Electrochemical Oxidation of Organic Pollutants in Aqueous Solution Using a Ti4O7 Particle Anode

At a Glance

Metadata	Details
Publication Date	2023-05-17
Journal	Membranes
Authors	Andrey Kislyi, Ilya A. Moroz, Vera Guliaeva, Yuri Prokhorov, Anastasiia Klevtsova
Institutions	Kuban State University
Citations	9
Analysis	Full AI Review Included

Executive Summary

Core Technology: The study successfully implemented a substoichiometric titanium oxide (Ti₄O₇) particle anode in an electrochemical flow cell (EC-FC) for the Advanced Oxidation (AO) of common organic pollutants.
High Efficiency: The system demonstrated high performance, achieving near-complete mineralization (>99% removal) of oxalic acid and high removal rates for hydroquinone and benzoic acid within 6 hours.
Current Efficiency: A high initial Instantaneous Current Efficiency (ICE) of up to 40% was observed for hydroquinone oxidation at 36 mA/cm². Optimal average ICE (25%) was achieved at the lower current density of 9 mA/cm², indicating mass transfer control at higher rates.
Anode Stability: The Ti₄O₇ particle anode exhibited excellent stability, showing no significant polymer fouling (confirmed by FT-IR and SEM-EDS) after 108 hours of operation at 36 mA/cm².
Design Advantage: The particle bed design (1-3 mm granules) provides a high surface area and reduces transport limitations, offering a scalable, low-cost alternative to traditional plate electrodes or complex 3D-printed Reactive Electrochemical Membranes (REMs).
Hydrodynamic Independence: The degradation rate was largely independent of the solution flow rate (110 to 1100 mL/min), suggesting that the mass transfer is controlled primarily by the internal structure of the separator mesh rather than bulk flow velocity.

Technical Specifications

Parameter	Value	Unit	Context
Anode Material	Ti₄O₇ (Substoichiometric Oxide)	N/A	>98% purity, non-active electrode
Anode Granule Size	1-3	mm	Particle anode structure
Anode Layer Thickness	~10	mm	Dimension within the EC-FC chamber
Cathode Material	Platinized Titanium (Pt-Ti)	N/A	Coating thickness 5.0 µm
Initial COD Concentration	600	mg/L	Standard initial concentration for all tested organics
Supporting Electrolyte	0.1 M Na₂SO₄	M	Background electrolyte concentration
Maximum Current Density (Continuous)	36	mA/cm²	Used for high-rate testing
Optimal Current Density (Average ICE)	9	mA/cm²	Yielded 25% average ICE
Anode Stability Duration	108	hours	Tested at 36 mA/cm² without significant fouling
Maximum Initial ICE (Hydroquinone)	~47	%	Observed at 18 mA/cm²
Final pH (Hydroquinone Oxidation)	9.3	N/A	Maximum value reached after 6 h
Flow Rate Range Tested	110 to 1100	mL/min	Total solution flow rate (no significant effect observed)
Impurity Content (SiO₂)	<1.30	Mass %	Highest identified impurity in Ti₄O₇ granules

Key Methodologies

Electrochemical Cell Design: A custom PTFE-cased Electrochemical Flow Cell (EC-FC) was utilized, housing a Ti₄O₇ particle anode bed (1-3 mm granules) and a Pt-Ti grid cathode, separated by a 3 mm polypropylene mesh.
Solution Recirculation: Experiments were performed in a continuous recirculation mode using a 500 mL reservoir. A membrane pump maintained constant flow rates (tested up to 1100 mL/min) through the cell.
Current Mode Testing: The AO process was studied under three constant current densities (36, 18, and 9 mA/cm²) to determine the transition between mass transfer control and current-limited control.
Pulsed Current Evaluation: Pulsed modes (1 min/1 min and 5 s/5 s pulse/pause cycles) were tested at an average current density of 18 mA/cm² to assess improvements in mass transport, though no significant enhancement was observed.
Performance Quantification: Degradation kinetics were monitored by periodic sampling and measuring the Chemical Oxygen Demand (COD) using the photometric method (ISO 15705:2002). Instantaneous Current Efficiency (ICE) was calculated based on COD reduction over time.
Material Integrity Assessment: Anode granules were characterized before and after long-term operation (108 h) using SEM-EDS for surface morphology and elemental analysis, XRD for phase identification, and FT-IR spectroscopy to confirm the absence of polymer fouling.

Commercial Applications

Industrial Wastewater Treatment: Highly effective for the mineralization of refractory organic compounds, including aromatic pollutants (like hydroquinone and benzoic acid) and short-chain carboxylic acids (maleic and oxalic acids).
Cost-Effective Electrode Systems: The use of low-cost Ti₄O₇ particle granules significantly reduces the capital costs associated with electrochemical oxidation systems compared to expensive Boron-Doped Diamond (BDD) or complex 3D-printed electrodes.
Fouling Mitigation in REMs: The large granule size (1-3 mm) and resulting pore structure (0.2-1 mm) in the particle anode minimize intrapore fouling caused by large polymerized organic particles or gas bubbles, a common weakness in small-pore Reactive Electrochemical Membranes (REMs).
High-pH Oxidation Processes: The chemical stability of Ti₄O₇ at high pH, combined with the observed increase in solution pH during operation (up to 9.3), makes this anode suitable for treating alkaline industrial effluents where other electrode materials might degrade.
Modular Flow Reactor Design: The particle bed configuration is ideal for scalable, high-throughput flow cells, providing a large active surface area within a compact reactor volume for continuous water purification applications.

View Original Abstract

Anodes based on substoichiometric titanium oxide (Ti4O7) are among the most effective for the anodic oxidation of organic pollutants in aqueous solutions. Such electrodes can be made in the form of semipermeable porous structures called reactive electrochemical membranes (REMs). Recent work has shown that REMs with large pore sizes (0.5-2 mm) are highly efficient (comparable or superior to boron-doped diamond (BDD) anodes) and can be used to oxidize a wide range of contaminants. In this work, for the first time, a Ti4O7 particle anode (with a granule size of 1-3 mm and forming pores of 0.2-1 mm) was used for the oxidation of benzoic, maleic and oxalic acids and hydroquinone in aqueous solutions with an initial COD of 600 mg/L. The results demonstrated that a high instantaneous current efficiency (ICE) of about 40% and a high removal degree of more than 99% can be achieved. The Ti4O7 anode showed good stability after 108 operating hours at 36 mA/cm2.

Tech Support

Original Source

DOI: https://doi.org/10.3390/membranes13050521

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