was added to the NaCl solutions with different pH values, and the suspension was stirred at 25°C for 48h. After 48 h, the final pH (pHfinal) was measured. The pHpzc of CCS is the value at which pHinitial is equal to pHfinal.33,34Adsorption process optimizationThis research adopted RSM based on CCD to optimize the adsorption process variables, including A (time, min), B (temperature, °C), C (dye concentration, mg/L), and D (CCS dosage, g/L), as well as the level of each variable, as shown in Table 2. Design-expert 8.0 was used to design the experiment and analyze the results. The response results were evaluated by a second-order polynomial, including individual, square, and interaction terms for each variable. The secondary response model is as follows35