Statistical optimization of process parameters for ultrafast uptake of anionic azo dyes by efficient sorbent: Zn/Cu layered double hydroxide

The extensive use and release of synthetic dyes by various industries is a primary cause of contamination of water resources. Herein, the adsorption efficiency of Zn/Cu layered double hydroxide (LDH) was estimated for the uptake of a series of anionic dyes, out of which maximum removal efficiency was observed for Congo red (CR) dye. The effect of processing parameters, mainly adsorbate and adsorbent concentration, contact time, and pH on the adsorption capacity of CR dye, was analyzed by making use of response surface methodology (RSM). Based on the analysis of variance and experimental results, the modified quadratic regression model was found to be statistically acceptable. Further, the ultrafast removal efficiency of the synthesized material was observed with the maximum percentage removal of dye (>99%) within 4 min of contact time. In addition, batch adsorption experiments were conducted under the optimized reaction conditions for equilibrium and kinetic studies. Langmuir isotherm (R-2 = 0.9965) and pseudo-second-order model (R-2 = 1.0) were found to be the best-fitted isotherm and kinetic models, respectively. Using Langmuir isotherm, the maximum adsorption capacity of the sorbent was calculated to be 167.22 mg/g. Furthermore, the adsorbent exhibited excellent regeneration capability and can be used efficiently for up to three cycles with >90% dye removal. The adsorption behavior of Zn/Cu LDH in different water matrices, that is, tap water, groundwater, and textile wastewater, was also investigated suggesting it to be an excellent adsorbent for real-time applications.