Formation of ammonium ions by electrochemical oxidation of urea with a boron-doped diamond electrode
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-01-01 |
| Journal | New Journal of Chemistry |
| Authors | Norihiro Suzuki, Akihiro Okazaki, Kai Takagi, Izumi Serizawa, Genji Okada |
| Institutions | Tokyo University of Science |
| Citations | 9 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study investigates the energy-efficient electrochemical conversion of urea (a major component of urine) into valuable ammonium ions (NH4+) using a Boron-Doped Diamond (BDD) electrode system.
- Core Value Proposition: Provides a potential low-energy, ambient-condition alternative to the high-pressure, high-temperature Haber-Bosch process for synthesizing nitrogen compounds (NH3/NH4+) from wastewater.
- Material Focus: BDD electrodes were used due to their wide potential window and high chemical/physical stability, enabling the generation of powerful hydroxyl radicals (OHâ˘) for oxidation.
- Decomposition Efficiency: Electrochemical treatment alone achieved almost complete urea decomposition (2 wt% initial concentration) within 18 hours at room temperature.
- Product Selectivity: The primary desired product, NH4+, was successfully formed and accumulated in the counter cell via electrical guidance across a Nafion membrane.
- Photocatalytic Enhancement: Integrating a TiO2/BDD photocatalyst with the electrochemical process significantly improved selectivity by promoting the rapid oxidation of the intermediate nitrite (NO2-) to the less desirable nitrate (NO3-) or, crucially, enhancing the pathway toward NH4+ formation.
- Mechanism Insight: The photocatalyst likely enhances OH⢠production and utilizes electrons in the TiO2 conduction band to influence the oxidation pathway of carbamic acid intermediates, favoring NH4+ generation.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Electrode Material | Boron-Doped Diamond (BDD) | N/A | Working electrode |
| Counter Electrode | Platinum (Pt) | N/A | Counter electrode |
| Separator | NafionÂŽ NRE-212 | N/A | Membrane connecting half-cells |
| Applied Current (Constant) | 75 | mA | Current applied to the BDD electrode |
| Initial Urea Concentration | 2 | wt% | Simplified artificial urine feedstock |
| Initial NaCl Concentration | 1 | wt% | Electrolyte/Feedstock component |
| Total Solution Volume | 50 (per cell) | mL | Reaction cell and counter cell volume |
| Operating Temperature | Room | Temperature | Electrochemical treatment condition |
| Urea Decomposition Time | 18 | hours | Time for near-complete removal (BDD only) |
| Photocatalyst Type | Mesoporous TiO2/BDD | N/A | Used for enhanced selectivity |
| UV Wavelength (Photocatalysis) | 207 | nm | Kr-Br excimer lamp source |
| UV Light Intensity | 2.0 | mW cm-2 | Irradiated onto the photocatalyst |
Key Methodologies
Section titled âKey MethodologiesâThe study utilized a controlled H-type electrochemical cell setup to separate the reaction and counter products, allowing for the accumulation of NH4+ in the counter cell.
- Cell Configuration: An H-type glass cell was used, consisting of two half-cells separated by a NafionÂŽ NRE-212 membrane.
- Electrode Placement: The BDD working electrode was placed in the reaction cell, and the Pt counter electrode was placed in the counter cell.
- Feedstock Preparation: Simplified artificial urine (2 wt% urea and 1 wt% NaCl) was used in the reaction cell. The counter cell contained 1 wt% NaCl aqueous solution.
- Electrochemical Treatment: A constant current of 75 mA was applied to the BDD electrode to initiate water electrolysis and produce reactive oxygen species (ROS), primarily hydroxyl radicals (OHâ˘).
- Photocatalytic Integration (Optional): For combined treatment, a mesoporous TiO2/BDD photocatalyst was introduced into the reaction cell and irradiated with 207 nm UV light (2.0 mW cm-2) from a Kr-Br excimer lamp.
- Product Separation: The negatively biased Pt counter electrode electrically guided the positively charged ammonium ions (NH4+) formed in the reaction cell across the Nafion membrane for accumulation.
- Chemical Analysis: Samples were collected periodically and analyzed using High-Performance Liquid Chromatography (HPLC) for urea concentration and Ion Chromatography for nitrogen-containing ions (NH4+, NO2-, NO3-).
Commercial Applications
Section titled âCommercial ApplicationsâThis technology leverages the robust properties of BDD electrodes for advanced oxidation processes, offering applications in sustainable resource recovery and chemical synthesis.
- Sustainable Fertilizer Production: Enables decentralized, low-energy synthesis of ammonium ions (a key fertilizer component) directly from urea-rich wastewater (urine), bypassing the energy demands of the Haber-Bosch process.
- Wastewater Treatment and Resource Recovery: Provides a method for the simultaneous mineralization of organic pollutants (urea) and the recovery of valuable nitrogen resources from municipal or agricultural wastewater streams.
- Advanced Oxidation Processes (AOPs): Utilizes BDD electrodes to electrochemically generate highly potent hydroxyl radicals (OHâ˘) for the efficient destruction or conversion of recalcitrant organic contaminants in industrial effluents.
- Electrochemical Reactor Design: The use of BDD/TiO2 composites demonstrates potential for developing highly selective photoelectrochemical reactors capable of controlling reaction pathways toward specific high-value products.
- BDD Electrode Manufacturing: Reinforces the demand for high-quality, stable BDD electrodes for use in harsh, long-duration electrochemical environments, particularly in environmental engineering.
View Original Abstract
Ammonium ions were formed electrochemically from urea with a boron-doped diamond electrode and increased by using photocatalyst together.