Preparation of SiO2 composites for efficient removal of Congo red via the combination of mussel-inspired surface modification and anionic ring-opening polymerization

SiO₂ nanoparticles have emerged as promising candidates for wastewater remediation due to their facile synthesis, tunable morphological characteristics, and customizable surface chemistry. These features enable effective sequestration of various aquatic contaminants. The adsorption capability of pristine silica nanoparticles frequently demonstrates poor efficiency, primarily due to the absence of targeted functional moieties essential for effective molecular binding interactions. This research introduces an innovative approach for nanoparticle surface engineering through the synergistic integration of mussel-inspired chemistry and controlled anionic polymerization, employing 2,3-epoxypropyltrimethylammonium chloride (PTAC) as the functional monomer to engineer silica nanostructures. The structural and morphological properties of resultant SiO₂ composites (designated as SiO₂-PDA-PTAC) were confirmed by various techniques. Quantities of laboratory investigations were conducted to assess the adsorption capacity of Congo red (CR) of the synthesized materials. The findings demonstrated a remarkable improvement in adsorption capability, where SiO₂-PDA-PTAC hybrid achieved a maximum capacity of 131.30 mg/g—approximately four times higher than that of unmodified silica (32.48 mg/g). Thermodynamic analysis confirmed the spontaneous nature of the adsorption process, characterized by positive entropy changes and endothermic behavior. The experimental data exhibited excellent correlation with established theoretical models, showing high regression coefficients for both pseudo-second-order kinetics (R² = 0.9918) and Langmuir isotherm (R² = 0.9993). Among various interactions between SiO₂-PDA-PTAC and CR, electrostatic interaction played critical roles in adsorption process. SiO₂-PDA-PTAC maintained substantial adsorption efficiency through successive regeneration cycles, demonstrating excellent reusability and stability in practical applications, highlighting their potential for practical applications in wastewater treatment.