Electrochemical Degradation of Venlafaxine on Platinum Electrodes - Identification of Transformation Products by LC-MS/MS and In Silico Ecotoxicity Assessment

At a Glance

Metadata	Details
Publication Date	2025-04-23
Journal	Molecules
Authors	Angelica Rebecca Zizzamia, Veronica Pasquariello, Filomena Lelario, Carmen Tesoro, Rosanna Ciriello
Institutions	University of Basilicata
Citations	1
Analysis	Full AI Review Included

Executive Summary

The research successfully validates Platinum (Pt) electrodes as a stable and highly reproducible alternative to Boron-Doped Diamond (BDD) for the electrochemical degradation of the antidepressant Venlafaxine (VFX).

Core Achievement: 94% VFX degradation efficiency was achieved in 7 hours (420 min) using a Pt anode under optimized, environmentally mild conditions (pH 9, 0.1 M Na₂SO₄, 25 mA/cm²).
Mechanism: Degradation proceeds primarily via an indirect oxidation pathway, mediated by electrochemically generated hydroxyl (•OH) and sulfate (SO₄•^-) radicals, confirmed by radical scavenging experiments.
Material Advantage: Pt electrodes offer superior operational stability and a well-established, reproducible cleaning protocol, mitigating the common BDD issues of delamination and complex maintenance.
Sustainability Focus: The method avoids chloride-containing electrolytes, preventing the formation of hazardous halogenated disinfection byproducts, a major concern in water treatment.
Ecotoxicity Assessment: In silico ECOSAR analysis of the 10 identified transformation products (TPs) showed that almost all intermediates, particularly the most abundant product V194, exhibited significantly lower toxicity than the parent VFX compound.
Kinetics and Energy: The process follows first-order kinetics (k = 0.0084 min^-1) and requires 98 kWh/m³ to achieve 94% removal of 25 ppm VFX.

Technical Specifications

Parameter	Value	Unit	Context
Anode Material	Platinum (Pt) foil	N/A	Selected for stability and reproducibility
Anode Dimensions	0.127 x 25 x 25	mm	Working electrode size
Cathode Material	Graphite plate	N/A	Counter electrode
Cathode Dimensions	3 x 20 x 60	mm	Counter electrode size
Electrolyte	0.1 M Na₂SO₄	M	Supporting electrolyte (chloride-free)
Optimized pH	9	N/A	Favored •OH radical formation
Current Density (j)	25	mA/cm²	Optimized operating condition
Initial VFX Concentration	25	mg/L (ppm)	Concentration used for long-term study
Degradation Time	7 (420)	hours (min)	Time to achieve 94% efficiency
Degradation Efficiency	94	%	Maximum removal achieved
Kinetic Model	First-order	N/A	Reaction rate model
Rate Constant (k)	0.0084	min^-1	First-order kinetic value
Half-Life (t_1/2)	82.52	min	Time for 50% degradation
Energy Consumption (E_C)	98	kWh/m³	Energy required for 94% removal
Number of TPs Identified	10	N/A	Transformation products identified by LC-MS/MS
Toxicity Assessment Model	ECOSAR V2.2	N/A	In silico prediction of acute ecotoxicity (LC₅₀)

Key Methodologies

The electrochemical degradation was performed using galvanostatic electrolysis in a two-electrode cell configuration.

Electrode Preparation (Pt Anode):
- Mechanical polishing using 0.05 µm alumina particles.
- Sonication in double distilled water.
- Chemical cleaning via sonication in hot 70% nitric acid.
- Electrochemical cleaning by cycling in 0.5 M sulfuric acid (potential range: -0.225 V to +1.25 V vs. SCE) until a steady-state current profile was achieved.
Electrolysis Setup:
- Mode: Galvanostatic electrolysis using a 263A potentiostat/galvanostat.
- Electrodes: Pt foil anode (8 cm² exposed area) and graphite plate cathode (8 cm² exposed area).
- Reactor: 100 mL solution volume, kept at room temperature under stirring.
- Conditions: Optimized at 0.1 M Na₂SO₄ electrolyte, pH 9, and 25 mA/cm² current density.
Mechanistic Studies (Radical Quenching):
- Differential Pulse Voltammetry (DPV) was used to monitor VFX concentration abatement.
- Ethanol (200 mM) was added as a selective •OH radical scavenger to confirm the dominance of the indirect oxidation pathway, showing a significant reduction in degradation rate.
Analytical Characterization:
- VFX Concentration Monitoring: HPLC-UV (C₁₈ column, acetonitrile/water gradient) was used to track the C/C₀ ratio over time.
- Transformation Product Identification: High-resolution LC-ESI-Orbitrap-MS and low-resolution CID-MSⁿ were employed to determine molecular formulas and elucidate fragmentation pathways, differentiating between isomers (e.g., V276a/V276b and V294a/V294b/V294c).
Ecotoxicity Assessment:
- The ECOSAR predictive model was used to calculate the median lethal concentration (LC₅₀) for Daphnia magna based on the chemical structures of VFX and its 10 TPs.

Commercial Applications

This research provides a robust, scalable, and environmentally conscious methodology for the treatment of persistent organic pollutants, primarily targeting the pharmaceutical sector and municipal water infrastructure.

Municipal Wastewater Treatment: Implementation of Electrochemical Advanced Oxidation Processes (EAOPs) as a tertiary treatment step for the removal of persistent Emerging Contaminants (ECs), specifically antidepressants like Venlafaxine (VFX).
Pharmaceutical Manufacturing Effluents: Direct treatment of concentrated pharmaceutical waste streams using stable Pt anodes, ensuring high removal efficiency before discharge.
Sustainable Remediation: Adoption of chloride-free EAOP systems to meet stringent environmental regulations by minimizing the formation of toxic halogenated byproducts.
Electrode Technology and Manufacturing: Validation of Platinum as a durable, high-performance anode material for industrial EAOP reactors, offering a reliable alternative to BDD where long-term stability and ease of maintenance are critical engineering requirements.
Water Reclamation and Reuse: Integration into water reuse systems where complete removal of endocrine-disrupting compounds and pharmaceuticals is necessary to protect public health and ecosystems.

View Original Abstract

Antidepressants are emerging contaminants that have raised global concern due to their abuse. Venlafaxine (VFX), a serotonin and norepinephrine reuptake inhibitor, can cause adverse and potentially toxic effects on aquatic organisms. Electrochemical advanced oxidation processes (EAOPs) are gaining attention as promising degradation techniques for a variety of drugs. EAOP methods proposed for VFX degradation mainly utilize boron-doped diamond (BDD) electrodes, characterized by low background current and high oxygen overpotential. However, challenges arise, including delamination from the substrate, difficulties in scaling up, and limited service life. In this study, platinum was employed as an anode for the galvanostatic degradation of VFX, due to its stability and well-established surface cleaning procedure, which ensured high reproducibility. A 0.1 M Na2SO4 solution at pH 9 was used as the supporting electrolyte, and a current density of 25 mA/cm2 was applied. After 7 h, a degradation efficiency of 94% was achieved for a 25 ppm VFX solution. The hydroxyl and sulfate radicals generated in the electrochemical system were the active species responsible for VFX degradation, which followed a first-order kinetic model with a rate constant of 0.0084 min−1. The main degradation intermediates were identified through LC-MS, including two isomers with a nominal m/z of 276 and three isomers with a nominal m/z of 294. The toxicity of the VFX degradation products was assessed by an in silico prediction model. This evaluation confirmed the sustainability of the developed method.

Tech Support

Original Source

DOI: https://doi.org/10.3390/molecules30091881

References

2022 - A review on emerging water contaminants and the application of sustainable removal technologies [Crossref]
2021 - Antidepressant drugs as emerging contaminants: Occurrence in urban and non-urban waters and analytical methods for their detection [Crossref]
2022 - Photochemical environmental persistence of venlafaxine in an urban water reservoir: A combined experimental and computational investigation [Crossref]
2016 - Effects of an antidepressant mixture on the brain serotonin and predation behavior of hybrid striped bass [Crossref]
2021 - A review of pharmaceutical occurrence and pathways in the aquatic environment in the context of a changing climate and the COVID-19 pandemic [Crossref]
2017 - Degradation of venlafaxine using TiO2/UV process: Kinetic studies, RSM optimization, identification of transformation products and toxicity evaluation [Crossref]