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The world is currently grappling with unprecedented levels of water pollution, largely attributed to the presence of detrimental chemicals and dyes posing substantial environmental hazards. This study endeavors to develop highly efficient materials capable of extracting anionic dyes from polluted water reservoirs. Utilizing the coprecipitation method, nickel-chrome and zinc-chrome layered double hydroxides (LDH) were synthesized and subsequently analyzed using advanced analytical techniques. The efficiency of both materials in removing anionic dyes Congo Red (CR) and Indigo Carmine (IC) was investigated by analyzing various parameters, including initial solution pH, adsorbent dose, dye concentration, time, and temperature effects. In binary solutions, ZnCr-LDH exhibited a higher adsorption capacity of 109.10 mg g-1 and 78.64 mg g-1 for IC and CR dyes, respectively. The competitive removal of a binary dye mixture is primarily influenced by electrostatic attraction. Isotherm models were employed for analysis, with the Freundlich model found to be the best fit for IC adsorption onto NiCr-LDH and the Sips model for IC adsorption onto ZnCr-LDH. In binary systems, the extended Freundlich and non-modified Redlich-Peterson models provided the best fit to the isotherm data. ZnCr-LDH demonstrated higher removal efficiency than NiCr-LDH. Furthermore, both LDH materials exhibited stability and maintained their activity over four successive cycles. [ABSTRACT FROM AUTHOR]

In the present paper, LDH hydrotalcite was synthesised via co-precipitation method. The LDO form was obtained by calcination of the LDH material at 500°C during 3 h. The as-prepared materials were characterised by TGA, XRD, N2 adsorption-desorption isotherms, SEM, FT-IR, and pH PZC techniques. Both solids were used as adsorbents of Indigo carmine (IC) and Congo red (CR) from simple and binary dyesolutions. The experimental results showed that the sorption equilibrium of each dye was reached within 100 min in the single and binary systems for both materials. The dynamical data were well fitted with the pseudo-second-order kinetic model. Based on the thermodynamic results,all the explored temperatures showed that the adsorption processes are endothermic and spontaneous. Based on the AICc and Wi values, it is evident that the adsorption isotherm data of IC onto LDH and LDO in a single solution were well fittedwith Freundlich isotherm and in the binary system were fitted more favorablywiththe Extended Freundlichmodel.For CR adsorption onto LDH and LDO in single solution,Sips model was the best.In the binary solution, the Extended Sips model was found as the best-fitting modelfor CR adsorption onto LDH. While for CR uptake onto LDO, the adsorption isothermdata werewell fittedwith the Extended Freundlichmore likely than another model.The competitive adsorption of IC and CR on LDH and LDO showed that LDO exhibited a greater affinity towards IC (168 mg/g) than that for the CR (80.94 mg/g). The adsorption mechanism was mainly monitored by electrostatic interactions between the positively charged LDH layer and the anionic dyes. However, for LDO the dyes molecules were effectively intercalated in the interfoliar space owing to the reconstruction of calcined LDH by the structural memory effect. [ABSTRACT FROM AUTHOR]