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

Abstract

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.

Graphical Abstract

Keywords

PFAS / PFOS / Biochar / Catalyst / Adsorption / Photodegradation

Highlight

•	Novel adsorptive photocatalyst Ga2O3@biochar achieved >99% adsorption and 80.8% degradation with superior 70.5% defluorination.
•	DFT verifies electron transfer from biochar to β-Ga2O3 for charge separation.
•	e−, ·O2−, and 1O2 contribute 35.0%, 39.1%, and 25.8% to stepwise chain-shortening mineralization.
•	Ga2O3@biochar enables concentrate-&-destroy of PFOS and performs effectively in reuse cycles and real groundwater.

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Funding

Natural Science Foundation of China(42577249)

Basic and Applied Basic Research Foundation of Guangdong Province(2025A04J0991)

Guangdong Key Laboratory of Environmental Pollution and Health(2016B030301005)

US Strategic Environmental Research and Development Program(ER18-1515)

US National Science Foundation(CBET-2244985)

RIGHTS & PERMISSIONS

The Author(s)