Two-dimensional NiO nanosheets for efficient Congo red adsorption removal

Strategies for developing new adsorbents are necessary for more efficient processes to remove contaminants from wastewater. Thus, it is essential to adjust the synthesis parameters of the adsorbent nanomaterial to control the surface area and morphology and, therefore, enhance the adsorption performance. Herein, α-Ni(OH)2 nanosheets were synthesized via a simple and fast microwave-assisted solvothermal method and converted to NiO nanostructures by calcination in air. The effect of different calcination temperatures (range of 300–600 °C) on the morphology, crystal structure, and adsorption performance of Congo red (CR) was evaluated. The calcination of α-Ni(OH)2 at 300 °C resulted in 2D NiO nanosheets, which showed the best performance to remove CR dye due to the increased surface area and porosity provided by the 2D morphology. The nanosheet-like structure is lost with increasing the calcination temperature and the nanoparticles become bigger, consequently, the CR adsorption capacities are significantly reduced. The 2D NiO nanosheets can adsorb a significant amount of CR quickly, reaching equilibrium after only 120 min, indicating a high affinity between the adsorbate species and the surface of the adsorbent. Additionally, the adsorption isotherm was compatible with the Langmuir model, which provides a maximum calculated adsorption capacity of 259.74 mg g−1. Thus, our findings showed how to adequate the synthesis parameters to obtain NiO nanosheets and improve the adsorption parameters to CR, which can be extended to the fabrication of new materials to promote advances in sustainable technologies. [Display omitted] •α-Ni(OH)2 nanosheets were synthesized via a microwave-assisted solvothermal.•2D α-Ni(OH)2 was calcinated in the air (300–600 °C) to achieve NiO nanosheets.•NiO nanosheets obtained at 300 °C is the best sample for removing Congo red dye.•2D NiO nanosheets reached adsorption (259.74 mg g−1) with 90% of dye removal.