Covalent Binding of Sodium Dodecyl Sulfate as C12 Hydrocarbon Chain to Silica Coated Magnetite Under Microwave Irradiation for Removal and Enrichment of Brilliant Green Dye Spiked Environmental Water Samples.

Sodium dodecyl sulfate (SDS) is conventionally bonded to positively charged bar adsorbents through electrostatic interaction. This mode of bonding greatly hinders their use for removing toxic species from sea water and highly saline waste water matrices, where the high concentrations of NaCl solutions strongly affect their stability. In this respect, the success of covalent binding of SDS to the adsorbent surface via a facile procedure is expected to support its stability and maximize its application. Accordingly, this manuscript enables the synthesis of a novel C₁₂ chemically bonded to silica coated magnetite nano composite (Fe₃O₄NPs@SiO₂@C₁₂), through direct solid-solid interaction between a pre-prepared silica coated magnetite Fe₃O₄NPs@SiO₂ NPs and SDS under a benign procedure adapting solvent free microwave irradiation conditions (700 W for 10 min). Different instrumental tools were used to characterize and confirm the success of the novel nano composite synthetic mode, including SEM, TEM, XRD, FT-IR (showing no vibration bands due to sulfate group), EDX (indicating the absence of sulfur content), and TGA (indicating starting decomposition higher than SDS melting point). The novel nanocomposite achieved its highest performance in removing brilliant green (BG) dye (98.33%) in batch mode, under optimized conditions of pH 6.3, contact time of 5 min, nanocomposite dosage of 70 mg and initial dye concentration of 30 ppm. It also showed a remarkable pH-independent profile across the investigated range (3.0-10.0), outperforming other adsorbents synthesized using multiple steps. Additionally, it exhibited resistance to salinity effects, with BG recovery values ranging from 96.75% to 96.25% in the 0.0- to 1.0-M NaCl range. This stability extended to seawater samples (T.D.S 31040 ppm), spiked with 25 and 50 ppm BG dye, with recovery values of 98.1% and 96.5%, respectively. The experimental data fit well with the Langmuir sorption isotherm (adsorption capacity of 158.7 mg/g) and the pseudo-second-order kinetic model, in addition to a high partition coefficient value of other 317.4 L/g. On the other hand, the Fe₃O₄NPs@SiO₂@C₁₂ nano adsorbent was successfully regenerated in situ for six consecutive cycles using an external magnet. Furthermore, a calibration curve for BG dye enrichment was established under optimized conditions, showing a linear dynamic range of 10-340 μg/L with a high coefficient of determination of 0.9974. The limits of detection (LOD) and quantification (LOQ) were determined to be 5.5 and 18.3 μg/L, respectively.