Adsorptive Optimization of Crystal Violet Dye Using Central Composite Rotatable Design and Response Surface Methodology: Statistical Analysis, Kinetic and Isotherm Studies

Water contamination is emerging as the most critical global issues in the world, calling for the treatment eco-techniques. Taking advantage of biowastes as adsorbent materials is not only in accordance with the purpose of environmental protection but also enhance the higher value-added products. In this work, water hyacinth (Eichhornia crassipes) powder was used as an efficient adsorbent for the removal of crystal violet from aqueous solutions. The structure of water hyacinth powder adsorbent was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy analysis. Based on the central composite rotatable design and response surface methodology, the effect of different parameters such as initial pH solution, contact time, adsorbent dosage, and initial crystal violet concentration was optimized. The maximum adsorption capacity of 180.336 mg/g was achieved under the optimum condition as initial pH solution of 6.246, contact time of 125.698 min, the adsorbent dosage of 1.382 g/L, and initial dye concentration of 615.865 mg/L. Moreover, the Langmuir isotherm provided the best fit with a high correlation coefficient of 0.9981 and a maximum monolayer adsorption capacity of 181.818 mg/g at 30 °C. The kinetic studies indicated that the pseudo-second-order model was adequately applied for the adsorption kinetic of crystal violet on the water hyacinth powder adsorbent. The utilization of the water hyacinth plant, an abundant species, as a low-cost biosorbent to remove crystal violet using the central composite rotatable design combined with response surface methodology approach is recommended for the real treatment of organic dyes.