Fabrication of nickel-iron layered double hydroxides using nickel plating wastewater via electrocoagulation, and its use for efficient dye removal

Abstract

Dye wastewater is one of the most challenging pollutants for environmental protection and safe human health. Therefore, development of high-efficiency, non-toxic, renewable, and low-cost adsorbents for dyestuff wastewater is imperative. Considering the recycling of sludge into a high value-added product and utilizing waste to treat pollution, for the first time, we present a novel electrocoagulation method for fabricating a two-dimensional layered material, Ni-Fe LDH, using nickel plating wastewater as a raw material. The obtained Ni-Fe-10 LDH exhibited excellent removal efficiency for Congo red wastewater, and the theoretical maximum adsorption capacity was 476.19 mg/g, which is a remarkable adsorption ability compared to that of previously reported LDH materials. The analysis based on the structural and morphological characteristics of the sample revealed that the excellent absorption capacity of Ni-Fe-10 could be attributed to the mesoporous structure and morphology of the nanosheet, which provided a high surface area, large pore volumes, and numerous adsorption sites. The adsorbed Congo red dye was desorbed using NaOH solution and methanol, and the regenerated Ni-Fe LDH could be reused in multiple regeneration cycles, achieving 78% removal efficiency even after five cycles. The adsorption process of the dye using the Ni-Fe-10 LDH adsorbent coincided with the Langmuir isotherm and pseudo-second-order kinetic models. XRD and infrared analyses indicated that the adsorption mechanism of Ni-Fe-10 mainly depended on the electrostatic attraction accompanied by simultaneous ion exchange and H-bonding.