Response surface methodology for modeling the adsorptive uptake of phenol from aqueous solution using adsorbent polyethylene terephthalate microplastics

Optimization modeling and the interpretation of the adsorptive uptake of phenol from aqueous solution using pristine (Pr), modified (Mod-) and aged (Ag-) polyethylene terephthalate microplastics (PET MPs) as adsorbents at optimum conditions have been investigated. The surface morphology and functional groups of the MPs were evaluated using SEM and FTIR-ATR systems, while the surface area of the MPs was estimated using the Brunauer-Emmett Teller (BET) model. Experimentally determined optimization and Response Surface Methodology (RSM) were used to simulate and interpret the adsorption of phenol onto PET MPs, to determine the effects of four adsorption factors (contact-time, initial concentration, pH, and temperature) on the response (removal efficiency) using central composite design (CCD). The results showed that optimum operating conditions for the PET MPs adsorption of phenol from aqueous solution corresponds to contact-time of 77 minutes, 50 mg/L initial concentration, pH of 6, and temperature of 298 K respectively. The maximum removal efficiency of phenol ions under this operating condition was found to be 93.72%, 92.78% and 95.80% for Pr-PET MPs, Mod-PET MPs and Ag-PETMPs respectively. To understand the nature of the PET MPs sorption process, Redlich−Peterson (R-P), Elovich and Dubinin-Radushkevich (D-R) isotherms were employed. The results proved that, D-R model best fitted the PET MPs sorption process at 0.7214 ≤ R2 ≤ 0.9043. Elovich model confirmed the performances of the PET MPs uptake of phenol ions occurred by physical and exothermic processes. Their adsorption capacities followed Pr-PET MPs (0.226 mg/g) > Ag-PET MPs (0.216 mg/g) > Mod-PET MPs (0.126 mg/g) respectively.