Enhanced electrooxidation of per and polyfluoroalkyl substances on Boron doped diamond anode in the presence of vacuum ultraviolet irradiation

At a Glance

Metadata	Details
Publication Date	2025-07-01
Journal	Scientific Reports
Authors	Yaye Wang, Haibo Xu, Ruoyang Li
Institutions	Hohai University, Jiangsu Provincial Academy of Environmental Science
Citations	1
Analysis	Full AI Review Included

Executive Summary

This research details the development and mechanistic analysis of an enhanced electrooxidation (EO) system utilizing a Boron-Doped Diamond (BDD) anode combined with Vacuum Ultraviolet (VUV) irradiation for the efficient degradation of Per- and Polyfluoroalkyl Substances (PFASs).

Core Value Proposition: The EO + VUV hybrid system significantly accelerates the degradation kinetics of representative PFASs (PFOA and PFHxA) compared to conventional EO alone.
Kinetic Enhancement: Surface area normalized pseudo-first order rate constants (k_SA) increased by 37.2% for PFOA and 70.1% for PFHxA at 10 mA·cm^-2 when VUV was introduced.
Mineralization Improvement: The defluorination ratio (F^- release) was substantially enhanced, increasing from 28.5% (EO only) to 48.6% (EO + VUV) at 10 mA·cm^-2.
Mechanism Elucidation: Time-Dependent Density Functional Theory (TDDFT) confirmed that VUV absorption excites PFAS ions, reducing the energy difference (ΔE) required for the rate-limiting Direct Electron Transfer (DET) process to the BDD anode.
Real-World Performance: The EO + VUV system achieved 96.2% total PFAS removal in real industrial wastewater within 20 hours, demonstrating high efficacy, particularly for short-chain PFAAs.
Material Focus: The BDD anode was selected for its high oxygen evolution potential (OEP) and robust reactivity, crucial for POP destruction.

Technical Specifications

Parameter	Value	Unit	Context
Anode Material	Boron-Doped Diamond (BDD)	N/A	Grain size 5-20 µm
Anode Immersion Area	20	cm²	Single side area used for normalization
VUV Source Wavelength	185	nm	Low-pressure Hg lamp (20 W)
Applied Current Density	10	mA·cm^-2	Standard test condition
PFOA k_SA (EO only)	2.31 x 10^-5	m·s^-1	At 10 mA·cm^-2
PFOA k_SA (EO + VUV)	3.17 x 10^-5	m·s^-1	At 10 mA·cm^-2 (37.2% increase)
PFHxA k_SA (EO only)	1.42 x 10^-5	m·s^-1	At 10 mA·cm^-2
PFHxA k_SA (EO + VUV)	2.42 x 10^-5	m·s^-1	At 10 mA·cm^-2 (70.1% increase)
Defluorination Ratio (EO + VUV)	48.6 ± 2.15	%	At 10 mA·cm^-2
Oxygen Evolution Potential (EO only)	~2.32	V vs. SHE	Measured via LSV
Oxygen Evolution Potential (EO + VUV)	~2.27	V vs. SHE	VUV reduces potential required
PFOA First Excited State (TDDFT)	216.25	nm	Corresponds to VUV absorption
PFHxA First Excited State (TDDFT)	217.60	nm	Corresponds to VUV absorption
Industrial Wastewater pH	7.5	N/A	Initial sample condition
Industrial Wastewater TOC	12.7	mg·L^-1	Initial sample condition

Key Methodologies

The degradation experiments were conducted in a batch reactor setup combining electrochemical oxidation and VUV photolysis.

Reactor Configuration:
- A 500-mL polypropylene beaker was used, containing 400-mL reaction solution.
- The BDD plate (anode) and two titanium plates (cathodes) were positioned with a 0.50-cm gap.
- Temperature was maintained at 25.0 ± 3.0 °C using a water bath.
Electrochemical Operation (EO):
- A constant current density was applied, ranging from 5 mA·cm^-2 to 25 mA·cm^-2 (10 mA·cm^-2 used for primary comparison tests).
- 100-mM Na₂SO₄ was used as the supporting electrolyte for spiked solution tests.
VUV Irradiation:
- A 20 W low-pressure Hg lamp, emitting primarily at 185 nm (VUV), was used as the radiation source.
Analytical Techniques:
- PFAS Quantification: Ultra-performance liquid chromatography coupled with a triple-stage quadrupole mass spectrometer (UPLC-MS/MS) was used, following strict QA/QC protocols with isotope-labeled internal standards.
- Mineralization Measurement: Fluoride ion (F^-) concentration was measured using Ion Chromatography (IC) to calculate the defluorination ratio (F_r).
- Electrode Characterization: X-ray diffractometer (XRD) and Scanning Electron Microscopy (SEM) confirmed BDD crystalline phases and morphology. Linear Sweep Voltammetry (LSV) measured the oxygen evolution potential (OEP).
Computational Modeling (DFT/TDDFT):
- Density Functional Theory (DFT) was used for structural optimization and frequency analysis (PBE0/def2-TZVP level).
- Time-Dependent DFT (TDDFT) was employed to calculate the excited states and UV-vis spectrums of PFOA and PFHxA ions, explaining the VUV-induced acceleration mechanism.

Commercial Applications

The enhanced EO + VUV system is highly relevant for industries requiring robust and efficient destruction of persistent organic pollutants (POPs), particularly fluorine-based compounds.

Wastewater Treatment:
- Remediation of industrial wastewater streams (e.g., chemical manufacturing, plating, textiles) contaminated with high concentrations of PFASs.
- Effective treatment of short-chain PFAAs (like PFBA and PFPeA), which are notoriously difficult to remove via conventional methods.
Environmental Remediation:
- Treatment of contaminated groundwater and landfill leachate containing complex mixtures of PFASs.
Electrochemical Technology:
- Utilization of high-performance BDD anodes in Advanced Oxidation Processes (AOPs) due to their stability, high OEP, and capacity for Direct Electron Transfer (DET).
Hybrid AOP Systems:
- Design and optimization of synergistic treatment systems combining electrochemistry with photolysis (VUV) to maximize energy efficiency and degradation rates for recalcitrant compounds.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41598-025-07386-8

References

2015 - Toxicological Effects of Perfluoroalkyl and Polyfluoroalkyl Substances [Crossref]