Promoted sequestration and photo-induced destruction of perfluorooctane sulfonate using photoregenerable β-Ga2O3-functionalized biochar: superior defluorination and mechanistic insights

The unique presence of perfluorooctane sulfonate (PFOS) in aquatic matrices has intensified the urgent demand for economically viable remediation technologies to comply with the stringent regulations. To address this challenge, we developed a novel β-Ga2O3-functionalized biochar adsorptive photocatalyst (Ga2O3@biochar) for successive sequestration and photocatalytic destruction of PFOS in both lab water and real groundwater. The composite material loaded with 1% Ga demonstrated the best performance. The incorporation of β-Ga2O3 into the porous structure of the biochar matrix modulated its physicochemical and optoelectronic properties, resulting in enhanced mesoporosity for improved PFOS mass transfer and adsorption, improved light absorption, a narrower bandgap, and better charge separation. Density functional theory (DFT) calculations corroborated an efficient interfacial electron transfer from biochar to β-Ga2O3. The composite exhibited exceptional PFOS adsorption due to concurrent hydrogen bonding, hydrophobic interaction, mesopore filling, and electrostatic attractions. Following the pre-adsorption, the material was able to photodegrade 80.8% of the pre-loaded PFOS, with 70.5% defluorinated, and the degradation process was accurately described by a delayed first-order kinetic equation. Photogenerated electrons (e−), superoxide radicals (·O2−), and singlet oxygen (1O2) acted as the predominant reactive species, contributing 35.0%, 39.1%, and 25.8% to the overall PFOS degradation, respectively. The PFOS degradation proceeded via a chain-shortening pathway initiated by desulfonation, followed by decarboxylation and a series of defluorination. The photodegradation regenerated the composite, allowing for reuse in multiple adsorption–photodegradation cycles. Moreover, the composite performed effectively in real groundwater. Overall, the new material appeared promising and may enable the concentrate-&-destroy strategy for treating PFOS and likely other PFAS in water.