Title: Nonswelling Silica–Poly(acrylic acid) Composite for Efficient and Simultaneous Removal of Cationic Dye, Heavy Metal, and Surfactant-Stabilized Emulsion from Wastewater

Abstract: The discharge of emulsion, cationic dyes, and heavy metals often coexists in wastewaters, greatly enhancing the difficulty of processing. In this work, we fabricated a nonswelling silica–poly(acrylic acid) (SiO₂–PAA) composite through the surface modification of SiO₂ using PAA to remove emulsion, cationic dyes, and heavy metal co-contaminants simultaneously. In the SiO₂–PAA composite, PAA exists in a linear and divergent form rather than a network structure. Thus, SiO₂–PAA can gain the nonswelling property, provide abundant carboxyl groups as the binding sites for removal of pollutants, which is an important advanced feature of PAA-based materials, and improve the potential of practical application. The characterization results of SiO₂–PAA demonstrated that PAA was successfully grafted on SiO₂. In a monocomponent system, SiO₂–PAA exhibited excellent separation efficiency for cetyltrimethyl ammonium bromide (CTAB)-stabilized emulsion separation and admirable adsorption capacity of 758.6 and 178.6 mg/g for methylene blue (MB) and Cr(III). This finding was ascribed to the exposure of carboxyl groups in SiO₂–PAA, which could increase the mass transfer efficiency. Importantly, the SiO₂–PAA composite exhibited high efficiency in the simultaneous uptake of CTAB-stabilized emulsion, MB, and Cr(III) co-contaminants. Thus, given the simple fabrication, efficient emulsion separation, admirable adsorption capacity, and excellent reusability of SiO₂–PAA, it exhibits striking potential for the efficient treatment of coexisting pollutants.