Hybrid central composite design approach for simultaneous optimization of removal of alizarin red S and indigo carmine dyes using cetyltrimethylammonium bromide-modified TiO2 nanoparticles

• Introducing cetyltrimethylammonium bromide-modified TiO2 nanoparticles as a new adsorbent.
• Hybrid central composite design for multivariate optimization of an efficient absorption system.
• Isotherm modelling of adsorption for a binary dyes mixture.
• Kinetic studies of binary mixture of dyes adsorption.

A novel adsorbent called cetyltrimethylammonium bromide (CTAB)-modified TiO2 nanoparticles were used for an efficient removal of anionic dyes (e.g. alizarin red S and indigo carmine) from water samples in single and binary batch systems. The influence of various factors such as initial pH, initial dye concentration and sorbent mass on the adsorption process was investigated. Statistical experimental design was utilized to optimize this adsorption process. A regression model was derived using a response surface methodology through performing the 416B model of hybrid central composite design. Model adequacy was checked by means of tests such as analysis of variance (ANOVA), a lack of fit test, and residuals distribution consideration. The proposed quadratic model resulted from the hybrid design approach fitted very well to the experimental data. The optimal conditions for dye removal were as follows: pH = 2, sorbent dose = 0.05 g, CAR (initial AR concentration) = 232.50 mg/L and CIC (initial IC concentration) = 298.3 mg/L. Moreover, the isotherms and kinetics of the adsorption process were also investigated.

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