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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]

NiCr-LDH/BiOCl and NiCr-LDH/TiO2 nanocomposites were successfully synthesised by co-precipitation and hydrothermal methods. Their structure, morphology and optical properties were analysed by XRD, SEM, UV−vis, XPS and FTIR techniques. The Rhodamine B (RhB) dye was used as a model pollutant to evaluate the catalytic activity for the nanocomposites under sunlight irradiation for 60 min. The results showed a significant enhancement in the photocatalytic activity of NiCr-LDH/BiOCl (up to 96.57%), higher than that of NiCr-LDH/TiO2 (89.58%), and pure phase NiCr-LDH (26.09%). The nanocomposites exhibited a high catalytic performance than TiO2 and BiOCl pure phases. This funding was not related to the Bi or Ti content but to the dispersion of the pure phase on the surface of the NiCr-LDH. The enhanced photocatalytic activity of the NiCr-LDH/BiOCl naocomposite mainly attributed to the formation of heterojunction between LDH and BiOCl for efficient separation of photoinduced electrons and holes. Hydroxyl radicals and holes were the main active species. Both NiCr-LDH/BiOCl and NiCr-LDH/TiO2 photocatalysts exhibited high stability and reusability even after four cycles. Based on the experimental results, a possible photocatalytic mechanism on both nanocomposites was proposed. [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]