and sorption sites (interlayer, basal, edges and junction sites). The existence of oxygen vacancies and formation of S-scheme heterojunction between γ-Fe 2 O 3 -Cd 2+ -Ni 2+ -Fe 3+ -LDH and Ni 2+ -Al 3+ -LDH, resulted in the improvement of the photocatalytic activity. The results obtained in this study demonstrated that Ni 2+ -Al 3+ -LDH/γ-Fe 2 O 3 - Cd 2+ -Ni 2+ -Fe 3+ -LDH composites were a promising adsorbent for degradation of MO and F − removal in practical multilevel utilization due to its simple synthesis, low-cost, recyclability, and high removal capability.