A strategy for the efficient removal of chlorophenols in petrochemical wastewater by organophilic and aminated silica@alginate microbeads: Taguchi optimization and isotherm modeling based on partition coefficient

Abstract

Through in situ encapsulation of cetyltrimethylammonium bromide (CTAB) and urea-functionalized SiO2 nanoparticles in alginate hydrogel, two types of new functionalized microbeads, CTAB-SiO2@alginate (organophilic) and urea-SiO2@alginate (aminated), were produced. Their adsorption behavior toward multiple chlorophenols (CPs: e.g., 4-chlorophenol (MCP), 2,4-dichlorophenol (DCP), and 2,4,6-trichlorophenol (TCP)) in petrochemical wastewater was assessed with the aid of Taguchi’s L9 orthogonal array at three levels. In terms of the partition coefficient (PC: μmol/g·μM (or L/g)), the use of three-parameter models (hybrid Langmuir–Freundlich and Redlich–Peterson) yielded the best fit (R2 ≈ 1). Furthermore, the performance evaluation in terms of PC metric indicated that CTAB-SiO2@alginate (7.85 L/g) was better to treat total CPs than urea-modified SiO2@alginate microbeads (3.83 L/g). The enhanced performance of the former reflects the significant contribution of CTAB functionality (sp2 carbon tail and quaternary amine (N+) cationic head sites) for accelerating uptake of molecular (or suspended) and ionizable CPs molecules (e.g., with the aid of salting-out effect at a high initial CPs concentration and salinity) via hydrophobic/electrostatic interactions. The high performance of the CTAB-SiO2@alginate was demonstrated against petroleum hydrocarbons, CPs, and phenol contaminants using real petrochemical wastewater (up to three reusable cycles).