Enhanced removal of sulfur-containing ions post persulfate advanced oxidation: Interfacial adsorption-mediated foam fractionation process by amphiphilic graphene oxide

The efficient elimination of sulfur-containing ions (S₂O₈^2- and SO₄^2-) from degraded wastewater remains a critical bottleneck for the practical deployment of Persulfate-based Advanced Oxidation Processes. To address this challenge, a nanoscale amphiphilic graphene oxide functionalized with N-dodecylamine (GO-DDA) was designed as foam fractionation agent. By establishing a solid-liquid interfacial adsorption process, GO-DDA enhances the removal of sulfur-containing ions from wastewater through foam fractionation. The amphiphilic GO-DDA surface enables the preferential adsorption of sulfur-containing ions, thereby facilitating gas-liquid interfacial mass transfer and ion sequestration. Under optimal conditions (pH 4.0 with 10.0 mmol N-dodecylalanine), the synthesized GO-DDA exhibited superior foam stability and adsorption capacity, outperforming most previously reported adsorbents. Mechanistic investigations combining experimental characterization and theoretical modeling revealed a monolayer adsorption behavior governed by synergistic electrostatic attraction, hydrogen bonding, and intraparticle diffusion. In foam fractionation systems, GO-DDA enabled dual removal pathways: (1) three-phase (gas-liquid-solid) interfacial adsorption and (2) foam interstitial liquid transfer, achieving ultrahigh removal efficiencies of 96.1 % for S₂O₈^2- and 95.5 % for SO₄^2-. These values correspond to enhancements of 10.9-47.1 % for S₂O₈^2- and 9.6-23.5 % for SO₄^2- compared with conventional adsorption systems. Notably, GO-DDA demonstrated high selectivity toward sulfur-containing ions, strong adaptability in real wastewater matrices, and excellent long-term operational stability. Overall, the GO-DDA-mediated foam fractionation process provides a viable and efficient strategy for the remediation of high-sulfate wastewater and hold strong potential for integration into advanced wastewater treatment technologies.