Removal of cationic and anionic dyes using Ca-alginate and Zn-Al layered double hydroxide/metal-organic framework

In this study, a novel effective bio adsorbent was produced and employed to remove congo red and methylene blue dyes from water matrices. First, Zn-Al layered double hydroxide (Zn-Al LDH) was manufactured in a hydrothermal process. Next, through in-situ nucleation and growing of crystalline NH₂-modified Ti metal-organic framework (NH₂-MIL-125(Ti) on Zn-Al sheets by solvothermal method, Zn-Al LDH@NH₂-MIL-125(Ti) hybrid was produced. The prepared hybrid showed good adsorption capacity (q_max values: 294 mg/g and 158 mg/g) for congo red and methylene blue dyes in optimum condition (adsorbent amount = 5-7 mg, dye concentration = 100-150 mg/L, V = 10 mL, pH = no adjustment, and contact time = 2-5 h). Based on the isotherm and kinetic models, the Langmuir isotherm, as well as the pseudo-second-order model, were fit to the equilibrium data. In the next attempt, to improve the reusability of the powder and particle form of Zn-Al LDH@NH₂-MIL-125(Ti) hybrid, as well as prevent of formation of secondary contamination in water, Na-alginate, as a cheap and effective substrate, was used. Novel architectures of robust, reusable, and efficient Ca-alginate/Zn-Al LDH@NH₂-MIL-125(Ti) microgel beads were prepared and the performances of the microbeads were compared with pure LDH@NH₂-MIL-125(Ti) hybrid.