Enhanced coagulation performance of hydrophobic-modified carbon quantum dots in polymeric sulfate for oil-contaminated wastewater treatment

Oil-contaminated wastewater containing emulsified oil can severely pollute water bodies. Due to the action of surfactants, emulsified oil forms a stable emulsion system, making it difficult to remove through static separation methods. However, high-efficiency coagulants can purify the oil-contaminated wastewater, bringing it up to discharge standards.In this experiment, polymeric ferric sulfate(PFS) was prepared via direct oxidation method, usingFe(NO3)3·9H2O, NaHPO4, and NaHCO3 as the reaction precursors. Subsequently, the polymeric ferric sulfate was combined with oleic acid-modified(OA) carbon quantum dots(CDs) to synthesize the composite coagulant PFS + CDs + OA. The characteristic functional groups of the coagulant were analyzed using FTIR, and the crystal structure and morphology of carbon quantum dots were studied by XRD and TEM. The experimental results indicate that at a dosage of 300 mg/L, PFS + CDs achieve a turbidity removal rate of 86.3 ± 0.02% and an oil removal rate of 97.2 ± 0.01%. The composite coagulant PFS + CDs + OA, at the same dosage, demonstrates a turbidity removal rate of 92.8 ± 0.02% and an oil removal rate of 99.7 ± 0.01%, showing more significant effectiveness in treating oily mineralized water. Subsequently, a performance analysis of PFS + CDs + OA was conducted, revealing its mechanism in treating oily wastewater. The hydrophobic association effect of oleic acid-modified carbon quantum dots enhances the electrostatic neutralization, bridging adsorption, and net entrapment interactions between polymeric ferric sulfate coagulant and oily mineralized water, forming large and compact flocs. In summary, the preparation method of PFS + CDs + OA is efficient and straightforward, exhibiting excellent oil and turbidity removal performance for oily mineralized water, and holds promising prospects for practical applications.