Derivative spectrophotometric determination and Taguchi design optimization of simultaneous removal of binary mixture of direct red and Reactive black dyes using magnetic nanoparticles modified by dopamine

Derivative spectrophotometric and Taguchi orthogonal design was used for determination and optimization of simultaneous removal of Direct red and Reactive black by Cobalt ferrite nano-particles modified with PDA from an aqueous solution in a batch system. Cobalt ferrite nano-particles were prepared using the co-precipitation method. The sorbent was characterized by FT-IR spectroscopy, SEM, and XRD techniques. Effective factors on adsorption process, such as amount of sorbent, initial concentration of dyes, pH value, and time were considered using a L16 Taguchi orthogonal array design. Taguchi analysis is based on choosing the best run by analyzing signal-to-noise ratio (S/N), whose form depends on the experiment objective. Thus, the removal percentage (R%) and capacity uptake (q) of dyes were transformed into an accurate S/N ratio for a “high is better” response. The best conditions for adsorption of dyes were determined by the Taguchi method and desirability approach as pH = 3, sorbent dose of 10 mg , initial reactive black concentration of 200 mg L−1, initial Direct red concentration of 200 mg L−1, and contact time of 4 min.