The present study deals with the simultaneous adsorption of Alizarin Red (AR) and Congo red (CR) by cobalt hydroxide nanoparticles in a batch system. Cobalt hydroxide nanoparticles as novel and efficient adsorbent are successfully used to remove two anionic dyes from aqueous solutions simultaneously. Partial least square regression as a multivariate calibration method is developed for the simultaneous determination of AR and CR in binary solutions, to overcome the severe spectral overlap. The influence of various parameters was investigated on dye adsorption such as pH, initial concentration of dyes, and sorbent mass. A response surface methodology was achieved through performing the central composite design approach to optimize the removal percent of dyes by cobalt hydroxide nanoparticles. The proposed quadratic model resulting from the central composite design approach fitted very well with the experimental data. The optimal conditions for dye removal were pH = 5.5, sorbent dose = 43 mg, CAR (initial AR concentration) = 351 mg/L, and CCR (initial CR concentration) = 616 mg/L. Isotherm modeling and thermodynamic studies were also conducted. Furthermore, the sorbent was characterized by the Fourier transform infrared, scanning electron microscopy, and X‐ray diffraction analysis.
